# All Questions

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### Why does the El Niño Stop?

The reason for the initiation of the El Niño is unknown, but what is well known is how it progresses once initiated. The West Pacific warm pool begins to drift East, and the strength of the trade ...
145 views

### Does anyone know of a DBMS with global geospatial search?

We need to store coverage areas and search by location over arbitrarily large areas. It has to be able to handle polar searches and coverage areas that span multiple hemispheres. No GIS can do this. ...
93 views

### Does anyone know of a comprehensive listing of geostationary weather satellites?

Periods of operation at longitude--current as well as historical. The historical list on Wikipedia is incomplete. Is there a single site with status of operational satellites (real-time) or do you ...
256 views

### How do mantle plumes travel from the core of Earth to the crust?

As mantle plumes begin in the core and move towards the crust, I would have thought that the heat in the mantle plume would disperse to the surrounding mantle, and the plume would cease to exist by ...
14k views

### Coriolis effect and Cyclones

The Coriolis force predicts that winds in the northern hemisphere should be deflected in a clockwise pattern and winds in the southern hemisphere should be deflected in an anti-clockwise pattern. Why ...
1k views

### Why do tectonic plates have a tendency to drift closer to the equator?

There are many factors that drive the movement of tectonic plates on the surface of asthenosphere, and some of these factors have a larger contribution than others (e.g. slab suction). One driving ...
344 views

### Did the impact event that caused the Chicxulub-Crater definitively and single-handedly cause the Cretaceous-Paleogene extinction?

Opinions abound on the web. What is the state of the current science regarding this theory and what is the best evidence? Is the theory gaining or losing traction? If it's losing what's the best of ...
536 views

### Can concretions form in non-sedimentary rocks?

Most modern works (e.g. Nichols 2009; Allaby & Allaby 1999) seem to restrict the definition of ‘concretion’ specifically to formations in sedimentary rocks. I have recently come across a taxonomy ...
309 views

### Estimating the permeability tensor of an oil field by remote sensing

I work a lot with numerical methods to solve multiphase flow in porous media for oil applications. In our field, we often use Darcy's law which states that the flux is negatively proportional to the ...
464 views

### Equatorial bulge and tectonic plates

It is well known that the Earth is not a sphere, but rather it bulges at the equator. Also it is well known that the Earth's crust is composed of 7 or 8 (depending on definition) major tectonic plates,...
168 views

### How do we determine subsurface composition?

Let's assume that a seismogram $s(t)$ is the convolution $s(t)=r(t)g(t)$ between a source signal $r(t)$ and propagation effects $g(t)$. If the source signal $r(t)$ is known, then we can obtain the ...
579 views

### Why is a seismogram interpreted as a convolution?

I remember reading in a geology book that a seismogram is a convolution between a source signal and propagation effects. In layman's terms, what does this really mean?
9k views

### How to distinguish P, S, Love, and Rayleigh waves in a seismogram?

What features should I look for to determine each of these kinds of waves in a seismogram? What signal processing methods (filters, transforms, etc...) should I use to determine them?
344 views

### How are subsurface wave speeds determined without subsurface sensors?

This is something I've never quite understood from a geology class I took years ago: Consider the following picture (courtesy of wikipedia) Obviously, we can't possibly have sensors deep in the ...
917 views

### What is a good definition of the word “rock” for teaching?

Note that it needs to include coal and chert, therefore the common answer "a rock is made of minerals" is incomplete.
474 views

### What would it take to confirm or refute the Snowball Earth Hypothesis?

Since Harland's sedimentary work and Budyko's models in the 1960s, geologists have hypothesized that the Earth may once have been completely frozen. There are various lines of evidence for this event. ...
17k views

### Why does the colour of amethyst fade if exposed to too much light?

It is well known that the purple hue that is characteristic of the amethyst quartz ($\ce{SiO2}$) will fade if the crystal is exposed to light for a prolonged period of time. What is the underlying ...
930 views

### Why does the meandering pattern of the jet stream itself propagate?

It is well known that the jet stream follows an overall meandering pattern, but what is less well known is that this meandering pattern itself moves as a wave with a velocity much slower than the ...
790 views

### How can the following equations for meandering rivers be theoretically obtained?

It has been observed that the shape of a meandering river is roughly circular, not sinusoidal (Leopold and Wolman 1960). It has also been observed that the following mathematical relationships tends ...
3k views

### How does a meandering river form?

I read this explanation about rivers: "As the river erodes laterally, to the right side then the left side, it forms large bends, and then horseshoe-like loops called meanders" Why does the river ...
115 views

### Checking the bedrock with radiowaves - how does it work?

I've heard long ago that the rock material deeply below surface are checked by a device that acts like radar - it sends radiowaves into the ground, and geologists find out from reflections that what ...
3k views

### What's the difference between the upper & lower mantle?

Recently I checked a picture about the geologic layers of the Earth, and I saw that the mantle is divided into upper and lower mantle. What's the reason of this differentiation?
2k views

### Why does a subduction zone produce a serpentinization diapir rather than volcanism?

The classic Troodos Ophiolite in Cyprus has been uplifted by a 'serpentinization event'. Upper mantle (peridotite) has been serpentinized creating a buoyant diapir. This has uplifted the ocean crust ...
2k views

### Horizon letter for bedrock

What is the official letter for the bedrock soil horizon? I know that the letters to represent the A, B, and C horizons are widespread, but the fourth layer (bedrock) is referred to with different ...
314 views

### Naming convention for sea ice thickness per unit area of ice or ocean

When defining an area average of sea ice thickness, it is important to distinguish between an average taken over an ocean area h_1 = \sum \frac{\text{sea ice thickness (in area)}}{\text{area}_\text{...
5k views

### 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 ...
16k views

### Why do crystals, like quartz and diamonds, form in different colors?

Some crystals, like quartz and diamonds, form in a variety of different colors. For example, quartz can be clear, 'foggy', pink, yellow, and even blue. What happens during the crystal's formation to ...
2k views

### What is the cause of the jet streams?

Jet streams are fast-flowing currents of air in our earth's atmosphere. An enormous amount of energy is necessary to keep a jet stream going. Where does this come from and why?
319 views

### How can I improve the numerical stability of a coastal hydrodynamic model?

I am working with a coastal hydrodynamic model in the MIKE3 modelling package. MIKE3 uses the finite volume method to solve the shallow water equations with explicit timestepping, over a triangular ...
960 views

### How are the banded-iron-formation iron-ores formed?

Many of the richest and purest iron ores are found in so called banded iron formations, cm thick magnetite or hematite layers intermixed with iron poor rock layers. Since these are usually of pre-...
1k views

### What influences tide-height the most? Can I guess the height by looking on a globe?

I hope that the question title is resonably clear: What are the most significant factors which influence the tide height? I'm aware of the following couple of them: Sun-Earth-Moon relative position (...
517 views

### What is caesium-137 used for in fracking?

Caesium-137 is used in the fracking process. What is it used for?
1k views

### What are rare earths and why do they cluster near alkaline magmatism?

'Rare earths' play a vital role in the modern economy, and they are becoming more of a point of focus in geopolitical realms. What are 'rare earths' and why do they appear to cluster in association ...
4k views

### Correlating the Caledonian and Appalachian Orogenies

The Caledonian mountains and Appalachian mountains are recognised to be the roots of the same Palaeozoic orogenic belt. This has since been split in two with the opening of the Atlantic. On the ...
2k views

### What causes 'positive' lightning to be rarer, higher charged, and longer lasting than 'negative' lightning?

Why is 'positive' lightning rarer, brighter, higher charged, and longer lasting than 'negative' lightning? Are there any other unique characteristics to positive lightning that sets it apart from ...
5k views

### What do quasi-geostrophic and ageostrophic mean?

I know that geostrophic flow means straight wind flow that is balanced by the pressure gradient and Coriolis forces. But what do quasi-geostrophic and ageostrophic mean specifically?
373 views

### How is global weather model skill measured?

The models I have in mind are the major global models such as the Global Forecast System (GFS) and the European Center for Medium range Weather Forecasting (ECMWF). These models produce numerous ...
468 views

### Were dinosaurs with feathers common?

More and more evidence of fossilized dinosaurs with feathers are appearing. Did many dinosaurs have feathers and did this change during the Mesozoic?
473 views

### What caused the Cretaceous uplift of the Harz mountains (Germany)

What are the likely stresses that caused the uplift of the Harz mountains? Was the uplift connected to another orogeny, lithospheric-scale folding or a mantle process?
110 views

### Is there a database of the geologic/stratigraphic units of France?

Is there a page where I can look up rock unit definitions for France similar to: https://www.bgs.ac.uk/lexicon/home.cfm http://www.bgr.de/app/litholex/index.php I did some searching for this, but ...
140 views

### Is there a standard definition of a hill? [closed]

I think we can all agree that these are hills: Image from Wikipedia They're kinda gentle, not too tall, and altogether nice-looking. But it's always bugged me that I can't come up with an objective ...
1k views

### Can pyroclastic flows cross water?

While reading the Wikipedia article on pyroclastic flows, I noticed that there's a section called 'Interaction with water'. This piqued my interest, as I was under the impression that lava generally ...
132 views

### Placement of crustal thickness estimation from 1D inversion of surface wave dispersion curves

Seismic surface waves present a characteristic dispersion behavior in which different frequencies travel at different speeds. This characteristic dispersion curve depends on the shear and ...
18k views

### What are the differences between geology, petrology, and lithology?

What differences are there between geology, petrology, and lithology? If I were to get into any of those fields, what exactly would I be studying? Also, are petrology and lithology just branches of ...
195 views

### Is the Grand Canyon the “greatest” canyon in the world? [closed]

The Grand Canyon is nearly 446 km (300 miles) long, 29 km (18 miles) wide, and over 1,8 km (1 mile) deep. To the best of my knowledge, there is no other canyon of comparable size in the world. Is ...
154 views

### Paleogene transantarctic seaway

Lawver & Gahagan (1998; 2003) hypothesized, based on sea level records and the isostatically adjusted bedrock surface of Antarctica, the existence of a Trans-Antarctic Seaway linking the Ross Sea ...
199 views

### How to measure stretching direction on chocolate-tablet boudins?

This has always bothered me during field mapping: A boudin with two stretching directions has the form of an M&M candy (or almond shape). What do I do to measure the two stretching directions if ...
104 views

### Biogenic origin of authigenic zeolites

Bohrmann et al. 1989 advanced the idea that the silicate phase from some clinoptilolites come from the diagenetic degradation of biogenic opal (from radiolarians in that case but presumably also other ...