# How do Glaciers move?

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How do Glaciers move?

In: Physics

For the most part, they move simply by growing. As they get bigger, they expand further and further away from the polls, causing their farthest edge to move.

My understanding is they don’t move so much as grow. As more ice is formed at the origin, the older ice at the edges get shoved away from it.

Downhill.

Yep, that’s it. The glacier grows when more water falls onto it. It’s huge weight presses down against the uneven mountain under it. Since the hill is inclined, the glacier slips downhill until it gets low enough to melt or it cracks and falls into the ocean (= icebergs).

The forces involved are huge, and if you press hard on ice it crumbles. The bottom edge crumbles and melts and that lubricates the downhill sliding motion.

Ice isn’t perfectly solid. While a small ice cube seems solid enough, large amounts of ice will deform and flow under their own weight. Think about pudding: a small blob in a dish will hold its shape, but if you try to build a five-foot-tall pudding pyramid it’ll just collapse and flow out over the tabletop. Ice is like that, but a little stronger, somewhere between pudding and steel.

Other posters here have suggested that glaciers move because they’re growing, and stop moving when they recede. This isn’t quite right. Glaciers have an “accumulation zone”, typically at the top of the mountain, where more snow falls than melts, and an “ablation zone”, typically at low elevation, where melting is greater than snowfall. Ice builds up in the accumulation zone, and its weight causes it to flow downhill. It flows until there’s enough glacier in the ablation zone to melt all the ice that accumulated at the top of the mountain: this point, when ablation equals accumulation, is called “mass balance”.

A glacier in mass balance is *still moving*: ice is constantly being carried from accumulation to ablation zone, even though it’s not getting bigger. If climate changes and ablation becomes stronger, the toe of the glacier will retreat, but typically *the ice will still flowing downhill*, toward the retreating toe of the glacier.