The wikipedia page on Ice-sheet dynamics claims that:

Ice will not flow until it has reached a thickness of 30 meters (98 ft)

And this geography website claims that

To be called a glacier, a mass of ice must be capable of motion.

Together, these two claims seem to imply that if it's not thicker than 30m, it's not a glacier. Are either of these claims correct, and do they indeed imply my conclusion?

N.B. The question arises because I've been working with some literature and databases that refer to things less than 30m thick as glaciers.

Update: looking closer at GlaThiDa, I notice that it contains 490 glaciers listed with mean_depth less than 5m. However, all of these are from a single article (Cogley, 2008) and some of them are apparently only centimeters thick. Something must be wrong with this data; I'm looking into it.


1 Answer 1


The straight answer is no. The definition of a glacier requires the body to be of ice and snow, to move and deform under its own weight. If the body is pure ice the pressure needed to make ice deform corresponds to about 30-40 m of ice pressure.

The definition makes any body not consisting of ice and snow not a glacier. As an example, so-called "saltiers" are bodies of rock salt that move like glaciers. You find such features in the southern part of Iran. They would not qualify as glaciers from the first part of the definition.

The second part says that they must move. In mountainous terrain snow packs and also thin features of ice can move because they slide downhill. Because these are too thin there is no internal definition so the third part of the definition prevents such features from being glaciers.

Hence what remains are bodies of ice and snow that have sufficient thickness to induce deformation and hence they will be of a minimum thickness.

As a glaciologist, I do not find this definition very academic. With glaciers reducing in size around the globe many glacier will, in time, pass the limit and cease to be glaciers but knowing when this happens requires physical measurements which for practical reasons (and current technology) can only be made on a very small subset of the about 160 000 glaciers (not counting the ice sheets) on the earth. It is hence of little practical use when trying to figure out when particular glaciers cease to fit the definition.

  • 1
    $\begingroup$ This definition does seem to conflict with common usage. By this definition, would we have no glaciers at all in the Sierra Nevada? On USGS topos, there are symbols that I think laypeople like me all read as being glaciers, although I see that in the USGS's key of symbols they call them symbols for "glaciers and permanent snowfields." To a mountaineer, glacier travel certainly includes travel across snow 20 m deep, because glacier travel is a certain set of techniques that are needed to avoid getting killed by falling into a crevasse, and 20 m is plenty to kill you. $\endgroup$
    – user2927
    May 22, 2015 at 4:59

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