MODIS Surface Reflectance Data State QA Aerosol Quantity field meaning is unclear I am trying to compare NDVI values computed from MODIS Surface Reflectance(MOD09) with the NDVI product (MOD13).

MODIS Surface reflectance Collection 5 products include a Data State QA field that I am using to estimate which pixels are best suited for computing NDVI.

A part of this field is labeled Aerosol quantity. The values in this field seem to significantly affect the result of NDVI computation.

The explanation of the possible values of this field in the MOD09 Users' Guide  seems not entirely clear to me.

         | 00 - climatology
aerosol  | 01 - low
quantity | 10 - average
         | 11 - high

The last three values are clear, while the meaning of the climatology value is somewhat non-intuitive.

I have selected a crop field and calculated NDVI for all pixels clear of clouds or cloud shadows during one vegetation period and observed the following:

It seems that results with low aerosol quantity (green points) match well with the results obtained with the complex rating algorithm used in the standard NDVI MOD13Q1 product. While the data with climatology state (orange points) seems far off.

What does the climatology attribute mean and how to treat it?

Most likely, climatology means there was no retrieval at all.

Bayesian retrievals combine information from an a priori with information from measurements.  When the retrieval fails for whatever reason, or the measurement contains insufficient information, instead of reporting no measurement at all, they copy over information from the a priori and use the flag to indicate that the reported "measurement" is in fact simply the climatology.

For details, see optimal estimation, in particular the book by Rodgers:

Clive D. Rodgers (2000). Inverse Methods for Atmospheric Sounding: Theory and Practice. World Scientific.


How and when people first realized that Antarctica is a continent? Recently I got startled by this question I asked myself and I can't seem to find any sources of answers.

I have hypotheses about how it could have happened:
It could have been by the fact that if you stand there you don't drift anywhere as opposed to the North Pole. Also perhaps by altitude.

Am I right?

What about nowadays? Do we use measurements of seismic activity to infer the shape of Antarctica? Are there other methods?

The idea of a southern continent is older than the actual discovery of the Antarctica. There was an expectation of the possible existence of a Terra Australis balance the global landmasses and the theory went far back. However, those models were not based on true evidence but rather aesthetic arguments that later just happened to come true. In contradiction, landmasses were also expected to surround the North Pole in the Arctic, and that turned out to be wrong.

Mercator (1595) map of the North Pole and surrounding continent. Some practical canals are suggested to facilitate the short cut from Atlantic to Pacific

There have never been any human population on Antarctica prior to western explorers but Maori navigators, had experienced the cold waters for centuries.

From the 18th century, famous explorers as James Cook and Bellingshausen came close and made sightings that pushed the limits of whaling and hunting, but there was little interest or possibility to actually land and map the area. Cook's circumnavigation rather limited the expected extent of a much larger Terra Australis.

Landings and activities were focused on the sub-antarctic islands and to a minor extent, the peninsula. There was little reason for anyone to cross the dangerous roaring fourties, furious fifties and screaming sixties to get to icy waters with little prospect of economic profit or even survival. Stories about early explorers have been questioned and proved wrong multiple times.

Map from 1770 before the continent was descovered

The first concepts of an Antarctic continent based on actual sights probably originate from The United States Exploring Expedition (1839-42). Wilkes described the findings as a

  vast Antarctic continent [protected by] an impenetrable barrier of
  ice

It's not easy to access the coast and the landing opportunities are few, especially in East Antarctica. USEE's findings have been questioned later and there seems to have been little substance in the claims. The sighted coast might as well have been just clouds. Ross even accused him for cartographical deceit.

Even as exploration continued and increased from the 1890s, the nature of the continent continued to puzzle explorers and adventurers. There was e.g. no consensus whether East and West Antarctica belonged to the same continent or if an icy sea, similar to the Arctic, separated the isolated visited outcrops.

Taylor (1914) http://www.jstor.org/stable/1778593

Griffith Taylor, Geologist to Captain Scott's expedition writes in his very entertaining report from 1914:

  Undoubtedly one of the most fascinating geographical problems, if
  not the most attractive now that both poles are discovered, is to determine if there are one or two continents at the South Pole.
  At an animated discussion in the hut, I pointed out that the South Georgia loop carried the "Pacific" type of coast into West Antarctica, whereas Victoria Land (and apparently Prince Leopold Land) belong to that type characterized by block faults and known as the Atlantic type.

Even as the geologists of the time had a developed vocabulary for rock types and correlations, they still couldn't be sure that Antarctica was indeed one continent or two. As a side note, it should be mentioned that they are indeed right in the doubts. Today we know that East and West Antarctica have very different history and properties. See e.g. Boger (2011).

Large areas of Antarctica is ice-free, eg. this valley in Vestfold Hills, East Antarctica. The area was first explored in the mid to late 1900's but sightings of outcrop would assure explorers that they actually saw the continent they were expecting and not floating ice.

Geologists could also early correlate the rare findings from Antarctica with surrounding continents and started to reconstruct the Gondwana assembly, a work that is still ongoing and due to the lack of outcrops in Antarctica is to a large extent based on geophysical data. Still, geologists and geophysicists are looking for similarities in Africa, India and Australia to understand the nature of the Antarctic geology under the ice cover.

With aviation, it was finally possible to map the hinterland of the continent, and great discoveries were made as late as 1946–47 during Operation Highjump and during the Soviet's expeditions in the 50's.
 (Don't miss this short footage of the discovery of Bunger Hills:
Youtube)

As far as I know, it was not until the International Geophysical Year (IPY) 1957-58 an international effort deploy scientists and collect data firmly defined the physical shape of the continent, that we are still refining today. International collaboration appears to be the key to successful research in Antarctica.

Seismic data is indeed very important to understand the Antarctic lithosphere, but the resolution is low due to the low seismicity and especially the limited number of deployed seismometers. This is, however, improving during recent years and a number of new studies are using seismic tomography and receiver functions to measure the continental shape of Antarctica. See e.g. An et al (2015a) and An et al (2015b). Seismic data is also used to understand the ice sheets and to derive the heat flux that causes basal melting.

Also very important is satellite potential field data. Gravity data e.g. GOCE from ESA is and important constraints, but the resolution is low.
Magnetic data especially from airplanes but also satellites as the flight lines are still sparse is used to map and understand geological terranes covered by ice. The ICECAP project is collecting high-resolution data from flights to improve our understanding of the ice sheets, glaciers and also the bedrock under.

A good start to look for data and information about the physical nature of Antarctica is to download the datasets in the Quantarctica package. It includes gravity and magnetic data (that should be updated soon). The bedrock elevation data can show you that actually large parts of the Antarctic continent are submerged under sea level due to the weight of the ice sheets, subglacial erosion and lack of major endogenic processes that can cause rapid uplifts. For a geologist, it's however not the elevation that the chemical composition and thickness of the crust that define it as one continuous continent.

Rather inaccessible.

Finally, it's worth notice that the Internet is flooded by ridiculous conspiration theories about the lack of information about Antarctica. Whiles being entertaining to watch (with a couple of beers or so), there is not any truth in them, but the phenomina gives in insight in how myths and lies are created and blooming on the internet and how important it is to stay critical about unreliable sources. The reality is that Antarctica is very difficult and expensive to access and, thankfully, its sensitive nature is well protected by international agreements.


Could we control the weather with a disk in space? There is recorded evidence from solar eclipses that the moon's shadow has a detectable weather effect.

If we placed a disk in space we could project a cold spot onto the planet and control it's position using the position of the spacecraft. In simple terms warm air moves towards cold, so that could be used to pull weather systems out of their normal track.

What is the smallest disk that would create a 300km shadow

Where would be the best place to put it between the earth and sun

What size of effect would you have?

Could you move a monsoon from flooded Asia to drought Australia
How big would the shadow need to be to have an appreciable effect?

If it was always "on" (i.e. you could turn it "off" by rotating it on edge), would the cooling effect be significant?

It's not going to stop global warming but it might buy some time and help redistribute the water more evenly.

Maybe this question belongs also into the space department here.

The only Lagrange point that makes sense is Earth - Sun - L1, and it is unstable (needs continuous correction). Satellites have already been put there, e.g. SOHO. But what we really need to do is cut down greenhouse gas emissions, anything else is not sustainable, or not practicable (a 300km sail in L1 belongs to the latter). Looking at the problems NASA has with the heat shield of the James Webb telescope i am tempted to say that it is not makeable with current technology.

Geostationary orbit is not an option. The spacing between satellites is much too small and the shield would only cover the equator. Even in geosynchronuous orbits the satellite spacing is down to 73km (https://en.wikipedia.org/wiki/List_of_satellites_in_geosynchronous_orbit) i read, so that's also occupied for such a frond. It'll collide in the ascending/descending nodes with other stuff.

The risks of geo- and climate engineering, e.g. lack of knowledge about possible side effects and the potentially drastical acceleration of global warming when engineering efforts cease (out of money error ;-)) and the time when they were in effect has not been used to cut down greenhouse gas emissions, are huge.


Satellite ocean near-surface air temperature data For my study, I need to use satellite Sea Surface Temperature (SST) and at the same time I also need satellite air temperature data (Ta) for the first few meters above the ocean.

For SST I'll be using data obtained from infra-red measurements collected by several satellite radiometers and statistical interpolation.(https://podaac.jpl.nasa.gov/dataset/OISST_UHR_NRT-GOS-L4-BLK-v2.0?ids=Measurement&values=Ocean%20Temperature&search=%22Black%20Sea%22)

So far, I understand that remote sensing of Ta can only be estimated using several methods. My question is: Are there satellite data or products regarding the Ta above the ocean that I can use in my study?

I hope I was clear, thanks in advance.

This is not a definitive answer but a few points from someone who has spent some time with remotely sensed temperature data.

I guess your best bet to get high spatial and temporal resolution surface air temperature would be to get reanalysis data from weather models and augment it with weather data from ships.

Purely satellite retrievals of surface air temperature are not very reliable as this is a rather indirect measurement. Consider Level 2 AIRS 50 km (approx. 0.5 deg) Surface Air Temperature data layer (https://disc.gsfc.nasa.gov/datasets/AIRS2RET_V006/summary?keywords=airs%20version%206). The spatial resolution is much lower compared to surface radiative temperature products. This is in order to compensate for the uncertainty in the atmospheric state and for lower resolution of the sensor that needs to balance its very high spectral resolution with lower spatial resolution to achieve usable SNR levels in each spectral channel.

Speaking of the reanalysis data the NCEP Global Data Assimilation System has 1 deg (approx. 100 km) spatial resolution. However depending on the region of study you might get higher resolution from regional weather models provided by local meteorologists. So you could start with the NCEP data spatially interpolated from 1 deg to 0.01 deg as an initial approximation.


What are Tetens coefficients? Tetens coefficients appear in a few meteorological/climatological models that I've been looking at,for example APSIM:

svp_A = 6.106
svp_B = 17.27
svp_C = 237.3

These same values appear in at least two other models, but I can't find any documentation about what they represent, or where they come from. What are these numbers?

Edit: Oroud, I. M., 2001, Dynamics of evaporation from saline water bodies uses these constants and references Tetens, O. 1930 "Uber einige meteorologische Begriffe." Z. Geophys. 6: 297-309, but that text doesn't appear to be available online, or in my university's library.

The Tetens coefficents are the empirically derived coefficients of an equation for calculating the saturation vapour pressure of water. From wikipedia:

a very good approximation can usually be made using the August-Roche-Magnus formula (usually called the Magnus or Magnus-Tetens approximation, though this attribution is historically inaccurate):
$e_s(T)= 6.1094 \exp \left( \frac{17.625T}{T+243.04} \right)$
e_s(T) is the equilibrium or saturation vapor pressure in hPa as a function of temperature T on the Celsius scale. Since there is only a weak dependence on temperature of the denominator of the exponent, this equation shows that saturation water vapor pressure changes approximately exponentially with T.


Did we ever record a reduction in sea level when the Panama canal was constructed? Are any instruments today or at the time of the creation of the Panama canal capable of detecting a reduction in sea level from the creation of it? Given the size of the canal in comparison to the ocean I'm not sure that we have anything with the precision needed to measure this but I was curious if it was recorded or when the second and third lanes were added if it was recorded.

It's important to note that major man-made navigational canals often are often routed so that only a smaller bit of new waterways is dug; they are typically made by connecting existing waterways with smaller cut\cuts across higher mountainous areas, plus shortcuts in any place where straightening the route saves significantly.
It seems hard to find detailed construction maps (unfortunate!)  But here is a map of the area before the canal was made from the USF historic maps archive:

Comparing that to the Wikipedia map of the Canal shows two main areas of new waterway creation

However, the largest creation on the map appears to be the expanse of Gatun Lake created by damming the river to create a wider channel (with other connected benefits like power and water storage).  Damming rivers is of course a widespread practice around the world for purposes including water regulation, power generation and agriculture.
Looking at rough estimates of water changes (hopefully with no errors!):
Note these use the US\UK definitions of billion as $10^9$ and trillion as $10^{12}$.  Replace billion with millard and trillion with billion in other regions.

The Culebra Cut "has an average depth of about 43 feet (13 metres) and extends some 8 miles (13 km) to the Pedro Miguel Locks" and "throughout its length the canal has a minimum bottom width of 500 feet (150 metres)" [Brittanica].
So that would be about 7 billion gallons (26 billion liters).
The Wikipedia articles lists Gatun Lake as 4.2 million acre*feet.
That's 1.4 trillion gallons (5.2 trillion liters).
Lake Alajuela is another 150 billion gallons (600 billion liters).

Given that the lakes are the significant amounts of water, 2 trillion gallons (8 trillion liters) would seem an extremely generous estimate for the amount of additional water impounded by the entire system (including widening the river and the water in the Gatun, Pedro Migual, and Miraflores Locks). If assumed all of that ends up being removed from the ocean, averaged over the 140 million square miles (362 million square km) of ocean surface area, that would be roughly 20 micrometers of depth (less than 1/1000th of an inch), comparable to the width of a human hair.  Again, remember that's a very generous estimate.
Given that Wikipedia lists 48 reservoirs around the world that each are more than twice the amount of the water estimated above, it would seem more significant to ask how much those remove in total from ocean.  Still, all those combined would seem only to be on the order of perhaps centimeters of depth lost in aggregate.


Why is my pond / lake melting when the temperature is still far below freezing? I recently moved into a new house with a 2 acre lake behind it. We’ve had 15 consecutive days below freezing, and the last 12 of those have been below 20 degrees (Fahrenheit)! Six days ago I shoveled off a small spot to test out whether it would be good to ice skate on the surface, with the plan that yesterday I would shovel off a much bigger area. Yesterday morning, however, I woke up to a big area straight across starting to melt! The temperature was about 5 degrees F. This morning it’s even larger. The temperature did not exceed 20 degrees yesterday. Though there has been frigid cold it has been sunny. Is it possible that the area I shoveled caused this? The rest of the lake looks exactly the same (About 2” of snow all over it. No signs of melting anywhere else.) I’ve attached before and after pictures. Can’t figure out how in the world this could happen. Any ideas?

My guess is that since ice (and the liquid water underneath it) is much better at absorbing thermal radiation than air, then even if the air temperature is below zero, the ice can heat up in the sun and melt a little bit. It will presumably then refreeze at night when there is no sun to keep it warm.

This was probably also happening on the surface of the snow as well before you cleared it but you didn't notice it because there was no colour change.


Regeneration rate of nature after environmental catastrophes It sounds logical, but I wonder if the regeneration rate of nature (natural absorption of $\ce{CO_2}$) is decreased after an environmental catastrophe (resource stock depletion, etc.)?

Or are most catastrophes mainly caused by the decrease of regeneration rate of nature?

I would really appreciate academic references on this issue.

It sounds like you are asking about plants taking up carbon at different stages of Ecological Succession that occur after some catastrophic event (e.g. a wildfire or lava flow).

If the prior ecosystem was dominated by live vegetation such that the detritus emitting $\ce{CO_2}$ was much less than the $\ce{CO_2}$ uptake by plants, then a catastrophe will generally lower the $\ce{CO_2}$ uptake.

When the catastrophe (e.g. lava flow or land slide) creates a new land-surface, then primary succession begins with the establishment of generally small forms of life and $\ce{CO_2}$ sequestration would be minimal. Otherwise, if the catastrophe leaves behind some form of the prior ecological community, then secondary succession can occur and the region would be able to return to higher $\ce{CO_2}$ sequestration rates much sooner relative to a primary succession event.

You might enjoy the following references:

"Carbon sequestration is related to mycorrhizal fungal community shifts during long-term succession in boreal forests."
available here: http://www.ncbi.nlm.nih.gov/pubmed/25494880
"Chapter 3: Effects of Disturbance, Succession and Management on Carbon Sequestration" in the book "Carbon Sequestration in Forest Ecosystems" available here: http://link.springer.com/chapter/10.1007%2F978-90-481-3266-9_3


Coral Reef and Volcanic Islands I have two questions regarding coral reef and volcanic islands.

When a new volcanic island is formed, how much time generaly passes before a coral reef starts to form around the island?

Another question: Are there any volcanic islands in warm pacific waters which do not show fringing or a barrier reef? If so, is this because the island was formed recently and is still too hot for a coral reef to flourish?

I just came upon this paper by Tomascik et al. (1996). It does not answer directly your question, but I found it sufficiently relevant to post it here anyway. It's a study of coral colonization after emplacement of a lava flow. They found that only five years after emplacement of an andesitic lava flow from Gunung Api in 1988, large parts of this new coastline was already covered by coral. They mention a previous study (Grigg and Maragos 1974) on Hawaii where it took 20-50 years for coral to colonize a submerged lava flow.

Of course, in those cases the coral could come from nearby reefs, while in the case of a new island it has to come from further away. So those fast colonization timescales are not directly applicable to your question.


Nepal earthquake of 25 April 2015 On the 25th of April at about 11-12pm, an earthquake whose epicenter was in Nepal was felt with a magnitude of 7.5 in Delhi NCR, as well as in other Indian states (Rajasthan, Bihar, Jharkhand, and many more).

What were the reasons behind it?

A brief, very simply explanation.

The earthquake that struck Nepal on 25 April 2015 occurred in a region with a history of catastrophic tremors.

The Indian tectonic plate is slowly moving at an average rate of 45 mm/year underneath the Eurasian plate. Such movement is never smooth and sometimes the plates get temporarily stuck. Eventually the force producing the movement of the Indian plate increases the pressure on the snagging point, or points, and the plate can jolt. This jolt sends out shock waves through the neighbouring rock which causes the earthquake. The bigger the jolt the stronger the earthquake.

More detail:

From the news services and the US Geological Service

  the USGS wrote in its summary, the quake "occurred as the result of thrust faulting on or near the main frontal thrust between the subducting India plate and the overriding Eurasia plate to the north. At the location of this earthquake, approximately 80 km to the northeast of the Nepalese capital of Katmandu, the India plate is converging with Eurasia at a rate of 45 mm/yr towards the north-northeast, driving the uplift of the Himalayan mountain range. The preliminary location, size and focal mechanism of the April 25 earthquake are consistent with its occurrence on the main subduction thrust interface between the India and Eurasia plates."

  According to the USGS, a quake in the region in 1934 is believed to have killed roughly 10,600 people. Another in 1988 killed 1,500.
  But the experts said big quakes in the area are not necessary common.
  "Although a major plate boundary with a history of large-to-great sized earthquakes, large earthquakes on the Himalayan thrust are rare in the documented historical era," the UGS wrote. "Just four events of magnitude 6 or larger have occurred ... over the past century."


Is glacier growing a hoax? There is a wikipedia page on glacier growing, and also a Master thesis has apparently been written on the subject, investigating this practice in Northern Pakistan.

On the one hand, I have read (I'm a physicist, I know next to nothing about glaciers!) that glaciers are highly nonlinear systems, displaying strong hysteresis effects. On the other hand, I would expect that relevant time scales for glacier growth are more in the hundreds of years and not decades.

Therefore, I would love to know if this is practice is scientifically grounded in any way?

There is a decent explanation in Glacier Man Science 30 Oct 2009:
Vol. 326, Issue 5953, pp. 659-661. (alternative link)

  Norphel’s idea was to divert the lost winter
  water from its course down the mountain,
  along regularly placed stone embankments
  that would slow it down and allow it to spread
  and trickle across a large, shaded surface
  depression a few hundred meters from the village.
  Here, the slowed water would freeze and
  pack into a glacier that would begin melting
  when the sun rose high enough in spring to
  expose the thick ice

...

  Norphel has built nine glaciers since that
  first one, which he began in the late 1980s
  and worked on until 1994. They average
  250 meters long by 100 meters wide; the
  Phuktse glacier remains the largest. Norphel
  estimates that each one provides some 6 million gallons (23,000 cubic meters) of water,
  although there has been no accurate analysis to
  date, and the undulating ground makes it difficult to guess the volume of ice in each glacier.
  Each artificial glacier is built using local
  labor and materials for about 3 to 10 lakh
  Indian rupees (6000 to 20,000 US dollars),
  depending on the size and site, compared
  with about US$34,000 for a cement water
  reservoir, Norphel says.

Personally, I wouldn't call these glaciers.  It is more that water is being dammed so it freezes rather than runs off, and stays frozen into the spring then eventually melts before the end of the season.


Does flow banding only occur in silicic rocks? I made a video about what I learnt in my A Level Geology course so far, about igneous rocks.

One thing I mentioned was that flow banding is mostly only found in silicic rocks (and so mostly rhyolite) because that's what the textbook says.

However, someone commented that this may not be true, so I'm curious - what rocks can / does flow banding occur in?

Flow banding can occur in all igneous rocks, regardless of their composition. Any kind of molten rock that flows may eventually cause some flow banding. Sometimes the flow banding is not even obvious to the eye and can only be detected using geophysical methods such as magnetic anisotropy.

Here's an example of flow banding in a mafic rocks from Skaergaard intrusion in Greenland:

source

This looks like a sedimentary rock, but it's in fact igneous. Those are layers of minerals such as olivine, pyroxene and plagioclase that settled from a melted magma chamber.

It doesn't even have to be a silicate rock, here's a picture of natrocarbonatite lava from Ol Doinyo Lengai volcano in Tanzania:

source

Obviously, this rock exhibits flow banding and it hardly has any silica in it.


Recreating the rock cycle I want to recreate the rock cycle using some item that can behave as a rock. The purpose of this is to get a point across to my students about how really there is a reason why the rock cycle is called rock cycle.

Most of them find rocks dull and uninteresting, so I was thinking about proving the rock cycle some other way. In a couple of hours researching I came across some surprising ideas, such as crayons, chocolates, wax, etc.

I wanted some feedback on how well you think I can get the point across of the rock cycle being a cycle. To them, thinking that something liquid, turn into solid, then gets destroyed, and mixed into something else, then melted again, is really hard to understand. Using something that does not take millions of years to form might be a better strategy I think.

Here's an idea:

You can use dark chocolate and white chocolate. Use a grater to create "sediments": layers of alternating grated dark and white chocolate.

Now heat them up just before melting so you can stick them together with pressure, preserving the layered structure. Now fold them. There's your "metamorphic" rock.

Then, just melt the entire thing to create some chocolate-lava flows. Grate them again and eat!


What is the difference between mobile & molten rock? In the book Fundamentals of Geomorphology (Routledge Fundamentals of Physical Geography) by  Richard John Huggett there is a  sentence " Intruded rocks, which must be mobile but not necessarily molten, may have a direct effect on landforms by causing doming of the surface." What is the difference between molten & mobile rock?

Molten rock must be a liquid, mobile rock is any rock capable of moving, sand and mud can be mobile.


Is there a 'standard size' for volcanic eruptions in terms of gas output? We saw recently the Iceland volcano Eyjafjallajökull produced significant gaseous output that impacted the flight paths of several planes.

When we look at volcanic gas components, we see they produce:

water vapor (H2O)
carbon dioxide (CO2)
sulfur either as sulfur dioxide (SO2) (high-temperature volcanic gases) or hydrogen sulfide (H2S)
nitrogen
argon
helium
neon
methane
carbon monoxide
hydrogen

I'm trying to answer the question - "how many 'standard volcanic eruptions' does it take to product X moles of sulfur dioxide." Can I do it in terms of Y number of Mount St. Helens 1980 eruptions?

My question is: Is there a 'standard size' volcanic eruption in terms of gas output?

There is no "standard volcano" or "standard volcanic eruption". However, to perform the calculation you want to do, you could use the "typical" of "average" volcanic eruption.

The characteristics of the "average" volcanic eruption can be found by calculating the average parameters of many volcanic eruptions. Such averages are not often reported, because the variability of volcanic eruption sizes and compositions is so large that averaging them doesn't makes much sense. But it does for your very particular application. So let's try to estimate how the "typical" volcanic eruption looks like:

Let's first figura out the typical volume of ejecta produced by a volcanic eruption: this is usually measured by the VEI (Volcanic Explosivity Index), and the formula to turn VEI into volume is

$\text{Ejecta volume}=10^{-4+\text{VEI}} \, \text{km}^3$

If we download NOAA's Significant Volcanic Eruption Database, it contains 646 recorded eruptions from 1750 to the present, and 498 of them have reported VEI values. Computing the volume ejected by each eruption (using the above formula) and taking the average we get that the "typical" eruption produces 3.2 km$^3$ of ejecta.

Using an average density of volcanic ejecta of 2 g/cm$^3$, this average volume corresponds to $6.4 \times 10^{12}$ g or 6,400,000 tons.

In typical magma, about 0.5% of its mass corresponds to gases, and for our "typical" mass that would corresponds to $3.2 \times 10^{10}$ g or 32,000 tons of gases in a "typical" volcanic eruption.

Now, about 7% of the gases corresponds to SO$_2$. That means that 0.035% of the mass of the ejecta is SO$_2$, and for our "typical" mass that would corresponds to
$2.24 \times 10^9$ g or 2,240 tons of SO$_2$ in a "typical" volcanic eruption.

As you will see if you follow my references, I've pulled the above figures from multiple sources with varying degrees of reliability. Therefore, if you want a more precise estimate you can search for more accurate and updated values and repeat the exercise.


How do Kelvin waves determine surface temperature variations? Kelvin waves are basically waves that balance out the Coriolis force against topographic boundaries like coastlines and mountains. It seems very important in the oceans, for example.

My question is this: are Kelvin waves important in determining the surface temperature variations of regions that are, for example, on the west side of mountain slopes like the Andes or Rockies?

Coastal trapped Kelvin waves are important processes contributing to variability in the sea surface height and temperature near the coast. Field studies have measured large temperature fluctuations mainly made up of low-frequency internal Kelvin waves mostly of semi-diurnal tidal period at the continental shelf on the great barrier reef (Wolanski, 1983). Because they are balanced by Coriolis, in the Northern Hemisphere they remain fairly stable if they are propagating towards the North if the coast is on the right, or to the South if the coast is to the left.

  My question is this: are Kelvin waves important in determining the surface temperature variations of regions that are, for example, on the west side of mountain slopes like the Andes or Rockies?

It is pretty clear that Kelvin waves and associated upwelling play a crucial role in introducing nutrients, larvae and other components into the ocean's coastal regions (relatively cold water). However, the connection between surface temperature variation in the coastal waters and the temperature in the regions west of mountain ranges you mention is not so clear.

One thing that could happen is that, because upwelling is associated with relatively cool water being introduced to the near shore from the deep abyss, the coastal marine layer will have a lot of moisture. As the moisture laden air traverses a coastal mountain range, it will rise due to orographic lift and cool adiabatically, thereby raising relative humidity all the way to 100% resulting in rain. So the coastal side is cool and wet, whereas on the other side of the coastal range it will be much warmer and drier.

Wolanski, E., and G. L. Pickard. "Upwelling by internal tides and Kelvin waves at the continental shelf break on the Great Barrier Reef." Marine and Freshwater Research 34.1 (1983): 65-80.


How do tectonics work on other planets? What kind of tectonic plate activity exists on other planets in the solar system, or even large moons? Are there any deeper studies of what is needed for a planet or large moon to have tectonic activity, and how that activity might differ from planet/moon to planet/moon?

It's a huge field of research and a lot of interesting studies have been published over the years, but also a lot of speculation. Models and theories are mostly based on surface structures observed by remote sensing. Potential field data, as gravimetry can also add good constraints when available.

Tectonic forces might be rather common in large young planets, but as they cool the process usually stops. In our time and solar system, plate tectonics as we would recognize it, is only known on Earth (and maybe Titan). Other tectonic forces can cause similar features by local uplifts, volcanism and cryovolcanism.

Venus appears to have some kind of tectonic forces, at least in the past. An important part of the present research focus on the dynamics and chemistry of the Venusian mantle and how the topography helps us understand the development of the planet. The data from Magellan in the early 90's are particularly important. Studies of Venus also helps us to understand how tectonics developed on Earth. It's been suggested that lack of water as a lubricant in the Venusian upper mantle makes continental drift impossible, but mantle dynamics can still cause local/regional uplift and volcanism.

Europa is also supposed to have an odd kind stress that resembles tectonics, but caused by the tidal force from Jupiter that deforms the moon. We have the same tidal deformation on Earth, but it is much stronger on Europa and can cause dynamics that mix the interior. Somehow similar to how one should roll and press a lemon before cutting it to squeeze out the juice. Galileo is the main source of data, still.

Titan could be the candidate that most resemble Earth, but it's under debate and more data is needed.

The reasons to have plate tectonic on a planet are complicated and debated. I wouldn't say that we even have a good understanding of the continental drift on Earth yet. The best approach to understand what is needed for tectonism is to look at the planets energy budget, how much heat is generated and how can it leave the planets internal system. The chemistry of the mantel is also important, some dishes boil, other dishes fry. Water or other fluids appears to be crucial.

A rather interesting suggestion for Earth's unique plate tectonics is that it depends on additional energy harvested by the photosynthesis in green plants. It might be that life is the cause of mountains instead of the other way around.


What is the effect of sea-level changes on the extent of the Earth's atmosphere? If sea-levels rise, does the Earth's atmosphere extend to the same distance out to space, with the pressure increasing, or does it expand?

If sea levels rose 10m, how much change would there be to the volume of the atmosphere?

90% of earths atmosphere is from 0-10000m this means an increase of 0,001%.

But this is wrong the melting ice will be replaced by air so there will not be any change in volume.

Ice have a larger volume than water have so the result will be a very slight drop in air volume.

I have not taken hight for air under pressure in the ice here but you get the point,You are only redistributing material on our planet so nothing is added or removed from the system.


How significant is organic cotton agriculture to the USA's total global ecological footprint? The ecological footprint of a human activity can be measured in global hectares (gha). Cotton's ecological footprint to produce one ton of product ranges from 2.17 gha for organic cotton to 3.57 gha for conventional cotton (see this analysis).  How significant is that, relative to our total global ecological footprint?

The ecological footprint is the impact of a person or community on the environment, expressed as the amount of land required to sustain their use of natural resources.  A global hectare (gha) from Wikipedia:

  One global hectare represents the average productivity of all biologically productive areas (measured in hectares) on earth in a given year.

and...

  The global hectare is a useful measure of biocapacity as it can convert things like human dietary requirements into a physical area, which can show how many people a certain region on earth can sustain, assuming current technologies and agricultural methods. It can be used as a way of determining the relative carrying capacity of the earth.

and ...

  The total number of global hectares is approximately 11.3 billion, averaging about 1.8 global hectares per person (2004).

I highly suggest you read this page here:
http://www.footprintnetwork.org/en/index.php/GFN/page/frequently_asked_questions/
and here:http://www.footprintnetwork.org/en/index.php/newsletter/bv/humanity_now_demanding_1.4_earths

which explains global footprint quite nicely and puts it into perspective.

  The data show that humanity’s demand on the biosphere for providing natural resources and absorbing carbon dioxide emissions is 44 percent more than what nature can provide. This ecological overshoot means it now takes approximately 18 months for the Earth to regenerate what we use in one year. The urgent threats we are facing today - most notably climate change, but also biodiversity loss, shrinking forests, declining fisheries and freshwater stress - are symptoms of this trend.


DC component in Hilbert transform concept for seismic data In The Leading Edge tutorial article Phase and the Hilbert transform (Purves 2014), there is the following line:

  So we apply a Hilbert transform by multiplying all negative frequencies by i and all positive frequencies by -i, leaving any DC component untouched.

I have two questions following this:

1) What is the DC component?

2) What is the significance of not affecting any DC component?

The 'DC Component' is a standard term used to describe the mean energy of a signal ( https://en.wikipedia.org/wiki/DC_bias ), which in the frequency domain corresponds to the component of 0 frequency. The DC component does not depend on the time -- while the other frequencies 'wiggle' around it. In seismic signals I think we don't generally have a DC components: the signal moves around a point of 0 pressure/displacement.

The authors then make their statement in a bit of an awkward way in my opinion. What they mean, is that the Hilbert transform applied to any 'DC component' is 0: thrown away!


Is there any experiment to prove that CO2 with the atmosphere concentration can have greenhouse effect? All gas molecules have the capability to absorb radiation energy. $\rm{CO}_2$ has much less capability to absorb radiation energy, comparing with water vapor.
In Earth's atmosphere currently $\rm{CO}_2$ constitutes only about 0.04% (400 parts per million) of the atmosphere. On average, about 2 to 3% of the molecules in the air are water vapor molecules. In the air the water content is about 50 times higher than $\rm{CO}_2$.
So it seems that $\rm{CO}_2$ content increase in the air should not have any measurable contribution to global warming.
Is there any experiment to prove that $\rm{CO}_2$ with the atmosphere concentration can have greenhouse effect?

Your question about water vapour is quite a common one among people learning about the greenhouse effect. Once you discover the relevant proportions of water vapour and CO2 in the atmosphere, it's perhaps natural to assume that the CO2 can't be playing a major role. In reality it doesn't work like this, for at least a couple of reasons. First, let's look at what the 98% actually means in practice.

It's not just about the concentration

The concentration of a gas in the atmosphere isn't the only thing that determines its warming potential -- otherwise nitrogen, at 78% concentration, would be the most important greenhouse gas. Each gas has a different radiation absorption spectrum, and a different warming potential. So despite its much greater prevalence in the atmosphere, water vapour only has about twice as much long-wave absorption potential as CO2.

At this point, you may be thinking ‘but twice as much is still a lot more, so the CO2 can't be significant!’. But there's another non-obvious factor here, which has to do with the difference between feedbacks and forcings.

Forcings versus feedbacks

In the climate system, CO2 concentration is a forcing, whereas the water vapour concentration is a feedback. To illustrate the difference, here's a crude analogy:

Suppose that I'm trying to lose weight, but I'm reluctant to reduce the 300 grams of delicious chocolate cake that I eat every day. Having read that the human body is around 80% water by weight, I conclude that the cake can't be a problem: after all, I drink 2 kg of water per day, so it would make more sense to reduce that! So I cut down to 1 kg of water per day and maintain my cake intake. Several weeks later, I'm surprised to find that I haven't lost any weight! What's happened? It turns out that the human body regulates its water content, so reducing my intake just reduced my output. Fat storage isn't regulated in the same way, so the cake keeps piling up.

It's a similar story with CO2 and water vapour: CO2 concentration in the atmosphere actually changes for a long time (decades to centures) when we release more gas. Water vapour is, in effect, self-regulating. If we could wave a magic wand and instantaneously remove all the water vapour from the atmosphere, here's what would happen:

(source)

Within 50 days, the water vapour is back to  within 1% of where it would have been without our intervention.

So, if the water vapour concentration isn't controlled by input, what is it controlled by? Temperature. The warmer the atmosphere is, the more water vapour it can hold. This means that when the temperature goes up due to increased CO2, the water vapour content also increases, which further intensifies the greenhouse effect. It's acting as a positive feedback.

Since you're not the first person to ask this question (by a long way), there are already some good resources online specifically addressing the different roles of water vapour and CO2 in global warming.

"Common Climate Misconceptions: The Water Vapor Feedback" is a 2008 piece in the Yale Climate Connections series saying more or less what I've said above, but in more detail and without the cake analogy.
"Water vapour: feedback or forcing?" is a great 2005 essay by Gavin Schmidt explaining the role of water vapour in climate change.
"Explaining how the water vapor greenhouse effect works" is a brief Skeptical Science piece mainly focusing on the positive feedback effect.

Laboratory measurements of CO2 absorption

You seem to be particularly interested in laboratory experiments on
carbon dioxide absorption. As an excellent starting point, I can
recommend the (currently) 26 publications in AGW Observer's list of
papers on laboratory measurements of CO2 absorption properties. If you're really keen to see experimental confirmation that CO2 can still absorb radiation even at atmospheric concentrations, you could take a look at (for example) Taylor and Yates (1957), Yates and Taylor (1960), or Streete (1968), all of which clearly demonstrate that CO2 absorption bands are present in normal atmospheric air.

As an aside: personally I find find that the numerous spectroscopic observations of the whole atmospheric column -- from satellites or ground stations -- provide a more compelling demonstration of the greenhouse effect. After all, the atmosphere isn't a homogeneous bottle of gas that can be faithfully scaled down into a lab sample. But your question and subsequent comments indicate that you're not interested in measurements of the atmospheric column itself, so here I'm just concentrating on ground-level experiments which demonstrate the long-wave absorption properties of CO2.

Answers to comments

  If there is a such positive feedback exist without other negative feed backs, the earth will get warmer without co2 contribution.

I think you might be a little confused about the definition of a feedback here. As I've tried to explain above, the term ‘feedback’ means that the water vapour content is determined by other factors within the climate system. It can amplify the effects of forcings, but it can't in itself ‘push’ the system one way or the other. So you can't have a positive feedback without some kind of forcing: the forcing is precisely the input which the feedback is ‘feeding back’ into the system, in this case via the global temperature increase.

To understand the difference, it might be helpful to think about another form of feedback familiar to a lot of people -- audio feedback through an electric guitar and amplifier system. As you can see in the linked video, there's no sound until the guitarist plays a chord. But once he does play a chord, the guitar pickup itself detects the amplified sound and feeds it back into the amplifier, creating a loop which sustains the sound indefinitely. You can think of the initial chord as analogous to the CO2 input, and the feedback loop as analogous to the water vapour effect: the audio feedback, like the water vapour feedback, doesn't do anything until it's got an initial input from some other source.

  All co2 released from fossil fuel was in the atmosphere during the dinosaurs time. If co2 release from all fossil fuel, it will restore the dinosaurs time atmosphere status. ... you can not deny that those co2 was in the atmosphere in earth history and earth animals and plants flourished

This doesn't really have much to do with your original question! If you want to ask about this, please go ahead and post a new question; StackExchange isn't a discussion site, and we try to keep each question focused on a single topic.

With this in mind, I'll just give a very brief answer here. Your formulation is a little inaccurate: the age of the dinosaurs spans at least 135 million years, there was a lot of carbon burial before it started, and all the carbon currently in the ground wasn't in the atmosphere at the same time. However, it is true that the Earth has seen higher CO2 levels than at present, and that much of that excess carbon is now locked up in fossil fuels. So what would happen if we put a lot of that carbon back in the atmosphere and tried to recreate the high-CO2 atmosphere that, say, T. rex breathed in the Late Cretaceous? Back then, the Earth was a lot warmer, with little or no ice at the poles. One of the biggest effects of re-releasing all that carbon would be the melting of our current polar ice sheets, raising sea levels by some tens of metres. The problem is not that the Earth will become completely uninhabitable by any life form whatsoever (although many current species will go extinct). The problem is that a lot of species, including Homo sapiens, are poorly prepared for a climate change of this magnitude. Ten percent of the world's human population and 8% of its urban land area is in low-elevation coastal zones, and would be completely submerged by a 10-metre sea-level rise -- which is still far less than the sea levels seen during the age of the dinosaurs.

Sea-level rise is just one effect among many, but for now I'll leave it at this since (as I mentioned above) this isn't related to your original question.

  If a person cut his water intake in half, he will get sick before he can get fatter.

This is a little peripheral to the question, I think :-). If you don't like the analogy you can ignore it: it's not essential to the explanation. However, just to reassure you: the EPA Exposure Factors Handbook (2011 edition) gives a mean value of 1,043 ml for the daily drinking water intake of an adult in the US. Thus, I don't think that restricting one's water intake to 1 kg per day, as in my thought experiment, would necessarily cause sickness.

References

Streete, J. L. (1968). Infrared measurements of atmospheric transmission at sea level. Applied optics, 7(8), 1545-1549.
Taylor, J. H., & Yates, H. W. (1957). Atmospheric transmission in the infrared. JOSA, 47(3), 223-226.
Yates, H. W., & Taylor, J. H. (1960). Infrared transmission of the atmosphere (No. NRL-5453). Naval Research Lab, Washington DC.


Future geology professor wants to know quick fixes to get me through unstimulating period So I am a science nerd. I am literally the guy in high school who would run up to people and say "hey, I just learned quartz is formed from rapidly cooling magma. Isn't that awesome!" I'm actually currently working towards a high school biology degree but when I'm done with that I will continue with an earth science degree until I can teach college. Not just a dream, I WILL make it happen.

Anyway, I was wondering what sorts of tricks I can do right now to play with geology until I actually can get into the field. Like is it possible to analyze the composition of my own backyard using basic tools? I have the gusto, I literally just launched some R-candy rockets using a mix of 63% KNO3, 32% sucrose, 4% aluminium and 1% iron sulfate.

Also, is there any self employment for amateur geologist? Like if I figure out how to analyze my own yard, can I then do the same for others for a small fee? (I'm a substitute teacher now so I'm always broke).

What cool things can be done by an amateur geologist with no prior geological schooling (and very limited funding) but with a strong drive to understand the world we live in?

PS. I built a primitive forge from homemade clay bricks that I use to melt aluminum from scrap into art so is there any uses for that in amateur geology?

I'd suggest to get out and do some mapping. Get a map, look for local outcrops and mark them on your map. Try to find the same type of rocks or unit in more than one location and try to connect them. Compare it with published maps and see if it makes sense. Then start to think about the reasons why the units are located as they are and read a bit about tectonics. Your chemical interest is useful to define the rocks you find (e.g. use acid to recognize carbonates) and your biological interest is useful if you are fortunate enough to live in an area where you can find fossil bearing rocks to help you with the dating. The experiences you make whiles learning the trade can suggest what the local work market looks like. Learn GIS and mapping.

Geology is a great way to combine theoretical studies with fieldwork and use some excess energy. Let your interests define what branch of geology you would like to focus on.

If you are looking for professional projects, I'd contact local engineering companies that work with infrastructure or similar and check if the need extra crew for fieldwork. There are sometimes casual workers needed for geophysical surveying or sampling.

Depending on where you live, groundwater could be another option, contact local drilling companies, learn how to handle a rig and learn some hydro-geology. With a detailed geological map of an area, groundwater modellers can make better decisions - maybe even paying something for the data.


What caused this waterfall to have rounded formations? This is at Bua Tong Waterfalls in  Chiang Mai, Thailand.

Tried to find scientific information about this waterfall, but google turns up only travellers' vague guesses, suggesting calcium carbonate rich waters. The rock itself seems to have formed by layers of crystallised minerals, and is soft enough to be scratched with a strong stick. It is also quite grippy, allowing tourists to walk up unusually steep surfaces.

What causes such waterfalls and rocks to form, and what are its characteristics?

Looks like alkali earths ( Ca, Ba , etc.) carbonates deposited from a supersaturated hot spring. As the water emerges from the spring, carbon dioxide leaves the water and the water cools, it precipitates the carbonate ; you could call it limestone. There may be other minerals that will precipitate from a spring. From the foliage , it looks like a relatively recent development.


If there's acid rain, is there such thing as acid snow? If so, would the acid snow just be as damaging?

As explained by user voltaic at reddit:

  Yes, there is, and it can be more of a problem than acid rain.

  For one, when snow is falling it spends more time travelling through
  the atmosphere before hitting the ground than rain. As a result of
  this, it has more time to collect pollutants, and can become more
  acidic than typical acid rain for the same region. There's additional
  factors that complicate this however, such as the solubility of the
  pollutant, the temperature and the water content of the snow, etc.
  (e.g. warmer snow which is more "wet" is going to dissolve more than
  cooler, drier snow.)

  Once the snow hits the ground, the dissolved pollutants are going to
  stay in solution, or trapped within the crystalline structure of the
  snow until it melts. Because of this, snow can pile up and then thaw,
  releasing all the pollutants and acidic water in a relatively short
  amount of time. This can have fairly substantial effects on the
  environment.

  You can read a bit more about this here:

  http://www.elmhurst.edu/~chm/vchembook/191acidsnow.html
  http://dwb4.unl.edu/Chem/CHEM869V/CHEM869VLinks/www.qesn.meq.gouv.qc.ca/cc/acidrain/info6.htm

Acid snow is also mentioned in passing on the acid rain wikipedia page.

The "fairly substantial effects on the environment", as described by the links above, largely involve a large release of acid during the spring thaw, which effectively releases all of the acid built up over the winter in a relatively short period. This can result in lowered pH in waterways, which can affect fish, amphibians and crustaceans.


What are the differences between alluvial, eluvial and colluvial deposits? There's always confusion and disagreement when these terms are mentioned. Need to be sure of their exact meanings.

Your question is almost a duplicate of What is the difference between eluvium and alluvium?, but you also ask about colluvial deposits. The accepted answer for that question references this convenient guide from the Australian Museum, which also covers colluvial deposits:

Alluvial: Detrital material which is transported by a river and usually deposited along the river's pathway, either in the riverbed itself or on its floodplain.
Colluvial: Weathered material transported by gravity action such as on scree slopes.
Eluvial: Weathered material still at or near its point of formation.


How Old Are the Verkhoyansk Mountains in Northeastern Russia? The multi-brown "hand" at the middle of this image is the Verkhoyansk Mountain Range in northeastern Russia.  The best information I got regarding its age is simply "Cretaceous".  But when in the Cretaceous?  Because that is a pretty extensive chapter in Earth's geological history, spanning from 145 to 66 million years ago.

Depends on what exactly you are looking for.

The mountains contain material which is much older, some as old as the Permian. This material is hosted in detrital sandstones, so obviously that area was not a mountain back then.

The deformation of that area, is indeed Cretaceous:

  The early stage of deformations dated as 160 Ma, the main stage dated as from 70 to 90 Ma.

So to answer your question, the mountains formed throughout the entire Cretaceous duration, but mostly in later (younger) times.


To what degree does historical measurement inaccuracies contribute to climate change models? Often the graphs depicting the earth's historical temperature, the time axis extends well over couple of centuries. Also there are few that extends over thousands of years.
I wonder to what degree the measurement inaccuracies are taken into account while using these charts to communicate the ongoing climate change. Its a valid question that older temperature measurement suffer a higher error compared to modern day's methods.
Even the feared 2.5°C temperature rise over the industrial revolution time is a minute variation over centuries. To what degree has the climate models taken into account these measurement errors into account? (In short, the question is basically from a climate change sceptic that goes like - "Thermometers have gotten better and we are just measuring the true temperature and it's not that the world is warming up. So how can we accept climate change/global warming?")

I would estimate 0%, as long as we are considering the same types of models. See, climate models and in the regard that you may think of observations. Climate models aren't really initialized on observations of the system, but rather on inputs/forcings and mean state.
Observations of today's climate may validate the accuracy/tuneness of a climate model, but the types of observations used to run climate models may be different from what you expect. For example, the thermometer was invented either near 10 AD or in the 17th century, so it was obviously not a widespread invention then. Usually, those temperature measurements are taken as proxies, such as the amount of oxygen isotope or atmospheric composition in ice cores. So the answer to the climate skeptic is that it isn't just the temperature itself, but the modern day observations of temperature proxies that show past warming.


Geological Differentiation: variables and size requirement Geological/Planetary differentiation is one of those topics that gets glossed over in intro Geo courses. We know that differentiation occurs over deep time (and will never end) and is a result of the heating of rock. Heating in this case can be driven by collision, accretion (planet formation), and radioactivity. So, we know that the Earth, Mars, and Moon have all differentiated. On the other hand, smaller asteroids will never differentiate. Are there any set/known size requirements on a body before it attains a high level of differentiation like the Earth?

Not really.

Assuming even minor igneous bodies differentiate (stocks), and that differentiation is basically a process of decantation of the solid magmatic phase (a process known as fractional crystalization) and fractionation of the fluid magmatic phase, virtually any solid mixture can differentiate. If you're not convinced, here's another argument.

Let's take an analogous situation to differentiation: exsolution. They're not the same. Exsolution involves ionic migration in a solid structure. Differentiation involves ionic migration in a fluid (magma), which lacks structure. But both involve an outcome of different chemical phases. And exsolution can happen in microscopic sizes of milimetric crystals. So its fluid-ambient counterpart would, as a logical conclusion, be also able to happen on such minute conditions, and perhaps on smaller even.

And I'm not sure what you mean that differentiation will never end? On a long term geological scale - I'm talking about hundreds of millions to billions of years - that idea is perhaps correct, assuming the upper mantle and crust are constantly changing their compositions. But if you're saying that differentiation is a process that happens widespread (the entire crust, or the entire planet), rather than on specific locations (where partial melting occurs), under a small timescale (millions of years), then you're not correct, because differentiation only occurs in mixtured fluids (and I'm not sure whether it's used for any other fluid than magma).


Were there any plans or proposals for "unilateral geoengineering deployments" before this paper was publsihed? I saw the catchy Phys.org news title Artificially cooling planet 'risky strategy,' new research shows and then looked at the open access article, in Nature Communications (14-Nov-2017 online) Impacts of hemispheric solar geoengineering on tropical cyclone frequency, Jones et al. doi:10.1038/s41467-017-01606-0

Abstract:
Solar geoengineering refers to a range of proposed methods for counteracting global warming by artificially reducing sunlight at Earth’s surface. The most widely known solar geoengineering proposal is stratospheric aerosol injection (SAI), which has impacts analogous to those from volcanic eruptions. Observations following major volcanic eruptions indicate that aerosol enhancements confined to a single hemisphere effectively modulate North Atlantic tropical cyclone (TC) activity in the following years. Here we investigate the effects of both single-hemisphere and global SAI scenarios on North Atlantic TC activity using the HadGEM2-ES general circulation model and various TC identification methods. We show that a robust result from all of the methods is that SAI applied to the southern hemisphere would enhance TC frequency relative to a global SAI application, and vice versa for SAI in the northern hemisphere. Our results reemphasise concerns regarding regional geoengineering and should motivate policymakers to regulate large-scale unilateral geoengineering deployments. (emphasis added)

The paper seems to warn against single-hemisphere solar geoengineering. Was that the plan to begin with, and nobody until now thought that cooling one hemisphere but not the other one might be problematic?
Or is this paper simply stating something more common-sense, for example "if you do it wrong, it won't work right".
Was there in fact any plan for unilateral geoengineering deployments before this was published, or is there a bit of grandstanding along with the science?

I think the introduction of the paper itself covers this adequately:

… a growing number of studies have investigated regional SG application scenarios, which could prove preferential to a global application by restricting the geospatial magnitude of the climate response or by being used to target specific climate changes8,9,10,11.

The cited references are:

Robock, A., Oman, L. & Stenchikov, G. L. Regional climate responses to geoengineering with Tropical and Arctic SO2 injections. J. Geophys. Res. 113, D16101 (2008).

MacCracken, M. C. On the possible use of geoengineering to moderate specific climate change impacts. Environ. Res. Lett. 4, 045107,  https://doi.org/10.1088/1748-9326/4/4/045107   (2009).

MacMartin, D. G., Keith, D. W., Kravitz, B. & Caldeira, K. Management of trade-offs in geoengineering through optimal choice of non-uniform radiative forcing. Nat. Clim. Change 3, 365–368 (2013).

Haywood, J. M., Jones, A., Bellouin, N. & Stephenson, D. Asymmetric forcing from stratospheric aerosol impacts Sahelian rainfall. Nat. Clim. Change 3, 660–665 (2013).

Of those, [9] seems the most obviously relevant, although it covers more techniques than just SAI. One particularly relevant passage from [9] reads:

… materials lofted this high and staying
in the atmosphere for extended periods tend to spread out to
cover the globe. As a result, both their climatic influences
and any unintended side effects (e.g., increased scattering
of incoming solar radiation that diminishes the efficiency of
direct-beam solar energy technologies) tend to be global in
extent.

Since [9] is focused on discussing regionally-targeted geoengineering techniques, the presumed global spread of SAI is here being mentioned mainly as a potential disadvantage.
I think Jones et al. are actually raising two concerns with their work:

Unilaterally deployed SIA targeted at a particular region could have negative side-effects. This is the topic most relevant to your question. As the references show, there were indeed plans for this, at least in the sense that it had been discussed in the literature for some years. I don't know of any state drawing up concrete plans for SIA stations yet, but it's probably a good idea to raise these concerns before the policy train gets rolling.

SIA might be deployed at a single site as a globally targeted SG technique, with the assumption (as seen in [9]) that it doesn't matter where you do it because the aerosols will spread evenly over the globe in any case. Jones et al. show that this will not necessarily happen.


Identifying serpentinite reworked during high-T metamorphism What kind of mineralogy results when a serpentinite is reworked during high-T or UHT metamorphism? I am envisaging a possible scenario where an obducted ophiolite terrane is buried and metamorphised within thickened orogen.

Since seprentinite is hydrated/altered mafic or ultramafic rock, I would assume dehydration would be the first pathway. With further heating are serpentinites likely to yield melt? Could they end up as a 'normal' mafic granulite? Are there mineralogical or geochemical characteristics that could be used to identify a mafic granulite that started out life as a serpentinite?

Of course, any ultramafic rock will ultimately melt at about 2000 deg C, but long before that there will be some interesting phase transitions, possibly involving serpentine > talc > olivine + orthopyroxene.
Various subtle changes occur in the rock during its original hydration from peridotite to serpentinite. There is high- and low-temperature serpentinite. Isotopic studies have shown that most exposed serpentinite exposed in outcrop has hydrated at ambient groundwater temperature. Consider what happens. The Ca from the clinopyroxene in the original peridotite ends up as Ca- or Ca-Mg- carbonates, of which much is lost or precipitated elsewhere. The Fe in the original orthopyroxene, clinopyroxene and olivine is either lost from the system or re-precipitates as a mesh-texture of goethite. Cr from the silicate phases is excluded from the serpentine crystal lattice and from the surface of chromite crystals leaving a zoned Magnetite-Chromite structure in previously homogeneous chromite crystals. Since these are inert and refractory, they should survive any subsequent dehydration process. Any Ni will probably survive within the serpentine lattice. Summing up, when the serpentine is metamorphosed and turns back into peridotite, look for zoned chromite, reduced Ca (as clinopyroxene), and either reduced Fe, or Fe as a relict ghost sieve structure. Depending upon local circumstances there may, or may not, be a slight loss of silica during the hydration-dehydration cycle.


Why don't cold fronts and other steep-gradient weather effects just dissipate? Why don't cold fronts and other steep-gradient weather effects just dissipate? Why do they last so long? Why doesn't the heat dissipate toward the cooler region?

Good question.  It would seem without much thought, that air in a high pressure zone should move towards the air in low pressure zone, resulting in a disappearance of the pressure gradient.  The reason this does not occur is because there other forces (or pseudo-forces) at work, acting in addition to the force resulting from the pressure gradient.  I will outline such forces below:

1.  Pressure Gradient:
This is the force resulting from the pressure difference between a high and low pressure zone.  We term this a pressure gradient, because the pressure change is continuous rather than a discrete change between a high and low pressure zone.  We can model the acceleration in a particular direction resulting from a pressure gradient using the equation:

$$\alpha=\frac{-1}{\rho}\frac{dP}{dz}$$

where $\alpha$ is the acceleration at a given point, $\rho$ is the density of air at that point, and $dP/dz$ represents a small change in pressure over a small change in horizontal distance.  More generally, we can model the acceleration vector in 3-dimensions using the equation:

$$\vec{\alpha}=\frac{-1}{\rho}\vec{\nabla}P$$

Now if the pressure gradient was the only force at work, it is obvious from above that the acceleration would be directed from high pressure areas to low pressure areas, ultimately resulting in a dissipation of such gradients.

The next pseudo-force to consider however is the Coriolis effect.

2. Coriolis Effect:
The Coriolis effect influences winds away from the equator that move horizontally.  Such winds in the northern hemisphere are deflected to the right, whereas winds in the southern hemisphere are directed to the left.  This is a result of the Earth's rotation.  (More information on this effect can be in the question and answer here).  The acceleration resulting from the Coriolis psuedo-force is given by the following equation:

$$\boldsymbol{a}_C=-2\Omega\times\boldsymbol{v}$$

where $\Omega$ represents the angular velocity of the Earth and $\boldsymbol{v}$ represents the velocity of the wind.  The cross product here is of significance and indicates that the deflection of the Coriolis effect will be at right angles to the direction of the wind's velocity.  More details of deriving the specific result for the Earth at different angles of latitude can be found here.

So how does this Coriolis effect stop wind from moving from high pressure to low pressure?  Well imagine that wind begins to move North (in the northern hemisphere) from a high pressure region to a low pressure region.  Due to the Coriolis effect, this wind will be deflected to the right, and will continue to be deflected in such a manner until the pseduo-force resulting from the Coriolis effect exactly balances the force due to the pressure gradient (ignoring friction for the time being).  At this time, we say the wind is said to be in geostrophic balance.  The wind therefore is no longer moving directly from the high pressure region to the low pressure region, and it is for this reason that the pressure gradients do not dissipate straight away. (See friction force below)  This can be represented by the picture below, and I will include the formula when we have access to mathjax (note the Coriolis term is represented a bit differently in this diagram, but don't worry I'll explain how it is the same when mathjax is added - basically it just a certain direction component of my more generalized vector above):

3. Friction

As I mentioned previously, the geostrophic balance presumes the absence of friction.  In reality, friction acts to slow the flow of wind, in turn lessening the influence of the Coriolis effect. Thus ultimately the wind does tend to spirally slightly inwards towards the low pressure zone.  The effect of friction is more noticeable in the lower atmosphere, and in the upper troposphere the geostrophic motion approximation is more accurate, and therefore the pressure gradients will take longer to dissipate in the upper atmosphere than the lower atmosphere.

The force of friction is given by:

$$F = cV$$

where $c$ is a constant, and $V$ is the velocity of the wind.

4.  Gravity

Pressure gradients can also be sustained vertically, due to the influence of gravity.  When the force of gravity balances the pressure gradient, this situation is known as hydro-static wind balance, and is represented by the equation:

$$dP/dz = -{\rho}g$$

where $\rho$ is density of air, and $g$ is the acceleration due to gravity, which is approximately $9.8 m s^{-2}$.

Net Effect:

While I have already answered the question, I have decided include the equation combining all 4 forces for completeness.  Combining all these forces acting on the wind, the net acceleration of wind can be determined by the equation:

$$\frac{D\boldsymbol{U}}{Dt}=-2\Omega\times\boldsymbol{U}-\frac{1}{\rho}{\nabla}p+\boldsymbol{g}+\boldsymbol{F}_r$$

where $\boldsymbol{U}$ represents the velocity of the wind, and $t$ represents time.  The quantities in bold are vectors, and act in a specified direction.  (e.g. $\boldsymbol{g}$ acts vertically, where as $\boldsymbol{F}$ acts in the opposite direction to $\boldsymbol{U}$).  Below is in image of this:

This image shows how the forces act (excluding gravity) around high and low pressure zones.  PGF is the pressure gradient force, CF is the psuedo-Coriolis force and F is the frictional force opposing the velocity of the wind.  Note that the wind moves slightly in wards towards the low pressure region, rather than perpendicular to the gradient predicted by geostrophic motion.  This is due to the frictional force.


Can an Atlantic hurricane enter Mediterranean sea? I can't find any examples, has it just never happened before or is it impossible because of environmental factors?

Apart from the fact that only a few tropical cyclones follow a more southerly route (a list bellow) after going around the North Atlantic, I think the main problem is that tropical cyclones would weaken significantly after landfall in the Iberian Peninsula. An example of this is Hurricane Raphael in 2012.
 Source Weather.unisys.com.

There is no "easy" path from the Atlantic into the Mediterranean for a system the size of a tropical cyclone. Other examples that followed a similar path but never made it the Mediterranean: Gordon (2006), Jeanne (1998), Ivan (1998), Frances (1992), Bob (1991), Arlene (1987), Chloe (1967), Carol (1965), Dolly (1953).

While the cyclones at the point of approaching the Iberian Peninsula are still tracked as tropical depressions, their characteristics are often similar to other extra-tropical storms.


converting SU file to ASCII format in seismic unix using OpenSeaSeis I have tried to convert a Seismic SU file to ASCII format in seismic unix using openseaseis module named "sutoascii".

I have already tested the SU file by opening it in SeaView Seismic Viewer and then tried to convert it to "ASCII" format using the following command:

sutoascii <inputSUFilename >outputASCIIFilename bare=0 index=1

The ASCII file is created as an output file but it gives an error while converting that "number of samples in header differs from number for first trace"

Now to check whether the Resulting ASCIIFile is valid and working, I have tried to open it in SeaView Seismic Viewer again to cross-check but it shows an error and is unable to open the file.

Can anybody tell me how to correct this?

The number of samples in the input binary header from the SEGY file does not match the NSAMP trace header.  I would first confirm:

What # of samples is in the binary SEG-Y header.
The number of samples you expect in each trace
Dump the su trace header for     number of samples. You can use
SUGETHW and the keyword for # of samples is "ns".

If the error is in an individual trace header, you can overwrite that with SUSETHW.


How older is this snail shell possible could be? Last weekend I was in Xınalıq(the village in Azerbaijan) and found this snail shell. I am wondering how old is this?

That's not a snail per se it's the shell of an ammonite which is more like a squid with an external shell than anything else I can think to compare it to. They went extinct with the dinosaurs so it's at least 65 million years old and could be much older.


Why do heat waves affect Australia unevenly? Firstly, I would like to express my deepest condolences to those affected by the extreme heat and catastrophic wildfires on NSW's south coast and in Gippsland (east of Melbourne).

When I was looking at temperature maps in Australia, I noticed something I thought was strange.

If there's extreme heat in NSW/Vic/SA, then often WA will escape the worst of it. Conversely, if Perth is going through an extreme hot spell, then eastern Australia will escape the worst of the heat.

These were the temperatures on December 25 and 30, 2019 (adjusted for time differences). As you can see, on Christmas Day, Perth was roasting, but the eastern capital cities were much cooler. And yesterday, the east coast (including Tasmania!) saw record heat, but Perth did not.

I don't think the time difference completely explains the variance in temperature. For some reason, heat waves rarely affect all major non-tropical capital cities at once (Sydney, Melbourne, Perth, Adelaide, Canberra, Hobart). There will be one or two cities that escape the heat. I wonder why this is.

It primarily has to do with the pattern on high and low pressure systems as they present themselves over the continent.

In the southern hemisphere, high pressure systems rotate anticlockwise and low pressure systems rotate clockwise.

Because the north of Australia is close to the equator, generally the north of Australia has a low pressure trough over it. High pressure system tend to centered from the mid latitudes of Australia southwards.

If there is a high pressure system just to the south west of Australia, and particularly if there is a low pressure system just to the south, in the Great Australian Bight, cold air from the south will affect Perth and the south west of Australia.

As the high pressure system moves eastwards a low pressure trough can develop over the west coast of Australia. With or without the trough, the high pressure system moves hot air from the central and northern parts of Australia and Perth and the south west experience hot conditions. If the high pressure system is slow moving this can mean prolonged periods of hot weather - heat wave. A low pressure trough along the west coast reinforces the movement of hot air from the central and northern parts of Australia.

With the same high pressure system over the central region of Australia, as hot is drawn from the central and northern parts of Australia over the western parts of the continent, cooler air from the Southern Ocean is drawn over the eastern part of Australia, particularly the south eastern region where Hobart, Melbourne, Canberra and Sydney are located.

When the high pressure system moves to the east of Australia, particularly to the Tasman Sea, between Australia and New Zealand, hot air from the northern and central parts of Australia will be drawn over the south eastern parts of the country and the regions between Adelaide and Sydney will experience hot conditions.

In the synoptic chart below, for 29 December 2019, there is high pressure systems to the west and east of Australia and low pressure system to the south. The effect of these systems is to draw cold air from the south over Perth and the south west of Australia and hot air from the central and northern parts of Australia to the south east of the country.

This is why one part of the Australia with fry, while the other doesn't.


Coal self-heating and spontaneous combustion, how does this happen? I finally broke down and read the Wikipedia article on spontaneous combustion and I was surprised to see how serious of a problem this can be. Wet hay, oily rags, there really are exothermic reactions in these combinations that speed up as the temperature increases.
Then I saw the following:

Coal
Self-heating in coal has been extensively studied. The tendency to self-heat decreases with increasing rank of the coal. Lignite coals are more active than bituminous coals, which are more active than anthracite coals. Freshly mined coal consumes oxygen more rapidly than weathered coal, and freshly mined coal self-heats to a greater extent than weathered coal. The presence of water vapor may also be important, as the rate of heat generation accompanying the absorption of water in dry coal from saturated air can be an order of magnitude or more than the same amount of dry air.

I understand that coal is a complex material, it's more than a lump of carbon. But what are the types of chemical reactions within coal that will cause a pile of it to self-ignite? Is moisture always required? Is there moisture in freshly mined coal naturally, or is it absorbed hygroscopically from the atmosphere or is a liquid source necessary (getting wet)?

Sulphur/sulphides in coal may be one of the causes of self combustion.

A slight diversion - in some metal sulphide mines, such as copper, at high level of sulphides in the ore, the sulphides can oxidize thus creating sulphide fires. If a lot of dry dust is produced during stope blasts, during the mining process, sometimes the  sulphide dust can cause a secondary, unwanted, explosion.

Most coal deposits contain sulphides/sulphur. Most lignite (brown coal, also low quality or low grade coal) deposits are nearer the surface, thus if lignite has lots of sulphur & it oxidizes with atmospheric oxygen combustion can occur.


Compute direction of gravity vector As I understand to compute vector of gravity not saficient to compute normal to elipsoid, but we need to computer normal to geoid (by definition geoid is a surface to which the force of gravity is everywhere perpendicular).

So I have some questions:

How to compute normal to geoid?
What is the maximum discrepancy of angle between elipsoid normal and geoid normal?

Update:

About practical application of gravity normal:

I have some tall object that stand on Earth (like Leaning Tower of Pisa) and I can obtain GPS coordinates of it top and bottom points by using photos taken from air and applying photogrammetry methods. Then from GPS coordinates of top and bottom of object I can get vector in ECEF coordinates and find angle betwen this vector and gravity vector.

Also my question:

If difference in angle between ellipsoid normal and geoid normal("deflection of the vertical") is about 100 seconds of arc (0,0277778 degree) is it safe to use ellipsoid normal for this practical application?

Update 2:

First:

I'm trying to understand if normal to ellipsoid is sufficient for practical application.
In real life object is mounted by using spirit level and on this picture we can see that theoretically I need normal to geoid, but if deflection of vertical small enough I can use normal to ellipsoid as approximation.

Second:

I'm trying to estimate the error of angle measure, I have some error in calculating of GPS positions of my object top and bottom points say epsilon_1, also I have some error in calculating gravity vector because of I'm using normal to elispoid say epsilon_2 and I'm trying to understand how epsilon_1 and epsilon_2 affects resulting angle between object vector and gravity vector. So I need to derive the formula that will give me measurement error of angle using measurement error of GPS points and gravity vector(epsilon_1 and epsilon_2).

First, a distinction between "gravity" and "gravitation" as used in geophysics. "Gravitation" pertains to Newton's law of gravitation. (Nobody uses general relativity to model gravitation for small, lumpy masses such as the Earth, Mars, or the Moon.) "Gravity" pertains to how things appear to fall from the perspective of an observer fixed with respect to the rotating Earth. Thus gravity includes gravitational acceleration (inward, more or less toward the center of the Earth) and centrifugal acceleration (outward, away from the Earth's rotation axis). This question is asking about gravity rather than gravitation.

As I understand to compute vector of gravity not saficient to compute normal to elipsoid, but we need to computer normal to geoid (by definition geoid is a surface to which the force of gravity is everywhere perpendicular).

It's the other way around. The geoid is a calculated surface. Before the satellite era, one of the key sets of inputs to the calculation of the geoid were observations of deviations of local gravity, particularly the deflection of the vertical. Which way gravity pointed at several locations gave clues as to the local shape of the geoid.
Observing the orbits of satellites provides a global measure Earth's gravitational field. Satellites have been specially constructed for this job, most recently, GRACE and GOCE. The Earth's gravitational field is published in terms of spherical harmonics coefficients. The gravitational vector for a point in space on or above the Earth's surface can be calculated directly from these coefficients. Vectorially adding in the centrifugal acceleration due to the Earth's rotation results in the gravity vector. The position also yields the nominal gravity vector assuming an ellipsoidal Earth.

So I have some questions:

How to compute normal to geoid?

As noted above, a geoid is not needed. Modern models of the geoid are calculated from those same spherical harmonic coefficients (plus Earth rotation) that used needed to calculate the gravitational acceleration and gravity.

What is the maximum discrepancy of angle between elipsoid normal and geoid normal?

The technical term is "deflection of the vertical" (with variations). Per Hirt et al., it's up to 100 seconds of arc, about 10 kilometers south of the peak Annapurna II. This is a calculated value based on various satellite models (which are a bit coarse) coupled with digital terrain maps coupled with some more hairy mathematics to create fine-scale models.
C. Hirt, et al., “New ultrahigh‐resolution picture of Earth's gravity field,” Geophysical Research Letters, 40.16 (2013): 4279-4283.


What would the equilibrium temperature be at the poles in a world without seasonality? Inspired by: How does Antarctica stay frozen?

If the Earth was in a fixed solstice state - northern winter and southern summer (e.g. the axis obliquity rotated with the Earth's orbit), what  would the equilibrium temperature be at each pole? Assume daily cycle and convection and so on operate as usual, just that it's permanent midnight in the Arctic, and permanent midday in the Antarctic.

Bonus questions: Would the equilibrium temperatures be significantly different if it was northern summer and southern winter (e.g. would land masses and orography have much effect, relative to the solar imbalance)?

If we consider that by "Assume daily cycle and convection and so on operate as usual" you meant that all heat transport from/to the pole remain as it is today. Then, we can do a back of the envelope calculation. This calculation will at least give you an order-of-magnitude answer, and we can then consider everything that would affect the result.

Currently both poles radiate more energy than they receive trough direct solar irradiation. This is because they are colder than the rest of the planet. Therefore, there is a neat heat transport from the equatorial latitudes to the poles. That heat travels on atmospheric and oceanic currents. This figure nicely summarize this radiation balance:

Figure from here ©The COMET Program

If we consider that the heat transport depicted at the bottom of the figure remains the same. The only change in the energy budget would be from solar irradiation, and once they start warming the only way to release the additional heat and reach equilibrium would be trough infrared radiation (black body radiation).

The poles receive zero energy on the equinox and the winter solstice and 12.64 kWh/m$^2$ per day on the summer solstice. Therefore a rough yearly average would be 3.16 kWh/m$^2$ per day. So, if we were locked on a summer solstice state you would receive four time more energy, and none if locked in a winter solstice state.

Summer solstice locked pole

Let's consider the summer solstice case first. If we call $E_1$ the current amount of outgoing radiation from the pole, and $T_1$ the current temperature. The Stefan–Boltzmann law states that

$E_1 = \sigma T_1^4$

Analogously, if $E_2$ and $T_2$ represent the summer solstice locked state, you have

$E_2 = \sigma T_2^4$

Considering that $E_2 = 4 E_1$

You can write that

$4 = \frac{T_2^4}{T_1^4}$

Or

$T_2 = \left(\frac{1}{4}\right)^4 T_1 = 1.41\, T_1$

Therefore the temperature would increase 41%. It doesn't sounds much, but considering that the temperatures above are in Kelvin, it es a lot! In fact, with the current mean temperature in the north pole of -16 °C (257K), it would go up to +89°C!! And the South pole would go from the current -49°C (224K) to +42°C.

This diverges from any posible reality because with 89°C at the north pole there would not be a net influx of energy from the equatorial latitudes as we are assuming. Instead, atmospheric and oceanic currents would take a lot of that heat down south and the temperature would equilibrarte at a much lower value.

Note that in the above calculation I've ignored the energy flux due to advection in atmospheric/oceanic currents. I did so because that flux is about five time smaller than the flux from solar radiation, so it won't change much the results and ignoring it simplifies the math. You can do the calculation considering those flows if you want.

Winter solstice locked pole

In the case of a pole locked to a winter solstice. There would be no incoming solar radiation at all. Therefore, all incoming energy would be transported by currents from equatorial latitudes. In that way, we can see in the above figure that the north pole receives about 150 W/m$^2$, and the south pole about 100 W/m$^2$. The equilibrium temperature would be reached when they radiate the same amount. So, using Stefan–Boltzmann law again we can do some rough calculations.
Let's call the south pole temperature $T_{SP}$ and $T_{NP}$ for the north pole. Then:

$T_{SP} = \left(\frac{E_{SP}}{\sigma}\right)^{1/4} = \left(\frac{100 \,W/m^2}{5.67\times 10^{-8}}\right)^{1/4} = 205 K= -68°C$

And for the north pole

$T_{NP} = \left(\frac{E_{NP}}{\sigma}\right)^{1/4} = \left(\frac{150 \,W/m^2}{5.67\times 10^{-8}}\right)^{1/4} = 227 K= -46°C$

But again, with such cold temperatures the actual inflow of energy would be grater and the equilibrium temperature would not be that extreme.
In any case, that condition would be favourable to the growth of a massive ice sheet in the corresponding polar area, in the same way I describe in this question and answer.

As a final thought. For this condition to happen in real life you would need something analogous to Tidal locking to lock the period of Earth's precession (currently about 26,000 years) to exactly one year. And don't know of any mechanism that could achieve that.


What color(s) would Earth be without water or life? Many of the celestial bodies in our solar system have well-established color schemes, at least in the minds of the public.  Mars is pale-red and black, Venus (beneath the clouds) is generally shown in rich yellows and oranges, the Moon ranges from dark to light gray, etc.

And, of course, Earth is famously blue and green.  However, this is entirely because of the presence of large oceans and life.  We're not seeing Earth's geology represented in these colors, as we are with the other planets, we're seeing overlaid colors from other processes that don't apply to Mars, Venus, or the Moon.

So I'm wondering, if you stripped away life and the oceans, what color(s) would Earth be?  Based on types of rock, etc.  Would the seabed be a different color from the continents?  Would it be more uniform, or would it vary in color quite a bit from region to region?  Would it be a similar gray to the Moon, or would other chemical processes (like the rusting of Mars) give it a more unique palette?

That's actually an interesting question. Let's try to answer it, but first let's make a few assumption.

Oxygen on Earth is biogenic, so without life there would be no oxygen. However, let's assume that some magical process keeps the oxygen in the atmosphere.
Oceans play an important role in plate tectonics, and without it it might change. Let's assume that plate tectonics keep on running regardless of the state of the oceans.

The majority of the Earth's surface is covered by oceanic crust. This crust is composed of basalt, an iron rich rock. This iron would rapidly oxidise and rust, giving a red tint (possibly Mars-like) to most of the Earth's surface. The mid ocean ridges will most likely be black, but it will get redder the farther you get away from there.

The continental crust would like slightly different. Mountain ranges would appear grey, perhaps slightly pinkish - not too different from the highest peaks you see today. Most of the continental crust is composed of granite (sensu lato), a grey-pinkish rocks. Because there's no life and no vegetation, that barren landscape you see high above the mountains would go all the way down to the base of them mountains. At the mountain's base, you would get deserts of quartz sand, slightly yellow. Think the sand dunes of the Sahara desert. This sand comes from the breakdown of the granites. Quartz, the most resistant mineral in the granite forms sand, I guess from the action of wind. The other minerals (mostly feldspar) break down to form all kinds of clays, aka dust.

So to sum it up:

Most of the surface will be covered by dark red low lands, with high lands of sandy desert and Himalaya type mountain belts sticking out of them.


Can we call the Precambrian eons (i.e. Archaic and Proterozoic) eras? A diagram in a book I have places Archaic and Proterozoic under "eras".

Is such naming correct? ICS says they are eons, so do most sources I could find, but a 1979 volume of "Treatise on Invertebrate Paleontology" seems to name at least Proterozoic as an era.

Is applying the term "era" here en error? Obsolete usage, once popular, but now generally abandoned? Or perhaps a rare, but correct and accepted, convention?

It is and is not an an error depending on how it is used. They are Eons but in older literature they were also, sort of, eras as the Eons were not subdivided as they are now. Especially in literature dealing with the transitions they might refer to them indirectly as eras, such as "In the previous Proterozoic era", proterozoic being possessive. At the time this was technically sloppy but not a big issue, but now that they are subdivided this would be incorrect to do now.

You also have the issue of plurality in older literature. Spelling can vary from country to country and Paleontology is very much a international discipline. Occasionally in older literature Era can sometimes be used as the plural for Era (like sheep and sheep), so a reference to the Proterozoic era may be referring to the multiple eras in the Proterozoic. Again technically sloppy but in the time before electronic word processing a spelling error that might be ignored.

in a time scale they be grouped with era, as eons were often not included, and again they had no named eras in them. If the diagram included eons however this would be incorrect, but was sometimes done to conserve space since otherwise you would have a large blank section in all the smaller subdivisions to make room for fitting them in the eons, technically wromg but often ignored.

Without knowing the context of usage it is hard to say whether it is an error.


Shouldn't India Get an Uplift Too? For the past 50 million years, India has been crashing into mainland Asia, creating the Himalayan range and uplifting Tibet, north of the mountains, to a current average height of 4500 meters above sea level.

But why is Tibet the one getting an uplift? Why isn't India, instead?

The simple answer is 'crustal thickness'. The two crustal plates of India and Eurasia are very different in character. The Indian plate is thin, the Eurasian plate is much thicker and more rigid. Both plates are so buoyant with respect to the underlying mantle that neither can subduct in the normal sense. But India is moving so fast that something has to give. The Indian plate is buckling a bit, but mostly being under=plated at low angle as the Eurasian plate rides over it - as it did is such spectacular fashion during last year's Nepalese earthquake.

PS the main continent-continent crunch occurred some 40 to 20 million years ago.


What is the difference between lunar and earth soil I know that the moon has lunar regolith and earth has earth soil, but what is the difference between them?

The single biggest difference is the lack of chemical weathering in lunar soils which are subject to physical weathering almost exclusively. If you exclude biological processes, terrestrial rocks undergo significant weathering from water and atmosphere, which the moon lacks.

For example, both earth and moon contain feldspar-rich rocks, however, clays, the result of chemically altered feldspars, are not found on the moon. Neither are oxidized minerals, as the moon has no oxygen-rich atmosphere to speak of.


How big does a pointed piece of tungsten need to be to self-propel into the earths core by gravity alone? Density is 19.25 g/cm3, hardness ~9 (Tungsten carbide might apply), and melting point is at 3695 K.

It will never get past the mantle.

The tungsten (or tungsten carbide) will chemically react with the rocks surrounding it to dissolve and form other minerals (silicates), or even worse: get diluted to trace levels in mantle minerals. Compare this with dropping some grains of salt in the ocean and asking when they will arrive to the sea floor. Your block
of tungsten will probably need to be on the scale of tens of metres or more (km?) to escape that.

Furthermore, the mantle is convecting so it will keep your thing from sinking directly down. Compare with leaves falling from a tree in a thunderstorm. This will encourage the chemical mixing I mentioned before.


Is the epicenter always directly above the hypocenter? All the graphics I've seen showing epicenters with a hypocenter (labeled focus in the graph below) appear to show that epicenters are always directly above their related hypocenters. Is this correct?

By definition, the answer is yes:

  epicenter, the point on the earth's surface vertically above the focus of an earthquake, or the Hypocenter

according to Merriam-Webster or a many other sources.