How big is a glacier?

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This question is similar to asking, “How long is a piece of string?”, because the answer is: “It depends”.  Glaciers are masses of ice that flow slowly under their own weight and persist year to year, so the snow bank remnants around New England are not glaciers.  Some of the smallest glaciers I’ve seen are the size of small hills.  Some of the largest glaciers (ice sheets) are large enough to cover continents.  These ice sheets are large enough and heavy enough to weigh down the continental crust and push the land below sea level.  We know that the Laurentide Ice Sheet, which covered northern North America during the last ice age, depressed the land enough that you can find shorelines and old deltas 180 feet above present-day sea level in coastal Maine.  Think of how a waterbed or foam mattress sinks under your weight, this is similar to the crust sinking under the weight of the ice sheet.  Fancy word: Isostatic depression or isostatic rebound (rebound occurs after the ice sheet melts away and the land rises up out of the sea).

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