To understand, we need to add some details:

1) For the basic density of the oceanic and continental components (but this is true even if we think about an ocean-ocean subduction zone, i.e., where one section of oceanic lithosphere subducts beneath another) we need to expand our view to the whole lithosphere. Plates represents mobile sections of lithosphere which includes crust and the upper portion of the mantle. This means that the relevant density to consider is the integrated density of the different sections of lithosphere which will reflect the individual densities of the crust and mantle components, their thicknesses, and any spatial heterogeneities in these properties. Finally, we need to consider the density of these sections of lithosphere with respect to what they are sitting on, and in the case of subduction, sinking into, i.e., the asthenosphere.

2) The integrated density of a section of oceanic lithosphere depends on its age. This is for two primary reasons, A) the oceanic crust component gets a bit denser as it ages and thus cools (as it moves away from the mid-ocean ridge at which it was produced) and B) the mantle lithosphere component effectively grows as a function of age, again also primarily as a result of cooling (in detail, it grows, implying that the oceanic section of the plate thickens, but not as a constant function of age, the growth rate asymptotes towards zero after a certain age). Taken together, this means that as a section of oceanic lithosphere ages, it gets more dense.

3) Finally, we get to the real crux of subduction, specifically that given above, eventually a portion of the oceanic lithosphere reaches a density where it is more dense than the aesthenosphere beneath it, which is unstable, allowing it to start sinking. Once an edge begins to sink, assuming the strength of the rest of the plate is sufficient to not have the tip simply break off and sink into the mantle, this "negative buoyancy force" of the subducted slab starts pulling the rest of the plate down with it as it sinks.

A simple analogy would be imagining pushing a plastic sheet out across a pool. If as the leading edge of this sheet was advancing into the pool, you were adding little weights to the end, eventually the positive buoyancy of the sheet floating on the pool surface would be overcome by the weighted edge, and this edge would start to sink. As this edge sunk, it would progressively drag down the rest of the sheet as long as that negative buoyancy force (both of the original weights, but also the added mass of the portion of the sheet now submerged) persisted and was enough to overcome the positive buoyancy of the remaining floating sheet.

Thus, ultimately, the density of continental lithosphere is relevant in the sense that it generally precludes it (i.e., continental lithosphere) from being subducted, i.e., there are limited circumstances and processes by which the positive buoyancy of continental lithosphere can be overcome for sections of it to sink (or be drug) into the mantle, but its not really relevant for understanding why some sections of oceanic lithosphere can subduct - which is really the origin of your understandable confusion. For this, the key contrast is the density of the section of subducting oceanic lithosphere and the underlying mantle, and this, hopefully is much more intuitive, i.e., dense material on top of lighter material pretty much always leads to the denser material sinking.

There are of course, many technical caveats. In reality, the sticky part of what you're asking about is how a subduction zone starts, i.e., subduction zone initiation, which is definitely probably one of the least understood parts of subduction. That's not to say we don't have good hypotheses for how this process operates, but as we'll see, they're non-unique and their remains disagreement about many of the details. Once a subduction is operating, it's definitely the negative buoyancy force of the slab, i.e., that on average, the slab is denser than the surrounding mantle, that keeps it sinking and driving sudbuction, but how does that start? Broadly, there are two mechanisms proposed, what we would call either induced or spontaneous (e.g., Stern, 2004, Stern & Gerya, 2018), which are sometimes also referred to as horizontally forced or vertically forced initiation (e.g., Shuck et al., 2022).

In short, induced (or horizontally forced) subduction initiation relies on the preexistence of compressional forces that are able to shove a tip of oceanic lithosphere into the mantle a bit (even though the density of the oceanic lithosphere might be insufficient for it to really sink). Once that happens though, the oceanic crust begins to metamorphose which causes its density to increase (e.g., by transforming into eclogites) and at the same time, release water (as a product of the metamorphic reactions occurring) that serves to "loosen" the area of the mantle which is resisting the intrusion of this small oceanic lithosphere section. Together, these can lead to stable subduction, i.e., the slab tip gets dense enough, along with decreased resisting force of the surrounding mantle, for it to start to sink and transition into a subduction zone (e.g., Soret et al., 2022).

In contrast, spontaneous (or vertically forced) subduction initiation relies instead on the density of the oceanic lithosphere to reach an unstable condition (i.e., denser than the asthenosphere/mantle) via aging and/or with the presence of an additional downward vertical force (e.g., the collapse of a mantle plume head) often in the presence of an existing weakness (e.g., an oceanic transform fault). Once started, the same processes (e.g., metamorphism of the slab, release of water, etc) from the induced example likely play a role in making the subduction zone self-sustaining.

As highlighted in the Stern papers, we have examples of both occurring and the Shuck paper highlights how the initiation of a subduction zone in one place by one mechanism (induced) can drive lateral propagation and the start of subduction elsewhere by the other (spontaneous). There are still many details we don't quite understand, so this is very much an active area of research.

> how would a world be with Two Rings of Fire or more?

The "Ring of Fire" is just a colloquial term for an ocean basin mostly surrounded by subduction zones and associated volcanic arcs and has no real formal definition. While the current plate configuration has one semi-continuous ocean basin that is partially rimmed by subduction zones (i.e., the "Ring of Fire"), you could expect a later stage of a supercontinent cycle to have two ocean basins with some amount of subduction going on around their edges (though there are definitely some open questions here). I.e., at the moment, there is dominantly subduction happening around the Pacific, which is effectively the remnant of Panthalassa, i.e., the former exterior ocean surrounding Pangea, but assuming the next supercontinent forms via "introversion" (i.e., closure of the "interior" ocean basin, namely the Atlantic, to form the next supercontinent, see Murphy & Nance, 2013 for additional information on extro- vs introversion in this context), then we would expect some period in the future where subduction (and volcanism) may still be occurring around some portion of the Pacific perimeter, but has also initiated around portions of the Atlantic. Ultimately though, there's generally the expectation of having one semi-continuous ring of subduction zones (i.e., the "subduction girdle") that reflects a particular style of large-scale mantle flow (i.e., "degree 2 mantle flow") that has two broad zones of upwelling (centered above antipodal LLSVPs) and then a circular girdle of downwelling, i.e., subduction, between them (e.g., Mitchell et al., 2021). Thus ultimately, assuming mantle convection, tectonics, and the supercontinent cycle works vaguely like it does on Earth, we primarily expect there to be one "Ring of Fire" that would be coincident with this subduction girdle feature.

> How would it interact with the various species Carbon or nay?

I don't know what you're asking here.

> And what happens if a planet has no Rings of Fire?

If we interpret this to mean that a planet has no active subduction zones and thus no active volcanic arcs, given that subduction is the primary driver of plate motion (e.g., see our FAQ on this subject), we would have to interpret this to mean that said planet did not have active plate tectonics, or at least did not have mobile lid tectonics in the same style as Earth. If we relax our definition of "Ring of Fire" (and since it has no real formal definition, that's fine) to just mean that there are subduction zones, but not a configuration where one ocean basin is largely being consumed from all sides, again, this is potentially a viable part of the supercontinent cycle. I.e., there could be a period during future introversion where subduction has ceased around large swaths of the Pacific and at the same time, large-scale subduction of the Atlantic has not yet started around enough of the rim to be meet our arbitrary definition of the "Ring of Fire". The feasibility of such a state really depends on how many subduction zones and how continuous they need to be to satisfy the condition of being, or not being, a "Ring of Fire". Ultimately, as described in the Mitchell et al. paper from above, the extent to which the "subduction girdle" and associated 2 degree mantle flow is a persistent feature or something that switches between that and 1 degree mantle flow (one zone of upwelling and one somewhat more concentrated zone of downwelling, i.e., subduction zones), with or without some potential intermediate behaviors, as part of the supercontinent cycle remains an open question, but would be relevant for understanding whether we expect for the "subduction girdle" to ever truly shut down.

> This may be a silly question, but how much weight would it take to cause this?

Mathematically, there's not a minimum threshold, but in practice, there's going to be mass distributions that are going to produce such a small predicted deflection they are not really measurable. The math for flexure is laid out in a variety of places, Wickert, 2016 provides a pretty complete view if you can't get your hands on a copy of Turcotte & Schubert. Thus, you can calculate the predicted flexure for any mass, but in practice, that mass may be insufficient to produce a measurable flexure. The other big complication here is that the response also depends on the duration of the load and/or the rate of change of the load through time as the way the lithosphere responds to loads (i.e., purely elastic, viscoelastic, etc.) depends on the rate of change of the load (e.g., Watts et al., 2013).

> Also, does it depend on the makeup of earth that sits below said weight?

Yes. If you look through the math in Wickert, you'll see a few terms that potentially vary with location, specifically the density contrast between the infilling material and the mantle and the flexural rigidity (D). For the former, this means that the density of the load (i.e., is it rock, water ice, liquid water, etc) matters, but also that theoretically the density of the mantle in that location matters. In practice, we often assume a standard density for the mantle (not necessarily always) so we don't often consider this term to vary by location (but in reality, it might). However, flexural rigidity definitely does vary by location. If you go to the appendix, you'll see a definition for D that includes Young's modulus, the Poisson ratio, and the effective elastic thickness (Te). We typically assume Young's modulus and Poisson's ratio are constants for the lithosphere, but Te can vary a lot by location (e.g., Watts, 1992, Burov & Diament, 1995, Burov, 2011), e.g., the oceanic lithosphere generally has a narrow range of Te with most being ~10-20 km whereas continental lithosphere has a pretty wide range of Te with some in similar ranges as oceanic lithosphere but others being significantly thicker. The effective elastic thickness is kind of what the name implies, i.e., it's an approximation of the thickness of a purely elastic sheet that would explain the observed deflection for a given mass distribution. Te is generally not a physical thing (many of the cited papers are trying to find relations between Te and something we can actually measure like crustal thickness, temperature profiles, age, etc) but is something we estimate from observed deflections (though for oceanic lithosphere, it is more explainable as a function of lithosphere age/temperature). In general, for the same surface mass and mass distribution lower Te means more "local compensation", i.e., larger deflections with much shorter wavelengths, whereas larger Te means less deflection distributed over a much longer wavelength. In practice, Te is the main thing that we consider to vary as a function of location (and in turn, flexural ridigity) and this has a pretty important influence on how that area responds to a given load.

I stand corrected :)

With respect to GIA in the areas with extant ice sheets, there have been arguments that it could slow ice mass loss in certain areas (e.g., Vaughah et al., 2006, Zeitz et al., 2022), but broadly, these are pretty complicated dynamics with a lot of uncertainty in terms of how they'll actually play out.

They're definitely included in terms of detailed projections for local relative sea level rise in certain areas. Relative sea level change is the rate of sea level change relative to a local datum, which differs from global eustatic sea level change, which is the change relative to a fixed global datum (e.g., the center of the Earth). For example, in a hypothetical scenario where global eustatic sea level rise is 3 mm/yr, but the local rate of surface uplift at the coast in a particular area is 5 mm/yr from isostatic or tectonic forces, the rate of relative sea level change would actually be a 2 mm/yr apparent sea level fall in that location.

With respect to projections of global eustatic sea level rise over time frames like 50-100 years, most won't necessarily include projections of isostatic responses to recent (i.e., anthropogenically related) ice mass redistribution and resultant changes to ocean basin volume, because the effects will be relatively small given the time frame of responses (see correction by u/agate_ below) and the pretty large uncertainties in other aspects like the "right" concentration pathways and associated ice sheet responses (e.g., Horton et al., 2020) or steric components of projected eustatic sea level change (e.g., Camargo et al., 2020).

I assume you're asking about the surface elevation of the topography beneath the ice sheet, like those constrained in papers like Morlighem et al., 2017? In short, the reason for the below sea level elevations are the mass of the ice and the isostatic response of the crust to this mass.

In detail, the Earth's crust behaves somewhat like a giant elastic sheet. When a surface load, like an ice sheet, is placed on the crust, it deflects downward analogous to how if you put a weight on the center of a trampoline, the surface of the trampoline would deflect downward by an amount proportional to the mass, the distribution of that mass, and the 'rigidity' of the trampoline itself. The added extra complication is that in the analogy, the trampoline is the crust and the air is the mantle, but in reality the mantle is extremely viscous, so the flexural response to a mass is not instantaneous (like it effectively is in the trampoline example, because air can flow out of the way beneath the trampoline very quickly), i.e., it is dictated by both the elastic properties of the crust, but also the viscosity of the mantle as the mantle has to flow (reminder the mantle is a solid, but behaves like a fluid on long timescales, i.e., it's a rheid) away from the depression to accommodate the deflection. Similarly, when the surface mass is removed (or reduced), there will be an isostatic/flexural response, i.e., the surface elevation will 'rebound'. When this is discussed in reference to reduction of ice sheet mass, this is described as glacial isostatic adjustment (GIA) or 'glacial rebound'. Because of the moderating effect of the high viscosity of the mantle (i.e., it takes time for the mantle to flow back to allow for rebound), GIA is actually still occurring from large ice sheet reductions during the end of the last glacial period, and we can measure the vertical rate at which the Earth's surface is still rebounding in response to melting of the large northern hemisphere ice sheets.

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Yeah, but I would say that falls into the last paragraph category, i.e., as already stated, if the bulk composition of the starting solar nebula / protoplanetary disk is significantly different than our own, then the possibility of exotic rocks gets much more likely.

Yes, though it's also worth remembering that while most carbonates are biotic to some degree or another, there are abiotic sedimentary carbonates that can form in specific chemical environments and rare igenous carbonates (i.e., carbonatites), so we would want to be careful with a blanket assumption that carbonates = life and thus are wholly unique to a planet that has or had life. Though, certainly something like a bioclastic limestone would be unique to a planet that had life.

In short, yes, but with some caveats. The simple answer is based on an assumption that the bulk composition of hypothetical other planets are not that different from the rocky planets of our solar system and more broadly that the bulk composition of our solar system (which sets the available elements for all of the planets in that solar system) are not that different. If we accept that assumption, from there the rocks we observe on said planet(s) would be dictated by the underlying laws of chemistry and thermodynamics (which we would expect to function similarly regardless of location, i.e., reactions between particular elements/compounds at particular temperatures and pressures will still behave the same). In terms of tests of this assumption, we have limited data, but broadly the rocks we've been able to observe (in here I'm lumping a lot of different types of observations) on extraterrestrial bodies (primarily the Moon, Mars) and meteorites conform to and/or are similar to rocks we observe on Earth.

One thing to note though, generally, Earth has a pretty wide array of rocks compared to most other bodies we've been able to explore to some degree. This is primarily due to the existence of active and long-lived mobile lid tectonics, which is the root cause of, or at least allows for, many of the igneous differentiation processes that allow for the formation of intermediate and felsic rocks (e.g., this igneous rock classification diagram) like granite (felsic). In contrast, most of what we've found on planets that either did not have plate tectonics (or had likely short lived tectonics or something like mobile lid tectonics) are ultramafic and mafic rocks and things derived from them (e.g., sedimentary rocks, which are still very enriched in iron and magnesium and thus geochemically would "look" like ultramafic or mafic rocks).

Finally, if we circle back to our original assumption, a lot hinges on this idea that the bulk composition of our hypothetical planet(s), and by extension the solar system and star within which the hypothetical planet(s) formed is similar to both Earth and our solar system/star. The limitations of this assumption are understood and discussed by people studying expolanets, e.g., Putrika et al., 2021 discuss this directly in considering some possible differences in bulk composition (e.g., things like the relative abundance of iron, magnesium, and silicon within a given solar system) and how this might influence the composition of rocks that can and do develop. As a specific example, Putrika & Xu, 2021 highlight that you could expect some exotic compositions in extreme environments (e.g., exoplanets that develop around a "polluted white dwarf").

As has been stated several other times in this thread, if you look at the Badyukova paper, they describe previous interpretations, none of which are glacial outburst floods, largely because the internal stratigraphy and sedimentology is not consistent with such an origin.

As described in the original answer, these are not wind blown features and they are definitely not gypsum dunes like those in White Sands.

None of the explanations for these features as summarized in the Badyukova paper cited in the original answer focus on megafloods like those that generated the scablands as a possible origin. Ultimately, with many geomorphic features, shape alone is not diagnostic for the formation mechanism.

These are referred to as "Baers Mounds" or "Baers Knolls" after the scientist who first described them in detail in the mid 1800's. There have been a large number of hypotheses put forward to explain their formation, with aeolian (wind blown sediment) being one of the more popular as they do have a similar form to some windblown features, but subsequent work has shown that their internal structure and sediment characteristics are inconsistent with this. At present, there is still not a single explanation for their formation as far as I know, but recent publications have suggested they may be related to deposition during flow of water in a former connection between the Black and Caspian Seas, i.e., the Manych Strait (e.g., Badyukova, 2018) or as a result of deposition during rapid fall of the level of the Caspian Sea (e.g., Melnikova & Pokazeev, 2020).

Yes, designed for earthquakes though, not creep.

The obvious answer is yes, basically any time there is damage of these or other structures during an earthquake (of which there are of course numerous examples), ultimately the root cause is plate movement as this is driving the storage of elastic energy that is released during an earthquake.

That being said, I assume you're more asking about whether slow and steady motion along plate boundaries can damage infrastructure. This depends a bit on the nature of the faults in question. For those that fail seismically (i.e., with earthquakes) the answer would generally be no. During the interseismic period, i.e., the time between earthquakes, while strain is accumulating, this deformation is distributed over long enough distances that the differential rate of motion over even "long" features like bridges, etc., will be very small and generally less than things like thermal expansion which are accounted for in the design of most of these structures.

However, there are "creeping" faults, or creeping sections of faults, i.e., portion of faults that experience slow and steady "creep" near the slip-rate of the fault as opposed to accumulating strain to be released during an earthquake. If a structure spans a creeping fault, it will gradually be displaced. Classic examples of this can be found along several creeping faults that go through cities, probably one of the more famous being the Hayward fault that goes through Berkeley, CA. Within Berkeley, along the fault, there are a variety of structures like curbs and even large sections of the Cal football stadium - scroll down to page 13 and after that are offset by creeping motion of the Hayward. Specific to bridges, probably one of the most famous examples of fault creep deforming a bridge is a bridge near Parkfield, CA being deformed by creep along the San Andreas fault.

Let's rephrase the question to, "If global CO2 concentration in the atmosphere was constant, would global average temperature stay constant?" Considering even moderately long timescales (e.g., a few thousand years), the answer would be no because even hypothetically if CO2 concentration stayed exactly the same (which itself is basically an impossible hypothetical considering any part of Earth history if considering more than a few hundred to thousand of years), the amount of incoming solar radiation would change because of a variety of changes in Earth's orbital parameters (e.g., eccentricity, obliquity, precession). These orbital induced changes in solar radiation (i.e., insolation) are typically described in the context of Milankovitch cycles and are broadly the main drivers of most (but not all) climatic changes on millennial timescales with CO2 largely acting as a reinforcing feedback on these timescales. On longer timescales (e.g., several million to hundreds of millions of years), the amount of CO2 in the atmosphere represents a primary driver for climate with orbital changes influencing smaller scale variations (both in terms of magnitude and time scale). So broadly, major and long-lived changes in CO2 concentration (that reflect long-term balances between carbon stored in the atmosphere/hydrosphere vs lithosphere/mantle) drive transitions between Icehouse vs Greenhouse climates where as Milankovitch cycle type controls drive things like interglacial-glacial transitions within an Icehouse climate (i.e., what we have now). Both of these are discussed in significantly more detail in a variety of places, like this FAQ entry.

I assume this question is sparked by the ending of a recent episode of the >!Rings of Power!< (tagging as a spoiler since this is a new show, any subsequent details that refer to the events in said show will also be spoiler tagged). In general, the interaction of water with a magma body can definitely produce a major eruption. There are two broad types of eruptions that can result, either phreatic or phreatomagmatic, where (following the definitions from Brown & Lawless, 2001), both are eruptions primarily caused by flashing of water after encountering magma, and the distinction between the two is basically whether any lava is erupted, phreatic eruptions just expel solid products of overburden/country rock, whereas phreatomagmatic include eruptions of liquid magma/lava. >!Based on at least the quick glimpse we see of the eruption at the end of Episode 6, it's a little hard to know how to classify it, but I would lean toward a phreatomagmatic. There is clearly a pyroclastic flow and what are probably lava bombs, though to be really sure, would like to see some more clear evidence of fresh lava erupting, probably will get some clarity in the next episode!<.

Typically, in real scenarios, the water that is encountered by magma is groundwater, usually in the process of magma ascent interacting with ground water, but can there can also be phreatic or phreatomagmatic eruptions from interactions with sea water, sub-glacial water, or lakes, and there have been cases of caldera lakes basically being injected by eruptions and thus triggering phreatic/phreatomagmatic eruptions (e.g., Houghton et al., 2015, Rouwet & Morrissey, 2015). In terms of a hypothetical diversion of a river into an active volcano, whether this would trigger a phreatic or phreatomagmatic eruption depends on the details. We can consider Valentine et al., 2014, which is basically highlighting that whether you get a phreatic or phreatomagmatic eruption when magma interacts with water depends on the volume of both water and magma (and the ratio between the two) as this will set the explosive force and then the depth of where the interaction is occurring, as the for there to be an eruption, there needs to sufficient explosive force to overcome the strength of the overburden.

While phreatic and phreatomagmatic eruptions are definitely a thing (and tend to be some of the most destructive and violet type of eruptions), the feasibility of diverting a river into the active magma chamber of a volcanio is more problematic. In general, it's actually kind of hard to open up a sustained hole into a magma chamber, because it tends to seal itself. For example, when the magma chamber of the Krafla volcano was accidentally drilled into (e.g., Elders et al., 2011), the base of the hole was quickly filled with quenched magma (i.e., rock), effectively plugging the hole. Thus, arguably, artificially reaching a magma chamber to add water to it to induce an eruption would be a bit of a challenge, >!especially in the specific instance here, i.e., digging what amounts to a canal and then breaching the side of a volcano with hand tools!<. Finally, with reference to the specific representation of the "magma chamber" in the particular show in question, >!the depiction of a literal chamber full of molten rock and air is not particularly realistic.!< Broadly, magma chambers are best pictured as spaces filled with mixtures of liquid rock and significant amounts of crystals (i.e., a "crystal mush"). We would not generally expect significant air filled spaces in these chambers, especially magma chambers at depth. Lava tubes, which tend to be much more shallow, can have periods where they have both molten rock and air (i.e., they are not totally filled with molten rock), but this would broadly not be the case for magma chambers.

TL;DR If there was a feasible way to introduce a large amount of river flow into an active magma chamber, depending on the depth of the magma chamber, this could be a very effective way to produce a violent eruption, specifically either a phreatic or phreatomagmatic eruption. The less feasible part relates to how this diversion could actually reach the magma chamber as holes dug/drilled into magma chambers would probably tend to be sealed by erupting lava before the diversion could be completed. There might be some narrow set of conditions that could allow for this to happen, but >!probably not in the way depicted in the Rings of Power!<.

Ok, then that narrows it down to sparse/noisy underlying data and some issues with interpolation. If you look at something like the NOAA bathymetry viewer you can see where we have either multi- or singlebeam sounding data. Generally in the area you're looking at we have very few tracks, so the bathymetry is going to be primarily from satellite gravity data (e.g., this). This is a sparse dataset, and one that I would expect to broadly have issues at the poles especially.

At the end of the day, these are clearly a data artifact and anyone who works with gridded topographic/bathymetric data immediately recognizes it as such, but given the available data, it's better than nothing.

There’s not a lot of bathymetric data in that area in general and broadly Google Earth does a pretty bad job of representing data at the poles. Ie these might not be present if you downloaded the gridded data from a source like GEBCO, but instead come from the way Google Earth is stitching rasters.

Those are almost certainly artifacts from sort of raster processing that was done on this data. I.e., we're looking at a visualization of a gridded dataset of depths based originally on scattered points and those derived rasters themselves that likely have been reprojected and/or stitched together. In going from scatter to gridded data, when raw point spacing is large relative to the interpolated grid spacing, artifacts are pretty common and the exact type of artifacts you get will depend on the algorithm used (e.g., IDW, kriging, spline, nearest neighbor, etc). Similarly, when reprojecting or merging/stitching raster tiles together, depending on the algorithm used (e.g., nearest neighbor, bilinear interpolation, cubic convolution, etc), artifacts can be introduced. I'm not 100% sure which step produced these exact artifacts, but I've definitely produced similar artifacts in data when I've merged rasters via nearest neighbor (which is the least computationally intensive algorithm for stitching rasters together and what several GIS programs default to).