Ice that flows
How Do Glaciers Move?
Pile ice deep enough and it stops behaving like a solid — it creeps downhill.
-
Step 1 of 5
It starts where snow does not melt.
In cold high places more snow falls each winter than melts each summer. The surplus accumulates year after year for centuries.
-
Step 2 of 5
Weight squeezes it into solid ice.
Fresh snow is 90 percent air. Buried under more snow, it compacts, air is driven out, and it becomes dense blue glacier ice.
-
Step 3 of 5
Thick ice deforms under its own weight.
Above roughly 50 metres deep, ice crystals slide over each other rather than holding rigid. The ice starts behaving like extremely thick treacle.
-
Step 4 of 5
Meltwater underneath lets it slide.
Pressure and friction melt a thin film at the base. The glacier then slides on its own meltwater, sometimes faster than it deforms.
-
Step 5 of 5
It bulldozes the landscape as it goes.
The ice drags embedded rock across bedrock, grinding U-shaped valleys, and dumps its load at the end as heaps called moraines.
Most glaciers move under a metre a day, but some Greenland outlets manage over 30 — visibly, if you watch closely.
The short version
Piled deep enough, ice deforms and slides downhill, carving U-shaped valleys as it travels.
Try it yourself
Squeeze a handful of loose snow into a hard ball. You have just done in seconds what a glacier does over centuries.
Topics