Ice floats. That’s fortunate, because if frozen water was denser than liquid, earth would be a very different world. Ice would build up at the bottom of the sea until only a thin surface ocean would be left, perhaps only seasonal at that, affecting climate in dramatic ways. But floating ice combined with warmer temperatures can also cause glaciers to speed up. Moulins form more often and earlier, lubricating the interface between ice and land below and buoying up the ice sheet. That now seems to be happening in Greenland:
(TG Daily) — The researchers used satellite images along with new feature-recognition software to monitor nearly 1,000 lakes over a 10-year period. They discovered that as the climate warms, such catastrophic drainages are increasing in frequency, being 3.5 times more likely to occur during the warmest years than the coldest. During such drainages, about a million cubic meters of meltwater funnels to the ice sheet’s underside within a couple of days. Once there, it lubricates the ice sheet’s glide into the ocean.
The article notes that Moulins and underground channels, in moderation, can actually help restrain glaciers by allowing water underneath to flow away. But too much water at the base will inevitably do to the ice what it always does, less friction, more float. As less and less of the heavy glacier is attached to the bedrock it moves faster and faster. This opens up stress cracks in the river of ice, allowing more water to spill in and more ice to melt. The process could conceivably run away with itself and the glacier might transform into an ice-choked river. Once that happens it won’t speed up by a few percent or double the leisurely rate its moving now, the glacier could collapse and its icy remains dribble into the sea in the space of a few years.