Will Venus eventually overheat? When it happens, what will happen to it exactly? Venus is a runaway greenhouse planet, so it won't let any of the heat absorbed from the Sun out by radiation, yet it will still take rays of energy from the Sun. So what will happen to Venus? Will it overheat? And if it will overheat, what will actually happen to it? I couldn't find any speculations over the internet...

Venus does radiate away heat, but not enough to prevent the surface and lower atmosphere heating to 460C. Too late to prevent overheating, it has already overheated. In the long term, its atmosphere will gradually leak away into space, reducing the present pressure of 90 Earth atmospheres. Exactly how far this process will have gone in 5 billion years' time when the sun swells up to become a red giant is impossible to say. When the sun becomes a red giant, Venus will be inside its tenuous outer layers and therefore scorched by much higher temperatures than it has now, probably reduced to a ball of molten rock spiralling inwards towards the sun's interior.


Why does phosphate rock contain uranium? I have been doing some research on the issue of phosphogypsum pollution.  Phosphogypsum is a waste by-product formed with the "wet process" method of extraction of phosphoric acid out of phosphate rock, which uses sulfuric acid and water to break it:
$$\ce{Ca10(PO4)6F2 + 10H2SO4 + 20H2O -> 10CaSO4.2H2O + 6H3PO4 + 2HF}$$
Returning the phosphoric acid and gypsum (calcium sulphate, or CaSO4). The problem here is that the uranium in the phosphate rock produces 226Ra (among other radionuclides) during its decay, and since 226Ra is an "Alkalin Earth Metal" (it's on the 2nd column of the periodic table), it can form radium sulphate and mimic calcium, leading to radioactive gypsum.
The point here is, why is the phosphate rock enrichened in uranium that can produce radium? Is there a trend for phosphate and uranium to accumulate together, and if so, what is the geochemical reason??
I have already found out that:

Sedimentary rock phosphates contain much higher concentrations of
potentially hazardous elements (As, Cd, Cr,Pb, Se and U)than
igneous rock phosphates. (1)
Phosphate rock varies considerably in content of U, Ra, and Th, depending
on the geographical area from which it was mined. (2)

1 - Mamdoh Sattouf, Identifying the Origin of Rock Phosphates and Phosphorous Fertilisers Using Isotope Ratio Techniques and Heavy Metal  Patterns.
2 - John J. Mortvedt and James D. Beaton, Heavy Metal And Radionuclide Contaminants In Phosphate Fertilizers.
Thank you in advance for your help!!

To understand why sedimentary phosphate rocks (hereafter referred to as phosphorites) have elevated uranium contents we first need to understand what are they made of and why do they form in the first place.

Phosphorites are rocks that are made of apatite, a mineral with the formula $\ce{Ca5(PO4)3(F,Cl,OH)}$. This mineral (especially the OH variant) is one of the main constituents of skeletons of living organisms. The hard mineralised part of your teeth and bones are made of apatite, for instance.

Skeletons of dead marine animals (e.g. fish) are deposited on the ocean floor as apatite. The source of apatite need not be biogenic: it can also be sourced from igneous or hydrothermal activity occurring on the ocean floor, or derived as clastic material from the continents. The end result, is the deposition of apatite as phosphorites.

An important property of apatite is that it can accommodate some uranium. The mechanism is not yet completely understood, but it's most likely the incorporation of $\ce{U^4+}$ in the mineral structure of apatite, replacing calcium. Now here's the interesting part - uranium in sea water is mostly present as $\ce{U^6+}$ (in the form of the uranyl ion). The uranyl ion is more soluble than $\ce{U^4+}$ so it mostly remains in solution in the sea water. But, as we mentioned earlier, apatite deposits form by the decay of dead marine animals. This accumulation of decaying organic material reduces the $\ce{U^6+}$ to $\ce{U^4+}$, facilitating its incorporation into the apatite structure.

That's only one side of the coin. Apparently $\ce{U^6+}$ can also be adsorbed on apatite grains. This is even used in some cases to stop uranium contamination from migrating through soil - by adding apatite to it in order to immobilise it.

Whatever the exact process (or combination of processes) that make uranium such a good friend of apatite, the end result is that apatite (and rocks containing it) is enriched in uranium relative to its environment.


How to interpret the values of moisture flux convergence? I have a time series of moisture flux convergence. The values show positive and negative. What are these positive and negative values say? Can somebody help me how to interpret it? How it is related to precipitation?

Whether positive values shows week precipitation and negative values shows strong precipitation?

MFC can be employed to detect frontal structures and possible storms, which can be related with high values of MFC, which means convection of winds with high quantity of moisture...

In a field map, you will be able to identify fronts as structures with high values of MFC. Try to plot along with pressure field for better understanding if you are able to.

Find more info here:
http://www.spc.noaa.gov/publications/banacos/mfc-sls.pdf


How can I tell if a rock is really petrified wood? I found a rock in the Mojave desert and it resembles a tree branch including what appears to be wood grain. Is there some test or observation that can be done at home to conclusively answer my question?

I don't think there is a really conclusive absolute test one can carry out without further preparations. In the case of a permineralised fossil, this would probably require thin sectioning and close examination to see if any cellular structure diagnostic of wood remains. Overall I'd think though that if it looks like wood and has been replaced by minerals, it probably is fossilised wood. However, you say  you found it in the desert, which perhaps could mean it is some kind of sub-fossil or mummified wood.

The first thing to do would be the standard mineralogy tests to attempt to find out which mineral(s) replaced the wood.


What are the dominant elements that oxygen is bonded to on earth? Elements are found in different minerals and chemical compounds on earth. Oxygen is dominantly found in silicate minerals which, aside from silica, contain other elements. One way of looking at the chemical form of oxygen is to look at its bonds within the compounds. Is oxygen dominantly bonded to silicon? If so by how much and to what other elements does it most likely bond to?

This answer is basically an expanded version of my comments on this answer here.

If you consider the crust and the mantle, then the most abundant metals are magnesium, silicon, iron, nickel, calcium, aluminium (in that order). Other notable elements would be titanium, chromium, and just about all lithophile elements. The key is to understand that any single oxygen is not exclusively bonded to a single metal. It's bonded to several (different) metals at the same time.

There is an important point to be made here: because we call the minerals "silicates", it's often thought that most of the stuff in there is silicon (and oxygen). In fact, there is actually more magnesium in most of the Earth. Ideal Mg-olivine (forsterite) has double the amount of magnesium than silicon. Enstatite, an orthopyroxene, has the same amount of both elements. It is a common misconception to think of oxygen as being bonded to silicon while the other metals just "hop along". Silica, as SiO2 doesn't actually exist. Not in quartz and not in other silicate minerals. It's not like CO2 that exists as an independent molecule. It's just a convenient, charge-balanced way of representing oxidised silicon that has no existence if there are no oxygens around it. These oxygens are bonded to this silicon cation, but they are also bonded to everything else around it, be it magnesium or iron or whatever. An olivine is not a solid with molecules of SiO2 and MgO, it is an (almost) infinite solid with oxygens bonded to both Si4+ and Mg2+ in a three-dimensional structure. It's just a pile of cations (metals) and anions (oxygen), that happen to conform to combinations of "conventional" oxides because of charge balance.


How much would a nine inch slice of the Earth's inner core weigh? If one took a slice of the Earth's inner core measuring nine inches across how much would that slice weigh? Or, conversely, how much mass would that contain?

An oddly specific question, but quite straightforward to calculate. Let's start by calculating the volume of your slice. I'm taking values for the inner core's physical characteristics from this Wikipedia page.

9 inches is ~0.229 m.
Radius of inner core: 1.21e6 m

We'll approximate your slice as a cylinder: even if we imagine the inner core is a textbook sphere down to the centimetre scale, its curvature would be miniscule over such a thin slice.

$\pi \times  (1.21 \times 10^6)^2 \times 0.229 \approx 1.05 \times 10^{12} \,\,\mathrm{m^3}$

So the volume of your slice is around a trillion cubic metres -- about one-fifth of a Lake Michigan, if Wikipedia is to be believed. Now we just need to turn this into a mass:

Density of inner core: 12800 kg/m³

$12800 \times 1.05 \times 10^{12} \approx 1.348 \times 10^{16}\,\,\mathrm{kg}$

So, roughly 13 trillion metric tonnes.

As jamesqf points out in a comment, this calculation just takes an estimated average density for the inner core, and assumes that this is the constant density throughout. In reality, the density increases with depth. Kennett (1998) gives a model for this density gradient.

The inner core is represented by the line section on the bottom right, below the horizontal discontinuity. Eyeballing the graph seems to imply a slightly higher average density than the estimate I pulled from Wikipedia (maybe around 1.3e4 kg/m³), varying by roughly 300 kg/m³ from the inner-core boundary to the centre. The Wikipedia estimate (for which they cite Hazeltt et al. (2006), p. 346) is actually 12,600–13,000 kg/m³ (I just took the mean for my calculation), so I suspect that uncertainties in the overall density values would swamp the inaccuracy introduced by my naïve, constant-density simplification. It's likely that a more reliable characterization of inner core density has been published since 2006; finding it and performing the requisite integration is left as an exercise for the reader ;-).

References

James S. Hazlett, Monroe, R. and Wicander, R. (2006). Physical geology: exploring the Earth (6. ed.). Belmont: Thomson. ISBN 9780495011484.

B. L. N. Kennett; On the density distribution within the Earth, Geophysical Journal International, Volume 132, Issue 2, 1 February 1998, Pages 374–382, https://doi.org/10.1046/j.1365-246x.1998.00451.x


How are minerals classified? What exactly is done to classify minerals in Earth Sciences such as Geology? How can it be known if one mineral is the same as another if they should be visually different?

Minerals are defined by chemical composition and crystallography. Dana classification scheme or new Dana classification scheme divides known mineral species in eight broad groups based on primary chemical properties and crystal form.

Organic vs inorganic

Silicates vs non-silicates

  Subdivided silicates into smaller groups by crystalline structures

Metals vs non-metals

  Subdivide non-metals into smaller groups
      metal oxides
      metal sulfides
      metal and non-metal acid salts organized by dominant anion (1)(2)

(1) In chemistry, a salt is an ionic compound that can be formed by the neutralization reaction of an acid and a base.1 Salts are composed of related numbers of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge). These component ions can be inorganic, such as chloride (Cl−), or organic, such as acetate (CH3CO−2); and can be monatomic, such as fluoride (F−), or polyatomic, such as sulfate (SO2−4).  (from wikipedia)

(2) Some these subgroups represent hypothetical acid-base reactions not actualy seen in nature but modeled after known acid-base reactions. My opinion here is that this approach was used because it was popular theory in chemistry at the time when James Dwight Dana published his work in 1837.

There are other minerals classfication systems

1) By crystal system -triclinic, monoclinic, orthorhombic, tetragonal, hexagonal, and cubic.

2) By Cleavage, parting, fracture, and tenacity

3) By mineral hardness

4) By specific gravity or density

5) By mineral association (my favorite and often the best way of identifying and unknown mineral especially when the location is known.


Are there lava flows inside a volcano? (source: netdna-ssl.com)
In these popular diagrams for the three types of volcanoes, it seems as though the lava flows are inside the mountain. I suspect that they're trying to show rivers flowing on the surface (with an awkward illustration), though. So my questions are:

Are these rivers flowing on the surface or are they inside the mountain?
Is the lava flowing down from the top of the vent or is it branching out from somewehere in the pipe?
Why doesn't the cinder cone have any lava flows?

This is largely an issue of trying to show three dimensional structures in a two dimensional medium. It is also an issue of trying to differentiate between different materials and volcanic behaviours.

Volcanoes can be composed of three types of material: Country Rock is the material they're erupting up through it's usually sedimentary near the surface and gets buried under volcanic rocks relatively quickly, so much so that few diagrams include it. The other two rock types are volcanic in origin these are Cinders and Lava. Cinder is material thrown out of the volcano, this is usually Scoria but can include other Tephra as well, importantly it lands as a solid. Lava is the liquid rock that flows continuously from a volcanic vent. These two volcanic rock types are usually mutually exclusive, eruptions with lava have few cinders and vice versa.

There are three basic "plan-forms" of volcano Basalt Shields, Cinder Cones, and Composite Cones.

Basalt Shields form slowly from layer upon layer of lava flows that solidify one atop another over long periods of time they are correspondingly flat.
At the other end of the eruptive spectrum are steep Cinder Cones formed from more violent eruptions that throw a lot of material out of the volcano, that rock solidifies as it flies through the air and lands around the vent. The closer you are to the vent the more material there is landing and the bigger it tends to be so a cone builds up, the angle of it's sides being governed by the average size of rock landing at that point.
Composite Cones are exactly what the name says; cones built up from a combination of Cinder and Lava from separate eruptions, some gentle and others violent.

The diagrams you've presented are an attempt to differentiate between these three plan-forms based on the nature of the volcanic material involved, using a deceptively simple palette. In active volcanoes there usually are lava distribution systems that move laterally through the visible cone, these feed lateral vents or lava tubes moving material far from the central vent.


How to calculate humidity using outside temperature and outside relative humidity? I would like to ask how to calculate the relative humidity that a heated indoor area would have using only outside temperature and outside relative humidity.

I found the Relative Humidity Calculator at https://www.lenntech.com/calculators/humidity/relative-humidity.htm.
I tried to understand the source code, but I am confused with the formulas (absMoisture1, RH2) used for the calculation of relative humidity.

Please, have you ever face up to the similar problem?
Many thanks in advance.

You can easily achieve that assuming that there is no sources of water vapour inside, so the absolute humidity (mass of water per volume of air), remains constant. This excerpt from my undergrad tesis will explain the formula for absolute humidity

Once you know the absolute humidity, you can adapt the same formula to calculate the relative humidity of a parcel of outside air (of now known content of water), that is taken from outside to inside a building where its temperature risen to a new value. If we add subscripts "e" to exterior temperature and relative humidity and "i" for interior ones. Most of the constants can be dropped and the interior relative humidity would be given by


Calculate the latitudes of a Gaussian Grid I would like to calculate the latitude values of a Gaussian Grid of a size of my choosing. Unfortunately, I didn't find a method or a formula to do so. Where can I find this information? Alternatively, is there a function publicly available that can do the job?

I believe the NCL function NCL gaus should be able to give you the solution you are looking for. From the API documentation you are requested to provide - the number of latitude points per hemisphere and you should get Gaussian latitudes and Gaussian weights.

Here is a code sample from their website

nlat = 64  ; for globe
gau_info = gaus(nlat/2)   ; divide by 2 to get "per hemisphere"
glat     = gau_info(:,0)  ; gaussian latitudes ( 1st dimension of gau_info)
gwgt     = gau_info(:,1)  ; gaussian weights   ( 2nd dimension of gau_info)


What would be the impact on tides if the earth had no tilt? I would like to know what would be the impacts/effects on the tides if earth were to have no tilt (perpendicular to plane of ecliptic)?

A simple way to estimate the implications is to simplify the problem. If the orbits of Earth, Sun and Moon were circular and in the same plane, and the Earth had no tilt, the only remaining tidal constituents would be $M_2$ and $S_2$ (also the overtides and combination tides: $M_4$, $MS_4$...). The rest of the tidal constituents can be expressed as linear combinations of their rates of change based on the remaining forcings: orbital eccentricity and inclination and axial tilt.

The modulation of the amplitude $A_M$ of the main constituent wave, $\eta_M = A_M cos (\omega_M t)$, by another constituent of amplitude $A_c$ is: $\eta_t= (A_M+A_ccos(\omega_c t))cos(\omega_Mt)$. Expressing it as a linear combinations of the rates of change gives $\eta_t= A_Mcos(\omega_Mt)+{A_c\over2}cos(\omega_M-\omega_c)t+{A_c\over2}cos(\omega_M+\omega_c)t$, such that the original amplitude remains unchanged, while two extra components with slightly different frequencies appear.

In the case of the effect of the axial tilt, it modulates the main frequencies based on the solar parameters (the inclination of the Moon orbit is not affected by the axial tilt). The period of the solar declination is a sidereal year (365.2564 days). In the case of the modulation of the $M_2$, the resulting periodicities are 1 cycle/solar day ± 1 cycle/sidereal year. The two resulting constituents are $P_1$ and $K_1$. $P_1$ is known as the solar declinational diurnal constituent. The case of $K_1$ is slightly more complex as the inclination of the Moon also results in a contribution at this frequency. The rest of the tidal constituents are also modified accordingly, but their amplitudes are much smaller.

In short, the removal of the axial tilt will result in the removal of the $P_1$ tidal constituent (and some other minor ones) and an amplitude decrease in the $K_1$ constituent.

$K_1$ amplitude and phase from AVISO. The maximum $K_1$ amplitudes of around 0.4m are found south of Alaska and west of the Kamchatka Peninsula in the Sea of Okhotsk. The amplitude of the $P_1$ constituent is about half of $K_1$ with a maximum of around 0.2m in the Sea of Okhotsk. Overall, the effect of the tilt on tides is pretty minor relative to the rest of the effects.


CO2 Storage, it's possible, but what about It is possible to store $CO_2$ geologically similar to natural burial. But at the rate that it needs to be buried, how do we know it is economic enough that more fossil fuels wouldn't have to be burned than what can be buried at an effective rate?

It is possible and there are several demonstration projects running. In Europe, the carbfix project quotes a price of $24.8/ton for carbon sequestration. Geothermal power is used to pump the CO2 underground, so no energy from fossil fuel is required.

There are concerns about the available capacity for storage using these mechanisms, and the pumping process does trigger seismic activity (e.g. wikipedia).

It is likely that carbon buried in geological formations will be sequestered more reliably and for longer that carbon which is simply absorbed by trees ... but there is no guarantee on that there will not be some leakage.

Because of these concerns, and because generating electricity from sustainable sources is cheaper than burning fossil fuels and then trying to manage the pollution, the main focus of dealing with global warming should be reduction of fossil fuel use to near zero.

There may well still be a significant role for carbon sequestration in dealing with some CO2 emissions which are difficult to avoid.


What causes bottom water to rise? The water close to the deep ocean floor is called bottom water.  It may be located in deep valleys or trenches.  I understand that water flowing to the Arctic will sink there, because it's saltier and therefore heavier than the surrounding water.  But once it sinks to the bottom, for example, inside trenches, what causes it to ever leave?  As far as I know, there aren't any significant sources of heat down at the ocean floor, like there are at the bottom of the atmosphere, but we still seem to have a highly dynamic system.  What causes this bottom water to mix again?

Figure obtained from University of Washington page

The density of a water parcel evolves as it moves in the ocean. A parcel of bottom water (e.g., Antarctic Bottom Water (AABW) the densest water mass) is much denser than the surrounding water when it is formed near the surface (in the case of the AABW in polynyas and below the ice shelf in the Weddell and Ross Seas).

As the parcel of AABW sinks, it flows down the Antarctic continental shelf and slope and moves north along the bottom at speeds of 2-8 cm/s. The issue is that the water parcel of AABW will be interacting and mixing with the surrounding water.

Thus, a parcel of AABW that when it was formed had a temperature of around -0.8°C and a salinity of 34.7, will get mixed with warmer water masses (e.g., Antarctic Intermediate Water, North Atlantic Deep Water) and as it becomes less dense it will be more easily mixed with the surroundings.

If you have surrounding waters that are more saline and with comparable temperatures, then the less saline water parcel (modified AABW for instance compared to NADW) will rise. The interior circulation of the ocean is predominantly driven by thermohaline processes (differences in density) and the thermal wind equation can be used as a simplification of the dynamics, especially away from the edges (surface, bottom).


Are Helium 3 and 4 being produced by earth's core? J. Marvin Herndon claims that the evidence of the georeactor comes from 3He/4He ratios released to the oceans at the mid oceanic ridges. Georeactor-produced 3He/4He ratios are related to the extent of actinide fuel consumption at time of production and are high near the end of the georeactor lifetime. Georeactor numerical simulation results and the observed high 3He/4He ratios measured in Icelandic and Hawaiian oceanic basalts indicate that the demise of the georeactor is approaching. Is Herndon correct in claiming that the 3He and 4He in oceanic basalt are being produced by a georeactor in the Earth's core? If not, what is their origin?

Reference:
Nuclear georeactor origin of oceanic basalt 3He/4He, evidence, and implications (or as PDF).

Are Helium 3 and 4 being produced by earth's core?

tl;dr no.

The paper you are referring to has major flaws in it. Claims that should not be in any respectable scientific journal such as:

  ...the demise of the georeactor is approaching. Within the present level of uncertainty, one cannot say precisely when georeactor demise will occur, whether in the next century...

or

  At some point in time after the georeactor dies, there will be no geomagnetic field and life on Earth will never be the same.

etc., have no place in a scientific article that is to be taken seriously by anyone. This is scaremongering that belongs in tabloids. This was publish in PNAS which is a reputable venue, so I don't know how it got through. Was this even reviewed? No idea. But let's talk about the actual science presented in the paper.

I'm not an expert on nuclear reactions so I can't comment on that actual model presented in the paper, but I can comment on the assumptions that are simply wrong. His model assumes a certain volume of uranium that exists in the core. Such a "block" of uranium doesn't exist. Uranium doesn't go in the core. He says:

  The background as to why a large portion of the Earth's reservoir of uranium is expected to exist in the core, precipitate, and ultimately collect at the center of the Earth has been set forth in refs. 8–11...

But refs 8–10 are actually his own papers. So he made up a theory that uranium goes in the core, completely ignoring years of published experimental work by different groups saying that uranium does not go into any significant amounts in the core, and then bases his story on that. This is wrong. Some related questions:

Why is uranium only in the crust, really?

What percent of the Earth's core is uranium?

Also note the lack of neutrinos, as mentioned by David Hammen in one of the answers, something that should happen if this was true.

So your questions:

  Is Herndon correct...

No, he is not.

  If not, what is their origin?

Mantle sources with different 3He/4He ratios. There are many reasons for that. Mid ocean ridge basalts are mostly generated by melting of depleted mantle, that is, mantle that was already melted (at least) once. So it will not have too much of primordial 3He in it, and the ratio will be low. Hotspots such as Iceland or Hawaii tap a deeper mantle source that still has 3He in it, so the ratio will be higher. There are other factors that can modify the ratio. Episodes of depletion and recycling, metasomatism (by aqueous fluids or carbonatites, each with their own capability to transport U and Th), and some more than I can't think of at the moment. Anyway, there's no nuclear reactor in the core of the earth and we're not going to die due to its demise because it doesn't exist.


Why are there no subduction trenches on continental land? The ocean has some of the deepest locations on earth, typically caused by subduction zones. Why are there no subduction trenches on land?

Continental crust is thick and relatively buoyant.  Ocean crust is much thinner, and relatively dense.
Hence ocean crust "goes down" more easily, and the density can even help pull the ocean slab due to metamorphism.
In contrast, the continents are almost like floating scum which won't go down! When they collide, you get faulting and folding, and the building up of very thick continental crust. Tibet is the best example today. Yes the Tibetan Plateau is high, but the crust is over 100km thick! (think of an iceberg, most of it is below)


At what sea level would beach area be maximized? If the sea level was 30000 feet, all land would be submerged and no beaches would exist.

If the sea level was -30000 feet, no sea would exist and there would also be no beaches.

The beach area maximizing sea level must be between  these values. What is it?

There are multiple ways one can look into this. For example, one simple way of increasing the length of coastline and, thus the beach area, would be to expose all of continental shelf.

The shelf break, where the continental shelf ends is pretty uniform globally and is in most cases at a depth of 140 m. As such, lowering water level by this amount will produce a large increase in beach areas.

Alternatively, it might be possible to increase the overall length of the coast by increasing the water level by ~100 m. While here we lose a substantial amount of coast due to flooding of low-lying areas of continents, there will be substantial gains as well.

Such an increase firstly will create a lot of new inlets resulting in minor increase of coastal areas, but most importantly this will cause the water level to reach bases of several mountain ranges - Alps, Himalayas, Caucasus to name a few. This will create an extremely rugged coastline with ridiculous amount of fjords and bring huge increase to the coastline length.

The issue with the latter option is that I'm not sure how likely you are to have a 'beach' in a fjord environment or what exactly we should consider a 'beach' for the purposes of your question.

In reality it's a pretty complicated question and it can only be solved by sitting down with modelling of coastline length at different water levels.

EDIT: Another interesting option is to reduce water level by ~3-4 km. This will maximize the land area while maintaining water in the deep oceanic basins and at the same time the longest mountain range in the world - the mid-ocean ridge - will get exposed above sea level adding on to the overall coastal length.


For how long has the Earth been habitable for humans? Let's imagine that a human (male or female) could be sent to the
 past, anytime after the birth of our planet.  What would be their survival
 probability over time?

If this question is too hard to answer, I would also be interested in the first time (most distant) that a human could have survived their lifetime on Earth.

Assume that this human is someone like Bear Grylls, who is well trained to survive in nature.

One needs breathable air, drinkable water, and food to survive. Food as we know it was nonexistent prior to the Ediacaran, which began about 635 million years ago. Life was exceedingly primitive (single celled) prior to that. Breathable air is a more significant challenge. A breathable atmosphere means sufficient oxygen and not too much carbon dioxide. Oxygen levels rose to above half it's current amount in the atmosphere about 850 million years ago, but carbon dioxide didn't fall below 5000 ppm until about 450 million years ago, when it dropped precipitously and caused an ice age and an extinction event. Extinction events would be something to avoid, so about 440 million years ago.


What properties must a rocky body possess in order to exhibit plate tectonics? The Earth exhibits plate tectonics, but the other terrestrial planets do not (though Mars and Venus may have exhibited plate tectonics in the past).

What is "special" about Earth that allows it to have plate tectonics? Equivalently, what conditions are necessary for a rocky body to have plate-tectonic activity?

(I assume that papers like (1) and (2) are good surveys of the topic, but I lack the background to synthesize the information in these papers into a good answer.)

(1) Paula Martin et al 2008 Phys. Educ. 43 144 doi:10.1088/0031-9120/43/2/002

(2) C. O'Neill et al 2007 Earth and Planetary Science Letters 261 1-2 doi:10.1016/j.epsl.2007.05.038

Plate tectonics appears to require multiple factors all arraigned in feedback loops.

The planet must be large enough that it's surface to volume ratios is low enough to trap enough heat from radioactive decay to power tectonic motion. Convection requires a minimal threshold of energy trapped in the material before that trapped energy causes mechanical motion. Planets smaller than earth radiate internal heat away to quickly because of their larger surface to volume ratios. Thus little convection and little tectonic motion.
The planet must have sufficient mass such that it's escape velocity exceeds that of a hydrogen ion ejected from a water molecule via UV hydrolysis. If the planet does have sufficient mass, then the hydrogen release by UV hydrolysis will be recaptured. If not, the hydrogen will escape the planet and its orbit and the planet will eventually desiccate. Earth has enough mass to retain hydrogen, Mars and Venus do not. In the past, Mars had water but it leaked hydrogen over the eons until it became a desert. Venus likely suffered the same fate.
Oxygen producing life: Even with sufficient mass to trap hydrogen, a planet will still leak free hydrogen from having the hydrogen rise to the top of the atmosphere and there being knocked off by the solar wind. Free oxygen prevents this by a) forming ozone thus blocking the UV that breaks down water molecules and b) recombining with the free hydrogen that does form to produce water again.
The presence of large amounts of water produce hydrated minerals which, on the size and time scales of tectonic motion, behave more like a deformable putty than solid rock. These deformable minerals allow tectonic motion. Without them, tectonic forces would cause shattering instead of drift. (See: Plate Tectonics and Water, and, Role of water in the tectonics of Earth and Venus.)
Tectonic subduction recycles carbon trapped in carbonates by chemical weathering and organisms in the ocean. Subduction draws the carbonates down to the lower crust where they are "cooked" and the carbon converted to $\mathrm{CO}_2$ and $\mathrm{CH}_3$ which are returned to the biosphere via vulcanism. Without this recycling, all the carbon in the biosphere would end up as limestone on the ocean floor. Starved of carbon, all life would perish.
It appears that the Earth has a much thinner and much more heterogeneous crust than either Mars or Venus. Likely, this is a result of the collision that produced the moon. The thinner crust is easier for geothermal convection to move. Also, it's possible that the collision "stirred" the distribution of heat producing radioisotopes leaving more near to the top of the mantel.  On Venus and Mars, it is likely that the very heavy radio isotopes sank to the core. This would make the upper mantel on Earth hotter than the other planet and hotter than it would have been without the collision. That would drive convection faster.

Likely, the critical difference for Earth was the collision that formed the moon. That both "stirred the pot" and added more mass. Earth retains both heat and hydrogen. Retaining hydrogen means retaining water which means life and hydrated minerals. Life produces oxygen that protects the water. Hydrated minerals provide the elasticity needed for tectonic motion. Tectonic motion recycles carbon needed for life.

Take away anyone of these factors and a planets tectonic motion will eventually wind down in less than a billion years.


Do winds behave like waves? Like a sound wave, there are compressed and dilated regions in the air. But do compressed regions also occur in winds. If one considers squalls, they feel like a compressed region of air. Perhaps they are too great to be considered as a kind of amplitude, but is there anyway a kind of wave in wind?

In the other question/answer is not mentioned anything about forming waves. So does wind behave (perhaps only a little bit) with sound-wave compressions and dilations?

Yes, there are a lot of waves in wind. The wave you may be looking for is called a gravity wave (aka buoyancy wave). To name a few other waves
Rossby Waves, Gravity Waves, Inertio-Gravity waves, Sound Waves, Kelvin Waves

I am sure there are more than just those few waves out there.


What factors bring sand into or out of the beach? I like to walk my dog along a beach, but in medium to high tide, there is no beach at all, as the water reaches the bluffs.

The thing is, the height of the sand seems to vary drastically as well. Sometimes, I'll be fine walking at medium-high tide because so much sand has deposited that there's still a path. (I first noticed this when I couldn't find the usual caves and crevices along my walk—I realized they were buried in six feet of sand.) Other times, even at low tide some of the waves reach my ankles, even the cliffs. In those times, I also end up walking on rock instead of sand at parts, and can see this rockbed extend out toward the break.

What brings the sand in or out?

I know the obvious answer is the incoming or outgoing tide, but I've walked at low tide when the sand was very, very high (therefore, didn't flush out with the tide), such that the beach seemed gigantic. I've also gone surfing in high tide when I couldn't stand on my feet near the bluffs, because the sand never came in. And I don't think it can be rip currents since the sand height is more or less uniform throughout the beach.

The amount of sand on the beach at any one time is a dynamic quasi-equilibrium between a whole raft of processes. These include wave power, frequency and direction, seabed angle, longshore drift, rips and undertow, wind strength, direction and continuity, fetch, coastal geomorphology, sediment availability, offshore currents, and probably other variables.

The entire system is too complex to summarize here, so I recommend Robin Davidson-Arnott's excellent book: 'An introduction to coastal processes and geomorphology'. Cambridge University Press, 2010.


Did the Geothermal Power Plant contribute to Pahoa's Lava Fissures? There was lava in the area near the wells that the Puna Geothermal Venture facility created.

  The plant has nine wells that run as deep as 8,000 feet, according to Wil Okabe, managing director for the County of Hawaii. -Washington Post

8,000 feet is really quite deep. While I understand that those are not the deepest wells created for geothermal energy, in Hawaii that seems deep enough to get to where lava would also be pooling.

For example, it would be deep enough to hit the pool at one of the main volcanoes.

  Rocks that are moving upward in the mantle beneath Hawai`i begin to melt about 40 to 60 miles (60 to 100 km) depth. The molten rock, called magma , rises because of its relatively low density. The magma "ponds" in a reservoir 1 to 4 miles (2 to 6 km) beneath the summit. https://www.nps.gov/havo/faqs.htm

In addition to the availability of lava in the area near the wells, it seems that geothermal energy has also been linked to earthquake activity in the past.

  An analysis of earthquakes in the area around the Salton Sea Geothermal Field in southern California has found a strong correlation between seismic activity and operations for production of geothermal power -UC Santa Cruz

Moreover, the facility itself is basically right on the location that the set of fissures opened up.

As location of seismic activity is in question here, I also found a map from the US Geological Survey with 30 days of activity for this portion of Hawaii.

The largest circles are a 5.4 and 6.9, the smallest ones are equal to or greater than 2.5.

Given the proximity of the facility, as well as the fact that these wells were not only near underground lava, but also have been known in other areas to produce earthquakes, what roll, if any, could the Puna GeoThermal Venture have played in the recent fissure activity in Pahoa, Hawaii?

I think we can confidently enough answer "no".

From this report (p. 23):

  Kilauea eruptions occur either at its summit or within two well-defined swaths (called rift zones) that radiate from the summit.

In the same report, you can see those rift zones on the map page 3, or on the sketch of the plumbing system page 24. Most lava flows are emplaced along these rift zones. For instance, look at this map of the 1955 eruption (public, USGS):

You can see that the flows were emplaced in a zone very similar to the 2018 eruption. Apparently the power plant opened in 1993, and the first exploratory wells were drilled in 1961-62, so after this event.

Actually, the rift zones are in the lava flow hazard zone 1, i.e. the most severe. The zone is defined as follow by Mullineaux et al. (1987):

  Zone 1 consists of the summit areas and active parts of the rift zones of Kilauea and Mauna Loa; in those areas, 25 percent or more of the land surface has been covered by lava within historical time, during the 19th and 20th centuries. These areas contain the sites of most historical eruptions, and a large majority of the lava flows that will affect other zones on Kilauea and Mauna Loa in the near future probably will originate in zone 1. [emphasis added]

So the real question is: why was the plant (and estates...) built in an area well known for lava flow hazards?!

To conclude, by researching the plant I found that it is actually where people accidentality drilled through a magma pocket for the first time (Teplow et al. 2009)! They hit a pocket of dacite; it did not trigger an eruption. This happened later in Iceland: this time, they even used it as an experimental well (there is a whole issue of Geothermics on this). Again, no eruption.


Model types: Robust diagnostic versus prognostic I wonder whether someone knows a clear definition/description of

1) Robust diagnostic models
   Forcing with data from initial state aimed at future predictions?

2) Prognostic models
   Tie model results back to observations using a relaxation factor?

'Googling' didn't help me much unfortunately.

As far as I know in the ocean modeling community the terms diagnostic and prognostic have quite different meanings from what you are stating.

A prognostic simulation is used to predict future state of the system (forecast) using the model equations. The model is initialized with the initial conditions and it is used to predict using the Navier-Stokes equations the future ocean state under specified boundary conditions. There is no constraint by observations because the model numerically follows the specified equations. In the case of models with data assimilation, the prognostic solution is statistically modified (e.g., Kalman filter, adjoint method) to optimally adjust to the observations, but the new solution can't be considered prognostic as there has been a departure from the primitive forward (Navier-Stokes) equations.

On the other hand, a diagnostic simulation does not provide a prediction of the fluid state. There is no time-evolution based on the model equations. An example of such simulation is the case in which the velocity field is calculated based on a fixed density (temperature and salinity) field. While these simulations can be useful for short-term ocean state estimation, they can't be used for ocean state evolution as the dynamics are restricted.

As far as I understand it, this is the standard in the ocean modeling community, but I don't know if it can be expanded to other fields.


Ore Deposit Determination How are ore body sizes determined? What are the most reliable techniques of determining the size of ore deposits as well as their content?

The initial stage of mineral exploration involves finding a site to investigate. In some situations this may result from the discovery of a surface outcrop of mineralization, which is the exposure of a mineral deposit.

Surface outcrops are becoming more difficult to find because some have already been mined or they are buried under sediments or lava flows. To get an indication where buried mineral deposits occur, geophysical exploration techniques are required. Generally this will require the use of either gravity measurements and/or magnetic surveys, usually aeromagnatic surveys. In some situations geochemical exploration methods may be used as well. This requires wandering over land taking samples of the surface rocks and assaying them for minerals and metals. The assaying method used will be determined by the metal being explored for. Fire assays, when they are used, are used for gold, not base metals.

When a prospective area has been found, exploration drilling is undertaken. Initially reverse circulation drilling may be done because it is cheaper and quicker. The cuttings from the drill holes are analyzed by a geologist to ascertain the rock types and samples of prospective rock types are assayed for their metal content.

If the mineral deposit is large enough and rich enough, diamond drilling will be undertaken. Depending on the condition of the ground being drill, this generally provides a solid core of rock that can be inspected for rock type. Usually the core is split in half lengthwise and half the core for prospective rock types are assayed for metal content.

To get an accurate understanding of the size the mineral deposit and the amount of metal present. A grid of holes, drilled on a 20 m by 20 m or a 10 m by 10 m pattern is drilled over the deposit. The length of the drill holes will largely be determined by the depth of the mineral deposit. The results of this, outlines the size of the deposit.

The assays for metal content and subsequent modelling by geologists determines the amount of metal in the deposit (its richness). This may involve the use of geostatistics.

Classifying the deposit as either a mineral deposit or orebody is done by mining engineers who evaluate the models created by the geologists by creating possible mine designs and evaluating the economics of the potential mine. If the deposit is economic to mine is called an orebody, if not it remains as a mineral deposit.

As part of the mine design and evaluation process, the mining engineers must engage with metallurgists regarding how any ore from the deposit will be processed and the costs involved. In developed countries they must also consider the rehabilitation of any potential mine, once it has been mine out, during the evaluation of the mineral deposit.


What kinds of remote sensing required to observe methanogenic life on Titan? Inspired by Chris McKay's Possibilities for methanogenic life in liquid methane on the surface of Titan. In the paper, the PI's found that the consumed acetylene, ethane, and other organic solids would produce enough energy for bacteria to live. They hypothesize that because the Cassini-Huygens probe detects a depletion of acetylene, ethane and hydrogen on Titan's surface, that living bacteria could be a possible causation for this anomaly.

Obviously, there is some fantasy in this paper, but it is interesting none the less.

My question is, How could a scientist falsify this hypothesis? What biomarkers would be useful to look for? What kinds of sensors would track these biomarkers?

Note: As I discovered after writing most of this answer, this question on Space Stack Exchange is closely related, and called2voyage’s answer uses some of the same early points that I do, as it discusses the paper you referenced.
It’s worth noting that the results of McKay & Smith were purely theoretical, and their paper was originally received by the journal on the exact day the Huygens lander reached Titan: January 14, 2005. The paper was revised that April, but data from the spacecraft does not appear to have been published prior to that date. In other words, the authors had no idea what Cassini-Huygens would find on Titan. The empirical results confirmed their calculations; the “anomaly” you speak of had not yet been observed.
Later that year, Niemann et al. published results from the Gas Chromatograph Mass Spectrometer (GCMS). The results agreed with predictions of what Titan would look like with methanogenic life. Specifically, McKay & Smith stated that there would be three main observable effects:

No acetylene (C2H2) on the surface
Very low levels of ethane (C2H6) compared to the expected amounts from photolysis. Photolysis on Titan has been studied by, among others, Romanzin et al. (2005), who include graphs of levels of ethane (and acetylene) at different altitudes.
A “sink” of molecular hydrogen at the surface, leading to a non-zero change in concentration per change in altitude
Niemann et al. found only trace amounts of acetylene, low levels of ethane. They provide a description of the GCMS (better summaries are in this presentation and Niemann et al. (1999)); I’ll give a quick overview here.

Gas from the atmosphere enters the gas sampling system, where it is first moved through a gas chromatographer (the carrier gas is hydrogen, chosen for storage efficiency), which separates gases using capillary columns. Gas is then sent through the ion source, which utilizes something called electron impact ionization, involving electron beams of 25 eV or 75 eV. A quadrupole switching lens can deflect the beams through mass filters; electron multipliers enhance detection in the low-mass regime.
The GCMS also found slightly lower levels of H2 on the surface than higher in the atmosphere; however, this difference was within the limits of uncertainty and so is not at all conclusive. That said, the Ion and Neutral Mass Spectrometer (INMS) onboard the Cassini orbiter did observe a gradient in the H2 mixing ratio. Strobel (2010) viewed this in the interpretation of the gradient supporting the methanogenic predictions of McKay & Smith. The INMS, like the GCMS, uses an ion source and then directs the ions to a quadrupole mass analyzer; the two instruments are quite distinct, but they are still quite similar, so I’ll omit a description. A good overview can be found here.
The predictions contained in the paper you cited contained three predictions, all of which have been verified. It is true that they can be explained through abiotic phenomena, as the authors have pointed out. However, the Cassini-Huygens results mean that in order to conclusively prove that methanogenic life does not exist on Titan, other predictions would need to be falsified.
One prediction involves an azotosome, a hypothetical analogue of a cell membrane composed of acrylonitrile (created by Stevenson et al. (2015)). It is considered one of the best hopes for the construction of cells in a world based around methane and ethane, like Titan. Assuming the stability of azotosomes - which Stevenson et al. consider over about 100 years - one barrier for this type of methanogenic life on Titan would be a lack of atmospheric acrylonitrile. However, the INMS confirmed previous detections of acrylonitrile (see Nixon et al. (2010)). That said, concentrations would need to be high enough for life to be possible. More detailed mass spectroscopy on the surface, including samples from liquids, could answer this question.
Another potential piece of evidence which McKay & Smith mentioned in passing is different levels of isotopes of carbon. Schulze-Makuch and Grinspoon (2005) note 12C/13C ratios of 95.6 found by the INMS, which would be caused by lifeforms processing carbon-based compounds, but Atreya et al. (2006) notes that this is only in the upper atmosphere; lower ratios (82.3, which is not drastically low but still too low) were found in the lower atmosphere. This would seem to be another strike against methanogenic life.
Finally, as McKay wrote in an article in 2010, there are abiotic explanations for the discrepancy in molecular hydrogen:

The Cassini-Huygens measurements are incorrect.
H2 particles are being physically moved down in the atmosphere.
There is a catalyst mediating a hydrogenation reaction. McKay writes that (referring to the existence of a catalyst operating at the low temperature of 95 Kelvin)

That would be quite interesting and a startling find although not as startling as the presence of life.

In summary, there are quite a few different factors that could influence whether or not methanogenic life can exist on Titan:

A lack of acetylene would indicate the presence of methanogenic life.
Low ethane levels could also be consistent.
A vertical gradient of molecular hydrogen would indicate a “sink”, possible biotic in origin.
The presence of high enough concentrations of acrylonitrile would indicate that life based on azotosomes is possible.
High carbon isotopes ratios could be positive indicators of methanogenic life.

Cassini-Huygens covered all of these to some extent using the Gas Chromatograph Mass Spectrometer and the Ion and Neutral Mass Spectrometer. Follow-up measurements to confirm these results, likely using mass spectroscopy, would shed more light on the possibility for methanogenic life, while new instruments designed to detect McKay’s alternative hypothetical catalyst could show that there is no need for life to explain the Cassini-Huygens measurements.


What are these river/canyon-like carvings in the ocean? Browsing around Google Maps, I came across this off the south-west coast of Ireland

It looks very consistent with the shape rivers and their tributaries might make, but it has me puzzled since it's all underwater!

The main, most "river-like" one is in the middle-left of the picture but there are more (which look more like fjords) at the bottom.

What caused this feature?

The carvings are submarine canyons, a part of the continental slope leading from the continental shelf to the continental rise and ultimately the Abyssal plains. They are a product of :

erosion through currents and
slumping of the continental shelf

Like other erosive or slumping effects, they can be self-reinforcing, leading to canyon-like structures. The highlighted canyon here is the Gollum Channel system, seen here.


What is the mixing ratio of a cloud? A cloud has relative humidity of 100% or more. Is it correct to say that the mixing ratio of a cloud is undefined? My reasoning is that dry air in a cloud is negligible therefore $w = \frac{x g}{ 0 kg}$

No, it is not undefined.

A relative humidity of 100% refers to cases in which the atmosphere holds as much water, as the temperature would allow. The term "dry air" denotes the fraction of the air not contaning any water vapor (or explicitly not any water molecules). Dry air is therefore never negligible in clouds.

The saturation vapor pressure over a plane water surface can be calculated by the Magnus formula (which is an empirical approximation to the Clausius-Clapeyron-equation valid in a temperature range from -45°C to 60°C):

$E_{H_2O}(\vartheta)=6.112hPa \cdot exp{\frac{17.62 \cdot \vartheta}{243.15 ^\circ C + \vartheta}} $,

where $\vartheta$ is the temperature in °C.

The water vapor mixing ration $r$ itself is calculated by:

$r=\frac{0.622e}{p-e}$,

where $p$ is the air pressure and $e$ is the water vapor pressure. In case of a cloud you equate $e$ and $E_{H_2O}(\vartheta)$, since the relative humidity is defined as:

$r.H.=\frac{e}{E_{H_2O} (\vartheta)}$

As a sidenote: Oversaturation in clouds may occur frequently but is usually smaller then 1%. For back-of-the-envelope-calculation this should be sufficient.

Please note, that different text books use diffent symbols for $e, E, ...$


What's the geological period of the birth of the river Ganges? Avatarana or Descent of the Ganges (extracted from Wikipedia):
  "In late May or early June every year, Hindus celebrate the avatarana
  or descent of the Ganges from heaven to earth."

There are several Hindu versions for the birth of the river Ganges.
I'm here interested in the scientific version:

  Question: When (and how) this river was born (geological period)?

From How Old is Our Ganga, the Ganges "formed as a consequence of the India-Asia collision around 55 million years ago resulting in the formation of the Himalaya. This provided a large continental mass which together with large rainfall in the catchment area and long term erosion generated /enlarged the river valleys".


Are there books or on-line resources about graphic design for geology? Maybe someone knows books that are about graphic design like visual identities, colors, forms, symbols for this industry - Geology?

In short - resources that are about graphic design from Geology point of view?

There is an very detailed "Digital Cartographic Standard for
Geologic Map Symbolization" by the Federal Geographic Data Committee (FGDC) including e.g. color and pattern charts.

Check the main website for the latest version of the Standard, availabe in PostScript format, as pdf, or as ArcGIS10 template.


If matter is constantly being cycled through an ecosystem, does that mean a given ecosystem has a fixed mass? Due to the food chain and the cycle of life, matter is constantly moved between plants, primary consumers, secondary consumers, and so on, until the consumers die, giving matter they consumed back to the ecosystem via dung and corpses. This should mean that there is a constant flow of mass and energy moving through an ecosystem. Does that mean we could (theoretically) weigh a given ecosystem in metric tons?

You can always weigh the biomass of the (global) ecosystem in metric tons, or any other unit, even when this mass would not be constant.

I don't see a reason why the total biospheric mass should be constant (maybe because it reached a saturation limit long ago) on short timescales. On long/geological timescales it is certainly not, as the available carbon, silicate, oxygen etc. for the bottom of the nutritional chains a.k.a. microbes, lichen, fungi... evolves, as the planet itself changes.

That is however not true for the total mass of Earth, which is essentially constant since its time of formation, but the biospheric mass is anyways only a small fraction thereof.


Does subduction of plates make them stretch and form the oceans? Ocean plates subduct beneath continental plates. Does this make the oceanic plates stretch and become thinner so that the elevation of the sea flow is lower? Is this why oceans form where they do - when water collects in these low areas?

Ocean plates subduct beneath continental plates. Does this make the oceanic plates stretch and become thinner so that the elevation of the sea flow is lower?

When a continental plate collides with an oceanic plate, or when two oceanic platers collide, the result is subduction of an oceanic plate. This subduction makes oceanic crust recycle rather than build up over time. When two continental plates collide, the result is the Himalayas and the Tibetan plateau. Continental crust isn't recycled to anywhere near the extent that oceanic crust is. Excluding the rather rare ophiolites, the oldest continental crust is about 20 times older than is the oldest oceanic crust.

This quick recycling of oceanic crust versus the slow build up of continental crust is the primary reason that oceanic crust currently is considerably thinner than is continental crust. The very first continents would have had have had fairly thin crusts. Continental crust has become thicker and thicker through the ages, while oceanic crust has not and cannot thanks to subduction.


How to determine the number of bytes in the SEGD Revision 1 interblock gap How can one determine the number of bytes in the SEGD Revision1 interblock gap?

The quantity is present on page 5 of the standards document.

There are no bytes in an IBG. SEGDrev1 is a tape format, and the schematic you are referencing in the standards document is a map of how the data is physically stored on a tape. Tape gaps are actual physical spaces on the tape between blocks of data. An IBG is, quite literally, a gap between blocks of actual data.

If you are reading a tape, you should be able to advance the tape to the next block as needed. If you are working with a SEGD file that has been copied to a hard disk, then gaps are nonexistent and you can pretend they are not there.


How reliable is sea-ice concentration (fraction) data in ERA-Interim? I am using sea-ice data from the European Reanalysis from ECMWF (ERA Interim), but some grid cells over land have sea-ice information. Not a big issue so far, because spatial discretization must always lead to some discrepancy in land-sea mask. But these specific grid cells, those closest to the coast (or even on land) show very weird values sometimes.

Should I just remove the first couple of grid cells, that are closest to the coast, of sea-ice data? Is this a well-known issue? Or should I just use another source of data? If so, which other source?

I would recommend changing from ERA-Interim to ERA-5, since ERA-Interim will be outdated soon. This is the information currently given by the data provider:

  ERA Interim is being phased out. Users are strongly advised to migrate to ERA5. The last date to be made available in ERA Interim will be 31 August 2019, which will be released at the end of October 2019.

It would still be good to solve the issue you are currently having with ERA-Interim.

  [...] some grid cells over land have sea-ice information. Not a big issue so far, because spatial discretization must always lead to some discrepancy in land-sea mask. [...]

As you mention, spatial discretization can lead to discrepancies. Do you use the land-sea mask from the data provider? If the land-sea mask is given in a fraction, you would have the possibility to put a threshold on the land-sea fraction and thereby filtering out "coastal" gridpoints. The best value for this threshold depends on your application.

  [...] But these specific grid cells, those closest to the coast (or even on land) show very weird values sometimes.

Is the dataset conforming to the CF conventions? If so, the variable considered most likely has a valid_range attribute. There are specific rules specified how software should treat the data. You should check that your software adheres to these rules. Inspecting the data with another software package can be helpful. If this does not solve the problem, I suggest contacting the data provider, since there might be a real issue with the data that they should be aware of.


Would the subsurface event leading to tree death at West Tern Lake in Yellowstone be visible in thermal imaging? The New York Times article It’s Warm and Stealthy, and It Killed Yellowstone Trees and Turned Soil Pale describes an even that took place over the past few decades where a small and well-defined forested spot in Yellowstone National Park underwent some change, killing all of the trees growing there.

Credit: United States Geological Survey

The article explains the possible explanation that the trees died from changes in subsurface water chemistry.

  Dr. Vaughan perused the aerial shots taken of the suspicious region. In 1994, nothing seemed amiss and trees were growing healthily. However, from then through 2017, trees had perished, and the soil had turned a sickly off-white color. The only reasonable explanation was that a new thermal area had been covertly growing in the region since the late-1990s, altering the ground’s chemistry with its superheated fluids.

Parenthetically speaking, to me "superheated fluids" sounds like something that could kill trees thermally, even without chemistry.

Would heating like this show up as a hot spot in thermal IR Earth imaging? Or is this likely to have been too deep to result in a significant surface temperature change?

Google maps screen shot centered at 44.663584 N, 110.278843 W:

If it’s hot enough to alter the groundwater chemistry that is killing the trees, then you would see it in satellite thermal imaging. Remember, tree roots only go down about 20 to 30 feet at the most, so this is all pretty shallow stuff. This is actually quite a strong thermal anomaly. Like you said, the heat alone may have killed the tree/tree roots.the white areas of the photos are likely salt deposits from the thermal water left behind after evaporation. So again, the thermal water is shallow, indeed, it’s right at the surface. Pretty cool.


When sediments are deposited, do they sink into the earth? I was listening to a geology podcast describing how sedimentary rock forms and later turns into metamorphic rock. As a river lays down sediment, the lower layers can eventually be several kilometers below ground, where heat and pressure are significant.

How does this happen? Does the river bed get built higher and higher until the first layer of sediment is buried deeply, or does the bottom layer get pushed down into the earth? In other words, is the elevation of a given section of river increasing while this happens, or does it remain the same?

The rivers transport most of the sediments to the coastal or marine basins where they accumulate. An exception are lacustrine basins, but most of world rivers sediments are deposited on shallow or deep marine basins.

When the stack of sediments is large, listric faults develop, and the bottom layer get pushed down into the earth. This process is called subsidence.

Source: apg-pro.com

As new sediments accumulate, faults are activated and the basin becomes larger. Elevation of a given section of the basin remains approximately the same, as this is a slow process.

In the case the bottom layer reaches great depth, burial metamorphism can develop:

  "Burial Metamorphism: occurs when sedimentary rocks that had undergone diagenesis are buried
  even deeper. Diagenesis grades into burial metamorphism, a relatively
  mild type of metamorphism resulting from the heat and pressure exerted
  by overlying sediments and sedimentary rocks. Although partial
  alteration of the mineralogy and texture may occur, bedding and other
  sedimentary structures are usually preserved".

  Source: uh.edu


When calculating a precipitation index, should it be constrained to a basin? I am writing a script for calculating a precipitation index using satellite imagery, and am wondering if it can be applied to an arbitrary area or if it should be constrained to a basin. My gut says that it should depend on your research question and the information you derive from the results, but it would be good to hear an expert's thoughts! To answer Earth science questions you'd probably want to isolate the basin, but for applications outside Earth science (e.g. questions about crop yields in an administrative area) I think it could be useful.
P.S. I will post the application here when I'm done with it, the idea is to make this type of analysis accessible to people without this expertise.

Normally you could calculate a precipitation index for any location with a long-term record.  A basin will have nearly the same index, regardless of which station location you use, so it can be appropriate to just calculate a single value for the whole basin, as you've suggested.  The project scope will determine what level of spatial variability you need, and sometimes political boundaries are good enough (e.g. counties). Applying this same idea to a satellite-derived product, you could use a simple ecoregion boundary (see here) to determine the spatial resolution.  You may also want to determine spatial boundaries baed on an environmental condition that can interfere with the accuracy of the satellite retrievals you are using (e.g. surface albedo or elevation).
I'm intrigued by the prospect of calculating a precipitation index from satellite imagery (instead of ground stations) and wonder which instrument(s)/products you are planning to use, especially since the calculation involves a climatological component that is difficult to build without continuous records. I suppose it is possible to train your algorithm to give results consistent with ground stations, otherwise I would worry about accuracy.  Good luck!


How can temperature be calculated given relative humidity and dew point? While looking into the better indicator of how miserable it feels outside, either dew point or relative humidity, I came across this statement:

  The optimum combination for human comfort is a dewpoint of about 60°F
  and a RH of between 50 and 70% (this would put the temperature at
  about 75°F).

Source: http://www.theweatherprediction.com/habyhints/190/

This led me to this calculator that will calculate the temperature given relative humidity and dew point - for example a dew point of 70°F and a relative humidity of 90% results in a temperature of 73.11°F.  The web site for this calculator says the values are based on the August-Roche-Magnus approximation and gives the following equation to calculate temperature:

$T =243.04 \Large \frac{\frac{17.625\ TD}{243.04+TD}-\ln\left(\frac{RH}{100}\right)}{17.625+\ln\left(\frac{RH}{100}\right)-
\frac{17.625\ TD}{243.04+TD}}$

Given the equation, I'm still having a hard time figuring out how the temperature is being calculated. Can somebody please explain how the temperature is being calculated in simple terms?

To understand that formula, it's better to start from the more intuitive dependence of dew point with temperature and relative humidity, as illustrated by the following graph from Wikipedia:

As for any solvent with a solute, the higher the temperature of the solvent the more solute it can hold. That's why hot water can dissolve more sugar than cold water. Or, for a given quantity of sugar, hot water dissolves it faster than cold water.

The figure above says basically the same: Hotter air dissolves more water. Condensation happens when the amount of water in the air is more that the amount the air can actually hold. The dew point is the temperature at which condensation appears. Therefore, for a given relative humidity, the hotter the air, the higher is the dew point.

As you can see, in the Magnus approximation, the relationship is just a straight line, with a slope and constant changing for different values of the relative humidity.

I'll assign letters to each constant for simplicity, so that

$b=17.625$

and

$c=243.04$

With that, the dew point can be calculated as

$TD= \large c \LARGE \frac{\ln\left(\frac{RH}{100}\right)+\frac{b T}{c+T}}{b-\ln\frac{RH}{100}-\frac{b T}{c+T}}$

(see Calculating the dew point)

I won't do the algebra, but if you rearrange that formula so that $T$ is written as function of $TD$ and $RH$, you will go back to the formula you presented.


Peaty soil vs laterite soil The weather conditions of both peaty soil and laterite soil are the same, i.e. high rainfall & temperature. But the former turns out to become 'excessive organic' whereas the latter becomes 'excessive decayed' soil.

What is the reason of this, that even after same climatic conditions they turn out to show opposite bacterial activity?

I didn't study tropical soils in any depth, but I've studied quite a bit about wetland soils. In my experience most peaty soils are waterlogged, which would encourage anoxia and prevent decay. Laterites are, from what I've read, usually dry at least part of the year, which would allow bacteria to munch on the organic matter.


Why did the Laki eruption of 1783 produce so much fluorine? The Laki fissure eruption of 1783/4 in Iceland was not particularly large or explosive, but it is infamous for the large quantities of fluorine (or hydrofluoric acid) and SO2 that it produced, and the resulting local mass poisonings and Europe-wide vog (volcanic smog).

How come a number of Icelandic volcanoes are capable of producing hydrofluoric acid in such large quantities?

First things first about Laki: it's in Iceland, which means its source is a combination of an ocean ridge and a mantle plume. The plume contribution means that the source composition is relatively undegassed (unlike the source for most mid-ocean-ridge basalts (MORBs)!) and very basic, so contains relatively high concentrations of sulphur and other volatiles.

Secondly, it was actually a pretty high-volume eruption: per Gudmundsson (2011) it has been estimated that it produced 14 km3 of lava - compare with the estimated average global rate of magma emplacement and volcanic output of 26-34km3 per year.

The eruption style during the Laki eruption - not dissimilar to other Icelandic eruptions - is believed to have promoted volatile emissions during the eruption, including liberating up to 50% of F originally dissolved in the melt:

  The high degree of degassing at the vents is attributed to development of a separated two-phase flow in the upper magma conduit, and implies that high-discharge basaltic eruptions such as Laki are able to loft huge quantities of gas to altitudes where the resulting aerosols can reside for months or even 1–2 years.

Thus the significant fluorine release at Laki seems to have been due to a large-volume eruption degassing halogens extremely efficiently, with a relatively high initial fluorine concentration in the melt (~400ppm).


When sea water evaporates does it carry small amounts of salt into the atmosphere? I’m interested to know, because we live near the beach and all the metal on the outside of our house is corroded.

My dad says it was from the wind picking up spray from the surf, but I’m not so sure.

Listen to your father ! Yes droplets of spray are carried on the wind several miles . There are any number of corrosion tables listing atmospheric corrosion more severe on sea coasts.  Much of the testing was / is being done at Kure Beach ( N or S ) Carolina.


How and why do these tree-like river structures form? I noticed these detailed tree-like river structures in Google Earth

Google Maps link

How and why do these form?  Rivers don't typically split.  What would cause the water to keep branching off again and again, forming these tree-like fractal patterns?  I count as many as 7-8 branch splits even in the smaller trees.

I expect the answers will provide qualitative explanations, but if anyone can connect it to quantitative physical models that would be even better (e.g. diffusion limited aggregation, viscous fingering, dielectric breakdown all have analogous mechanisms behind them; could this one be related?)

The river isn't splitting. The picture shows a number of dendritic drainage channels flowing into a larger river/stream. They are the most common form of topographical draining system. They develop in gently sloping topography and they ...

  develops in regions underlain by homogeneous material. That is, the subsurface geology has a similar resistance to weathering so there is no apparent control over the direction the tributaries take. Tributaries joining larger streams at acute angle (less than 90 degrees) [Earth Drainage Systems].

You'll notice in the picture all the drainage channels intersect the river at approximately 90 degrees. Also it appears the channels dendritic channels have formed in what looks like a sandy/silty sediment, again homogenous material.

Other sources that may be helpful:

Experiment to Examine Dendritic River Systems

Dendritic river flow simulations

Flow direction & branching geometry

Dendritic Design


Would it be wise to monitor real time human activity to anticipate earthquakes? Documented strange behaviors of animals before an earthquake could invite us to believe that some of them anticipate tectonic activity. We also know that human complex organization makes it difficult for all of us to get in touch with our deepest instinct.

Is it possible that this hypothetical natural ability to anticipate earthquakes still remains as some instinctive input in our daily behavior?

If yes, and to try to measure how much global human activity could reflect some anticipation, I think we could with modern technologies, monitor all our connected device hmi's (Mouse, touchpad, keyboard, phone, voice spectral data's) (anonymously of course) and study delta's on long periods.

I also want to point a risk: Is it not dangerous to do so if those anticipations are among the strongest booster of human intellect and progress in general?  (Pandora box problem)

But maybe, those hypothetical intuitions are source of evil momentum...

If you have no prior information that event B depends on event A, it's a logical error to claim event A causes event B just because you find they are correlated.

Let's say you collect a large data set of how people use their computer-mouse, and show that there is some change in a statistic of this data preceding an earthquake. That cannot not prove that the anticipation of an earthquake is causing people to behave differently, because the data will always correlate just as well with some other unrelated event C (such as a swing in the stock-market.)


How do I calculate Per capita $\ce{CO2}$ emissions? I need to find the per capita $\ce{CO2}$ emissions for Canada in 2010 (expressed in kg/day). I know that Canada had $\ce{CO2}$ emissions of 0.55 (Gt) and a population of 34 million in 2010.

I am just having trouble on how to calculate it per capita emissions.

I tried dividing 0.55 by 34,000,000 (I looked up my question and saw someone suggest this) but having an answer of $1.6\times10^{-8}$ doesn't really seem correct to me.

You have the right idea, but you have your units and orders of magnitude confused.
You have started with knowing that Canada has 34 million people, and emits 0.55Gt - i.e. $0.55 \times 10^9$ tonnes - per year.

Now rather than just using those figures, think about the units that you have, and the units that you've been asked to give the answer in. How many kilograms are in a gigatonne? Once you have a figure for kilograms per year, how will you convert this to kilograms per day?

NB I haven't checked your actual figures - only your arithmetic!


Eliminating range folding error in doppler radar returns With weather radar, it's not uncommon to see large areas of the image blocked out due to detected range folding.  It's my understanding that this occurs when a reflection outside of range comes back after the next pulse has been transmitted, making the receiver think that a late reflection from the first pulse is actually for the second pulse and near by.

Graphic Source:  http://www.wdtb.noaa.gov/courses/dloc/topic3/lesson1/Section4/Section4-5.html

It seems to me that it if we could differentiate between pulses, we could eliminate the possibility of range folding error.

Frequency

My first thought was that each pulse could be sent at different frequencies.  They would have to be close enough to not affect the amount of energy reflected, but far apart enough to be easily detected and not assumed to be part of doppler shift.  Even something as wide as 1MHz seems to fit this characteristic.  Is there a reason we don't use this method today?

Polarization

If we have to use the same frequency for both pulses, could we instead mount two antennas on the transmitting rig, one polarized clockwise and the other polarized counter-clockwise?  In this configuration, the exact same equipment could be used for transmitting with something that just switches between antennas for each pulse.

I'm curious if either method would work, and what the possible pitfalls are.

Frequency

Most high-power radio-frequency amplifiers (klystrons, cavity magnetrons) have a very limited frequency range.  A dual-frequency radar would essentially be two radars hooked up to the same antenna.

Polarization

Horizontally-polarized radar waves reflect more strongly from the ground than vertically-polarized waves, while circularly-polarized waves reflect only weakly from rain.  Consequently, vertical polarization gives the best results for weather radar.  A dual-polarization radar would sacrifice detail to eliminate range error.


How to determine that sustained wind speed exceeded the threshold value? Certain maritime ports and airports have ranges of operation relation to the wind, usually according to a given threshold value of sustained wind speed. If I have the instantaneous values from anemometer every 50 seconds, how can I determine that the sustained wind speed exceeded the threshold?

You are essentially asking how to determine what the sustained wind speed is, and as pointed out in a comment, this is merely temporally averaging your 50 s instantaneous wind observations.  The specific application you are targeting likely has a standardized definition of a time period over which the averaging should occur.  This might be a 3 minute wind, a 5 minute wind or some other value.  Once you know this value, you can calculate a rolling average over your time series of instantaneous wind and this rolling average is your "sustained" wind.

If your application is aviation, you'll want to keep the sustained wind and the peak winds, as the difference between sustained and peak gust is important to landing aircraft (we call that difference the "gust factor" and is generally more important than the sustained wind alone).

METAR define wind direction and speed as 2 minute averages and define gusts as a minimum 10 kt deviation over the mean during a 10 minute period. See  this page for more information on observing wind for METAR applications.


Ocean water coming from Mantle vs coming from meteorites Posibly duplicate from
  Water on Mars and Earth

I remember well a hydrology course where our teacher made some calculations of the total flux of water from Mantle ejections in Earth's history. He said the result gives you the total amount of water presently in the oceans.

Then I started to hear theories about water coming from meteorites, and I wonder how much water has truly come from each source?

The answer of this post clarifies also this related question:
Water on Mars and Earth

  If water on Earth came from meteorites, why doesn't Mars have
  substantial water?

  First off, that's a conjecture regarding the origin of the Earth's
  water rather than a known fact. A few times a year or so, a new
  journal article will appear that argues that the Earth's water is
  primordial, then another arguing that it came from comets, then yet
  another arguing that it came from asteroids.

  If the Earth's water is mostly primordial, most of it is over 4.5
  billion years old. If it came from asteroids or comets that collided
  with the Earth after the Earth had formed, it's still very, very old.
  Regardless of the source, almost all of the Earth's water has been
  here for at least 3.8 billion years old, since the end of the late
  heavy bombardment.

Mars and Earth are both rocky planets. If the water was there, at Mars or at the Earth on Archaic, then I guess degassing of Mantle was more quick than I thougth and what my hydrology teacher told us had not a lot of sense. "Regardless of the source", so then water came from both sources but probably meteorites are not the main source.


Estimation on how cold will my pond get - intent is to know if certain fish can survive in it I want to get an estimate on how cold my pond will get.

It is a 1 acre pond in Central Florida USA. It has an average depth of 4 feet. There is not much circulation in the pond. It gets direct sunlight during these cold months.

These are the average temperatures (high + low)/2 in Farenheit.

              °F       °C
November      65      18.3
December      60      15.6
January       57.5    14.2
February      60      15.6
March         65.5    18.6

What is the warmest temperature the water will remain? Its not as simple as looking at the numbers and will take some judgement. The top half of the water will certainly be warmer than the bottom, and the 1 foot shallows near the bank will be even warmer due to the direct sun.

The fish I am considering putting into this pond will have normal feeding behaviors recommended at 68 degrees but I estimate that it will go into conservation mode and not eat at around 60 degrees or possibly die.

Is it likely that the fish will be able to find water at or above 68 degrees during these months (on the bank or near the surface for the greater part of the day?)

I don't have tools to measure the temperature of different parts of the water, and with the large amount of rain we have had lately the temp would be off.

Thank you for any insight.

I doubt a pond temperature will stay above 60 in central FL winter.Without circulation there will be large temperature gradients caused by stratification, especially on warm days. Surface plants probably lower the maximum temperatures. For such a large pond ,the relative humidity and wind will make a temperature difference ( evaporation is a major heat loss).  As a comparison , I have a small ( 1000 gal) pond with circulation and although our air temperatures are usually 98 -day and 76-night, I have never measured a temperature over 83 F and usually lower. So the water temperature is definitely lower than the average air temperature in summer. In winter I protect my pond from low temperatures but it gets to 52 F . However, tropical fish like danios, swordtails and mollies survive that temperature in pond conditions , although books will say such temperature will kill them . What fish do you plan to have ? With the history that FL has for raising tropical fish , I would think there would be information available , such as from the FL Dept of Agriculture.


Which theory is stronger, that iron came from outside or was formed within earth? Where is the current body of science learning towards, that iron came from meteor or it was somehow formed on earth?

The only elements that were formed on Earth are those produced by radioactive decay. There are four natural decay chains that start with transuranic elements and none terminate in iron; neither do the decay chains that are artificial or those that result from cosmic radiation. So all of our iron is from the Earth's formation or meteor impacts since then.


How are lightning and thunderstorm intensity linked? I have lightning data that contains individual strikes and their location, time, polarity, amplitude and type (cloud-to-ground, intracloud). I am trying to develop some metrics that will help me assess if a thunderstorm is intense or not. By intense, I mean if it has the potential to generate heavy rain, large hail and strong winds. I plan on using radar reflectivity as my best guess of storm intensity and building a statistical model between the two datasets.

By browsing through the litterature, it seems that a sharp increase in positive cloud-to-ground lightning frequency is a sign of storm intensification to come. I was wondering if there was anything else that I could work with. Is amplitude useful in any way? Is the ratio of IC to CG lightning relevant? Is there another metric I could develop?

Thanks!

Is the ratio of IC to CG lightning relevant?

Yes. Primarily, severe storms tend to have very few cloud-to-ground (CG) strikes. Thus, the ratio of IC:CG is likely going to be very high.1 2 However, some severe storms do produce a significant amount of positive CG strikes. They would still have a high IC:CG ratio, but they would distinguish themselves by having more positive CG strikes. However, both of these types -- low-CG and some-positive-CG -- are potentially severe.2
It is important to note that the amount of CG strikes can be dependent both on where in the lifecycle a storm is, and the physical location of a storm (CG characteristics appear to be region-dependent). In tornadic supercells, the total amount of lightning seems to decrease during tornadogenesis, and the CG rate appears to increase after the tornadic stage of that supercell ends.3
There doesn't appear to be any existing literature on amplitude as a measure of severity. Perhaps, through this work, you might be able to identify whether this is an area which should be studied further.
References
1 Donald R. MacGorman, Donald W. Burgess, Vladislav Mazur, W. David Rust, William L. Taylor, and Brenda C. Johnson, 1989: Lightning Rates Relative to Tornadic Storm Evolution on 22 May 1981. J. Atmos. Sci., 46, 221–251, doi: 10.1175/1520-0469(1989)046<0221:LRRTTS>2.0.CO;2.
2 Timothy J. Lang and Steven A. Rutledge, 2002: Relationships between Convective Storm Kinematics, Precipitation, and Lightning. Mon. Wea. Rev., 130, 2492–2506, doi: 10.1175/1520-0493(2002)130<2492:RBCSKP>2.0.CO;2.
3 Scott M. Steiger, Richard E. Orville, and Lawrence D. Carey, 2007: Total Lightning Signatures of Thunderstorm Intensity over North Texas. Part I: Supercells. Mon. Wea. Rev., 135, 3281–3302, doi: 10.1175/MWR3472.1.
Further Reading

Lawrence D. Carey, Steven A. Rutledge, and Walter A. Petersen, 2003: The Relationship between Severe Storm Reports and Cloud-to-Ground Lightning Polarity in the Contiguous United States from 1989 to 1998. Mon. Wea. Rev., 131, 1211–1228, doi: 10.1175/1520-0493(2003)131<1211:TRBSSR>2.0.CO;2.

Yeung, Linus HY, E. S. T. Lai, and S. K. S. Chiu. "Lightning Initiation and Intensity Nowcasting Based on Isothermal Radar Reflectivity-A Conceptual Model." The 33rd International Conference on Radar Meteorology. 2007.

C. Emersic, P. L. Heinselman, D. R. MacGorman, and E. C. Bruning, 2011: Lightning Activity in a Hail-Producing Storm Observed with Phased-Array Radar. Mon. Wea. Rev., 139, 1809–1825, doi: 10.1175/2010MWR3574.1.


Can volcanos change the climate? I have heard politicians claiming that volcanoes are the sole cause of global warming and using so called "NASA data" to show that the Earth is actually cooling instead of warming.

While the nature of this site is for specific questions and not for political debate, we all know from the Year Without a Summer that volcanic gases can impact the weather severely making it very cold or hot.

My question is this:

Can a volcanic eruption, either a single or multiple explosions, be the sole cause of global warming at the planetary scale? Can volcanoes really change the climate so fast, relative to the geological timescale, that they produce the abnormal levels that we see today?

I'm aware of the year without summer, but that ended in a nanosecond, geologically speaking.

Can volcanos really change the climate so relatively (geological timescale speaking) fast, up to the abnormal levels that we are seeing today?

Even more so.

You wrote about the 1815 eruption of Mount Tambora. While that was an extremely large eruption in terms of written human history, it was rather tiny compared to the absolutely colossal volcanic events whose histories have been written in the rocks. Multiply the Tambora eruption by a factor of 10000 or more and you'll get things like the Deccan Traps and Siberian Traps.

A number of geologists think that it was the formation of the Deccan Traps rather than the Chicxulub impact event that killed the dinosaurs. A much larger fraction think the combination of the two dealt a one-two punch that ended the reign of the dinosaurs.

The Siberian Traps are still deemed by many, if not most, geologist as the leading contender for the cause of the Permian–Triassic extinction event. This was by far the most severe extinction event ever, much greater in impact than the Cretaceous–Tertiary extinction event that killed the dinosaurs. The lava released by the Siberian Traps covered an area the size of Europe (or larger, depending on who you read). It may have triggered massive fires in coal deposits, significantly adding to the greenhouse gases.

That said, what's happening to the Earth's atmosphere now is not a result of volcanic activity. It's us. (That of course is assuming that the massive amounts of hot air that comes out of the mouths of politicians is not classified as volcanic.)


Academic but accessible defense of the scientific understanding of anthropogenic climate change? I'm an intelligent and well-educated guy, but all of my schooling has been in economics, statistics, and public policy. I'm interested in reading a thorough explanation/defense of the scientific understanding of anthropogenic climate change that is intended for somebody who doesn't know anything about meteorology or climate science. However, I'm also looking for something fairly academically/scientifically rigorous. Something on the level of "An Inconvenient Truth" is probably just going to annoy me more than anything.

The definitive place to start is the Summary for Policy Makers at the start of the IPCC AR5 Working Group 1 on the physical science basis of climate change.

This also acts as a suitable introduction to the massive rest of the physical basis report, and will, together with the contents table for the full report, enable a reader to quickly find the sections of interest that cover greater detail. And to burrow deeper again, if there are specific sections that you'd like to know more about, the thing to do is to follow through and read the references from those sections.


How strong can a glacial icequake get? While researching Antarctic geology, I came across the term 'icequake' in the abstract to the article Seismicity within a propagating ice shelf rift: The relationship between icequake locations and ice shelf structure (Heeszel et al. 2014).

These events are also known as cryoseisms - in reference to glaciers, the Wikipedia article describes a cryoseism as:

  a non-tectonic seismic event caused by sudden glacial movements. This movement has been attributed to a veneer of water which may pool underneath a glacier sourced from surface ice melt. Hydraulic pressure of the liquid can act as a lubricant, allowing the glacier to suddenly shift position. This type of cryoseism can be very brief, or may last for several minutes.

and describe them as being able to

  have an intensity of up to VI on the Modified Mercalli Scale

Is there a limit to how high glacial icequake magnitudes (Richter Scale) can be?

One way to estimate the upper limit of the magnitude is through observations and measurements.  According to the article Seismic Wave Interactions Between
the Atmosphere - Ocean - Cryosphere
System and the Geosphere in Polar Regions, a couple of difficulties with determining how large ice-quakes can get, asides from the regions not monitored, are due to the sources of the recorded motion and delineating cryoseismic and tectonic observations. From the article:

  Such cryoseismic sources include the movements of ice sheets, sea-ice,
  oceanic tide-cracks, oceanic gravity waves, icebergs and the calving fronts of ice caps. At
  times, it can be hard to distinguish between the waveforms generated by local tectonic
  earthquakes and those of ice-related phenomena.

However, in the Scientific American article Long-Overlooked "Ice Quakes" Data Provides Insights into Calving Glaciers, they can be identified by their location and unique waveforms identified relatively recently.

According to the first article, unlike tectonic events, cryoseismic (= ice-quake) events are seasonal and heavily climate-dependent, with the article detailing that observations have shown that in polar regions

  microseism amplitude is attenuated during local winter for both primary and
  secondary microseisms

Observations of body-wave magnitudes (Mb) between 1987-2007 in an Antarctic station were up to 6.5-7.0

A recent observation are the related 'glacial quakes', which generated log period surface waves (greater than 25s) which, according to the article, is

  equivalent in strength to those radiated by
  standard magnitude five earthquakes, and were observable worldwide. The glacial
  earthquakes radiated little high-frequency energy, which explains why they were not
  detected or located by traditional earthquake-monitoring systems. These events are two
  magnitude units larger than previously reported seismic phenomena associated with
  glaciers, a size difference corresponding to a factor of 1,000 in a seismic moment.

Similar observations have been made in the Greenland ice sheet.

NOAA has some sample cryoseismic traces on their PMEL Acoustics page Icequakes.


How to handle negative cosine of Solar Zenith Angle while calculating clear-sky UV Index? I'm using this source to calculate the UVI value for every hour in a day (From 7am to 7pm). And using pysolar module to get the Solar Zenith Angle. The equation is below:

from pysolar.solar import *
from math import cos
import datetime

dobj = datetime.datetime(2017,7,1,8,0)
sza = float(90)-get_altitude(42.57952, 1.65362, dobj)
ozone = 300
raw_uvi = 12.50*pow(cos(sza),2.42)*pow(float(ozone)/300,-1.23)
print (raw_uvi)

The output is:
    0.4850283419701262+1.8890606693266203j

My question is when cos(sza) becomes negative it will give a complex number as output, how can I handle this ? Also, at 7 am the uvi results in 9.232276464148745 which is wrong. Am I missing something ? Or my interpretation of the algorithm is wrong  ?

This is only to address the title question.

You are right, in a way. I would recommend that you set an if statement up such that

if cos(sza)>=0:
   raw_uvi = 12.50*pow(cos(sza),2.42)*pow(float(ozone)/300,-1.23)
else:
   raw_uvi=0.0

This makes it so that when the sun is beneath the horizon, the sun is not 'taking back' the energy


Interdisciplinary sciences which combine earth sciences with computer science Are there interdisciplinary sciences which combine earth sciences (like geophysics, climatology, meteorology etc.) and computer science? or something like biotechnology which combine biology with several fields.

Pretty much all Earth Sciences combine deeply with computer sciences. In many areas where the underlying physical phenomena are not well understood, machine learning is often used, and numerical models are a very common tool in pretty much all fields in Earth Sciences.

I think some notable examples where Earth Science is working side by side with leading edge computer sciences are large scale numerical models. A large fraction of the work done by today's larger supercomputers is running atmospheric models for weather forecasting. Similar models are often run also for reanalysis of historic climate, long term climate evolution, oceanic currents, models of Earth's core and its magnetic field, mantle convection, and the list could go on and on.

Inverse modelling and tomography are also areas were leading edge computer sciences are applied to Earth Science problems. Such as reconstructing the structure of earth interior from seismic tomography, inverting for the basal conditions of glaciers, or in a more applied field; electric, seismic and magnetic tomograhies to find minerals and oil.

It terms of formally mixed fields, you can think of many, starting from my own field: Geophysics, where physics is used to understand the Earth system. Although, many geophysicist work in Planetary Sciences, where the same methods are applied to other bodies beside the Earth, of course they work shoulder to shoulder with astronomers and space scientists. And like that, there are many others, like Geochemistry, Biogeochemistry, Geomicrobiology, Biogeography, Chemical oceanography, and many others.