Was the Earth's sea-level significantly lower in ancient times? A lot of times, ancient artifacts or even whole ancient civilizations are found buried very deep into the ground surface of the earth.

Entire civilizations that had high buildings have been found many meters below the earth.

Does that mean the earth's sea-level was much lower than it is now? If this is true, then are we experiencing a lower level of gravity?

How can just sedimentation of sand, bury big building to such depths?

If lack of habitation by humans eventually results in burying of things, then what about the places like Chernobyl, which has not been inhabited for a long time?

I am not a physics grad or anything, just a curious guy.

Any help is much appreciated.

There are several questions here, I'm only focusing on the question regarding sea level in the past as per the title question.

In short, global mean sea level (GMSL) has been both lower and higher than present in the past. As recently as the last glacial maximum around 25,000 years ago GMSL was around 120m below present as much of the water was held on land as ice.

However, GMSL doesn't really exist because sea level is not level, but is a useful way of summarising global trends. What people living in coastal areas experience is relative sea level (RSL), which is defined as the mean level of the sea surface relative to the level of the land. There are two key components affecting RSL: isostasy and eustasy. Put simply, isostasy refers to the vertical position or motion of the land (the Earth's solid crust sits on a molten mantle and is subject to vertical displacement from its equilibrium state governed by the balance of overburden pressures  i.e. a concentration of mass on land causes subsidence of the land beneath it whilst uplifting the land extending beyond the focus of the mass. Eustasy refers to a uniform, global change in sea level caused by fluctuations in the balance between water held on land (usually as ice) and in the oceans, or by a change in the capacity of ocean basin (usually tectonically related). RSL can vary considerably from GMSL (unsurprising since this is a mean measurement). For example (I'll use a British example here since that's where I'm from), at the last glacial maximum ice sheets covered the northern part of the British Isles from Scotland down to around the middle of England  (the exact southern extent is still debated in the scientific literature). The overburden of this ice effectively turned the British Isles into a giant see-saw with the land in northern part subsiding and the southern part uplifting. The effects of this are still felt today long after the ice has melted (and contributed a eustatic sea level component) as the land level readjusts to its equilibrium state( glacio-isostatic adjustment); the land in Scotland is rising and the land in the south of England is subsiding. So, whilst is true that globally sea level is rising  (at a rate of around  3.2 mm/yr), when combined with local land level changes then some places actually currently experience a sea level fall (in Scotland this is up to -1.5mm/yr) whilst in regions of isostaic subsidence the rate of sea level rise can be considerably greater than GMSL.

Since you mentioned gravity in your question I'll breifly introduce another curious component  (there are others,see reference below) which results in globally  non-uniform sea level changes. We are not experiencing a lower level of gravity  (gravity is a constant).  The amount of gravity that something possesses is proportional to its mass and distance between it and another object. On Earth mass is obviously not evenly distributed, with each location on the planet experiencing a different mass-dependant   perturbation of the gravitational field. So for example, as an ice sheet forms and grows  mass increases which results in a gravitational perturbation which attracts the ocen toawrds the ice sheet but as the ice sheet melts and the gravitational perturbation reduces that water that was previously drawn towards the ice mass is redistributed in distant locations from the ice mass. This (counterintuitively) means that the greatest rates of sea level rise as a consequence of Greenland melt are actually experienced in the Southern Hemisphere.

Hope this serves as a useful introduction. I would usually include more references but I'm writing this on my phone right now whilst travelling on a train. One key reference,which is written in a non-technical style, worth checking out is :
Sea level is not level : The case for a new approach to predicting UK sea-level rise. / Gehrels, Willem Roland; Long, A.J.
In: Geography Compass, Vol. 93, No. 1, 01.03.2008, p. 11-16.


Diamond at the core of Jupiter Arthur C. Clarke, who correctly guessed there would be liquid water on Europa, posited a diamond core for Jupiter. Is this possible?

I would think this is questionable, though we don't have a definitive answer yet.

We usually think Jupiter has a roughly solar composition, which according to the solar abundance measurments of Asplund et al. 2009 would mean the total carbon mass of Jupiter is about $10^{-3}$ of Jupiter's total mass. So there's roughly $0.3$ Earth masses of carbon floating around in Jupiter.
Next we need an idea of where this stuff is floating around.

We know that Carbon is floating around in Jupiter's atmosphere and is enriched relative to solar values by around a factor of $\sim3$, which corrects our estimate of total carbon in Jupiter to roughly one Earth mass, if Jupiter is well-mixed.

The keyword here is "well-mixed". If carbon atoms stay solved in hydrogen at high pressures in Jupiter's core, then no diamonds can be formed. Only if there is a rain-out similar to helium (see also the phase diagram for hydrogen and helium-mixtures) then droplets or other accumulations of carbon can form, which will be pressed into diamonds.

The research however at the moment does not focus very much on carbon dissolution at high pressure, so I cannot cite anything reliable on what carbon will do. The reason for this is that the above cited helium-rainout and core erosion which are considered important at the moment.

I'll try and find some more sources on this as soon as I can go beyond the paywall to the research articles.

Comment on the high pressure-experiments and Juno: To my knowledge carbon-hydrogen mixtures are not being looked at in the labs, but this knowledge might also be flawed.

Juno will mostly be sensitive to Jupiter's density distribution at pressures up to ~1000 bars. Initial estimates show, that even if Jupiter has a dense, rocky core of 20 Earth masses, this will be barely visible in the data. To then filter out how much is carbon will be nigh-impossible with the current mission.


Why are mornings cooler than nights? In the morning, Google shows the temperature from four or five hours ago (around 2:00 a.m.). But then I update the report, and I get the temperature slightly lower than before.
Why is the temperature at 2:00 a.m. higher than the temperature at 7:00 a.m.?

The Earth is always radiating heat to the space. But in the day the Sun delivers some heat. The net heat flux is then defined as the sum of those two factors. If the energy delivered by the Sun is bigger than the cooling rate, the Earth is net warming (positive net flux – we can imagine it like heat is travelling "to us"), as opposed to the opposite case (cooling; negative net flux – heat is travelling "away").
In the day, the Sun warms the ground until the evening. The Sun's heating rate is higher than the cooling rate, so the temperature is rising until it gets to a point where the heating rate is same as cooling rate. This happens in the evening, so the temperature is steady at that point. But the Sun goes even lower, so the net flux becomes negative. In the night there is only cooling of Earth, so the temperature is falling steadily until the Sun is high enough that it balances the cooling. This happens at a point of a minimum temperature.
Of course, this is valid for most of the days, but we can have some other effects that can change the time of the minimum temperature (clouds, fronts or advection, for example).
On graph:

So, the temperature is falling over night after the sunset, but rises again after the sunrise. Thus, the temperature is at its lowest point in the morning.

Appendix for all you loving calculations:
Note: Simplified to toy model, no atmosphere
The cooling rate of the Earth is approximatelly given by the Stefan-Boltzmann equation:
$$j_E=\sigma\cdot T^4=5.670  \cdot 10^{-8} \frac{W}{m^2 K^4} \cdot (288.15 K)^4 = 390 \frac{W}{m^2}$$
The maximum heating rate of Sun in the zenith is $j_{\text{S max}}=1361 \frac{W}{m^2}$. So, the heating rate of Sun at altitude $\alpha$ is:
$$j_S=j_{\text{S max}}\cdot \sin{\alpha}=1361 \frac{W}{m^2}\cdot \sin{\alpha}$$
When is the heating rate equal to zero?
$$0=j_S-j_E=1361 \frac{W}{m^2}\cdot \sin{\alpha} - 390 \frac{W}{m^2}$$
$$1361 \frac{W}{m^2}\cdot \sin{\alpha} = 390 \frac{W}{m^2}$$
$$\alpha = 17 °$$
So, with our calculations, the minimum temperature is at the time when the altitude is equal to 17°.


Why do buoyantly rising mantle minerals melt, yet buoyantly rising atmospheric waters condense? In the mantle, minerals contained in buoyant plumes of rock undergo phase changes from solid to liquid (decompression melting). In the atmosphere, waters contained in buoyant plumes of air undergo phase changes from gas to liquid (clouds and precipitation).

Plumes in both systems experience decreasing pressure and decreasing temperature as they rise.  Why do the phase changes go in opposite directions, i.e. why do rising mantle minerals melt while rising atmospheric waters condense?

There is no comparing the chemical composition of "atmosphere" with that of mantle rocks and the consequences of rising in each have almost nothing to do with one another. The cooling of rising atmosphere is a fairly simple thermodynamic process requiring neither molecular change of ingredients, chemical release of water, nor thermally impervious boundaries.

By contrast, rising mantle materials will undergo different melting processes depending on their water content and chemistry. In the simplest case, like a mid-ocean hot-spot, unpolluted by melt fluxes like water and carbonates, rising mantle rock undergoes "decompression melting" in which 2 things happen:

1) The pressure needed to keep rising mantle material solid is released and the material becomes liquid (like that crudely drawn by Michael, above). Remember, given enough pressure, you can heat up ANYTHING and keep it solid...even hydrogen, like that believed to exist in the earth's core.

2) Constituent minerals undergo phase (mineralogical) changes on their way up to the base of the upper crust. Remember that mantle materials come to the earth's surface as basalts which are mineralogically different from the olivene-rich peridotites of the mantle. Despite being chemically similar, deep mantle rocks contain minerals that are crystallographically denser than those found basalts. As they are brought up, these minerals undergo a phase change that alters their crystalline structure; they become different minerals, lighter and more buoyant, further reducing the density of the rising melt.

So, there it is (in a nutshell): reducing pressure on hot solid material allows it to become liquid and also invokes phase changes in minerals that make the overall material less dense.


Can gemstones be cut into sheets? TL;DR: Without lasers, electricity, or otherwise modern tools, could large transparent gems be sliced (like glass window)?

So I’m world building.
On this planet they have caves with enormous gemstone/crystal/pretty mineral structures (think lechuguilla) which they mine and most often tumble for currency.
It occurred to me that they would use these for windows if they could manage to somehow slice the stuff.
It could be useful to know, their water-based tech is pretty advanced and certain regions have created small magnet-powered motors.

sliced (like glass window)

Window glass is not sliced into sheets. It is made as sheets from the beginning.

Since you're looking for a naturally occurring mineral that can be made into a glass-like material, look no further than muscovite.

Because your planet has nice and big crystals, it most likely come from pegmatites, which is a type of rock that has large crystals and many gemstones we know today come from pegmatites (emerald, tourmaline, topaz, kunzite, etc). Pegmatites also have huge crystals of muscovite as well, in some rare occasions several metres wide. Muscovite can be easily split into sheets that are flexible and mostly transparent. Not the best glass material (because it is not glass after all), but almost as good. Quoting from the Wikipedia page:

  The name muscovite comes from Muscovy-glass, a name given to the mineral in Elizabethan England due to its use in medieval Russia as a cheaper alternative to glass in windows. This usage became widely known in England during the sixteenth century with its first mention appearing in letters by George Turberville, the secretary of England's ambassador to the Russian tsar Ivan the Terrible, in 1568.

Here's a good video showing how this is working.

So the inhabitants of your planet can mine the other crystals in the pegmatite for currency or whatever, and use the muscovite as building material.


Making clouds for science project This is about a group project for our science class and we've decided to do a physical model on clouds.

We could use liquid nitrogen and hot water to demonstrate the formation of the clouds and we are aware that it doesn't form like that in the nature.

I just wanted to ask, what's the pressure required for clouds to form? I found out that it's -10o C temp. but nothing about pressure (lower than normal but don't have the exact number)

Any ideas? :( I'm starting to feel pretty desperate.

Can we use the nitrogen to decrease the temperature to -10 and then pressure, and wait for liquid water to condensate?

Any kind of answer will be appreciated. Thanks :)

To form a cloud, generally speaking, pressure does not play a significant factor (with the exception of the effect on temperature).

If you want to prove that to yourself, go outside when it is foggy and measure the air pressure. Fog is a cloud, and pressure likely hasn't changed as much as it does in the vertical direction.

As far a forming a cloud, it is actually relatively easy. You only need to decrease the temperature to it's dewpoint. You may want relatively dirty air, so that the solute effect makes it easy to form drops. Silver iodide would be good for this.

For reference, the Kohler curve describes the saturation needed for cloud droplets to form.


How is ground water mapped? This is probably a very easy question to answer but how are the USGS maps showing ground water locations mapped? Is it a guy going around taking core samples? Or is it done using satellites and aircraft?

Also related, how quickly do these flows change? Is taking measurements once a year fast enough or does it need to be updated daily?

USGS conducts regular survey in over 20000 wells across the United States. The frequency of data collection depends on the site with around 7000 providing daily data. For some of those wells (currently, 3777 groundwater sites) daily statistics are provided. An increasing number of wells are providing real time (updated every 15 or 30 min) data.

Source: USGS

You can visualize the daily changes using this animation.

Go to https://waterdata.usgs.gov/nwis/gw for  information as well as the ability to get the data directly from the source.


Catalog of all significant earthquakes since 1900? Where can I find a list of all earthquakes that happened on Earth since 1900?I need time, longitude/latitude, and power -- preferably in .csv format.

Okay so I got the data from
https://earthquake.usgs.gov

Since the website only allows to get 20k records at a time I made a little python script that downloads data for each month.

import os
import requests

for x in range(1900,2016):
    for y in range(1,13):
        url='https://earthquake.usgs.gov/fdsnws/event/1/query.csv?starttime='+str(x)+'-'+str(y)+'-31%2023:59:59&endtime='+str(x)+'-'+ str(y+1) +'-31%2023:59:59&minmagnitude=2.5&orderby=time'
        print(url)
        response = requests.get(url)
        with open(os.path.join("C:/Users/kristjag/OneDrive/delo/potresi", "potresi_"+str(x)+"_"+str(y)+".csv"), 'wb') as f:
            f.write(response.content)

Code above take some time to finish but when completed you get earthquake data for every month from 1900-2016


Estimating Average Rainfall In a question related to my previous one. I am in the process of building a fantasy world. I have the landmasses with elevation worked out along with the air/wind directions at the various latitudes and the temperature both average and seasonal.

What I am missing in determining the climates is the rainfall. I have a rough idea of probable rainfall as humid air goes inland based on elevation changes and temperature. However, if someone could provide a more exact formula or answer to exactly how much average (daily or monthly or whatever) rainfall should occur assuming the air mass hits the land carrying a certain amount of grams of water per cubic meter. For example at 20 deg centigrade air can hole 17.3 grams per cubic meter at 100% humidity. I may be incorrectly assuming rainfall will be largely based on how much altitude the air has to climb as it moves inland.

Second to that is what rate does the air mass gain humidity as it travels over water.

Imagine I have a air mass moving over ocean then over land and then perhaps back over another stretch of water before hitting land again. Those are the type of issues I am facing in trying to determine the climate

Probable rainfall is constrained by several factors, both spatial and temporal. Rainfall modelling is in itself a humongous topic. You may refer to this link for having a good idea of the simulation process & maybe adapt some of the basic equations for a rough estimate by assuming some parameters as minimally affecting your site.


How do I find the horizontal pressure level that divides the atmosphere into 2 layers of equal mass? Surface pressure given is p = 1000 hPa. (the temperature along the atmosphere is constant (T = −10 °C; hydrostatic equilibrium assumed). I tried using the hypsometric equation to find the height of the atmosphere's top and then going through that result, but it's not giving me the results I expect. I expect 500 hPa because I've seen the solution, but I obtained 700-ish hPa.

I'll answer my own question.
If there is hydrostatic equilibrium, then we have

So, assuming that the surface pressure is p (in this case 1000hPa) and that the atmosphere's top has zero (0) pressure and infinite height, then

In this case:

So, as the atmospheric mass above a surface area is rho times integral of "dz", and assuming that this area is 1 m^2 to simplify (dx.dy=1):

 Pa

If we want half of that mass M, then

 Pa , which is indeed 500 hPa.


Topography in general sense What does topography mean in topographical barrier? I can't fully understand the word topography. I have read the pages appearing on googling topography.

Topography is the arrangement of the natural and artificial physical features of an area. Could topographical barrier be any landforms like a mountain range,a plateau or even a forest?

'Topography' implies variation in altitude. A flat rain forest, such as most of the Amazon basin has very little variation in altitude, and therefore doesn't constitute a topographic barrier. By contrast, the topography of the Andean mountain chain, further west, has a huge altitude variation, and hence constitutes one of the classic topographic barriers in respect of air flow, rainfall, salt balance, etc.
So any mountain range or plateau may be a topographic barrier. Forests may or may not be topographic barriers, according to whether or not they have significant topographic variation. Hence the forests of Papua New Guinea constitute a t.b., but most lowland forests do not.


Creating a drought metric using precipitation data? I'm currently working on a project in which I need to create a metric to quantify drought. For the state of Pennsylvania, I have daily precipitation data from many NOAA precipitation gauges (inches of rain per day). I am attempting to create a metric that can quantify how much rainfall certain areas received, hopefully boiling it down to one number. The goal of the metric is to describe the 1960's drought. What's the best way to do this?

I've looked into many scientific papers for similar metrics, but most use more in depth models, and not just daily precip data. What are some good ideas? Average daily/weekly/monthly? Average number of days without rainfall?

One of the most widely used index to quantify the drought events is the standardized precipitation index (SPI) and it is actually based on precipitation time series only.
The index is used, among others, also by the NOAA.

I'll borrow the description of the index from a scientific article (Farinosi et al 2018)

  Standardized precipitation Index (McKee et al., 1993)

  The index is a measure expressed in standard deviation units of the
  variation of the precipitation of a specific number of months respect
  to the long run average (WMO, 2012). The number of months based on
  which the SPI could be calculated usually varies between 3 and 48
  months. Shorter time scales SPI is considered a good indicator of
  variations of soil moisture, while on longer scales (up to 24 months),
  it could be associated with groundwater or reservoir levels variation
  (WMO, 2012). That for, a shorter SPI (3 months) is often utilized to
  detect meteorological droughts; a medium SPI (6 months) is usually
  associated with agricultural droughts; a longer SPI (12–24 months) is
  associated with hydrological droughts. SPI was calculated using the R
  package SPEI (Beguería and Vicente-Serrano, 2014).

Usually the minimum requirements to have a robust estimation of the SPI is to have a precipitation time series of at least 30 years.

You could use the SPI to quantify the number of "droughts" (choosing a threshold under which you define the event - for instance see this) in a period for your area of interest and then aggregate the number of "meteorological", "agricultural", and "hydrological" droughts.


Could a "sunbrella" parked at L1 block enough solar energy to counter global warming? What part of the Earth should be "shaded"; the poles or the equator?

Since the size of the sunbrella would depend on its ability to reduce certain wavelengths of radiation; what material or technology would best provide the shade, and when parked at L1 what size would it need to be?

Once in place, could the amount of shade provided be regulated from earth?

In the event of an approaching ice-age, could the sunbrella be adapted to intensify rather than decrease heat generation?

If it could be built, would our scientists know how to properly employ it?

There are several journal articles on this topic, for example Optimal Sunshade Configurations for Space-Based Geoengineering near the Sun-Earth L1 Point.

Being truly at the L1 point is unsuitable because the radiation pressure of the photons acting on the shade (like solar sail) would disrupt the equilibrium, so the equilibrium point is shifted toward the sun from the L1 point and depends on the degree to which the shade reflects versus absorbs.

The shade should be made of black material to minimize the effect of radiation pressure on the equilibrium point, thereby permitting it to be as close as possible to the L1 point, and closer to the Earth, where it can more effectively shade.

The size required is roughly a 1,500 kilometer diameter structure.

All parts of the Earth would be shaded to some degree. From Earth, the sun would appear as it does during a transit of Venus or Mercury, but the position on the sun's disc would vary more with ones location on Earth since the shade would be much closer to Earth than Venus is.


What is the History of the Brooks Range? This here is a map of the Brooks Range in northern Alaska:

As you can see, it is an inland range shaped in a downward curve.  Why is that?  What is the history of the uplift of the Brooks Range?  How and when did a piece of sea or lowland rise up into a downward-curving mountain range far from the coast?

If you extend your map out a little bit further, you will see that the Brooks Range is just a continuation of the Rocky Mountains into Alaska.

Source: freeworldmaps.net, ©Daniel Feher (explicitly permitted use here)

The Brooks Range was formed at the same time as the front ranges of the Rockies in Canada and the Lower 48, during the Laramide Orogeny which lasted from abut 80 million years ago to about 35 million years ago.  This was caused by the subduction of oceanic plates (mainly the Farallon Plate but also the Kula Plate, and to a lesser extent, the Pacific Plate) beneath the west coast of North America.

The Farallon plate went under North America at a shallow angle; because of this, a large part of Western North America was uplifted, deep into the continent, with faults pushing ancient basement rocks up where the Front Ranges and the Brooks Range are today.

Pacific Ocean plates, 55 Ma. Source: Wikimedia Commons

The Kula plate is "all gone", and the Farallon Plate is mostly gone, except for a few remnants like the Juan de Fuca Plate. Because of the different direction that the Pacific Plate moves, subduction ialong the West Coast is mostly gone as the Pacific Plate slides past North America. The shallow subduction that created mountains deep in the interior is done.  A subduction zone further west has created the Aleutian volcanic arc, but this is a much steeper subduction.


Why don't scientists use fire entry suits to study volcanoes? It seems like the only personal protective equipment
(PPE) that volcanologists use are aluminized suits that don't provide any protection from direct contact with lava, making an unexpected splash lethal. There are suits that firefighters use to go directly into fires for prolonged periods of time, and they are able to resist temperatures exceeding 1100 °C (~2000 °F) for up to 15 minutes at a time. Most lava is around this temperature threshold, with the coolest lava erupting at a mere 650 °C (~1200 °F).

Why don't volcanologists use these suits to study volcanoes? Instead of using those awkward long metal rods to pick out the right piece of lava to study, couldn't they use their gloved hands to pick it up (perhaps on the colder erupting lavas like the ones that does so at 650 °C)?

I'm a volcanologist and I have worked on erupting volcanoes. First of all, volcanologists almost never actually wear those suits. Heat is almost never the hazard that matters in the situations in which we work. The hazards are usually the chance of being hit by ballistics, or getting gassed. The reason you see those suits so often is that they look really cool on TV.

I do know that Katia and Maurice Krafft wore them commonly, but their goal was to get as close to explosive eruptions as possible, as frequently as possible, for as long as possible. This strategy leads to death. It was a tragedy when the Kraffts (and 41 others) were killed at Unzen, but not entirely a surprising one, in retrospect. Modern volcanologists tend to be far more cautious and you might say that the heroic age of volcanology is over.

When you're working on an erupting volcano, some major things you can do to reduce risk are:

Wear a helmet. This would have saved lives at Galeras.
Reduce the amount of time you spend in the hazard zone. This means you need to work quickly, which often means carry less and don't wear silly protective gear like heat suits.
Wear a gas mask, usually with SO2 scrubber cartridge. Ever try to jog up a hill in one of these? It becomes hard to breathe, and the mask quickly fills up with condensation from your breath. Communication through a radio or otherwise is hindered. Everything takes longer, so sometimes the masks are left off in the interest of #2.
Increase your situational awareness. Maintain communications with someone who is watching data from instruments such as seismometers and tiltmeters. Also, make sure you have unobstructed vision so that you can potentially step out of the way of lava bombs which are falling towards you. Again, PPE such as a heat suit or even a gas mask can work against this.

As for the idea of "picking up" lava with your hands, remember that lava is extremely viscous, so it takes quite a lot of force to pull a sample out of a flow. The colder lavas to which you refer are even more viscous than hotter lavas. Anyway, I doubt there are any gloves that can deal with prolonged contact with a 650C fluid. (Remember that fluids and solids are far more conductive than a gas and will transfer far more heat.) I think trying to sample lava with hands would be far more "awkward" than using a pole, which is really quite a simple, easy way to do it.

Edit: I just thought of another reason volcanologists can't dress like firefighters. Expense. Volcanologists have an extremely hard time getting sufficient funding. I actually asked for an SCBA for my work in the fumarolic ice caves of Mt Erebus, where CO2 is high. We couldn't afford it on our grant. Instead, I just carefully monitor gas levels and there are caves which I cannot enter because we read dangerous levels of gas at the entrances.

Edit: I highly recommend that anyone interested in this subject read No Apparent Danger and Volcano Cowboys.


Can we predict which annular modes existed during the time of Pangaea? Some examples of annular modes include ENSO, NAM, and SAM.

I think one of the major mysteries of them is how they formed to begin with.

I'm just curious - do we have any idea of whether or not these annular modes existed in paleoclimates, particularly around the time of Pangaea? Do we have the computational power to predict them?

Since you're asking about Pangaea time, i would assume you're talking about the Permian (from 299Ma to 252 Ma).

We have a good idea of what Permian paleogeography was, a fair idea of how Permian oceans circulated globally (see one of your previous questions), enough data to produce credible models on how was the climate at the time (see e. g. Gibbs et al. 2002), even some idea on what atmospheric circulation (see e. g. Tibor & Montanez 2002) was like during that Period. So in theory i don't see any major hurdles to model these kind of oscillations (keep in mind that i am not a climate model specialist).

Now in my opinion, the big issue would be the data to back the model on, and particularly the time resolution needed to study these kind of oscillations: ENSO, PDO, NAM, SAM etc are annual to decadal oscillations (1-10yr).
A resolution "commonly"-achieved so far in detecting climatic oscillations in the Permian fossil record is for cycles of ca. 20kyr (i. e. 20 000 years; Milankovitch precession cycle). The kind of sedimentation rates and sediment quality needed to be able to record annual layers are extremely rare for such older sediments.

With that in mind, it's not impossible to find such sediments, in fact Anderson (1982) detailed the 260kyr-long continuous, annual varved Castille and Bell Canyon Permian evaporitic Formations, but even in such a high-resolution formation the shorter-length oscillation detected was still at ca. 180yr so way above that of any of the annular modes you mentioned.

References:
Anderon, R. Y., 1982. A long geoclimatic record from the Permian. Journal of Geophysical Research : Oceans, 87: 7285-7294.
Gibbs, M. T., McAllister Rees, P., Kutzbach, J. E., Ziegler, A. M., Behling, P. J., Rowley, D. B., 2002. Simulations of Permian Climate and Comparisons
with Climate-Sensitive Sediments. Journal of Geology, 110: 33-55.
Tibor, N. J., Montanez, I. P., 2002. Shifts in late Paleozoic atmospheric circulation over western equatorial Pangea: Insights from pedogenic mineral $\delta^{18}O$ compositions. Geology, 30: 1127-1130.


Does bathymetry affect ocean topography/height? Here is a map of ocean surface height or topography:

Source: http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2010/12/mean_dynamic_topography_of_global_ocean/9930795-2-eng-GB/Mean_dynamic_topography_of_global_ocean.jpg

How significant is the bathymetry or seabed elevation in shaping the surface topography? What are the major causes of variations in the topography?

Oceanic topography of the sea surface $\zeta$ can be defined as the height of the sea surface relative to a particular level surface, the geoid. The geoid to be the level surface that coincided with the surface of the ocean at rest (a list of geoids with application to oceanography can be found in Talone et al., 2014).

Variations in sea surface height (topography) are due to processes that result in ocean motion: ocean currents, tides, and changes in barometric pressure from the inverted barometer effect. As a result, we usually call it "dynamic topography" or "dynamic height". As geoid undulations are of order 100 times larger than the dynamic height, the shape of the sea surface is dominated by local geoid variations caused by gravity with the effect of the currents being much smaller.

In the image you provide what you have is "dynamic height" and thus is a deviation from the geoid and the result of oceanic currents. By knowing the dynamic height, we can get an idea of the surface geostrophic current:
$\mathrm{u_s= − {g\over f} {\delta\zeta\over\delta y}}$; $\mathrm{v_s= − {g\over f} { \delta\zeta\over\delta x}}$ where f is the Coriolis parameter,  g is gravity, and $\zeta$ is the height of the sea surface above the level surface (geoid).

Now, there is a direct effect between currents and bathymetry that sometimes is referred to as Taylor columns. The Taylor-Proudman theorem enforces that vertical columns of fluid move along contours of constant fluid depth. The basic idea behind this is that in order to conserve vorticity, fluid parcels tend to follow bathymetric contours (isobaths). So to answer your question, bathymetry affects ocean topography indirectly by affecting ocean currents.


If we could green the Sahara, would it be able to sustain itself? Let's say at some point in the future we have an abundance of fresh water (for example because we have enough energy to power many desalination plants) and we can turn the Sahara into green land by supplying it with a lot of watter and nutrients
What would happen once we stop the water supply? Could the green Sahara sustain itself?

The biggest detriment to keeping deserts green is of course water. With rainfall in the desert limited, afforestation is a tricky and potentially dangerous thing to do. China tried this for decades with afforestation efforts, planting billions of trees in steppe regions of China and Mongolia, only to later worsen because the trees consumed too much ground water and lowered the water table.

On the other hand, trees behave like humidifiers, the little moisture that accumulates at night may collect on the trees and fall as dew, replenishing some soil moisture. Reforestation campaigns in deserts are questionable efforts, without artificial watering or human maintenance they usually die. However active afforestation campaigns in semi-deserts bear some merit. However, there's no evidence of artificially planted forest sustaining itself in such an arid environment without human intervention.
Another example are drought tolerant trees, like acacias, planted in the Sahara. These may very well sustain themselves with their ability to settle and accumulate more water.

They provide shade and so prevent the surface soil from overheating, which has several benefits

With cooler soil, the little soil moisture that falls here can percolate into the ground without evaporating
It shades wildlife from extreme heat (who in turn produce fertilzer i.e. manure/urine)
The areas under trees become attractive nesting sites for birds who nest in winter

For more examples of greened ecosystems, there's the Hawaiian island of Ni'ihau. This is privately owned and very arid because of the rainshadow effect. The owners planted tens of thousands of trees a year for decades. As a result, the trees act as a humidifier to collect what little atmospheric moisture accumulates at night when it's cooler.
Another example is Ascension Island. In the 1850s, botanists (under encouragement by Charles Darwin) started shipping trees to the island. In mere decades, the peak of the island became a cloud forest.
I don't know if such examples are self sustaining. I can only say it's "Plausible". Ascension Island is not well developed, therefore little maintenance is done on the forest above, and it's a national park.
In more arid regions, it's possible but don't expect a full blown forest. You might see a semi-arid scrub forest.


Does over-cropping large areas really change the amount of rainfall? I heard that at one time the Sahara desert was cropped in wheat for the Roman Empire, and that cropping without adding back to the soil was what caused the desert to form. I also heard that this is going on in the U.S. (in the Great Plains, etc.). Really? Seems odd that the amount of rainfall would differ based on the health of the soil.

For an example of how bad agricultural practices can cause soil loss and end up with dust and sand, see the conditions that preceded the dust bowl in the USA.  Certain crops are bad for soil and if not rotated will eventually deplete the soil of nutrients leading to no crops.  With nothing holding the soil in place (roots) it will erode. The Sahara has other ill effects going on, such as synoptic scale atmospheric descent (interaction from the Walker Circulation and the Hadley cell) which promotes dry, warm conditions.

I'm not sure that rainfall will vary based on soil health, but one avenue to look into is soil moisture and other sources of water.  Rain begins as water vapor and that water vapor comes from evaporation (from bodies of water, entrainment), evapotranspiration (from soil and plants) and advection (blown in with the wind).  If the predominant flow does not bring in moisture and you lose the ability to hold water in the soil, this could conceivably locally reduce water vapor mixing ratios and impact precipitation.  That is just a guess and it would be worth searching the literature (you can freely download AMS articles older than 2 years old and search them here).


Is there a name for subduction boundaries at the North of Australia? I know the ridge at the South of Australia is named Southeast Indian Ridge.

I would like to know if there is a geological name for the three subduction branches that cross indonesian zone, at the North of Australia, as seen in this map.

  Source: researchgate.net Map by United States Geological Survey.

I do not think there is one name for the area. Rather it is a region with multiple plates, namely the Timor Plate, the eastern portion of the Banda Sea Plate, the Maoke Plate and the Woodlark Plate, all of which lie on the Arafura shelf which lies upon the Australian Plate. The Timor trough, Tanimbar Trough and Aru Trough would cover the western portion of the area you are questioning.

The Papuan Thrust and Fold Belt (PTFB) and the Aure Trough make up the northern and eastern portion of the area in question. Hope this helps.


How does the tornado chaser locate the spot? In my opinion, tornado is hard to forecast in three different aspects:

The size of tornado is about 100 ~ 1000 m which can't be represented well in weather model or detected by limited weather station.
The lifetime of tornado sustained is short(~hours). For now, the strong-convention activity can't be forecast well for 24 h or 48 h product.
The cause of tornado is complex. It also increase the uncertainty of the parameterize or numerical scheme which describe the process control the tornado.

But, I have heard some brave guy(Tornado Chaser) searching for tornado around US. It's really cool to experience the amazing nature  as the figure shown.

But how did they learned the information of where and when a new tornado would appear ?

PS: my question was came forward due to the sad news of 98 deaths by tornado in Jiangsu, China at 2016-06-23

It starts by identifying days with good overlay of shear and surface-based instability.  In the US we have the Storm Prediction Center that helps indicate such days looking at models.  Generally the very earliest signs that get chaser's attention are a reasonable trough moving into regions with adequate moisture and warmth (sometimes a cut-off upper-level low works too).

Then the day before and the morning of the event, final target regions get narrowed down further by looking at visible and water vapor imagery, upper level air maps, and surface weather data.  Basically the focus is generally on surface features... fronts, low pressure centers, drylines, and outflow boundaries.  Chasers will usually get into that region by early afternoon, as supercells and tornadoes are most common during the late afternoon and evening.

Once in the target zone, chasers keep an eye on any available satellite imagery, surface weather data, and also to the skies, looking for initial storm developments and any adjustments that may need to be made to the target area.  In many situations, clouds will start building up and perhaps pulsate in development, giving indication of favored areas long before the cap is broken and they develop into supercells.

Once the storms get going, the interest become identifying the stronger and more isolated storms as they develop rotation, becoming supercells.  In the northern hemisphere, the "business area" of a supercell is usually near the southern end, where a supercell will typically start to develop some sort of hooked shape, as all shown in this supercell image:

(Source: What is a Supercell Thunderstorm, by Dennis Mersereau, on Vane)

Most (though not all) supercells move approximately northeast.  So knowing that, as the day evolves, a typical chaser will make choices to help end up on the south half of the storm so their visibility and path are not blocked by the stronger rain and hail.  Then it comes down to road options, and paying attention to the storm and environment around you to watch whether the rotation is tightening up in the cloud base, as well as being aware of the temperature and wind for indications of how the storm may evolve.

When it comes to models, you're right that they absolutely can't identify the tornado.  However, convective models (like the HRRR) do often indicate the approximate areas where storms will develop a few hours ahead of time.  But it doesn't appear models will be forecasting where tornadoes will form with any great reliability for quite a while still.

But in terms of hunting down tornadic storms, convective models, and for that matter any large deal of real-time data, certainly aren't a necessity.  People have been chasing storms quite successfully long before all that was available.  It's more reasonable than most realize.  You choose the climatologically favorable tornado seasons to start, then seek out favorable areas within the large-scale pattern, and then refine your target by interpreting the conditions until you find yourself magically on the southern end of a hook, even without radar help.

For more input, I also suggest Mike Hollingshead's amazing high quality graphic tutorial, with a very useful snippet available on his StormAndSky website.

It looks like tornadoes are quite regular occurrences around China.  I know of chasers around Europe, Australia, and South America, but am surprised there aren't more in China.  Maybe that is soon to change?


Derivative of Exner function In chapter 13.1 in 'Mesoscale Meteorology in Midlatitudes' (Markowski and Richardson,2011) they use a Bernoulli equation and the hydrostatic equation and a lot of assumptions to derive an equation that predicts the height $z_{crit}$ at where an air parcel with an initial height of $z_0$ that is advected towards a barrier loses all horizontal velocity. In their argumentation they state the following identity
$$\dfrac{\partial p}{\partial z}(x,z) = \rho(x,z)c_p\theta(x,z)\dfrac{\partial \pi}{\partial z} (x,z)\tag{1}\label{wanted}$$
where $\pi(x,z)=\left(\frac{p(x,z)}{p_0}\right)^{\frac{R}{c_p}}$ is the Exner function with reference pressure $p_0\in\mathbb{R}_+$ constant, $p$ is pressure, $\theta$ is potential temperature, $\rho$ is density, and $c_p$ and $R$ are constant $\in \mathbb{R}_+$.

If I try to derive this equation by taking the partial derivative of $\pi$ with respect to height $z$ and use the identity $\pi(x,z)=\frac{T(x,z)}{\theta(x,z)}$ as can be found for example on wikipedia ($T$ is temperature), then I end up with (suppressing arguments $x$ and $z$ in favour of readability)
$$\dfrac{\partial \pi}{\partial z} =  \left(\frac{1}{p_0}\right)^{\frac{R}{c_p}}\dfrac{\partial}{\partial z}\exp\left(\frac{R}{c_p}\log(p)\right)=\left(\frac{1}{p_0}\right)^{\frac{R}{c_p}}* \frac{T}{\theta}*{\frac{R}{c_p}}*\frac{1}{p}*\dfrac{\partial p}{\partial z}.$$
Multiplying this by $\rho c_p\theta$ we get
$$\rho c_p \theta \dfrac{\partial \pi}{\partial z} = \left(\frac{1}{p_0}\right)^{\frac{R}{c_p}} \frac{T R \rho}{p}*\dfrac{\partial p}{\partial z}$$
and because $\frac{T R \rho}{p}=1$ by the ideal gas law we end up with
$$\rho c_p \theta \dfrac{\partial \pi}{\partial z} = \left(\frac{1}{p_0}\right)^{\frac{R}{c_p}}\dfrac{\partial p}{\partial z}.$$
This is almost what is stated in $\eqref{wanted}$, but not quite and I do not know how to get rid of the factor $\left(\frac{1}{p_0}\right)^{\frac{R}{c_p}}$ resp. do not see why it remains unmentioned in the textbook. Any help is appreciated.

Start with the original equation. Let's first write the Hydrostatic equation:

$$\frac{\partial p}{\partial z}=-\rho g$$

So let's prove that $$-g=c_p\theta\frac{\partial \pi}{\partial z}$$

If we use the product rule, we observe $$-g=c_p(\frac{\partial \theta \pi}{\partial z}-\pi\frac{\partial \theta}{\partial z})$$

Since $\pi=\frac{T}{\theta}$, we can say that $T=\pi\theta$, which makes the above equation

$$-g=c_p(\frac{\partial T}{\partial z}-\pi\frac{\partial \theta}{\partial z})$$

It can be shown that
$$\frac{\partial \theta}{\partial z}=\frac{\theta}{T}(\frac{\partial T}{\partial z}+\frac{g}{c_p})$$

which can be rewritten as
$$\frac{\partial \theta}{\partial z}=\frac{1}{\pi}(\frac{\partial T}{\partial z}+\frac{g}{c_p})$$

Substituting this into my fourth equation
$$-g=c_p(\frac{\partial T}{\partial z}-\frac{\pi}{\pi}(\frac{\partial T}{\partial z}+\frac{g}{c_p}))$$

From here I think you can figure it out.

Derivation for $\frac{\partial \theta}{\partial z}$
$$\theta=T(\frac{p_0}{p})^\frac{R_d}{c_p}$$
$$log(\theta)=log(T)+\frac{R_d}{c_p}(log(p_0)-log(p))$$
$$ \frac{1}{\theta}\frac{\partial \theta}{\partial z}=\frac{1}{T}\frac{\partial T}{\partial z}-\frac{R_d}{c_p P}\frac{\partial P}{\partial z}$$
Utilizing hydrostatic equation
$$ \frac{1}{\theta}\frac{\partial \theta}{\partial z}=\frac{1}{T}\frac{\partial T}{\partial z}+\frac{R_d \rho g}{c_p P}$$
$$ \frac{1}{\theta}\frac{\partial \theta}{\partial z}=\frac{1}{T}\frac{\partial T}{\partial z}+\frac{g}{c_p T}$$

$$ \frac{\partial \theta}{\partial z}=\frac{\theta}{T}(\frac{\partial T}{\partial z}+\frac{g}{c_p })$$


Why is the lithostatic pressure gradient 1 psi/ft? How is it derived from density? Why is the geostatic (or is it the lithostatic?) gradient 1 psi/ft?  How is that derived from g/cc? Thanks.

Lithostatic pressure might be roughly 23 kPa/m (about 1 psi/ft) in young basins dominated by siliciclastic rocks, but it varies substantially. Pressure has a linear relationship to density. Let's explore the relationship, and the variance.

First some definitions:

Lithostatic pressure — vertical pressure due to the weight of rock and fluid.
Hydrostatic pressure — vertical pressure due to the weight of fluid only.
Fracture pressure — the pressure at which the rock fractures.
Pore pressure — the pressure in the pores of a rock; usually close to hydrostatic.

There's a lot of jargon in this field — lithostatic pressure is sometimes called confining pressure, overburden pressure, vertical stress, total stress, and various other things. I hadn't heard of geostatic pressure before, and a quick bit of research revealed that some people call the pressure due to rock and fluid 'lithostatic' and some call it 'geostatic', reserving 'lithostatic' for the pressure due to the dry rock only. In my experience, it doesn't pay to be pedantic about these inconsistencies, all you can do is spell out what you mean.

We'll do a quick derivation (there's a more comprehensive one here). Pressure $P$ is force $F$ per unit area, and Newton told us that $F = ma$, where $m$ is mass and $a$ is acceleration. Since we're interested in vertical pressure, acceleration is due to gravity so we can use $g$. We know the mass of a rock normalized to volume as density $\rho$, and we're interested in a depth $d$, so:

$$P = \rho d g$$

The units are $[\mathrm{kg/m}^3] \times [\mathrm{m}] \times [\mathrm{m/s}^2]$ or newtons per square metre, N/m$^2$, which we call pascals, Pa, for convenience (10 kPa is 1.45 psi). Note that in the real world density varies with depth, so you'll need to integrate.

Because the pressure increases roughly linearly with depth, it's often convenient to talk about the pressure gradient, which is usually expressed in units of kPa/m, and of course is just the gradient of a line on a pressure–depth plot, like in the example below from a fictional offshore well.

So where does 23 kPa/m come from? If we take an approximate average density of sedimentary rock as 2300 kg/m$^3$, then $P = 2300 \times g$ Pa/m, or about 23 kPa (we often round $g$ to 10). Different mineralogies, different porosities, different fluids — all these will change the lithostatic pressure gradient.


Why Vp/Vs and not Vs/Vp? The relation between shear wave velocity (Vs) and pressure wave velocity (Vp) is often expressed as Vp/Vs. Wouldn't the opposite be more logic? Vs/Vp would never lead to division with zero and the relation would always be a neat number between 0 and 1.

What are the reasons behind this convention?

After quite a bit of conversation on Twitter, I think it's arbitrary. Tradition is probably the prevailing reason.

It would be interesting to go back through the literature to see who first used it. My hunch is that it goes back to the Zoeppritz equations (Zoeppritz 1919), which feature both $V_\text{S}/V_\text{P}$ and $V_\text{P}/V_\text{S}$. I bet Aki & Richards (1980) also had something to do with its propagation, at least in the exploration geophysics community.

Thinking about it, I think there are some good reasons to use $V_\text{S}/V_\text{P}$ instead of $V_\text{P}/V_\text{S}$.

It's well-behaved

As the OP said, $V_\text{S}/V_\text{P}$ behaves nicely, being constrained in the range [0,1) for rocks and fluids (and weird things like bitumen) — compared to $V_\text{P}/V_\text{S}$, which varies in the range 1 to infinity/undefined. I suppose you could call that 'neat'...

It's a good gas indicator

If you have a background of brine (say) and want to see gas anomalies, then my insufficient research suggests that $V_\text{S}/V_\text{P}$ is actually a better discriminator:

It's in the Aki–Richards equation

This is the formulation from Avseth et al. (2006):

$$ R(\theta) = \frac{1}{2} \frac{\Delta \rho}{\rho} - 2 \left( \! \frac{V_\mathrm{S}}{V_\mathrm{P1}} \! \right)^2 \frac{\Delta \rho}{\rho} \sin^2 \theta + \frac{1}{2} \frac{\Delta V^2_\mathrm{P}}{V^2_\mathrm{P}} \frac{1}{\cos^2 \theta_\mathrm{avg}} - 4 \left( \! \frac{V_\mathrm{S}}{V_\mathrm{P1}} \! \right)^2 \frac{\Delta V^2_\mathrm{S}}{V^2_\mathrm{S}} \sin^2 \theta $$

Refer to the book or SubSurfWiki for the symbol definitions etc.

Hmm, none of these are reasons why $V_\text{P}/V_\text{S}$ prevails. This is starting to look like the $\pi$ vs $\tau$ debate...

References

Aki, K, and PG Richards (1980). Quantitative Seismology: Theory and Methods. WH Freeman and Co.
Avseth, P, T Mukerji, G Mavko (2006). Quantitative Seismic Interpretation. Cambridge University Press.
Castagna, J, and H Swan (1997). Principles of AVO crossplotting. The Leading Edge, Society of Exploration Geophysicists, 17, 337–342.
Smith, T, et al (2003). Gassmann fluid substitutions; a tutorial. Geophysics (April 2003), 68(2):430-440. DOI 10.1190/1.1567211.
Zoeppritz, KB (1919). Erdbebenwellen VII. VIIb. Über Reflexion und Durchgang seismischer Wellen durch Unstetigkeitsflächen. Nachrichten von der Königlichen Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-physikalische Klasse, 66-84.


Why is aerodynamic resistance defined inversely? When I think of wind resistance, I always think of the friction co-efficient, in $\mathrm{ms^{-1}}$, because that's always the way that it was presented in highschool and undergraduate physics.

But in land surface modelling, aerodynamic resistance (basically, how much the roughness of the surface slows air movement down), is defined inversely. For example, this presentation states on page 18 that:

  $r_a$ = $f($wind speed, atmospheric stability, surface roughness$)$
  $r_a$ decreases with increasing wind speed
  $r_a$ increases with increasing stability
  $r_a$ decreases with increasing surface roughness

and then gives a bunch of examples in $\mathrm{sm^{-1}}$:

Surface type   ra (s.m^-1)
Ocean          200
Grass          70
Crops          20-50
Forest         5-10

To me, it seems really counter intuitive ("resistance is higher over grass than over a forest"?). Is the some benefit to defining resistances this way, or is this just some annoying historical mistake?

It's partly historical, partly point-of-view, but it's not a mistake.

The friction coefficient emphasises the effect of the surface on a property of the boundary layer, i.e., greater surface friction slows the near-surface wind more.  Aerodynamic resistance emphasises the effect of the boundary layer on surface-atmosphere exchange, i.e., greater mixing yields a lower resistance to evaporation.  Note that it's evaporation not advection that's being resisted.  You could turn the confusion around and argue that friction coefficient is a counter intuitive term: if there's more friction, why does evaporation increase?  This would be making the same category error.

Historically (IIRC) the electrical circuit metaphor was introduced by Penman and Schofield (1951) in an early modification of the Penman evapotranspiration equation to account for how vegetation limits the transpiration rate.  The original Penman equation is often quoted using aerodynamic conductance (or friction velocity or friction coefficient), i.e., a quantity using the the $m s^{-1}$ units that you're used to.  This is a natural choice for micrometeorologists trying to understand the bulk mass transfer properties of the turbulent boundary layer because it can be calculated from the boundary layer quantities that they measure.

Once you start introducing other surface effects on evaporation it's not really appropriate to extend the analogy of a turbulent fluid friction velocity down from the boundary layer to vegetation stomata, roots and the soil.  So we use the electrical metaphor instead, in which case it becomes slightly simpler to describe the system using resistances rather than conductances.  In the first instance it was just a case of calculating the total system resistance by adding a stomatal resistance to the aerodynamic resistance:

$E = \frac{\rho}{r_s+r_a}\left(q_{sat} - q_a\right) = \frac{\rho}{r_t}\left(q_{sat} - q_a\right)$

You can express this as conductances, but it's not as neat:

$E = \frac{g_a g_s \rho}{g_a+g_s}\left(q_{sat} - q_a\right)$

You can see in the later slides of the presentation you linked to that these resistance networks have got progressively more complex, so nowadays this neatness point might be moot.

Penman and Schofield (1951) Some physical aspects of assimilation and transpiration, Symp. Soc. Exper. Biol., 5, 115-129.


How to read and plot seismic waveform data in Ascii format using Obspy? I wish to plot seismic waveform data using Obspy, bu they are in Ascii format. Is it possible to read and plot Ascii file using Obspy?

If there is no direct function available, you can create a Trace/Stream object yourself.

The solution I use (example for one time series) is:

read the Ascii file into a numpy array
trace = obspy.core.Trace(data=numpy array, header=header dictionnary of your choice)
stream = obspy.core.Stream(traces=[trace])
stream.plot()


Relation between fault rupture aspect ratio and slip rate? I am modeling a fault surface (which I consider to be a plane rectangle). I got the area of the surface, but the orientation is unknown, which can be found out if the aspect ratio of the rectangle is known. Is there a way to find this using the average slip rate?

Ok, so this is a somewhat complicated question, and while this isn't a full answer I think I may be able to help you find the right direction.

It sounds like you are doing a completely theoretical study, so in this case I would advise you to look at Fault Maximum Displacement vs Fault Length Ratios (commonly referred to as D/L in te tectonics community). Here is an older but good study on D/L ratios: ftp://ftp.gps.caltech.edu/pub/avouac/OwensValley/Dawers-Geology-1993.pdf

You will have to make some assumptions based on the type of faulting that occurs in your model.

I found a observational study on D/L ratios and slip rate: http://www.sciencedirect.com/science/article/pii/S0191814101000360

Which seems to be a well cited article on the subject. It seems there is some correlation, but perhaps it is different depending on the area. I know that Mars, Earth, and Icy Moons around Jupiter/Saturn all have different average D/L ratio which is directly correlated to the strain rates and material properties. Slip rate should have a similar, if not identical correlation (though slip is usually calculated on the surface where strain is often subsurface from my understanding).

What software are you using to model this fault surface? Is it a homebrew or is it a community code? I realize you might need to be a little secretive about what you are researching when posting on the internet, but a little more information might or might not go a long way in helping people provide a better answer.

Hopefully this helped.


What influences tide-height the most? Can I guess the height by looking on a globe? I hope that the question title is resonably clear: What are the most significant factors which influence the tide height? I'm aware of the following couple of them:

Sun-Earth-Moon relative position (higher tide when co-linear)
Size of the land/peninsula/island (higher for larger lands I suppose?)
Shape of the surrounding seafloor (Hawaii has low tide partly because it has no shelf)

However, I'm really curious as which are the most important amongst them? Or is it even possible to guess the tide height if I know the Lunar phase and I have a good globe with sea depth?

I don't know about the size of land masses, but their distribution and the shape of ocean basins definitely play a big role.
When considering the ideal case of an all-ocean globe, i.e. one with no land masses (equilibrium tidal theory), the combined effect of sun and moon give a theoretical tidal range of less than 1 m(1). As tidal ranges can be much larger than this,  there are other effects that has a greater influence.

The Bay of Fundy for example, is one of the places with the largest difference between low tide and high tide, at about 16 m. The large difference in this location has to do with the shape of the bay. The bay has a natural frequency for waves that is about the same as the frequency of the tide itself, giving an amplification of the tidal amplitude. In addition there is a funnelling effect in the inner part of the bay, giving an additional contribution.(2)

Another example of large tidal differences is the English channel, particularly the French side. In this case the tides are large at least partly because the tide moves as a coastal trapped Kelvin wave. These are waves that propagate along land, with the land to the right when looking in the direction of propagation (on the Northern hemisphere, land to the right on SH). The amplitude of the wave is highest near the coast, decaying exponentially away from the coast. As the tide in the English channel moves northward, the largest tidal range is on the French side.

With regard to guessing the tidal range, this is not entirely straight forward.
First, when discussing tides, we generally split the tidal potential into a series of oscillations having different frequencies, mainly either diurnal (period of ~24 h) or semi-diurnal (period of ~12 h).
These given frequencies are obtained through trigonometric considerations, and depend on the latitude of the point, the declination of the moon or sun relative to the equator, and the hour angle.
(The hour angle is basically the longitudinal difference between the sub-lunar point and the point we consider.)
Each of these components can vary in time and space.

Further, the pattern of the amplitudes of each component is not necessarily simple. In addition to the differences in potential, the topography modifies it.
See for example:

from wikipedia

which shows the amplitude of the M2 tidal component.
This is the strongest semi-diurnal tidal component caused by the moon. You'll notice that there are places where the amplitude is zero, i.e. this component causes no tides here.
These are known as amphidromic points.

Also, depending on which components dominate at a given location, you can have either a mainly semi-diurnal tide, a mainly diurnal tide, or a mixed tide where there are two high tides in a day, but one has lower amplitude than the other.  A sketch of which can be seen here:

from wikipedia

(1) Pugh, David T. (1987) Tides, surges and mean sea level, chapter 3.

(2) http://www.bayoffundy.com/about/highest-tides/ (for lack of better sources)


Wobbly Tire Theory -- Is there an existing theory that fits the following description? I am not an earth scientist but for many years I have wondered about the following. I am curious if this has already been explored by scientists? If so, what is the theory formally called? and what is the consensus of the scientific community about such a theory?

CONCEPT: When you have new tires put on your car the mechanic will put the tire on a machine to check the balance and then add small lead or zinc weights on the rim to correct any wobble. Even though the weights are tiny by comparison they play a critical role in effective lifespan of the tires.

For the past couple hundred years humans have been moving "tiny" amounts of weight around the surface of the earth. We add weights when we build large cities, or dam rivers. We take away weights when we excavate and overdrafting.

There also of course are natural events that move "tiny" surface weights around, such as glacier movement, island formation, caldera eruptions, and meteor strikes. This last of course also imparts a vector of kinetic energy change due to impact force.

THEORY: I call this personal idea the "Wobbly Tire Theory" on the presumption that Earth has for millennia been dealing with axis wobble but has usually had time to adjust/stabilize between significant changes. However, in the past 200 years or so we have been making a lot of man-made changes in these weights in a timespan that is a geologic blink-of-an-eye.

I speculate that these rapid changes may be affecting the earths rotation in subtle ways. For example, I wonder could such changes affect the core's rotation vector in any way?

So back to my original Question: Does this theory (including OR excluding the last about man-made effects) already exist among geophysicists and others? What name(s) does it go by? And what details, if any, are there on the scientific consensus of this concept?

I don't know if this theory has any formal name, but of course you are correct in assuming that any mass redistribution on or in the planet will affect it's axis of rotation, causing a wobble. Small re-distributions are happening all the time with growing and melting ice, ocean currents sloshing water from one side of an ocean to another (as in the El Nino). Theoretically, a whale swimming across an ocean will create an axial wobble, albeit far too small to measure. Earth and sea tides, climate change, plate tectonics etc... The list goes on and on, with multiple processes each causing a slight tilt in the Earth's axis. This ranges from barely detectable sub-milimetre range to thousands of kilometers (over geological time - hundreds of millions of years).

In addition to the above random fluctuations there is also the 'Chandler wobble' which is a predictable cyclic wobble in the Earth's axis, of about 9 metres, over a period of 433 days.

As for human impacts, until recently I would have said that they were puny compared to natural processes. However, recent research points to significant and growing change in the Earth's rate of spin due to human induced climate change. This could have interesting 'knock-on' effects upon the spin axis. The effect is absolutely miniscule, but as the Earth's spin slows, there is likely to be further de-coupling of spin rate between the Earths crust/mantle and core which could well be an additional component to the axial wobble.


Is a hotter climate making trees grow faster and have lighter wood? I started thinking about this after seeing several articles about falling trees, in particular a few articles about very large trees falling in Los Angeles and New York City. Plus, just thinking about all the wildfires in the Western United States started by trees falling on electrical wires. Although I haven't done extensive research, I did some searching and found the following:
Trees and climate change: Faster growth, lighter wood. This article discusses how "wood density of European trees decreasing continuously since 1870."
So is this a current concern and a global phenomena? Are trees growing faster, but are less strong. Combining this thought with the fact that winds are getting stronger in North America seems very unsettling.

Nothing to do with climate change . Faster growth produces somewhat lower density and strength. There are strength tables for wood written more than 50 years ago that have separate listings for "new " growth and "old" growth. "New " growth being trees growing faster in clear cut areas with less competition for water, light and nutrients. Old is trees in areas that not previously been harvested and grew slower in crowded conditions.  Power line failure is related to the increase in numbers of power lines in expanding populated areas, and to how much money utilities spend trimming trees near the power lines.  When I drove in western Europe  in the 80's , I was impressed by how many of the forests had been "managed". Large old trees had been planted in regularly spaced straight lines ,maximizing growth speed = lower density . As silviculture is a minor hobby of mine I expect I noticed things others would not.


Has the Olema earthquake fence continued to spread apart? The earthquake fence at Olema shows the sudden transform motion along the San Andreas caused by the 1906 earthquake. 110 years on, has there been ANY additional displacement?

If your question is only about the location of said fence I can not answer it. If, however, you are interested in the greater area around that location or the San Andreas fault in General, the short answer is, yes, there has been additional displacement and the movement is ongoing.

This displacement is related to what one can call the earthquake cycle of surface deformation. Usually people differentiate between co-seismic (directly caused by an earthquake, the Olema fence is a beautiful example for this), post-seismic (caused by secondary earthquake effects, keywords are poroelastic and viscoelastic effects) and inter-seismic (which is the tectonically driven creep of a fault in between earthquakes).

Take a look at this article by Lisowski and others to see surface displacements along the SAF. Fig. 7 shows the area of interest and , though a bit hard to see, there is significant relative motion in between areas east and west of the fault. The number that they give for average relative plate motion is 35 mm/yr (which would be roughly 4m/13ft in 110 yrs).

To return to the fence, I can only assume that it has spread further apart in the last 110 years, but not having been there I can not be certain. It is possible, that the surface manifestation of the fault has turned to another spot. I do think it is unlikely that not at least part of the deformation can be seen at the fence's location. According to this book the co-seismic offset of the fence was 4.7 m, might be interesting to know what it is today.


Is an underground mine collapse or a tunnel collapse called a sinkhole? Imagine there's an underground man made structure e.g. a tunnel or an underground train station that collapses creating a depression in the surface. Would that technically be called a sinkhole? What is the exact definition of a sinkhole (for someone illiterate in earth sciences, please, thanks.)?

The wikipedia article on sinkholes seems to suggest that they should be called collapses and not sinkholes:

  Collapses, commonly incorrectly labeled as sinkholes also occur due to human activity, such as the collapse of abandoned mines and salt cavern storage in salt domes in places like Louisiana, Mississippi and Texas. More commonly, collapses occur in urban areas due to water main breaks or sewer collapses when old pipes give way.

(emphasis mine)

The media keeps calling them sinkholes. A google search on sinkholes will give numerous news articles that call these incidents sinkholes.

P.S. Sorry about the tags. Not sure what tags to use.

This is probably more of an English language question than a science question.
The answer to it depends on the extent of a person's vocabulary & knowledge of a particular field of engineering.

Over a period of time, in the media I have read & heard mine "tunnels" incorrectly being called shafts. Mine shafts are vertical or near vertical. What most people call mine "tunnels", people in the industry call drifts or drives - these are horizontal or near horizontal. The word tunnel is better applied to civil items of infrastructure rather than mines: such as rail or vehicular tunnels or tunnels to access underground bunkers or storage facilities.

Similarly, a tunnel or mine collapse could be termed a sinkhole and people not familiar with either the civil engineering or mining fields might do that - particularly journalists. People in the civil or mining fields would use terms such as tunnel collapse or mine subsidence hole.


How to strong winds cause baroclinic intensification in the upper ocean? Below is an excerpt from The Biology of the Indian Ocean,  Bernt Zeitzschel, Sebastian A. Gerlach

  The more vigorous atmospheric and oceanic circulation during the SW
  monsoon causes not only the development of a strong western boundary
  current, the Somali Current, but also intense upwelling in several
  places. The circulation appears to penetrate deeper, affecting the
  movements of water masses below the thermocline. The formation of the
  Somali Current as a strong western boundary current of the monsoon
  gyre causes a strong baroclinic adjustment of the structure along the
  coast of Somalia. This baroclinic structure is noticeable as deep as
  1000 m, but is especially pronounced in the upper 400 m. The strong
  winds parallel to the coast intensify the baroclinicity in the upper
  layer and cause, in addition, strong upwelling along the coast.

Through what mechanism do strong winds cause intensification of baroclinicity in the ocean?

Strong upwelling-favorable winds (like the ones described) cause coastal upwelling in the following manner:

Winds in these systems flow parallel to the coast (with the coast to the left in the northern hemisphere or to the right in the southern hemisphere) and generate upwelling dynamics.
Surface Ekman balance is setup (in deep enough waters) with water transport being to the right (left) of the wind in the northern (southern) hemisphere. The result is a deficit along the coast that requires a compensating flow in the deeper part of the water column bringing usually colder waters to the surface.

 Source Commons Wikipedia.

The resulting density (mostly controlled by temperature in these systems, but sometimes affected by salinity in areas with river influences) shows a strong horizontal gradient. A strong horizontal gradient in density is the definition of strong baroclinicity. That strong gradient can even be visible in a temperature front when the thermocline reaches the surface (SST image below).
Additionally, the density gradient can establish a thermal wind balance that results in a coastal upwelling current jet flowing in the same direction of the wind. The horizontal gradient in density is proportional to the vertical gradient in velocity
$\mathrm{{\delta\rho\over\delta x} \propto {\delta v\over\delta z}}$ . As velocity is zero at the bottom, this results in a strong velocity near the surface. This is what we understand as "intensifying the baroclinicity in the upper layer".

 Source: Satellite image of SST showing multiple upwelling centers and cold filaments off central California (Courtesy of E. Armstrong).


Why do some earthquakes and volcanoes occur within plates? I know that volcanoes and earthquakes occur on plate margins. But, do some of them also occur within plates?

Crustal plates are not homogeneous, uniformly continuous rock masses with uniform stresses. They are a mixture of rock types with variable stresses and stress concentrations. They are also discontinuous.

There are fault zones within plates. Some faults are active & others inactive.  When movement occurs along an active fault, usually due to in-plate localized stresses, an in-plate earthquake will occur.

Concerning in-plate volcanoes. These are due to geological hotspots. These are,

  thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle.[citation needed] Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths.


What generates the microseism? Looking at seismic noise around the Earth there is commonly a peak in the seismic noise around a frequency of 200 mHz.  This peak is typically referred to as the microseism (an example is shown below).  What is the source of these low frequency oscillations.

From experience I know that in southern Louisiana the motion at this peak is generally stronger throughout the winter than in the summer.  I have also been told that it is associated with water waves in the gulf, but it is unclear how those waves get converted to ground motion tens of miles inland.

The microseism is ocean waves that couple to the ground to make Rayleigh waves.  The ocean waves are gravity waves which are dispersive (different frequencies travel at different speeds), and 0.2 Hz (not 20 mHz) is the frequency of the waves that travel at the same speed as storm winds to which they couple.

The ground motion doesn't die off, even thousands of kilometers inland, because Rayleigh waves are bound to the surface (so waves from a point source would spread circularly instead of spherically).  The waves are produced all along the coast, which negates the circular spreading.


Equation for predicting contrail formation I am working on a data visualisation of airline flight paths and their probability of forming contrails.

Given weather data for a specific area (location, time, temperature, pressure and humidity) and aircraft data (location, time, altitude, speed and engine efficiency)

Is there an equation that will give me a rough estimate of the probability contrails will form at this point?

Schmidt-Appleman criterion (SAC) is used to model contrail formation. I advise reading in full Ulrich Schumann's article "A contrail cirrus prediction model" (http://www.geosci-model-dev.net/5/543/2012/gmd-5-543-2012.pdf) to get all the relevant formulae and literature references.

While it is possible to transcribe the formulae here, the reference cited does a better job of presenting state of the art (2012).


Does a table summarizing basic details of significant operational weather models exist? With all the questions we've had through the years that have tied into weather models, plus all the sites around the web providing weather model data, it got me wondering: is there any table that summarizes the basic details of the major weather models?  Details like calculation methods, spatial resolution, calculation timestep, vertical grid type, regions covered, parameterizations, run hours (and when the output is typically available), operating organizations, perhaps even some basic skill scores.  It would seem such a link would be useful in answering many questions, and be of use to many in trying to better understand how the models work or perform.

I'd think the obvious spot would be Wikipedia, as they seem to have similar collaborative lists for all sorts of useful things, but all I found was the very limited list on the models page.  Likewise searched AMS Journals for NWP summary and similar terms to no avail.  Does such a resource exist!?!

MetEd from NCAR has a good encyclopedia of models that summarizes some weather models. Of course, when models update, such as the GFS dynamical core being converted to the FV3, or changes in data assimilation systems, they may not be up-to-date. This also doesn't have ALL weather models, but some of the more common ones.

Of course, there are models missing from the encyclopedia, such as the SREF, GEFS, the JMA model, the Panasonic weather model, any iteration of the WRF model, statistical post-processed models, etc.


Wet and dry seasons - what are they and how do they form? While asking questions on Worldbuilding, I keep hearing about wet/dry seasons. Obviously, one has rain and the other doesn't, and I've gathered that they occur with regularity on an annual basis, but what exactly are they? What causes them, and when/how often do they form?

In the mid-latitudes we experience 4 seasons (winter, spring, summer and autumn) due to the large annual variation in sunlight due to the tilt of the earth in its orbit.   The tropical latitudes, however, do not see large annual variations in sunlight or temperature and instead define their seasons by precipitation changes e.g. wet and dry seasons.

Some examples of a wet/dry climate are monsoon climates and savanna climates.

The monsoon is driven by seasonal changes in wind directions.  The typical setup is offshore flow during the dry season and onshore flow in the wet season with a mechanism similar to the sea breeze (e.g. driven by temperature differences between land and sea).  During the dry season, dry  air flows out to sea and during the wet season, moist air flows inland from the sea, rises and produces rain.  The monsoon circulation occurs in parts of Africa, Asia, Northern Australia and arguably in the North America desert southwest (debatable because it lacks a true seasonal flow reversal).

The savanna climate generally have a dry season of varying intensity and length and a rainy season in the remainder of the year.  Total rainfall in savannas tends to be less than that in monsoon regions.

Both of these wet/dry climates involve interaction with the inter tropical convergence zone (ITCZ), which is a persistent band of rising air and thunderstorms near the equator.  It moves north and south with changes in location of the sun seasonally and responds to the monsoon circulations and ends up merging with them.

The other tropical climates are wet all year long (rainforest climates) and dry all year long (desert climates).  The rain forests are equatorial and dominated by the ITCZ year round.  The hot deserts are around 15-30 N/S latitude and are favored on the western extents of the continents.  The latitude preference derives from the descending branch of the Hadley cell, which suppresses precipitation and causes warming.  The western continental preference comes from the direction of the trade winds, which are easterlies in the tropics.


ERA Interim, how to handle total precipitation I am trying to compute accumulated annual precipitation for year 2000-2001 based on the ERA Interim, but I am stuck with some unresolved questions:

If I download the synoptic monthly means of "total precipitation" from ECMWF for year 2000-2001 with "Select time" set to "00:00:00" and "12:00:00" respectively, and chose "Select step" as "3", I get a *.nc -file with 48 time steps. The file also contains a "scale_factor" and "add_offset". I assume that I must use those values in (add_offset + (downloaded data * scale_factor)) to get actual precipitation in meters? And I assume that if I sum the 48 time steps of data (corrected with add_offset and scale_factor) and divide by 2 (2 years of data) then I get the average accumulated precipitation per year. Is this correct?

What then puzzles me is that the "scale_factor" is very low (3.9E-8), meaning that the values I get will be almost equal to the "add_offset" which is 0.0013. Are there any obvious mistakes I make? Or do any of you know of a guide that is more elaborate than the documentation found at ECMWF?

Thanks a lot in advance for any ideas.

First of all, these netCDF files follow the CF Metadata Conventions, which describe the use of scale_factor and add_offset in section 8.1 Packed data of the conventions description.  In short, you're applying them correctly:

  If both attributes are present, the data are scaled before the offset is added.

However, I think that you've selected the wrong fields for your purpose.  The total precipitation variable is an accumulation since the start of the re-forecast, and you've selected a monthly mean of accumulations over the first 3 hours of the 00Z re-forecasts and the same thing from the 12Z re-forecasts.  This means that you're missing the accumulated precipitation from hours 3 to 12 of the re-forecasts, so your annual mean estimates might only be 1/4 of any ballpark values you're expecting.  I suspect that you need to choose step=12 rather than step=3, as described in the ERA FAQ.

Also note, I think the comment in that FAQ about the monthly mean from daily mean data availability being "planned" but "not yet implemented" is out of date and that may be the better route to calculate the annual means (see also section 3 of Berrisford et al, 2011).


Divergent boundary and trenches between oceanic plates Why Divergent boundary create ridges between oceanic plates and rift valley between continental plates? I think that the ridges are formed because of the volcanic eruptions. But like rift valley in case of continental plates, can trench ever form because of the divergent oceanic plates?

The elevation of oceanic crust is controlled by Pratt isostasy, whereby hotter crust is elevated because it is less dense. Oceanic crust is produced at mid-ocean ridges and cools as it moves away from the ridge. Mid-ocean ridges are hot and therefore they are elevated above the colder, more dense adjacent crust.

In continental rifts, the dominant process controlling the topography is normal faulting, which leads to subsidence of the rift valley floor and uplift of the sides, leading to the formation of mountains either side of the active rift. Continental rifts form valleys because they have not yet reached isostatic equilbrium and their topography is controlled by extensional faulting.


Where can I download historical sesimic data in CSV/Excel format for processing in R? I'm not familiar with these kinds of data sets but I'm looking for some data for a project I'm working on. Essentially I would like multiple time series of seismic data from different stations over different periods. Is this sort of data freely available somewhere in a friendly CSV format?

Thanks for any help.

Luke

You can download seismic data in csv format at USGS, from past hour, past day, past week and past month.

If you wish to download ancient data you need to use the USGS API. There is a query option: format=csv.

This is an example of an URL that gives you seismic data in csv format from 2014-01-01 to 2014-01-02:

https://earthquake.usgs.gov/fdsnws/event/1/query?format=csv&starttime=2014-01-01&endtime=2014-01-02

User Kristjan shared a Python script to ask the API for all available data since 1900.


Generic pedo-transfer functions to compute field capacity and wilting point from sand/silt/clay? I have a model (Miguez et al 2008) that defines wilting point as the soil water content below which there is no transpiration (from Johnson et al 1993). Field capacity is defined as the volume of water that remains in wetted soil after excess has drained. Neither are truly constants for a given soil, but they are commonly used as such in modeling.

Are there are any generic pedotransfer functions that can be used to estimate these parameters from sand/silt/clay fractions? These estimates will be used as priors in Bayesian data assimilation, and will thus be subsequently constrained by observations of soil moisture and transpiration.

References:

Johnson et al 1993 The Implementation and Validation of Improved Land-Surface Hydrology in an Atmospheric General Circulation Model. J. Climate (pdf)
Miguez et al 2008 A semimechanistic model predicting the growth and production of the bioenergy crop Miscanthus  giganteus: description, parameterization and validation. GCB-Bioenergy (pdf).
Wikipedia "Field Capacity" and "Wilting Point".

As far as I know, there’s no one definitive pedo-transfer function (PTF) but there have been several studies that train functions against multi-site databases, rather than just deriving site-specific functions.  These PTFs typically define soil moisture-conductivity-suction relationships based on silt, sand and clay fractions from which you can read off field capacity (suction = -10 kPa) and wilting point (suction = -1500 kPa).  Which PTF you use will depend on the soil moisture-conductivity-suction hydraulic description that your model uses.

For Clapp and Hornberger hydraulics there's the Cosby et al (1984) PTF.  This is trained on data from the US.  It's quite possible that there are more recent PTFs trained on more and better data, but this one is still in use (e.g., by the UK Met Office).

For van Genuchten hydraulics there's the Wosten et al (1999) PTF (see also Wosten et al, 2001).  This is trained on the European HYPRES database, and you need organic percentage and bulk density in addition to the silt/sand/clay percentages.  There’s also ROSETTA (Schaap et al, 2001), which uses several PTFs hierarchically and is trained on data from North America and Europe.

Note that these hydraulic properties are difficult to measure in situ and in the lab, so the fitted PTFs often explain quite a low fraction of the variance in the training data.  You might be able to use this information to inform your priors, which should probably be quite conservative.


Evidence of a seismic trigger of the Storegga Slide ~8.2ka The Storegga Slide was a catastrophic underwater landslide that occurred off the coast of Norway about 8,200 years ago. This YouTube clip shows simulations that indicate that this slide resulted in landslides in the 10's of metres across the surrounding shorelines, including the Norwegian coast, Greenland, Iceland, Shetlands, Orkneys, Britain etc and by several accounts, it wiped out the now submerged North Sea land-bridge known as Doggerland.

A possible cause from the Wikipedia article (linked above) is:

  A likely triggering mechanism is thought to be an earthquake causing a catastrophic expansion of methane hydrates.

This earthquake scenario is also mentioned in this YouTube clip.

What evidence is there of a seismic trigger of the Storegga Slide?

Scandinavia experienced a lot of earthquakes due to post glacioisostatic rebound 10 - 7 ka. The most likely trigger for the Storegga Slide was a strong earthquake or a series of earthquakes. However, large sediment input from glaciation rather than earthquakes are the causes of the unstable slope. Release of overpressured gas hydrates was the driving force for the violent development of the slide.

  It is reasonable to relate the period with strong earthquakes with
  rapid  rebound  and  the  triggering  of  the  Storegga  Slide.
  Recent modelling shows that the seismic energy can induce
  ground shaking that lasts longer than previously assumed in
  the deep sedimentary Møre basin (Lindholm et al., 2005). In
  the Storegga region the isostatic deformation and reactivation  of  Late  Jurassic–Early  Creteaous  faults  because  of sediment loading on the North Sea Fan probably caused an elevated earthquake level. [...] The combined effects of excess pore pressure, exposure of ooze, relative steep slopes 10–20°
  and to the vicinity of potential  earthquake  centres  favour  an  initial  slide  in  the distal  area.

Bryn et al. (2005)

Bryn, P., et al. "The Storegga Slide complex; repeated large scale sliding in response to climatic cyclicity." Submarine mass movements and their consequences. Springer Netherlands, 2003. 215-222.
Bryn, P., et al. "Explaining the Storegga slide." Marine and Petroleum Geology 22.1 (2005): 11-19.
Lindholm, C., et al. "Probabilistic and deterministic seismic hazard results and influence of the sedimentary Møre Basin, NE Atlantic." Marine and petroleum geology 22.1 (2005): 149-160.
Berndt, C., et al. "Submarine slope-failure offshore Norway triggers rapid gas hydrate decomposition." 4th int. conf. on gas hydrates proc., Yokohama, Japan. 2002.
Bungum, H., Lindholm, C. and J. I. Faleide. "Postglacial seismicity offshore mid-Norway with emphasis on spatio-temporal–magnitudal variations." Marine and Petroleum Geology 22.1 (2005): 137-148.


Why is Massanutten mountain so dramatically different than surrounding mountains? See this aerial view from google maps. Massanutten is in the foreground, as straight as an arrow. The Appalachians are on either side, looking like more typical mountains, zig-zagging with outcroppings in every direction. I was lucky enough to find this video on exactly this topic, but I have zero geology knowledge, so it went completely over my head. Can anyone explain it in very simple terms?

If you look a wider view from above and a bit to the west, you will notice Massanutten is not that straight nor is it unique most of the surrounding mountains are the same, especially to west. Basically you camera is pointed in exactly the wrong direction to see the other mountains.

on a geologic map it becomes even more obvious.

A false color which hides the difference in plant life makes it even easier.

You can picture the appalachians as a flat section of rock that has been compressed like an accordion east to west, that's why they are more or less parallel, but not perfectly parallel becasue the rock is not completely uniform in strength or hardness. Plus the compression has a bit of a curve to it making it even less uniform.


Why do fjords have sills? I have read about some of the geologic processes that are related to the formation of fjords. Is the presence of sills in fjords related to the deposition of glacial moraine?

Fjords are formed as U-shaped valleys by the extreme erosion of glaciers. The glacier erodes large quantities of material that is transported by the ice.

The glacier can erode deep under the sea level (remember how an iceberg only has 1/10 of its mass above the surface) and if the postglacial rebound is limited, the fjord will remain as an estuary.

When the glacier slows down and withdraws, the sediments are dumped at the front of it to form a terminal moraine or sill. This is particularly pronounced if the front of the glacier had shrunken, growing again before melting due to environmental oscillations.

The sills are usually deposited at the mouth of the fjord, before the water depth increases. However, the biggest part of the glacial debris is deposited at deeper water.

You might also have shallow water in front of rias, were the flow slows down and sediments are deposited, but they will rarely form obvious sills as in a fjord.


What caused those colorations in bedrock? I took those photos in a hurry (sorry, the color is a bit off due to low light, the first picture is the most distorted one).

It struck me that the discolorations seem to follow the fissures in the rock.
Could somebody explain me what caused the red-brown colorations along the grooves?

IIRC the bedrock shown is glacially polished Rhyolite, location is the "Gleif church in Eppan, Italy". Further research told me that the glacial polishing happened in the Würm glaciation, ending 12000 years ago.

This answer is based on a cursory look at the 1:50000 Foglio Appiano, from the Geologic Map of Italy (in Italian Language only, as far as I can tell). As I pointed out in comment, I intend it as just a start for further investigations, which should be done with more detailed geological works and possibly more field work. I'd recommend contacting the office of the Geological survey of the Provincia di Bolzano as they certainly know the area well and may be able to answer on the phone or by email.

This is what I think, based on my cursory look.

The cross section C goes ~E-W just north of the town of Cornaiano, relatively close to the location of the Church, which is just West of San Michele (based on Google map link); I indicated its approximate whereabouts with yellow circle in the figure below. It looks like the rocks in your picture could be an outcrop of the ORA formation (in orange in the figure), a Rhyolitic tuff of the Atesino volcanic group.

Also the Schema tettonico below (look for Appiano) shows the Atesino volcanic group and is in contact with a very faulted sedimentary section (Successione sedimentaria permocenozoica); I'd say geothermal fluid circulation through these fractures causing hydrothermal alteration at surface is a plausible explanation for the coloration you captured.


If it rains harder, does it mean the rain's duration will be shorter? If it rains real hard, is there a chance the rain's duration will be shorter? I think the if the rain in the clouds disperses with such force the rain will be over faster than if it was just a light drizzle. Can anyone confirm/deny this? Is there a percentage or study shown on rain duration relative to the rain's strength?

The intensity of a rainstorm does not actually cause the duration of the precipitation to be shorter. There is a strong correlation, but not in the sense you may be implying here (let me get back to that in moment).
First you have to dispel the model that a cloud is a big container of water, and if it "rains harder", the cloud will run out of water quicker and the rain event will be shorter in duration. Rain doesn't really work like that.
The atmosphere everywhere (even outside the cloud) contains lots and lots and lots of water. And under a stable combination of temperature, pressure, and humidity, all that moisture is perfectly happy to exist in a completely gaseous state. But as differing air masses (different temperatures, pressure, and humidity) start to collide, the local atmospheric conditions can fall outside the range where water can exist in a completely gaseous state. That is known as the dew point.
A cloud is where two differing atmospheric conditions have met, and the resulting condensed water droplets simply do not have sufficient weight to overcome the updraft speed of the air around it. If the air masses mix slowly, the rate of condensation will occur slowly and over a longer period of time. The resulting clouds may simply "evaporate" as the local conditions stabilize, or the condensing water may slowly precipitate over the ground (gentle rain), or the precipitation may never reach the ground at all (virga). These gentler atmospheric changes tend to play out over longer periods of time because the air masses are moving more slowly so it takes longer for the differences to mix and settle down into a new steady state.
Here's the part where I talk about intensity
If two air masses have widely varying conditions (think warm moist air over the ocean meeting dryer hotter conditions over the land) and they meet more abruptly (higher wind speeds), this causes a more-violent disturbance; the moisture from the air will condense more quickly, the rain falls faster and harder, and the whole thing ends (relatively speaking) more quickly.
But the duration tends to be shorter because the reaction between the differing masses is occurring at a faster rate — so the whole event will generally play out more quickly. But it is perfectly conceivable that "harder rain" can last much longer if the storm system continues to pull in more of the moist atmosphere around it. In extreme circumstances, that's pretty much what a hurricane is; the storm itself gets so big that it starts to create it's own system that pulls in more and more atmosphere around it. The rain doesn't simply stop when all the rain has fallen out of the original clouds. It actually (continually) makes new clouds/precipitation as it continues to draw in the atmosphere surrounding it.
But speaking in broad generalities, the faster the disturbance occurs, the faster the moisture will condense, the harder the precipitation will fall, the more quickly the conditions will stabilize, and the duration of the rain will be less.