run the WRF model using ERA5 I want to run wrf chem with ERA 5. I followed this post https://dreambooker.site/2018/04/20/Initializing-the-WRF-model-with-ERA5/. Everything works fine unless I add surface pressure to surface data list(SP or 134.128). metgrid.exe threw out

Processing domain 1 of 1
 Processing 2015-06-01_00
    FILE
    PRES
ERROR: Error in ext_pkg_write_field
application called MPI_Abort(MPI_COMM_WORLD, 0) - process 0

Any help would be highly appreciated.

Did you use the right Vtable? That error message is saying that the soil temperature variable is missing/couldn't be read.


What is the meaning of the subscript in the abbreviations of some minerals? I have noticed that in many articles on minerals that I have read the abbreviation of some mineral has a numerical subscript, for example, occurs with the forsterite (Fo95-90, Fo92-84, Fo94, etc.). What is the meaning of this subscript?

Olivine is a solid solution between forsterite and fayalite, so it is generally expressed as molar percentages of these end-members, for instance Fo80Fa20. Often only one end-member is mentioned, as it is sufficient to infer the other (their sum is always 100 %).

It is the same with plagioclase, which is a solid solution between albite and anorthite and is often expressed as "Abxx" or "Anxx", where xx is the molar percentage of considered end-member.

Edit: As for the range, e.g. 95-90, I'd say they analyzed several olivine grains in the same sample, and the range represents the variability of compositions they found. It could also be the analytical error on a single composition, but I doubt it would be that large, although it could be in some old papers when the precision of chemical analyses was not as good as today.


Is there scientific evidence connecting the current climate in India with global warming? Experts say up to 40 % of India might witness drought this year.

Is there scientific evidence that this is due to the global warming and climate changes?

If you look at this link - Climate Of India there are four seasons affecting different regions of India

1) Pre monsoon showers 2) Indian Summer Monsoon 3) Post monsoonal rain. 4) Winter rain

Each of them have their own patterns and dynamics. From the perspective of the second and biggest impact on the country i.e. Indian Summer Monsoon it would be hard to find a single year where rainfall distribution has been completely well distributed i.e. all regions of the country had experienced surplus rainfall. But this unequal distribution would be made up in subsequent years mitigating drought. Or so it was thought.

For the monsoon to bring bountiful rainfall oceans must remain cool(relative to landmass) and land must warm during the crucial months of April and May. But this recent study published in Nature shows that there has been a  weakening of the land sea thermal gradient and drying up of Indian subcontinent/Drying up of Indian subcontinent due to weakening land sea thermal gradient. So according to that paper human influenced climate change causes the Indian  landmass to cool because increasing concentration of  aerosols suppress the surface warming.

Secondly there is an asymmetry in the El Nino forcing.

  Meanwhile, a recent study demonstrates that apart from the warming due to greenhouse gas forcing, the long-term warming trend in the western Indian Ocean is significantly associated with the asymmetry in the ENSO forcing. That is, while the quasi-periodic El Niño events induce a warming over the Indian Ocean via the Walker circulation, the La Niña events fail to do the inverse. Along with this, an increase in the magnitude and frequency of El Niños in the recent decades has accelerated this warming. The heat pile-up due to this ENSO forcing persists in the land-locked Indian Ocean that has a restricted thermohaline circulation, sustained by a feedback from the local air-sea interaction and ocean dynamics.

What this means is that the traditional monsoon dynamics i.e. cool Indian ocean and warm continental land mass has been disturbed by human influenced climate change as well as the natural geography of the land and ocean mass. One significant ISM phenomenon the tropical easterly jet stream has shown a  weakening trend over the last few decades. A significant fall out of this could be mid latitude atmospheric dynamics could come into play during the ISM(one can think of this as the weather during a break in monsoons where upper level subtropical westerlies come into play) and a disturbing trend has been noted in recent times with increasing frequency of hail storms.


Identifying thrust faults on a geologic map I am not able to upload the map as the file is too large, but I have a map which states there is an over thrust fault. It has two ticks on it indicating downthrow to the NE. The downthrow is pointing towards younger beds. The strike of the fault is parallel to the strike of the surrounding rock units (a fold).
What evidence on this map indicates that this is a thrust fault other than the label itself? Should I be thinking/looking at other evidence?

Geological maps are the interpretation by a number of geologists and are generally the synthesis of extensive field work. The only place with the real evidence is the field (including geophysical work and drillholes, if available obviously). In many countries geological maps are accompanied with a guide discussing certain interpretations, especially regarding faults, which are quite often up for discussion. Maybe you can find the author of the map and ask them if such a guide is available, or even directly ask on what base the fault was drawn? I think you'd find many geologists willing to discuss their interpretation.
Other indications ("evidence" is a bit strong) for thrust faults can include an unexpected contact between two layers, a sudden change in orientation and/or thickness of the layer(s).
If you're really sceptical, try to sketch a small geological profile and see if you can make a different interpretation.


How much gasoline in cubic meters is used per day? Many of us drive a car, trucks get driven each day and many other machines use gasoline as well. This gets pumped out of our earth continuously, making earth bit by bit more hallow. Not a real calculation, but seeing how many trucks I see just in my small country (The Netherlands) and extrapolate to the whole earth times the average gasoline usage per hour.. we should be thinking about small cities in cubic meters per day of gasoline usage.

That made me wondering.. What is the number a bit more exact? And could you give a relative estimate to compare that number to (like a football stadium).

I don't care for an error margin of 5% or numbers from 2013. Just want something to 'grab' and get an idea.

The total consumption of crude oil according to this site is around 100 000 000 barrels per day and is in SI units 10 000 000 cubic meters. Of course not all of that can be processed to gasoline, but the scale of things is revealed. That would be actually bigger than a football stadium's volume a day as it would effectively be a cube with all sides around 215 meters.


Large Scale lightning Strikes from Cloudless or Near Coudless Skies. How Does it Work? It is reported in the media that currently in Australia there are dozens of wildfires caused by lightning strikes. I am familiar with the mechanism of ordinary British lightning involving cumulonimbus and moisture, but I don't understand the Australian mechanism where hot,bone dry conditions cause lightning strikes on a massive scale, apparently from cloudless or near cloudless skies. The role of high temperatures and near cloudless skies obviously makes vegetation highly inflammable, but solar radiation hot enough to heat it to ignition temperature would kill everyone in Australia, so contrary to what some people appear to believe it can't be that. Perhaps someone can offer an explanation.

Revised answer

TL;DR After having just heard from two experts who actually work in this field(firestorms and dry lightning) in Australia I believe the lightning seen is what is known as "dry lightning" comes from isolated thunderstorms and sometimes storms associated with minor troughs and fronts that come through Australia and also originating from a pyrocumulonimbus cloud. So @David Hammen and @jamesql are correct in their observations that the large scale dry lightning is indeed originating from isolated thunderstorms as well as storms associated with minor troughs and fronts. This dry lightning the experts confirm  is associated with little rain.

In addition there have also been several  dry lightning strikes from pyrocumulonimbus clouds. As an example for today over 20 dry lightning strikes have been recorded originating from pyrocumulonimbus clouds.

The major driver for the current drought like conditions over Australia is the large anomalous positive Indian Ocean Dipole (positive IOD) that has persisted well into boreal autumn/astral spring.

What the experts mention is that while the dry hot conditions are sporadic (2-4 days) they are persisting over over many weeks.

The following articles written by two researchers  Firestorms and flaming tornadoes: how bushfires create their own ferocious weather systems
 and Firestorms: the bushfire/thunderstorm hybrids we urgently need to understand provide information on the dynamics behind firestorms and the formation of pyrocumulus clouds and the associated dry lightning.

Following is a  summary of those articles and the conditions that lead to dry lightning from pyrocumulonimbus clouds.

Not all bushfires lead to firestorms. If a bushfire has sufficient area the upward movement of air causes the fire to interact with the atmosphere above it and form what is known as a pyrocloud. If in addition  there is an atmospheric instability then this process leads to the formation of a pyrocumulonimbus cloud . Normally in meteorology we are taught of heat radiating from the ground but in this case the upward movement of air is due to the heat emanating from the fire.

Again from mesoscale meteorology one hears the word "downdrafts". Similarly in this context the appropriate word is "downbursts" and these are vertical drafts of air that hit the ground and move about in all directions. The unsettled conditions cause embers to carry over large distances.

These firestorms produce dry lightning that potentially can spark new fires that may end up creating a larger flaming zone.


How do the slow and fast carbon cycles influence climate change? I understand that the slow and fast carbon cycles are involved in the transport and storing of carbon, but how much of an influence do each of these cycles have on climate change, and how?

One example of the slow carbon cycle: Surface uplift of Tibet and Cenozoic global cooling

  Continental weathering on a global scale influences ocean chemistry and imposes a net drawdown of atmospheric CO2 that modulates global climate ... . This observation, in addition to seawater Sr records that suggest an increase in continental weathering after ca. 40 Ma, led researchers to suggest that the uplift and erosion of the Himalayan-Tibetan orogen over the past 40 m.y. has drawn down atmospheric CO2 and cooled the globe, leading to the glacial climate that persists today


Ozone gas (O₃) endurance in the atmosphere If I release some ozone gas (O3) to the atmosphere, for how much time will it stay there in its original form? Does it change to some other form by reacting with other atmospheric constituents?

$\mathrm{O}_3$ decomposes to $\mathrm{O}_2$.

The rate of decomposition increases with temperature.

At 20 degrees C, the half-life is about 3 days in air.

$\mathrm{NO}$ can catalyze the formation and decomposition of ozone.


When and where is the atmospheric greenhouse effect strongest? Is the greenhouse effect stronger in the ice covered area or in the equator?
Also is it stronger during winter or summer?
I am thinking it is stronger in the Ice covered area and during winter because of the bigger temperature difference but I can't fully support my answer.Any ideas?

It is strongest in the arctics,most radiation from this area will be long wave infra red and long wave infra red is absorbed and reflected by the climate gases in the atmosphere.

A large part of the heat from the sun is reflected by snow and ice,But as the snow and ice melts more heat is absorbed by the water in the ocean the effect of this is larger in the arctic(floatng ice)than it is in the antarctic(more ice on land and takes longer to melt)

Link https://en.wikipedia.org/wiki/Infrared

At the areas closer to equator the heating is higher so a larger amount of the radiation will be at a shorter wavelenght,And a larger portion of this will escape to space and not be stoped by the atmosphere.

The equator will heat up less than the arctics simply as a result of the shorter wavelenght in infrared radiation.

The winters will warm faster than the summers in the arctics and this too is a result of the longwave infrared radiation in the winter and the shorter wavelenght(hot summer).

The nights do warm faster than the days too as a result of longwave radiation at night(colder)and shorter wavelenght in the day(hotter)

The earth will keep getting warmer until a new equiriblium is reached where incomming and outgoing heat will be in balance(if we stop the realease of greenhouse gasses today the earth will keep on getting hotter for atleast 50-100 years).


Flexure of a viscous lithosphere - derivation I have been trying to figure out solution for the fourth order differential equation of flexure for a viscous plate.

The fourth order differential equation for a viscous plate is given as

$$Dv*\dfrac{\partial^4}{\partial x^4}\bigg(\dfrac{\partial w}{\partial t}\bigg) + kw = 0,$$

here, $Dv$ is a function of viscosity and elastic thickness, and $k$ is the specific weight.
My solution so far is
$$w = w_0*\exp(t/b)*\exp(-x/\alpha)*\cos(x/\alpha),$$
where, $w_0$ is the maximum deflection, $b$ is function of $Dv$, $k$ and $\alpha$; and $\alpha$ is function of $Dv$ and $k$.

The problem with my derivation is I am not sure if it correct and I do not have a way to check it. Moreover, the $b$ term is an issue as it resolves to constant integer, which is not physically likely.
Anyone out there, who could help me get on the right path? Any papers, any links?

The problem with my derivation is I am not sure if it correct and I do not have a way to check it.

Try dimensional analysis to check your solution. Is your solution consistent with dimensional analysis? Estimate a solution to a real example, based upon you knowledge of geophysics and geology. Does your solution even come close to a reasonable estimate? If you are unfamiliar with dimensional analysis and estimation methods, I recommend the online book (MIT course) Street Fighting Mathematics for some possible ways to stimulate ideas of ways to check your derivation.

For example, as you have written your solution, the $b$ and the $\alpha$ are constant over time ($t$) and location ($x)$. First substitute your solution into the differential equation, and carry out the differentiation to confirm that it is in fact a solution. If it can be verified as a solution, turn your attention to the dimensions of b and alpha. The dimension of b must be time and the dimension of alpha must be length. You are modeling the system as a viscoelastic solid, so the the initial condition ($t=0$) for your displacements $w(0,x)$ are just the elastic solution, and the time-dependent term is unity. Use the elastic solution to solve for alpha (the characteristic wavelength) because this does not change over time. Name the purely elastic displacement '$e$' and it has dimension of length.

You know you want to include viscosity somewhere, so let's try the kinematic viscosity $v$ (dimensions $M*M/s$). So try $b = -(L * L)/v$, or $b = -(L * 1)/v$, because this is a 2D problem and can be one unit deep. You'll need the negative sign to make the displacement grow faster for a smaller viscosity.

What could $L$ be? I would try $L=e$, or $L=e/2$. Because you really don't know the kinematic viscosity of the lithosphere, the factor is not critical.

Substitute $b$ and $\alpha$ into your solution. Does the result seem to make physical and geological sense?


If the Sun disappeared, how long would it take for the Earth to freeze beyond excavatable depths? If the Sun disappeared

How long would it take for the earth to freeze beyond excavatable
depths?
How long until it freezes to the core? (Is this different than without removing the Sun?)
Would we be able to live for a while by relocating downwards?

If so around what portion of the population and for how long?
Could we find a way to keep some oxygen with us or to extract what would turn liquid/solid on the surface?

Would the molten/ductile rock expand or contract?

Step wise approach:

Right now when the surface is very cold, the frost depth here (Alberta, -40 min winter temps) can reach 8 feet.  Below about 30 feet seasonal temperature changes are under a degree.

Around depths of 100 feet temperatures start to rise, increasing about 25C/km or 1F/70 feet.

First approximation then for zero solar input (effective temp -270K) would be that you would need (270+20)/25 = ~12 km of depth to have roughly room temperature conditions.

We currently can't dig holes that deep.

The world's deepest is 3.9 km in South Africa.  Note that at 25C/km the temperature at that depth is well over boiling point.  Air is compressed at the surface, then chilled.  Air expansion in the working levels of the mine expands and cools further.

This assumes that the earth's insulation value is linear with depth.

Now:  Time: We can put a lower bound on it:

A year's temperature variation right now reaches 30 feet, with most of that being in a fraction of that.  So suppose that it penetrates at 30 feet per year.  I think this is too much, but it serves as a bound.  At 30 feet per year it would take 33 years per thousand feet, or about 110 years per kilometer. At present depts of 3.9 km, we have about 4 centuries.

In practice you wouldn't do it like this.  Go deep enough to get away from the worst, built an insulated cave, and run heat exchange tubing deeper to heat your cozy refuge until whoever borrowed the sun puts it back.


How does SMAP detect soil statistics? So there's a NASA satellite called SMAP currently orbiting Earth right now, and it can measure soil moisture, and detect whether or not soil is frozen or thawed. It knows this since it uses radar to detect natural microwave emissions from the ground.

But what are natural microwave emissions, and what tools are necessary to detect and process the information (doesn't have to be related to NASA)?

The SMAP includes both an active L-band synthetic aperture radar and a passive microwave radiometer.

Any object above a temperature of absolute 0 will emit thermal radiation over a wide range of frequencies.  The spectrum of this radiation can vary from that of a theoretical "black body" depending on its physical properties, especially the dielectric constant.

Since the bulk dielectric constant of the soil depends on the soil moisture, the spectrum of the thermal radiation from the soil is related to the soil moisture.  The dielectric constant of frozen water is different than for liquid water, so there's a different signal depending on whether the soil moisture is liquid water or ice.  Needless to say, it takes a very sensitive and accurate instrument to measure this thermal radiation in order to estimate the soil moisture.

Similarly, for the active radar, the signal reflected from the soil depends on the dielectric constant of the soil, which is directly related to the soil water content.

The data from these instruments are combined to produce a surface soil moisture product- this is an estimate of the moisture in the top 5 cm (2 inches) of the soil.  It's important to understand that this is not an estimate of (and is a very poor substitute for) the root zone soil moisture available to crops or other vegetation.  This distinction is important in identifying drought conditions and in predicting transpiration from plants.

There's a large research literature on using passive radiometers and active radar to estimate surface soil moisture. Is there something more specific about this you'd like to understand?


Why can isotopes reflect the age of the Earth rather than the age of the supernova that created them? Radiometric dating is based on heavier elements decaying into lighter elements, for example uranium decaying to lead. But wasn't all uranium in the Solar System created in one or more supernova? And floated around in space for millions or billions of years before accreting to form the Earth and its meteorites.

How come the isotopes reflect the time of the accretion of the Earth? How come the accretion affected the ratios of different isotopes, changed the nuclei of atoms? Why doesn't radiometric dating just reflect the age of the supernova in which the isotopes were once created by high energy nuclear fusion processes?

Suppose you purify a sample of uranium 238, removing all of the lead. Half of those U-238 atoms will have decayed into lead 4.468 billion years from now. If the lead is removed from that half-uranium/half-lead sample 4.468 billion years from now, half of the U-238 atoms in that purified sample will have decayed into lead in yet another 4.468 billion years. The clock is reset when the decay products are removed. It doesn't matter whether those U-238 atoms were created in one of the very first supernova over ten billion years ago, a supernova shortly before the Earth formed 4.6 billion years ago, or even a supernova that occurred after the Earth formed. Those U-238 atoms do not have a memory.

Some natural processes do this purification and reset the clock when a rock first forms as a solid object. I'll address two; there are others. Zircons readily bond with uranium and thorium but strongly reject lead. Any lead present in zircons now is a result of the radioactive decay of uranium and/or thorium encapsulated within the zircon when it first formed. Potassium-40 sometimes decays into argon-40. The argon simply bubbles out If that decay happens in molten rock. They argon remains trapped if the decay happens inside a solidified crystal. Any argon present in a rock crystal now is a result of the radioactive decay. In both cases, (zircons containing uranium-238 and rock crystals containing potassium-40), the clock was reset when the rock first formed.


Why isn't $\ce{H2O}$ evenly distributed in Earth's atmosphere? I frequently read $\ce{CO2}$ have a spatially constant concentration sadly rising and at 415ppm at present. That concentration do not vary a lot spatially I think. You will find ~415ppm at Argentina or at Taiwan.

However this is not the case for $\ce{H2O}$; some regions are dry, some others are wet.

Can you explain to someone not trained in atmospheric sciences what makes $\ce{H2O}$ especial?

The brief answer is 'the water cycle' I think.

A longer answer is that water can exist in many states on and above the surface: at least snow, ice and liquid water on and below the surface and water vapour (gas) and aerosols of liquid water or ice (clouds) in the atmosphere. On the other hand $\mathrm{CO_2}$ can only exist in one: gas.

What that means is that $\mathrm{CO_2}$ is as well-mixed as any other long-lived gaseous component of the atmosphere over time, which is 'pretty well'.  Components of the atmosphere, such as $\mathrm{SO_2}$, which are not long-lived don't get mixed so well because they don't have time to be. For water the situation is even more complicated because there are complicated phase transitions going on within the atmosphere, and because the distribution of liquid water is extremely dependent on topography, and in particular it can move large distances from where it originates.

The phase transitions of water in the atmosphere are driven by temperature and pressure conditions in the atmosphere, and in turn alter those conditions, and the whole system is chaotic of course.  The result of some of these phase transitions is water leaving the atmosphere as precipitation.

How much water gets into the atmosphere depends on conditions on the surface and in the atmosphere, and also on where water is on the surface, which is extremely non-uniform (see above).

All of these transitions are driven by energy from the Sun which varies over the planet.

So the end result of all that is that

water vapour is not long-lived in the atmosphere as a result of all this, so it doesn't have time to become well-mixed;
water is not evenly-distributed on and below the surface because it's mostly liquid (and because snow & ice is only stable in some parts of the surface);
the behaviour of water entering, moving within, and leaving the atmosphere is extremely complex and chaotic (or 'there is weather'), resulting in large variations over a range of scales in distribution of the various states of water which can live in the atmosphere, and large variations in how much water leaves the atmosphere over various scales.


How much did temperature vary during the Ice Age? This article,

Old Cold: Living in Ice Age America

claims the average Earth temperature during the Ice Age was 12 degrees colder than today. Is this true? How much did temperature vary during the Ice Age?

Your article says an ice age was 12F (or about 6C) colder, while other sources quote 10C colder, so there is not complete agreement on how much colder an ice age was compared to the present day. This is not particularly surprising, as there were no meteorologists making careful records in those days. Temperatures for ancient times have to be measured in very indirect and roundabout ways, for example by measuring the ratio of deuterium to hydrogen in ice cores, and there are other vaguely similar ways, all subject to error.

All that is necessary to develop an ice age is that more snow and ice should form during the winter than can be melted away during the summer. This doesn't require a dramatic fall in temperature, and if it continues for long enough you will have an ice age. After a while, of course, the increased area of snow will reflect more of the sun's heat back into space, thus increasing the extent of the ice and the amount of heat reflected away in a sort of feedback mechanism.


Boundary problems in stratigraphy What do geologists mean when they say - Cambrian/Precambrian Boundary problems or Cretaceous/Tertiary boundary problems?

I believe what is being referred to here is the problem of determining where, in a continuous deposition sequence, a particular geologic time transition occurs.  If you have uniform depositional conditions you look for a transition in fossil communities that have been agreed on as marking the transition.  Life is not so simple and you could have a delta sequence overlaying a deep water deposit. Obviously the geologic aeon does not change everywhere at the contact between clay and sandstone and one must determine where in the clay the line is to be drawn and where in the sandstone.  On a larger scale a time boundary that, in the type section, starts or ends at an unconformity needs to be more precisely defined so that correlations across geologic provinces can be made.


Why does the loss of water from a felsic magma encourage crystallisation? Felsic magmas crystallise in the crust, unlike mafic magmas which tend to make it to the Earth's surface, for the following reasons:

They are more viscous than mafic magmas and therefore it is mechanically harder to ascend,
They are colder, so crystallise earlier, so travel less distance,
They are more hydrous than mafic magmas and the loss of water encourages crystallisation .

My question is, why does losing water encourage felsic magma to crystallise in the crust? Is it something to do with water being a network modifier?

This answer is based on Winter's presentation for his textbook. Look up chapter 7 on his website, and start at slide 39.

First let's go through some of your statements:

  Felsic magmas crystallise in the crust, unlike mafic magmas which tend to make it to the Earth's surface

Not necessarily. It is true the upper continental crust is composed mostly of felsic intrusive magmas, everything else is not. The lower continental crust, the oceanic crust, arcs, etc., those are all mostly mafic.

  They are more viscous than mafic magmas and therefore it is mechanically harder to ascend

This only means they ascend slower than mafic magmas. Eventually it all depends on buoyancy. If they're liquid and less dense than the surrounding rocks, they go up.

  They are colder, so crystallise earlier, so travel less distance

Not necessarily. Their final crystallisation temperatures (aka "solidus") are also lower than mafic magmas. That's why they are liquid at temperatures that mafic melts would already be solid. This has little implication to the distance they travel (to a first order approximation).

  They are more hydrous than mafic magmas...

True! The reasons for why felsic magmas are (generally) more hydrous than mafic magmas are not important now.

  why does losing water encourage felsic magma to crystallise in the crust? Is it something to do with water being a network modifier?

Yes. Water, or more precisely, H2O acts as a flux: it is a chemical component that strongly lowers the melting temperatures of various materials, including rocks. It follows the basic chemical reaction of $\ce{rock + H2O = melt-with-H2O-dissolved-in-it}$.

The important part is that to allow H2O to be dissolved in the melt, you need to have some pressure. Otherwise the H2O just exsolves out and leaves the magma, similar to opening a bottle of carbonated drink (think coke). While there is pressure, the CO2 is in the drink. When you open the cap and depressurise it, the CO2 comes out of the drink.

Something similar happens in magmas. You have a felsic magma with H2O dissolved in it (otherwise it wouldn't be liquid, it would be solid) rising upwards through the crust. Because it goes up, the pressure around it goes down, causing H2O to leave the magma as bubbles of water vapour (or a supercritical fluid, depending on depth). Then, as the magma loses the flux, it solidifies before it can even reach the surface. Here's a diagram to explain this, in the albite-H2O simplified system, which is a good model for granites and felsic magmas:

At surface pressure (bottom of the diagram) albite melts at slightly above 1100 °C. In a dry system, the higher the pressure, the higher the temperature. For example, at 5 kbar (0.5 GPa) the melting point of albite goes up to 1200 °C. If you add H2O at surface pressures, it doesn't change anything because there is not enough pressure to put the H2O in the (non-existing) melt. But at higher pressure it is possible for H2O to dissolve in the melt, thus allowing the existence of melt. For example at 5 kbar the melting point of albite with more than enough (aka saturated) H2O goes down to 800 °C. That's 400 °C below the dry melting point!

So what would happen if a melt containing some H2O starts rising upwards at constant temperature? For example at point a to d in the diagram. It will lose H2O as it rises, increasing the solidus temperature. Because the magma is not hot enough to be liquid at the surface, it will freeze before that, while still at depth.


Understanding a diagram of Earth's radiation balance Trying to understand this image. Can someone tell me if I have the right reasoning here:

Sun has 100% SW shooting to earth
30% of that 100% is reflected by clouds
70% remains
Of that 70%, 45% of that SW is absorbed by Earth's surface.
That leaves 25%, where does that go/factored into?

The entire right half of this diagram confuses me, what is happening there? Why is there a red line connecting 70%SW and 70%LW? What does "??%LW" mean?

Thank you

LW = Longwave radiation (i.e. Infrared  radiation)

SW = Shortwave radiation (i.e. Visible + Ultraviolet light)

For the left part of the diagram, it shows that the 30% of the total incoming energy (mostly delivered as shortwave radiation) gets reflected by clouds and the Earth's surface. Therefore, 70% is the total absorbed by the planet (45% of it is absorbed by the Surface and 25% by the atmosphere).

The red line refers to the fact that given that Earth energy budget is assumed to be in balance, meaning that the same amount of energy that goes IN the system (as shortwave radiation) must go OUT the system, in the form of longwave radiation, that is the main kind of radiation the Earth emits given its temperature (see Wien's law). This energy balance assumption is a good one, because even if you think that more energy gets IN than OUT, that would lead Earth's temperature to increase, increasing then the amount of emitted energy (according to Stefan–Boltzmann law), until it reaches a point where the outgoing radiation released equals the amount received energy from the Sun. Therefore, establishing the energy balance.

Due to this balance, the right part of the diagram shows that the same 70% of the energy must be emitted back to space as longwave radiation (the same amount that was absorbed), and for that to be true, it is asking you what would be the required amount of energy that the atmosphere must emit towards Earth as LW radiation to keep the system in balance. Or at least that's my interpretation of the question marks in the absence of further information.


Why would a Martian tsunami travel at only 200 km/hour, four times slower than on Earth? The news article Impact crater linked to Martian tsunamis describes results of numerical calculations which address the possibility that a giant martian tsunami triggered by an impact has left recognizable features on the martian landscape. The research is published in the Journal of Geophysical Research - Planets, but as of this moment the DOI link there doesn't seem to work. However, it seems to be:

Costard et al. 2017, Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean, DOI: 10.1002/2016JE005230,

  ABSTRACT:

  The identification of lobate debris deposits in Arabia Terra, along the proposed paleoshoreline of a former northern ocean, has renewed questions about the existence and stability of ocean-sized body of water in the early geologic history of Mars. The potential occurrence of impact-generated tsunamis in a northern ocean was investigated by comparing the geomorphologic characteristics of the Martian deposits with the predictions of well-validated terrestrial models (scaled to Mars) of tsunami wave height, propagation direction, runup elevation, and distance for three potential sea levels. Our modeling suggests several potential impact craters ~30–50 km in diameter as the source of the tsunami events. Within the complex topography of flat-floored valleys and plateaus along the dichotomy boundary, the interference of the multiple reflected and refracted waves that are observed in the simulation may explain the origin of the arcuate pattern that characterizes the thumbprint terrain.

Also see Editor Highlight

I can not access the article yet, but the BBC interview with Costard leaves me puzzled about the speed of tsunamis:

  Two successive waves were formed during the event, says François Costard.
  "It was a really large-scale, high speed tsunami. At the very beginning, a crater of 70km in diameter was created by the impact. This expelled a huge volume of water, with wave propagation at 60m/second," he explained. (emphasis added)

  "The initial wave was about 300m in height. After just a few hours, that tsunami wave reached the palaeo-shoreline located at a few hundred km from the impact crater."

  This gigantic wave washed over hills and plateaus and through valleys, leaving behind the lobate flow deposits.

  "Finally... due to the Martian ocean filling in that crater, which produced a kind of rebound, there was a second wave propagation," Dr Costard added.

60m/s is 216 km/h, and this is consistent with a few hundred km in a few hours also mentioned.

Question: If I just google the speed of a Tsunami on Earth, I see 800 km/h. The surface gravity on Mars is about 3.71 m/s^2, or about a factor of 2.6 lower than that of Earth. Does this explain the factor of 4 slower speed of the Tsunami wave quantitatively?

below: "The thumbprint terrains probably formed when two sets of tsunami waves interacted." from here.

The linked paper does numerical modelling of a hypothetical tsunami and predicts speeds between 60 m/s (at its point of origin) and 30 m/s (nearer to shore). We can try a back-of-an-envelope approximation to see if we get close, and to understand why the speed would be so much lower than on Earth.

A tsunami behaves as a gravity wave with a very long wavelength. In shallow water (and pretty much anywhere in Earth's oceans counts as shallow water for such a long wave), the speed at which it moves is approximated by

$$V = \sqrt{gD}$$

where $V$ is the wave's speed, $D$ is the depth, and $g$ is the acceleration due to gravity.

On Earth, $g = 9.81$ m/s2 and, in the deep ocean, we might assume a depth of 4 km and obtain a speed of 198 m/s, or 713 kph.

Let's try this for Mars. As you've identified, the acceleration due to gravity on Mars is about 3.8 m/s2, and the linked paper gives assumed depths of the ocean on Mars as between 100 and 1200 m (forgive me if this is not quite right - I've only skimmed the paper, and these figures come from Table 1). Let's assume a 1000 m depth, since the highest speeds will be found in deep water:

$$ V = \sqrt{ 3.8 \times 1000 } = 61.6\ \textrm{m/s} $$

which is close enough to their value for comfort. So a tsunami on the Mars described here would be much slower than on Earth due to the weaker force of gravity and the shallower depth of the ocean.


Width of strata in stratigraphic column I am trying to understand whether there is one "standard" meaning of the width of represented strata in stratigraphic columns, but I can find nothing online or in my geology books.

I notice that, sometimes, under stratigraphic columns there can be legenda explaining how the width of the represented strata relates to the measure of the clasts of a conglomerate, but I have also found stratigraphic columns with no stratum of conglomerate or breccia where not all the strata are equally large.

Is the width of strata usually an increasing function of the area occupied by the respective stratum? Can width represent other characteristics of the described stratum?

The width of a unit in a stratigraphic column, or 'log', sometimes represents the average  grainsize of the rock. I can imagine it being keyed to some other property, but grainsize is common. You'll find lots of examples with a quick search for 'sedimentary log'.

The height of a unit typically represents thickness if the vertical axis is length, height or depth. Alternatively, if the vertical axis is time, then the height of a unit corresponds to time duration.

I've tried to illustrate some of the typical layouts here:

On a wireline log, the horizontal axis is some physical property such as natural gamma-ray emission rate or bulk density. Check the legend.

There's no reason not to represent other parameters with the horizontal axis (or the vertical one, or the colour), but then you'd need to be careful about labelling things clearly.

Footnote: often colour is keyed to lithology. This may or may not closely follow the grainsize. Symbols may be added to represent other relevant characteristics of the rock, such as sedimentary structures and fossils.


What is meant by phase-change in mantle? Phase transition usually means changing from liquid to solid phase. But in geology literature we come across transitions from one mineral to other mineral. For example olivine-spinel transition at 410 km.

What is difference between this transition from other phase transitions like solid-liquid, liquid-gas or solid-gas transitions?

I'd like to add to Gordon's answer. A phase change in this context does not only refer to the change in the state of matter (e.g. liquid to solid) but a change in different solid states as well.

Olivine, $\ce{(Mg,Fe)2SiO4}$, is the stable magnesian silicate in pressures down to those prevailing at a depth of ~410 km below the surface of the Earth. As the mantle is mostly made out of magnesium, silicon and oxygen, this mineral is one of the dominant phases (or minerals) down there. But what happens below 410 km? Using geophysical methods, we know that something changes in the properties of the bulk mantle:

There are "jumps" in the densities and seismic velocities. From experimental work, we know that olivine changes to wadsleyite and ringwoodite at these pressures. Both wadsleyite and ringwoodite are chemically similar to olivine, their composition is also $\ce{(Mg,Fe)2SiO4}$. However, because of the high pressure, their structure changes from the olivine structure to a denser, more compact spinel structure. Note that this is not spinel the mineral ($\ce{MgAl2O4}$), but rather the olivine composition with the ions arranged the same way the ions are arranged in spinel.

At 660 km, the "spinel"-olivine changes to "perovskite"-olivine, causing the second discontinuity. This perovskite is not the mineral perovskite ($\ce{CaTiO3}$), but rather a magnesium silicate with the perovskite structure ($\ce{(Mg,Fe)SiO3}$). Here's a summary of the phases (i.e. minerals) you find in the Earth's mantle:

Both figures are taken from this excellent Uni Münster website, where you can see the high-res figures and read some more about it.


What would happen to the Earth if there were no seasons? If the Earth was in a fixed equinox state, what would the equilibrium temperature be at each pole? Assume daily cycle and convection and so on operate as usual, just that it's permanent sunset at both poles.

Bonus questions: Would the equilibrium temperatures be significantly different if Earth was fixed at solstice?

(Note: I misunderstood this question and wrote an elaborate answer that wasn't the answer to that question. So, to do not throw my answer to the trash, I'm asking here the question I did answer, which I find rather interesting anyway).

In a short timescale, let's say one or two years after a permanent equinox state, the temperature would be basically the current mean annual temperature. This is because if we take the premise of keeping heat transport by convection (on the sea and the atmosphere) as it it today, the total energy inputs and outputs would be the same. Therefore, the same mean annual temperature would occur but without seasonal variability.

To simplify things, let's use a simple model of temperature v/s latitude (that will also be useful in the discussion later):

Image originally from The Petroleum System Blog

Using that formula, the temperature at the poles (reduced to sea level) would be -16.8 °C (from the figure actual data points it can be seen that in real life the south pole is much colder than the north pole).

Now, the previous assumptions contradicts the requirement of "equilibrium", because the above scenario is far from steady state.

So now I will go on to try to describe what would happen to Earth's climate in your hypothetical scenario:

One thing that we learned by studying how the Milankovitch cycles trigger and reverse Pleistocene ice ages, is that to initiate an ice age cold winters are not necessary, what is needed are cold or mild summers.
Currently, the inclination of Earth axis (a.k.a. obliquity) varies between 22° and 24.5° , with a mean period of 41,040 years. When the inclination is 22°, mild summers occur and, therefore, the perfect condition to initiate an ice age (specially when combined with other ad-hoc orbital conditions). The permanent equinox situation you propose, is equivalent to an obliquity of 0°, that would lead to the coldest possible summer (this is, no summer at all). Therefore, such condition would set the Earth on track for an intense and never-ending ice age.

Let me explain how this could work: Using the formula above, the temperatures would be permanently below zero between the poles and latitudes 58.3°. Therefore, snow would start to accumulate in those areas, building an ice sheet and once the ice sheet gets thick enough it would start flowing outwards.

Figure from Lumen Learning.

The ice sheet then becomes self-sustaining due to two positive feedbacks:

Due to its high albedo, it would reflect most of the solar radiation back to the space, cooling down the Earth.
As the ice sheet advance, its thickness adds to the elevation of the terrain, therefore the surface is higher and colder, allowing snowfall beyond the 58.3° of latitude. The thicker it grows the more it can advance towards the equator.

Therefore, the polar ice sheets and their floating extensions (ice shelves), would slowly take over the Earth, and bring it to a state like the  Snowball Earth hypothesis that proposes that Earth surface's became entirely or nearly entirely frozen at least once, sometime earlier than 650 Mya (million years ago).

In your scenario, the equator would constantly receive maximum solar irradiation, therefore, perhaps it could be spared by the ice sheets, but you would need to run a model to figure that out.

But if we assume that the ice sheets would engulf the whole planet, it is easy to calculate the Earth's effective radiative temperature, that is equivalent to the mean temperature. To avoid going into the math (that is quite simple anyway), we can use the Indiana University's Planet Temperature Calculator, that shows that if we crank Earth's albedo from the current 29% to a 80% (a reasonable figure for snow), the mean temperature would drop from 15°C to -63°C. So it would be pretty cold. The actual temperature in the poles would depend on how much energy transport is there from the equator to the poles. A model would be needed to figure that out too.

Eventually, it will happen what is usually thought to have allowed Earth to escape from ice ages: As the land is covered in ice, it can't take up CO$^2$ from the atmosphere (normally happening due to the weathering of silicate rocks), but the volcanoes keep putting CO$^2$ into the atmosphere. Therefore, at some point the amount of atmospheric CO$^2$ is so large that the greenhouse effect can rise the temperature enough to melt the ice sheets and go back to what we call "normal".

This is already too long so I'll refrain to address that bonus question. However, I'll say that the orbital configuration to have permanent summer in either hemisphere would be quite difficult to attain. You would need the Precession period of the Earth to be (and remain) exactly one year long.


Book on the history of Earth and life on Earth I am interested in getting a better overview of the full history of the Earth and the evolution of life. Therefore I am looking for a book that goes through the different geological time scales of the Earth and discusses major changes that took place. I am not an Earth scientist or a biologist, so I don't want it to be too formal. However, I do like it to be quite informative and with rich illustrations if possible.
Does anyone have any recommendations on good titles?

Cowen's History of Life
Your best bet is  Cowen's History of Life, it is an excellent introductory textbooks for paleontology well laid out and clearly written with introductory students in mind so a laymen will be fine. It covers the entire breadth of the life. Check the edition though there are six of them now and the older ones are pretty outdated and not laid out as well. if it wasn't so expensive I would buy it to give to people.
I can recommend a few more specialized texts, to dig deeper [pun intended]
Terrestrial Ecosystems Through Time: Evolutionary Paleoecology of Terrestrial Plants and Animals which is an excellent review of terrestiral life.
Invertebrate Palaeontology & Evolution
by Clarkson which is a beautiful textbook yet still accessible to the laymen since it is written for undergraduates.
Introduction to Paleobiology and the Fossil Record by Benton and Harper is the best introduction to paleontology in general you can get, and may be worth a look if you are having trouble with the other books make.
A lot of searches will point you to Life: A Natural History of the First Four Billion Years of Life on Earth It is OK but the author very much has their storytelling hat on. Great for making it a more enjoyable read, bad if you want information. It reads more like a biography.


How and where do double-terminated crystals form? How and where do double-terminated crystals form?

Most terminated crystals form by 'growing' out of a rock. Which causes one side to be flat,(or whatever the shape of the rock it 'grew' out of was shaped like), and the other side to be 'terminated'. Meaning that the one side has a natural faceted end.

Double-terminated crystals obviously couldn't form like this.

Double-terminated crystals can from by crystallizing from a melt. The crystallization nucleus has to float freely in the magma chamber. As long as no other crystals obstruct the growth the crystal will grow in its own characteristic form (euhedral). This happens for example with feldspar crystals. (Example: http://www.erdwissen.ch/wp-content/uploads/2010/12/granit-feldspat.jpg)

If the crystal forms in a fluid cavity it can form double-terminations when it doesn't grow with the c-Axis normal to the wall. Sometimes crystals also grow with their c-Axis parallel to the wall (Example: http://wannenkopfe.strahlen.org/titanite.html). Probably super cooled pegmatitic melts also form free floating double-terminated crystals like tourmaline.

On the smaller scale (microscope and electron microprobe) double terminated crystals are pretty common in metamorphic rocks. Sections cut parallel to the stretching lineation (or the lineation which elongated crystals aligned themselves to) will show many porphyroblastic crystals with double-terminations.


What is the time period of these chalk/clay layers? These limestone-clay rocks are very common in the Alps, they come from weather changes.

How many years does it take to make one of the rock bands? 7 years, equivalent to an el-nino type event? 1000 years? 20,000 years?

From the wiki page which is only in French: https://fr.wikipedia.org/wiki/Formation_marno-calcaire

The layers correspond to thousands of years, i.e. 23,000 years in the Danien timeline:
The page sais that there is a variation of 23,000 for precession of the equinoxes and 100,000 for variation of ellipticity. https://planet-terre.ens-lyon.fr/image-de-la-semaine/Img421-2013-04-15.xml


Why is it hard to predict earthquakes? An analogy I came up with is:
Predicting earthquake strength and timing is like throwing a sheet of glass on the ground and predicting how many pieces it will break to and where they'll end up.

Is this a good analogy?
I have no geology background or anything similar -- I'm just a person that wants to understand why it's hard. I KNOW it's hard, but why?

The easiest way I can explain it is you haven thousands of different material joined in billions of ways with chunks of all different sizes, there are just too many varables for an accurate prediction. becuase earthquakes are caused by a slow build up of pressure it is impossible to predict exactly when it will break because the forces are not spread evenly and the material properties of the rock are not consistent.

look at material testing, if you have a uniform object under steady predictable force they can predict when it will break with some reliability usually within a few seconds. but across a geologic timescale that kind of accuracy would give you plus or minus thousands of years, and that is under perfect conditions, Add in the complexity of the plates make up and you get even more error. Worse with plates the force on them is not uniform there are several forces acting on it and they are not spread evenly.

to use your glass analogy, imagine a sheet of glass several yards in diameter, but this glass was poorly made its lumpy so the thickness varies by several inches and is full of bubble and impurities. now try to predict when it will break based on a a group of children randomly throwing pennies onto it. You know it will break eventually but predicting when and where is functionally impossible.


Why exactly is the feature on Io called a volcano, and the feature on Enceladus called a geyser? News of the long-lived and not unusual cloud on Mars associated with 21 km tall Olympus Mons has people commenting. This tweet by planetary scientist Dr. Tanya Harrison says

I don't understand the conspiracy theory contingent that's going off re: the clouds over Arsia Mons.
What possible reason would we have to hide volcanic eruptions on Mars? Heck, NASA has shared plenty of pics of volcanoes erupting on Io (shown here) & geysers on Enceladus!

(see the tweet for the video)
Why exactly is the feature on Io called a volcano, and the feature on Enceladus called a geyser? I understand they are substantially different, but I'm asking about how the geological classification works on bodies with different materials and temperatures than those on Earth.

The difference between a volcano and a geyser is defined by what is being ejected.

Volcanoes eject lava, which is molten rock. Molten rock that stays underground is called magma, but when it reaches the surface, usually via a volcano, it is called lava.

A rock is composed of minerals, such as sulphides and silicates. The volcanoes on Io eject lava that is "composed of various forms of elemental sulfur. The colouration of the flows was found to be similar to its various allotropes".

Some volcanoes on Earth also eject elemental sulfur, such as Mount Ijen in Indonesia.

Geysers on Earth typically eject water or steam. But elsewhere in the solar system cryogeysers exist; they eject "volatiles, together with entrained dust or ice particles, without liquid".

On Enceladus, the geysers eject water, ice particles "and smaller amounts of other components (such as carbon dioxide, nitrogen, ammonia, hydrocarbons and silicates)". Unlike in lava from volcanoes, the silicates ejected from geysers on Enceladus are a minor component of the ejected material.

In addition to volcanoes and geysers, there are cryovolcanoes, also known as ice volcanoes, on some bodies in the solar system. Like geysers, they eject volatiles "such as water, ammonia or methane, instead of molten rock. Collectively referred to as cryomagma, cryolava or ice-volcanic melt, these substances are usually liquids and can form plumes, but can also be in vapour form. After eruption, cryomagma is expected to condense to a solid form when exposed to the very low surrounding temperature."


what is the best way to actually make the Earth lose heat? I know that refrigerated air just moves heat around, and creates more by using fossil fuel energy in the process.  If we wanted to actually reduce the amount of net heat energy in an area on the planet, and not just move it around, how?

How does the Earth do it?  Is it all in radiating infrared back up through the atmosphere?

Can we humans help with this in a way that doesn't just need more carbon based energy?  Can we have thermoelectric (Seebeck) generators powering infrared spotlights pointing out into space or something?

What is the best way to actually make the Earth lose heat?

TL;DR: Stop pumping so much carbon dioxide into the atmosphere.

The easiest approach in terms of human effort would be to let the Earth warm up a tiny bit. Thanks to the Stefan-Boltzmann law, a tiny increase in the Earth's effective temperature will easily rectify the ~0.6 watts/meter2 imbalance in the Earth's energy budget. If the Earth was a perfect black body radiating at an effective temperature of 252 kelvins, all that would be needed would be a 0.17° Celsius increase in the effective temperature to make that energy imbalance disappear. Easy, right?

Wrong.

Thanks to feedbacks, that small increase in the Earth's effective temperature requires a significantly larger increase in the Earth's surface temperature, and that's ignoring the fact that humanity is currently making the energy imbalance worse. Temperatures are currently rising and will continue to rise for a while due to the large amount of CO2 humanity has already pumped into the atmosphere.

Continuing to pump ever increasing amounts of CO2 into the atmosphere (the "business as usual" scenario) will result in a 4° to 9° C increase in the Earth's surface temperature by the end of the century, with the uncertainty of the increase depending largely on the climate sensitivity to a doubling in CO2 levels. Even the bottom of that range represents a disaster. The only way to avoid this disaster is to stop pumping so much CO2 into the atmosphere.

  Can we have thermoelectric (Seebeck) generators powering infrared spotlights pointing out into space or something?

You wouldn't want to use infrared spotlights. You'd want the radiation to be in the visible range. The atmosphere is opaque in the infrared.

Playing "what if", suppose every last bit of energy currently consumed by humanity (18 terawatts) is used to power massive air conditioners, with lasers venting the generated heat into space. Suppose we somehow manage to get 17 times as much cooling as energy consumed out of the system, resulting in 300 terawatts of cooling. Dividing that by the Earth's surface area results in 0.6 watts per square meter -- i.e., the current energy imbalance.

This is of course utterly unrealistic.  We aren't plowing or harvesting our fields, manufacturing products, transporting goods, driving to and from work, heating or cooling our houses. To make this unrealistic "what-if" scenario worse, the hydrocarbons used to produce that energy are exacerbating the energy imbalance.

The best way to make the Earth lose heat is to stop pumping so much carbon dioxide into the atmosphere.


Fossil in Chert pebble picked up on a Kent beach Please identify the fossil in the picture below. size of pebble is around 40mm diameter and the pebble had been broken to reveal the internal structure.

It a sea urchin fragment, or at least a natural mold of them. They have both the rings and the angliar joints. It is not uncommon for them to break up into clusters of those plates.


where are the thickest limestone layers on earth ? (CaCO3) What is the maximum thickness of limestone layers on earth?

(Limestone or any other biochemical sedimentary rocks, for example chalk or coral reefs.)

Reading your comments I see that you're asking:

  so could we find for example 1km high limestone layers on earth ?

The answer is definitely yes. Here's an example of a stratrigraphic geological section from Israel:

source: Chronostratigraphic table and subsidence curves of southern Israel, Gvirtzman 2004, Israel Journal of Earth Sciences, 53
You can see that in the north of the country there is an almost entirely continuous section of "platformal carbonates" which is just a fancy name for limestones. That's 5 kilometres of limestone. And I'm pretty sure that's not the deepest - that's only the one I personally know.

That's a sedimentary basin where you can drill and still find fossil-bearing limestones deep down. This gets even better if you start adding tectonics to this. Plate movements can do funny stuff to rocks, including burying them really deep. If you take limestones and do that to them, you actually transform them into marble. Basically marble (proper) is limestone buried deep and cooked. And by deep I mean really deep. Some marbles from the Alps are known to come from more than 100 kilometres deep! Note that I'm not saying it's limestone all the way down, but there are chucks of marble (formerly limestone) down there.

If you want to be really extreme, there is an article where the authors say:

  ...carbonate sediments were subducted into the upper mantle...

Upper mantle is 200-300 kilometres deep. And you know what? That's only the ones we know of. Who knows, there might be some limestones that were subducted all the way down to the core-mantle boundary, almost 3000 kilometres deep.


What is the best way to stay safe while photographing lightning storms? Occasionally, I go out with my camera and tripod and capture cumulonimbus clouds from distance. Sometimes I am worried when I hear thunder that I could be hit by a lightning bolt. I have seen several "bolts out of a clear blue sky" and it reminds me of the danger (even though the probability is probably small).

Photography by ©Jeff Miles

A nice example of lightning comming out of cumulonimbus anvil - I've heard that you can even be hit hundreds of kilometres away (but it's extremely unlikely).

Additionally, I know that during thunderstorms it is very dangerous just to stay in contact with metals or water. This is why I never go out (or open windows) when I take photos of lightning from my flat. But... I have seen several amazing captures of lightning by storm chasers. How is it that they are so close to lightning, but do not get struck? Is there any trick or are they simply risking their lives?

I've considered how lightning strikes, and drew this image.  In this situation it seems that there are three possible targets. I drew a radius around each object because it my intuition suggests it would work like this.  If so, then the building on top of the hill has the highest probability of being struck.

If the lightning bolt hits the object closest to its path, could we completely protect ourselves from being struck by staying RELATIVELY close to some much taller objects, so that they would cover the sky around us with their large radius?

I would like to stay in safe, but take some beautiful photos of lightning too.  I know everyone says that "during lightning storms you should never stand under trees". But if located right, can you actually be protected from danger like this?  Or what practices are truly the best way to stay safe while photographing lightning storms?

Yes, most storm chasers are risking their lives to take lightning photos. Your likelihood of being struck is obviously higher the closer you are to where lightning is originating from. However, lightning is highly unpredictable, and therefore, there is not much you can do to avoid all odds of being struck. One suggestion would be to take photos from inside your vehicle. You could shoot from the back door of a van or truck with a cap, or set your camera outside and operate it with a remote.

I would advise against being close to tall objects, as although lightning is more likely to strike it than you, you can still experience deadly charge that reaches you through the ground.


Is earthquake prediction possible? After the Tohoku and East Coast quakes, I skimmed over several books discussing the validity of earthquake prediction as a discipline, yet found no significant breakthroughs. What should change in our methods and models to enable timely forecasts to reduce casualties?

To be clearer, I am not interested in general assessment of seismic hazards (i.e. magnitude distribution for the next 25-50 years), but rather in short-term forecasts precise enough to order evacuation. I am aware that evacuation is a contentious issue...

Earthquake prediction really is a contentious issue, especially after the l'Aqula trials. However, let me try to elaborate how predictions might be possible in the future and what is inhibiting this development.

We do have some understanding of earthquakes and rupture mechanisms. However, for prediction in a scale of hours (sufficient for evacuation), we have to take the following into account. The stress fields in the crust are basically applying the pressure necessary for earthquakes. However, these are difficult to measure and different stresses may apply to the same region (local, regional, global stress fields). Just look at the world stress map below, how chaotic the different influences are.

Stress

These stresses are also pretty difficult to measure. These methods include (Source World Stress Map):

Earthquake focal mechanisms
Well bore breakouts and drilling-induced fractures
In-situ stress measurements (overcoring, hydraulic fracturing, borehole slotter)
Young geologic data (from fault-slip analysis and volcanic vent alignments)

These may sometimes give contradictory stress tensors. One of these reasons is that in-situ measurements are often more localized than focal mechanisms (as an example). But when we look at the map, we do have a lot of data (27.000 data points). Here another big problem comes into play:

Material

While geophysicists like to assume that the ground is homogeneous, it really isn't. A rupture may occur when the material at a fault fails under pressure. Yet the material is highly diverse and includes cracks and fractures that make it virtually impossible to make an accurate assessment. The material may act elastic, ductile or brittle and that may be location-dependent. From this you cannot say if a small rupture triggers a larger earthquake due to stress transfer or if it stays a small earthquake.

What would be to improve

This would make a simulation highly chaotic and the prediction would have a high probability to be false positive or false negative, therefore, decreasing the reliability significantly.

In the end we would have to improve our understanding of:

Stress fields
Stress-Strain relations
Rupture mechanisms
Material science and location

Early Warning in California

Nevertheless, an earthquake early warning (EEW) system is being implemented in California (and tested). It's called CISN ShakeAlert. They can use the trick that so-called P-waves of earthquakes are faster (and less destructive) than surface waves. This can give valuable time to safety-relevant systems like nuclear plants or high speed trains. But this is in a very early stage, when an earthquake already happened and is bound to arrive somewhere.

(I would have loved to put down more links, but my rep is too low, so see Wikipedia for Rupture Mechanics, Stress-Strain relations, the World Stress Map website and the CISN ShakeAlert website.)


What is the CI chondrite concentration of REEs/rare metals, in ppm/grams per ton? I am researching the abundances of rare earth elements and rare metals in meteorite samples, because I want to investigate the notion that asteroids represent abundant stocks of rare resources. The literature on space resources speaks volumes about platinum group metals, but little about anything else, so I did my own homework. Unfortunately I have no background in mineralogy, and I cannot find data on the actual abundances (in ppm, percent, or micrograms/gram and so on) of REEs/rare metals in meteorite samples. I figure this is an appropriate place for this question, sorry if I'm wrong.

My understanding is that the abundances of non-volatile elements in CI chondrites represents the primordial abundances at the formation of the Solar system. Therefore, the REE+rare metal content of other types of meteorite, and thus asteroid rock, is generally given by comparison to the CI chondrites -- ie, how much more or less enriched they are.

The problem for me is that the CI abundances seem to be nowhere specified in ppm or any measure relevant to mining, so I have no idea how useful any of these rocks could be for evaluating asteroid ore viability. The literature on economically viable ore grades seems to specify quantities of rare elements between 0.1% and 10% per unit mass, for commercial mining. So what are the abundances of rare elements in different meteorite types in ppm/percent?

You should start with the GERM Reservoir Database. Not the easiest to use website, but the most comprehensive. You can look up elemental concentrations in all kinds of "reservoirs", including meteorites. For example, look up CI Chondrites to see the elemental values that are commonly used for REE-diagram normalisation. You can look up by specific meteorites, or averages of groups. You can see values by paper, and in most cases they also include a scan of the original data from the paper itself. Note that it's also usually good practice to actually read the paper to understand how the data were collected, analysed and what do they mean.

That said, as for your general idea of using asteroids as ore deposits for rare metals:

  ...because I want to investigate the notion that asteroids represent abundant stocks of rare resources.

As a rule of thumb, this works well for the PGE (platinum group elements) and related metals (Te, Au, Re). The reason is that those metals are chalcophile or siderophile, and in the Earth they are concentrated in the core and depleted in the mantle and crust. In (some) asteroids, this differentiation did not occur and the concentration of these elements is still (relatively) high in the bulk material.

However, the REE and other HFSE metals (i.e. Zr, Hf, Nb, Ta), are not concentrated in the core. In fact, being lithophile elements, they are particularly enriched in the Earth's crust. Going to mine them from asteroids will be pointless.

Here are some more questions and answers that will clarify some concepts:

Why is uranium only in the crust, really?

What is the difference between chalcophile and siderophile elements?

What are the high field strength and large ion lithophile (HFS or HFSE & LIL or LILE) elements?


Extract a GFS variable I'm trying to extract the APCP variable from a GFS file, with this code:

wgrib2 gfst.grb2 -match ":(APCP):"  - grib gfst.grb2.small

I get a

FATAL ERROR: too many grib files .. 1st=gfst.grb2 2nd=-

What am I doing wrong?

Just to expand upon my comments:

This page from CPC suggests that the error message is likely due to wgrib2 thinking subsequent arguments are actually additional grib files because they aren't properly given the - prefix.  That lead me to realize that you have a space between your last dash and grib which appears to cause the error:

  wgrib2 gfst.grb2 -match ":(APCP):" - grib gfst.grb2.small

should be

  wgrib2 gfst.grb2 -match ":(APCP):" -grib gfst.grb2.small

Hopefully that helps if anyone else comes across the issue at a later date!  You might also have forgotten a dash somewhere... or tried using too many arguments in an option?


What is a "show" in petroleum geology? Is a show when naturally ocurring oil seeps out of a fracture on the surface? Or is it when engineers fracture rocks in order to extract oil?

A show is a visual indication of hydrocarbons, in the jargon of petroleum exploration, it is typically used to describe a drilling. It could be e.g. a Gas show in the drilling fluid. Show evaluation is an important tool to understand a reservoir.

When hydrocarbons reach the surface naturally, we call it a petrolium seep.

Technically, I guess, a seep could be a show if it's used to map a play but I never heard the term used in that context.


Why is the Sahara so much larger than the other horse latitude deserts? Every continent has a dry strip between about 15º and 35º on its west coast, but they vary drastically in size:

The Baja/Mojave and Atacama are fairly narrow, stretching about 300 miles inland at the widest (using the "25 cm annual precip" definition of desert.
The Namib, about 600 miles.
The Great Australian Desert covers about 2,000 miles, most of the continent.
The Sahara, Arabian Desert, Dasht-e-Lut, and Baluchistan together stretch over 5,500!

These are all caused by the winds of the horse latitudes, in turn caused by the continental high-pressure zones, AKA subtropical ridges.  But why does this produce just a slim strip of desert on some continents but a massive span southwest of Eurasia?

The size of the continent is the obvious answer, but if so why is Australia almost all desert, despite being the smallest continent, surrounded by warm ocean?  Looking at the Andes, the Rocky Mountains, the mountains of Iran, Angola, and Namibia, and the Great Dividing Range, it appears that each subtropical desert tends to end at a mountain range, but not always: the southern Namib climbs half a mile before stretching across half of South Africa, and the Sahara has several highlands.

I think the size of the continent is a big contributor.  If there's very little cloud cover, and little rain, the air just keeps drying out the ground.  Try finding a good map of surface or lower-level winds, and just compare how long it takes an air parcel to go from over ocean to the Sahara.  Sometimes the winds will come straight from the oceans, but often they come from over land: the Near East and Asia.

But yes, all your examples end at mountain ranges.  Or rather, start there.  At the horse latitudes and on the equator-ward edges of the subtropical ridges, winds mostly blow east to west, not west to east.  A number of these deserts are thus in rain shadows of a sort (https://en.wikipedia.org/wiki/Rain_shadow).  This kinda ties in with the above: Since the wind blows east to west, the air that blows over the Sahara hasn't just been over Africa but also much of Asia, drying out along the way.

My explanation for Australia would be this.  It doesn't have major mountain chains, so it's not in a rain shadow.  But it doesn't have mountains, so there's nothing to initiate orographic precipitation.  It's convective precipitation or nothing, once you get inland.  And since the ground is dry, convective precipitation doesn't have much of a water source, so it doesn't rain much and the ground stays dry.  Someone with more background on Australia should chime in on that, though.


Seeming correlation between time of day and earthquakes I live in a generally geographically active area (Southern California, near the San Andreas fault, if that matters), that has had two relatively minor earthquakes that I have felt in the last week (in the 3-4 range on the Richter Scale, I believe), as well as frequently in the past. I am used to this, being born and raised in the region.

I was talking about these phenomena with a colleague who recently moved to the area from a non-earthquake prone place, and was not used to them. I realized that both of the earthquakes were late at night, when I was in bed, and searching my memory I can only recall encountering these minor earthquakes at similar times.

My question, therefore, is if there is any correlation between time of day and earthquakes? Or to put it another way, is my observation based on anything more than the fact that I am more likely to note and recall a minor earthquake what I am not engaged in another activity?

As noted by Barry Carter, you could take a look at https://www.emsc-csem.org/Earthquake/Map/zoom.php?key=75&typ=NAM#5 to see the earthquakes around San Francisco, with a table below giving the time and date of the earthquake(s). The USGS can create a similar data-set (try there). I used that to extract the earthquakes of magnitude 2.5+ in the SF area over the last 4 years:

Or the same data with a Kernel Density Estimator in a polar plot (the circle corresponds to 24 hours):

Based on these plots, I think that there is no specific trend suggesting that earthquakes are triggered at specific times.

Earthquakes tend to have their 'core' at depths of a few km's usually, which means that they are not very aware of day-night cycles. Apart from perhaps very minor influence of gravitational differences due to sun/moon locations (which vary over the course of a month), the earthquakes truly follow their own 'random schedule' with respect to our life-cycle!


Why are there no crystals with 5-fold symmetry? They say you can't pack objects like pentagons or octagons such that they fill up space entirely and that that's one reason there is no 5-fold or 8-fold rotational axis.

Are you telling me you can fill up space stacking dodecahedrons or hexakis octahedrons? I don't think so. Please explain this to me. I thought that crystals are built by stacking unit cells on one another.

All unit cells are parallel-sided hexahedra. These are six sided shapes with parallel opposite sides. Their three principle angles may or may not be 90 degrees. And the three side lengths may or may not be equal. All of these unit cells can be uniformly stacked.

Using these building blocks it is only possible to produce planes of reflection, diads (axis of rotational symmetry order 2), triads, tetrads, and hexads.

For example, a cube (all sides the same length, all angles 90 degrees) has diads, triads, and tetrads; plus planes of reflection.
A hexagonal symmetry can be used with 60 / 120 degree angles.

Note that it is impossible to produce a regular arrangement of unit cells to produce a pentad (order 5 symmetry). As @Nathaniel says, this can be almost achieved using Penrose Tiles (2d mathematical constructions), and quasicrystals (real 3d materials). Quasicrystals will produce an x-ray diffraction pattern with a pentad, but the actual atoms do not follow a true 5-fold symmetry.

I suspect your confusion is over the final (macroscopic) crystal shape and the unit cell shape. These are rarely the same. (Salt being an example where they are; but diamonds, garnets, do not)


What is this cloud formation? What is the cloud formation in this video? I don't know where this footage was taken.

Here's the link to the video again.

This a type of arcus cloud called a shelf cloud and is caused by moist air rising over cool thunderstorm outflow.  These clouds can look quite dramatic but do not pose any threats themselves.  However, they can signal the presence of strong winds behind the gust front.
These clouds can often be associated with strong convection -- squall lines, supercells, etc.  These storms often have strong inflow coming from ahead of the storm supplying the storm with moisture.  The storm is producing rain-cooled air and this dense air wants to spread out along the ground.  If the outflow becomes too cool (relative) or the inflow weakens, the storm outflow can race ahead of the storm.  This will produce strong winds as the gust front surges ahead and if the inflow is moist enough it will produce a cloud as it rises up and over the cool outflow.  This cloud marking the gust front as it the rises up and over is a shelf cloud.
These definitions are taken from a NWS storm spotter glossary:

Arcus - A low, horizontal cloud formation associated with the leading edge of thunderstorm outflow (i.e., the gust front). Roll clouds and shelf clouds both are types of arcus clouds.
Shelf Cloud - A low, horizontal wedge-shaped arcus cloud, associated with a thunderstorm gust front (or occasionally with a cold front, even in the absence of thunderstorms). Unlike the roll cloud, the shelf cloud is attached to the base of the parent cloud above it (usually a thunderstorm). Rising cloud motion often can be seen in the leading (outer) part of the shelf cloud, while the underside often appears turbulent, boiling, and wind-torn.


Is an Earthquake Large Enough to Cripple the Entire West Coast of North America Possible? I have an idea for a novel I want to turn into a reality, and I'm starting some research first to make my book at least plausible in very specific conditions. The main aspect of the story would be focused around the Northwest Coast of the US after an earthquake has completely demolished everything, turning it into a post-apocalyptic wasteland.
The main question I'm attempting to answer currently is if this is even possible. I know the Sand Andreas fault line is a major concern presently due to its high capability to release an exorbitant amount of energy in a single quake, but given all the conditions were perfect, is it possible that a single earthquake could cause enough damage to rip apart the entire West Coast? And if not in a single earthquake, can one quake, given it was powerful enough to trigger a series of seismic activity all along the West Coast, cause such a catastrophic, apocalyptic event?
Any advice would be greatly appreciated, and thank you all for your time!

Never say never, but it's unlikely.
Every geological fault is not uniform. There are bumps and snags of varying size and strength along its three intentional surfaces. As once fault surface moves over the other some of the snags can break off resulting in localized quakes at the site of the breakages.
Similarly, for very strong, robust snags (protuberances) which ride over the other surface as they suddenly hit a dimple in the other surface or simply just ride along another surface protuberance on the surface of the other side of the fault it slams into the other surface. This causes another form of localized earthquake.
For an earthquake to hit the entire north west region of the US, these type of events would have to occurs along the entire length of the fault simultaneously.


How to calculate the snow cover area from satellite data in better and efficient way? Satellite retrievals contain cloud cover, biases e.t.c which is the main challenge to prepare the data for further analysis.
After all, how we can efficiently calculate the snow cover and its temporal change in any language base platform from satellite  data?

Identification of snow in satellite images is done using multiwavelength measurements and including ancillary information. Snow obviously has far more reflectivity compared to barren soil, water or vegetation and any edge identification algorithm on visible channel images will identify their extent. The biggest trouble comes from clouds which can appear as bright as snow in visible channel images. Satellite measurements in the infrared region of spectrum help in the discriminate snow vs cloud. Infrared emissions of an object depend on temperature and clouds being at a higher altitude has far less temperature compared to snow. The algorithm may use other information also, for example, day to day variability. Clouds have a very short lifetime and display large variability whereas snow/ice disappears far slowly compared to cloud.


Do different lavas have different volcanic volatiles associated with them? This question was inspired by the question Predicting volcanic eruptions by experimentally proven volatile outgassing observations

Depending on the type of volcano, three types of lava are released by current volcanoes on Earth: basalt, andesite and rhyolite. Given the different compositions of each type of lava are there differences in the ratios of volcanic volatiles $\ce{SO2}$, $\ce{CO2}$ and $\ce{H2O}$ associated with each lava type?

I do not have access to the full-text, but the abstract of Giggenbach (1996)[1] suggests that

  The variability in the composition of volcanic gases accessible to sampling, therefore, is largely due to shallow processes, such as reequilibration in response to cooling and dilution by meteoric water, and interaction with fluids of associated hydrothermal systems.

The section Gas Compositions and Tectonic Setting in [2], from Oregon State University has quite a nice table showing that the different volcanoes do seem to have different gas compositions, depending on where they are found and consequently what type of tectonic setting they occur in. I am not sure if these variations are actually significant though, not being a vulcanologist.

This is certainly not a complete answer, but it does look like it might not be that easy to use the volatiles as a diagnostic feature. Hope that this helps somewhat....

http://link.springer.com/chapter/10.1007/978-3-642-80087-0_7
http://volcano.oregonstate.edu/gas-compositions-and-tectonic-setting


Where on Earth is the most windless lake with its own micro climate sea breeze? Would a circular lake have enough of sea breeze strong to create a gentle vortex in the center of the lake? Is there such a place on Earth where lake micro climate vortexes occur frequently?
The Vortex would still be a breeze and not visible during normal Lake Breeze conditions.

https://worldbuilding.stackexchange.com/questions/108896/could-a-city-be-built-out-of-balloons

Where is the calmest place on Earth?

Wind Vortex on a Lake: the only thing I can visualize is a Tornado on a Lake.

Examples: Pine Lake tornado, Lake of the prairies Tornado

Technically speaking, a breeze/wind cannot be contained within a Lake, unless the lake is covered by mountain-cliffs or canyons at all sides. Maybe something like Marietas Island's hidden beach or Melissani Cave, but much larger would sustain a self contained breeze.


What are the scientific consequences of the lost of the Nereus submersible? The Nereus submersible was lost at sea while exploring the Kermadec Trench at 10,000 meters during a May 2014 research cruise. During its life, it was planned for the ROV to help investigate the evolution and diversity of life in the deepest part of the ocean, and explore how species adapt to extreme environments. With the lost of the Nereus submersible, what other resources do we have to continue deep water exploration?

Nereus as is, is currently not replaceable, but it was insured at a replacement value of $3.1 million, and my understanding Woods Hole currently plans to replace it, though unlikely at this point that there's a solid timeline for this taking place.

Landers, fish traps, and sediment core samplers will still be actively used, but again, these are not really comparable to the areas of research that Nereus was able to cover.

UPDATE: These appears to be the last log entry for the Kermadec Trench 2014 expedition, and the official statement on the day of the event.


Why is the Ocean water on the west Coast so cold comparing to the East coast? Even at similar latitudes they appear to be quite different from one another.

This is a good overview of ocean surface currents, which includes a schematic like this one:

In the mid-latitudes, you get gyre circulations that move poleward along the eastern coasts of continents (the western edges of the ocean), bringing warm water. The water off the east coasts of these places is thus warmer than you would expect for that latitude. The return flow on the eastern edges of ocean basins (west coast of continents) brings cold water from poleward of that latitude.

There are a few things to note about this circulation, though, since that analysis applies to the mid-latitudes only. There are opposite gyres closer to the poles that make the east coasts much colder than expected. (Compare the Alaska current to the Labrador, which is off the east coast of Canada.) The circulation near the equator is a lot more complex and interesting, especially where it meets up with other gyres.

There are some strange and fascinating reasons why the circulation is the way it is, but that answer is the result of an entire oceanography course...


Is the iron on Earth's crust a leftover of the Iron catastrophe, or it was brought back by volcanoes? When pondering the hypothesis of the Iron catastrophe, that seem to be widely accepted nowadays. It surprises me that currently the crust still contain a significant amount of Iron (5.6% in weight).

I wonder if that much Iron is what didn't sink in the Iron catastrophe (just because the process wasn't perfect), or it can be explained by slow reloading with iron transported from the outer core and mantle to the crust trough convection and volcanic activity.

Or perhaps it cam from other sources like meteorites?

Picture from astro.hopkinsschools.org

Not all the iron sank to the core. Have a look at my answer to a previous question:

https://earthscience.stackexchange.com/a/7076/725

Your question is similar, but coming the other way. You're asking - why is there iron in the mantle/crust?

The answer is that there was enough oxygen left in the Earth after oxidising the other lithophile elements (Si, Mg, Al, Ca, etc) to oxidise some of the iron. And when iron is oxidised - it is not a metal anymore, but instead incorporated into rock forming minerals like olivine and pyroxenes.


How would Earth map look like if all ice melts? Is there somewhere a map which indicates which areas and cities become sea?

Calculated Earth is one of the better tools for this, you can either zoom in and get various flood stages or set a specific flood stage and see what would flood, it is in metric though so you may need some conversion software to deal with the units for you, depending how familiar you are with metric.


Variation of the atmospheric pressure By Hydrostatical Law, $p_a = \rho gh$, at a given $h$. However density varies with altitude and with temperature. Temperature varies by altitude. $g$ constant varies with altitude.
How to express the law of atmospheric pressure?

By Hydrostatical Law, $p_a = \rho gh$, at a given $h$. However density varies with altitude and with temperature. Temperature varies by altitude. $g$ constant varies with altitude.

That expression is for water, which has more or less constant density, and it is for depth rather than height.
Ynou need to change this to a differential equation. This is fairly easy: $$\frac{dP(h)}{dh} = -\rho g\tag{1}$$
This assumes the atmosphere is in hydrostatic equilibrium: Every layer of the atmosphere bears the weight of all of the mass above the layer.
Another key equation is the ideal gas law, $PV=nRT$. This can be rewritten in terms of local density as $$P = \rho R_s T\tag{2}$$ where $R_s$ is the specific gas constant, the ideal gas constant divided by the mean molecular mass of the gas. Combining equations (1) and (2) yields $$\frac{dP}{dh} = -\frac{g}{R_s T} P\tag{3}$$
Assuming that all of the factors $g$, $R_s$, and $T$ are constant results in an exponential: $$P(h) = P_0 \exp\left(-\frac{g}{R_s T}h\right) = P_0 \exp\left(-\frac{h}{H}\right)\tag{4}$$
where $P_0$ is the pressure at the surface and $H$ is the scale factor height, $H=R_s T / g$.
The exponential atmosphere model assumes constant temperature. This is not a valid assumption. Temperature drops with increasing altitude in the troposphere, rises with increasing altitude in the stratosphere, and drops again with increasing altitude in the mesosphere. Above the mesosphere, the assumptions of a specific gas constant and constant gravitational acceleration also fail.
The assumptions of a specific gas constant and constant gravitational acceleration are approximately valid in the troposphere. An approximate model for temperature in the troposphere is to assume a constant lapse rate $L$: $$T(h) = T_0 - L h\tag{5}$$
where $T_0$ is the temperature at the surface and $L$ is the lapse rate, the rate at which temperature decreases with altitude. Combining equations (3) and (5) results in a solvable first order differential equation, with solution $$P = P_0 \left(1-\frac{L}{T_0}h\right)^{\frac{g}{R_s L}}\tag{6}$$
This still assumes constant gravity and and constant atmospheric composition, and it assumes hydrostatic equilibrium (equation 1) and an ideal gas (equation 2). None of these are even approximately true above the mesosphere.
Increasing accuracy means that atmosphere models become ever more empirical. The models are still tied to physics, but they are also tied to observations. Lower atmosphere weather models have to eliminate the assumptions that pressure, temperature, and atmospheric makeup are functions of elevation only. Upper atmosphere models have to account for variations in solar radiation. One solar flare can make the upper atmosphere expand by over an order of magnitude.


How much time does water takes to reach to the ground? I want to understand the phenomena where water droplets after precipitation reaches to the ground.

How much time does it take to become ground water or in other words how much time is taken by water to recharge the ground after rain.

I am assuming the water droplets falls in the plain having no concrete human constructions.

It depends upon the hydraulic conductivity, the degree of saturation, and the depth to water table. Generally, water seeping down in the unsaturated zone moves very slowly. Assuming a typical depth to water table of 10 to 20 metres, the seepage time could be a matter of minutes in the case of coarse boulders, to months or even years if there is a lot of clay in fine sediment. Under saturated conditions, the water might move a lot faster. Other factors include the configuration of the wetting front, the unsaturated storage, temperature, and the hydraulic gradient. So basically, there is no simple answer - it's all a matter of the local hydrogeology.

There is no substitute for local measurement - water levels in an observation bore, in the case of water table conditions, or tensiometry in the case of the unsaturated zone.


regarding four-way closure in structural geology I am a little bit confused on the two concepts in structural geology, i.e., what is the relationship of anticline and four-way closure. My understanding is that anticline belongs to four-way closure. Is that right? I did not find any materials that discusses the relationship of these two concept. In the context of seismic image, are there distinguished features that can single out four-way closure?

I understand the term "four-way closure" to be a dome (structural). If that is what you mean...
In that case the 2 structures are similar, but domes are rather symmetrical, whiles anticlines are very asymmetrical, to the extend that we only consider them having to limbs. Although technically speaking anticlines have four, just like domes. Those limbs are called periclines. It's all just convention, both four-way closures and anticlines are folded structures that have an "ending" at some point, it's just that four-way closures are more symmetrical.


What is this? A sinkhole? Lat., long.38.47491, 43.48882, in the vicinity of Van in Turkey

I saw this when hiking. I want to know what it is and what are the dangers it poses. Lots of people hike that area in spring and summer, villagers collect edible plants in the area and graze livestock there.

Given there is no raised rim around the hole, it is not meteorite crater.

It is difficult to be certain given the perspective view in the picture, but it appears to be sink hole, also known as a subsidence hole. More pictures of the area & even an aerial view would help significantly.

If the region has a history of underground mining, the hole may be due to the collapse of underground openings resulting in subsidence on the surface.

If the is no history of mining in the region then an opening may have been created underground, by subterranean water sources and the surface material has subsided or sunk into the hole.

Another possibility is that the hole is a bomb crater produced by the military. This could occur if the site was used as a bombing range by the Turkish air force. Also, given the proximity of the area to Kurdish regions, another possibility is that a bomb could have been dropped during a battle with Kurdish or similar forces.


Can Monin-Obukhov Similarity theory be generalized to tracers? According to Monin-Obukhov similarity theory, Reynolds-averaged surface layer winds can be expressed by $$\frac{\partial \bar{U}}{\partial z}=\frac{u_*\psi_M(\frac{z}{L})}{kz}$$
The potential temperature can be expressed as$$\frac{\partial \bar{\theta}}{\partial z}=\frac{\theta_*\psi_H(\frac{z}{L})}{kz}$$ and I found one for moisture $$\frac{\partial \bar{q}}{\partial z}=\frac{q_*\psi_q(\frac{z}{L})}{kz}$$My question is whether this could be generalized to a tracer $\chi$ such that $$\frac{\partial \bar{\chi}}{\partial z}=\frac{\chi_*\psi_\chi(\frac{z}{L})}{kz}$$

If so, would this question the validity of the Gaussian Plume model?

Note: $u_*, \theta_*, q_*$ and $\chi_*$ are the scaled quantities. $\psi_M, \psi_H, \psi_q,$ and $\psi_\chi$ are the universal functions for each quantity. $k$ is the Von Karman constant.

Yes, the equation can be generalized as you mentioned. The method used to drive it is pretty close to humidity and temperature formulas.

I will start with neutral case and apply law of the wall, it is pretty simple to drive the following equation with Fc as diffusive flux and K as an empirical constant (NOT von-Karman) and also you can get C* from here by setting z = z0:

Remind yourself that Monin-Obukhov length scale (L) is simply the ratio of shear production to buoyancy in TKE budget and is NOT tracer dependent.

Now back to dimensional analysis. The group of variables are unique to our problem are :

1) z/z0 , 2) C/C* and
3) **z/L

where C is mean concentration (C bar in previous equation). Similar to what we do for temperature and humidity. A ψc can be calculated by choosing the second and the third group as independent variables and we would arrive at your equation.

Regarding the Gaussian plume, Remember that the equations you posted are only applicable near a boundary and only used to drive eddy diffusivity close to the wall layer e.g. wind tunnel, ocean, and earth. If I recall correctly Gausian plume model use different diffusivities compared to these and are more appropriate to interior of the flow.


Is there a table with decomposition temperatures of common minerals? I am about to perform a Loss On Ignition test on a material I know that contains among on things kaolinite, which will release water at 500 $^oC$. However, I tried finding a table with decomposition temperatures of common minerals that lose their water, or carbon, or whatever, at a certain temperature or temperature interval.

Anyone familiar with a freely accessible table?

I would have expected to find something here but there isn't a guide to ceramics there that I can find. This article and it's references may give you some guidance though. Found a limited table in this that will probably help too.


Soft Question: How Best to Thoroughly Exhaust the Literature I am trying to make sure I have done my due diligence in researching the literature when it comes to a particular topic in oceanography and/or atmospheric science.  My specialization is in a different subject altogether, where we have one website in particular that has a collection of abstracts and titles for nearly all papers that have ever been published (pre- and post-internet era) in this particular area.  Those of us in the field can search the one website for certain keywords, and once you have done this with some variations on said keywords and then combed the relevant citing/cited literature, it's pretty safe to say you've done your due diligence to comb the literature.  Is there a similar website for the areas of oceanography and/or atmospheric science or does one usually use Google Scholar?  Any help would be much appreciated, thanks!

I would suggest combing Google Scholar with the following methods:

Search keywords just as you've mentioned.
When you hit on a semi-relevant paper, check the citations for relevant information.
Additionally check the collected works of the authors of said papers.
Search specifically for review papers or graduate-level textbooks for context on a subject and more citations.

The perk of interdisciplinary Earth Science is that everything connects.  The downside of interdisciplinary Earth Science is that information is dispersed.  Good luck.