Most glaciers have friction points that keep the ice from sliding down too fast, to resist the enormous pressure of the built up ice sheets flowing downward fro

Most glaciers have friction points that keep the ice from sliding down too fast, to resist the enormous pressure of the built up ice sheets flowing downward from higher up. A typical glacier might be more narrow than it is long so the sides will be a source of friction. The ice will usually be in contact with the ground beneath it, causing even more friction. And there will frequently be islands or undersea ridges that can cause floating ice sheets to back up and keep the glacier from moving forward. The worry is that in some cases melting glaciers may be released from these friction points causing an accelerated movement and rapid calving at the ice front. This will cause an even faster increase in sea level on top of the gradual thermal ocean expansion and freshwater runoff of meting ice that we are already experiencing. An example of this is the Larson ice shelves on the Antarctic Peninsula that have had a series of collapses already. But luckily the Larson ice shelves do not have a huge sheet of ice behind them since the peninsula is rather narrow. Thwaites Glacier has been identified as a potential "perfect storm" for global warming caused sea level rise. It has a wide (90-100 mile) ice front and and there is no narrowing or potential bottle-neck from side to side. It has an enormous ice mass behind it reaching to the center of West Antarctica. The main friction point currently holding it back is the grounding line where the ice meets the sea floor. Between current grounding line and the center of West Antarctica there only seems to be one other ridge, known as the "Ghost Ridge" which is one of the subjects of the current expedition to determine if it is a true bedrock ridge or just silt and sediment deposited by the glacier. If the basin does in fact extend all the way back, the concern is that warm ocean water can work it's way under the ice and cause melting from below. As the ice melts it will float allow more water underneath. Meanwhile the ice front will calve and expose an even steeper front that will become unstable due to the height of the ice front. The icebergs will be washed out with the tide causing the process to continue. Here is the most recent talk by Richard Alley I've found on the subject: https://www.youtube.com/watch?v=WE9Gqy8Yy9w https://www.youtube.com/watch?v=WE9Gqy8Yy9w