Take a minute to really look at these maps. The first time I saw maps of velocity for Greenland and Antarctica I was surprised by what I saw. You might guess that the velocity would be fastest near the ice margins (the edge of the ice where it meets the ocean) and progressively slower towards the middle of the ice sheet. This is sort of the case, but there is a lot of variability. Do you notice the very fast flowing areas that resemble streams within the ice, almost like veins? Fittingly, glaciologists call these “ice streams”. Some of these streams start very far in the interior (near the middle of the ice sheet). While it’s all ice, these streaming areas move orders of magnitude faster than ice adjacent to the streams. Remember, you can see these streams when looking at a velocity map, however if you just look at a picture of an ice sheet from space (see below), you can’t really identify where the ice is moving fast and slow.
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