One glacier, two glacier, fast glacier, blue glacier

Oneof the tricky bits about glaciology is distinguishing between different ice features. There’s the question of terminology, such as figuring out when an icefield (a large mass of glacial ice, often with many glaciers flowing out of it) becomes an ice cap (same thing, but larger and tending to be dome-shaped) becomes an ice sheet (like an ice cap, but over 50,000 square kilometers.) Today my dad (happy Father’s Day!) alerted me to an article in the Anchorage Daily News discussing the difficulties of counting glaciers.

Glaciers, like rivers and streams, often flow into each other or split apart. Exactly when one glacier becomes two glaciers can be a tricky thing to determine, and now that so many glaciers are retreating, these points of merging or splitting may disappear altogether. So what was one glacier with three branches might become three glaciers. For instance, in the photo below you can see how several tributaries merge into a single calving front at Columbia Glacier.

Columbia Glacier in 2004

Columbia Glacier in 2004. Photo by W. Tad Pfeffer.

(I got this photo from Wikimedia Commons.)

And here’s an amazing timelapse video from the Extreme Ice Survey (I’ve seen it shown at a lot of glaciologist meetings and conferences) that shows how the front of Columbia Glacier retreats back until the several “tributaries” start to look like separate glaciers again. It goes so far and so fast they have to move their camera several times so that the front of the glacier stays in the frame.

Of course, for many purposes, the important thing is not how many glaciers there are, but how much ice there is in the glaciers. Although there’s not very much water stored in mountain glaciers like these compared to the water stored in the great ice sheets of Antarctica and Greenland, the mountain glaciers are melting extremely quickly (well, quickly by glacial standards) so a major percentage of current sea level rise is due to meltwater from glaciers like the Columbia. You can’t tell how thick a glacier is just by looking, so determining the volume of the world’s glaciers—and just how fast that volume is changing—is one of the important ongoing problems in glaciology.

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2 Responses to “One glacier, two glacier, fast glacier, blue glacier”

  1. Teri Says:

    Check the Quarrier for the re-post of this.

  2. mspelto Says:

    The recent retreat of Brady Glacier in Alaska illustrates this well. So many termini radiating from this glacier, creating new and expanding lakes.

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