This is scientific American 62nd Science. I'm Julia Rosen. Got a minute?

The world's mountain glaciers contain just 1% of all the ice on Earth, but their rapid melting accounts for about a third of recent

sea level rise. Most of these glaciers that start and end on land shrink away through gradual

surface melting, but others, known as Tidewater Glaciers, flow out into the sea.

And by calving off massive icebergs, these glaciers can collapse in the blink of an eye,

geologically speaking.

For example, the Columbia Glacier in Alaska's Chugach Mountains

is a Tidewater Glacier that once filled a long fjord. It's retreated 12 miles in just the last 25 years.

So this tiny little glacier in Alaska

is capable of producing 1% of the sea level rise budget.

And so we know that individual calving glaciers can do crazy things and can act really dramatically and can have this rapid response.

Shad O'Neill, a glaciologist with the U.S. Geological Survey and Anchorage, and co-author of a new study in the journal Geophysical

research letters. Scientists thought that Tidewater Glaciers, because of their unstable behavior,

might be an important source of the torrent of

meltwater flowing out of Alaska and northwest Canada where ice has been

disappearing at especially alarming rates. But all mountain glaciers,

Tidewater and Otherwise,

are notoriously hard to quantify.

So O'Neill and his colleagues

undertook the daunting task of assessing the health

of every glacier in the region.

Using data collected from airplanes, they tracked how the masses of 116 glaciers making

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