Parts of the Antarctic ice sheet touch bedrock that is thousands of feet under current mean sea level.
Assume that the ice sheets have retreated to those points. (The time scale of this retreat doesn’t matter.) Would the contact between the water and ice be just a sheer wall thousands of feet high? Or would there be a significant slope? If there is a slope, it doesn’t seem like there could be a very large slope since ice is lighter than water, so there would be a positive buoyancy to the downslope parts.
Or since there is a positive buoyancy to ice, versus a negative one for rock, would there be a wall of ice thousands of feet high with a slight negative slope?
I would think time scale does matter, since ice flows (hence, glaciers) so unless the ice wall calved yesterday, it would be flowing outward. Some glaciers can be measured in feet per year. The base would have the most pressure and most likely oozed the most. Also, the part at the top of the cliff would be most likely to experience cracking due to temperature gradients and spall. So for the same reason that a straight rock cliff (or especially, overhang) usually does not last, neither will an ice wall. Just, it will likely much decay faster. Or, more likely, just flow back over the water again.
Here’s an interesting look at the details of ice flow in Antarctica. The bit I find most interesting is the assertion the ice flows about 3m/day. Even if a vertical cliff did not spall from the top, the bottom flowing out at 3m/day would make it less vertical in a hurry. (And 150m thick is a lot of ice.)
If the Antarctic ice sheets were to retreat to the points where they touch the bedrock that is thousands of feet under current sea level, the contact between water and ice would not necessarily be a sheer wall thousands of feet high. The actual shape of the ice-water interface would depend on several factors, including the shape of the underlying bedrock, the thickness and geometry of the ice sheet, and the properties of the water.
In general, the interface between the ice sheet and the water would likely be sloping. This is because the ice sheet would not be perfectly flat, but would have some thickness and internal geometry. Moreover, the underlying bedrock is also likely to have some variations in elevation, which would affect the shape of the ice sheet.
Additionally, the ice sheet would be subject to gravitational and buoyancy forces. Although ice is less dense than water, it still has some weight and would exert a downward force on the water beneath it. At the same time, the water would exert an upward buoyant force on the ice. The balance between these forces would determine the overall shape of the ice-water interface.
If the ice sheet were thin and had a gentle slope, the buoyant force of the water could potentially overcome the weight of the ice, resulting in a negative slope or a slight concavity to the ice-water interface. However, if the ice sheet were thick and had a steep slope, the weight of the ice would likely dominate, resulting in a positive slope or even a convex shape to the ice-water interface.
In summary, the shape of the ice-water interface in Antarctica would depend on several factors, including the thickness and geometry of the ice sheet, the shape of the underlying bedrock, and the balance between gravitational and buoyancy forces. It is likely that the interface would be sloping, rather than a sheer wall or a perfectly flat surface.
I’m thinking that the speed of flow relates to pressure - so the stuff under a thousand feet of ice is under the same pressure as if a thousand feet of water; it’s more likely to flow than up on the surface. (Which is one reason glaciers are full of cracks - it doesn’t all flow perfectly smoothly in unison)
The ice would float above a layer of water. As global warming progresses, the ice will break up and the glaciers on the land will collapse.
That all happened in Europe and America at the end of the last Ice age; the English Channel formed as a vast outburst flood when the water of a lake finally carved its way to the sea.
The difference with regards to the West Antarctic Ice Sheet is that for the majority of it, the water level is above the grounding line. So like that picture, except extend the “water level” portion for hundreds of miles.
But it is not immediately collapsing into an ice shelf. It is currently on a “lip” of land in a lot of places that falls off in both directions - increasing depth in both the landward and seaward direction. So something is preventing the entire ice sheet from becoming an ice shelf. I am wondering if it retreats - thereby increasing the depth of the water rather than decreasing it like in the diagram - what the ice front would look like when the grounding line is a thousand or so feet below the water level.
Somewhere I read that the English Channel formed something like half a million years ago. Yes, it was by glacial outburst flood, but there’ve been 20 or more Ice Ages in the past 2.5 million years. So it was not the most recent Ice Age.
It’s complicated - parts of the Weald ridge were cut through in two ice burst flood events, ~425,000 and ~225,000 years ago. But the current Channel only fully formed when Doggerland was submerged, and that was at the end of the last Ice Age. But that wasn’t an ice dam burst event, just rising sea levels, IIRC. And strictly speaking, Doggerland was more Southern North Sea, not the Channel, which existed as a bay already.
