Ice hates water. Water is more dense, it’s warmer, and it moves faster than ice. So when there is a warm day and ice on the surface of a glacier melts into a pool of water, that water is not physically stable above the ice, it must find a way down. Cracks (crevasses) and holes (moulins) in the ice allow places for water to escape down into the glacier. There have been all sorts of tests to try to ‘map out the plumbing system’ of different glaciers, including strong color dyes and rubber duckies.
Why does glacier plumbing matter?
- Water can melt the ice it is in contact with and can make ‘Swiss cheese’ out of the glacier, making it weaker and likely to break or melt apart.
- If the water only goes part way into the glacier and re-freezes, the water must expand to become ice and forces the surrounding walls apart, like being in a packed subway and then shoving away all the people around you (not a good idea). This horizontal force can cause the ice to ‘explode’ apart, forming new cracks and weaknesses.
- If the water makes it all the way to the bed of the glacier (where the ice is in contact with rocks and sediment), it can cause the glacier to slide, water makes the bed slipperier and can cause the glacier to move faster, possibly causing the glacier to melt even faster!
Can we see evidence of glacier plumbing from the last ice age?
Yes, we can! Eskers are sinuous ridges of sediment that is usually well-rounded sand and gravel, just like sediment that you can find in some rivers. Eskers are what is left from rivers or plumbing, that was on top, inside, or underneath a large ice sheet. To find an esker near you, connect the dots of sand and gravel pits on a map, you might be in luck.