The Earth Story

Malaspina Glacier Malaspina Glacier in southeastern Alaska is the quintessential illustration of a piedmont glacier. In fact, it is the world’s largest piedmont glacier — almost 65 kilometers wide and up to 45 kilometers long from the mountains to the edge of the sea. Piedmont glaciers are wide and bulb-shaped lobes that form when moving glaciers confined by mountain valleys spread out into a broad, flat plain. 

Malaspina Glacier

You know when you’re making pancakes, you take a bit of pancake batter, pour it onto a griddle of some sort, the batter all falls in one spot, but as soon as its unconstrained it spreads out into a circle? You’re basically looking at a 3900 square kilometer version of that. Made of ice.

This is the Malaspina Glacier, currently considered to be the largest piedmont glacier on Earth. Glaciers in mountains commonly find themselves weaving and winding their way through valleys, often following the same routes rivers cut into the ranges when temperatures were higher. The Malaspina glacier starts its life as part of an icefield in the Wrangell-St. Elias Mountains, seen in the upper portion of this image. The ice from that field has found a crack through the mountains it can flow through, creating a tongue of ice that flows downhill called the Seward Glacier.

The glacier remains basically a classic valley glacier, forming moraines on both sides, until it runs out of mountain. Once the ice reaches the coastal plain, it is suddenly unconstrained and spreads out over the entire surrounding area. This pattern of ice spreading out over a wide area after being fed by a valley glacier occurs in several frozen areas worldwide and is given the name “piedmont glacier”.

Perhaps the most visibly interesting part of the Malaspina Glacier is the former lateral moraines – piles of dirt and rock that accumulate on the edges of glaciers moving through a valley. As the Malaspina spreads out, the ice moves chaotically, with different areas surging forward depending on local conditions. This motion has twisted and bent the formerly straight lateral moraines into highly sinuous arcs along the glacier edge.

Many Alaskan valley glaciers including the Malaspina have proven particularly unstable when faced with a warming climate. Previous measurements using lasers to measure the upper surface of the glacier have found that it is thinning by about a meter per year, with rates even greater than that observed during heat wave years. Based on those measurements it has been estimated that melting of glaciers in Alaska could contribute up to 10% of the currently measured sea level rise, with the Malaspina representing a substantial fraction of that amount. Alaska has been locked in a heat wave for more than a year now, so although we don’t have numbers for this year, it would be surprising if this glacier hasn’t continued rapidly thinning this year.

-JBB

Image credit: Astronaut Jeff Williams http://bit.ly/2663GBf

References: http://science.sciencemag.org/content/297/5580/382 http://earthobservatory.nasa.gov/IOTD/view.php?id=3421 https://nsidc.org/cryosphere/glaciers/gallery/piedmont.html http://earthobservatory.nasa.gov/IOTD/view.php?id=86767

Malaspina Glacier

Malaspina Glacier in southeastern Alaska is the quintessential illustration of a piedmont glacier. In fact, it is the world’s largest piedmont glacier — almost 65 kilometers wide and up to 45 kilometers long from the mountains to the edge of the sea. Piedmont glaciers are wide and bulb-shaped lobes that form when moving glaciers confined by mountain valleys spread out into a broad, flat plain. Malaspina Glacier was formed from the fusion of two valley glaciers — Agassiz Glacier on the left of the image and Seward Glacier from the right. To obtain this perspective view image of Malaspina Glacier, the scientists on the Shuttle Radar Topography Mission (SRTM) developed an elevation model and combined it with a Landsat satellite image. Shifting glaciers — how much glacial ice and snow accumulate or melt in a given period of time — are delicate barometers for global climate change. Observing glacial change is a task best suited from an aerial perspective, and since 1972, Landsat imaging has been the premier means for such a task.

-DC

Photo credit: http://1.usa.gov/1LOVBJF More reading: http://bit.ly/1KBbqn5 http://bit.ly/1G0xUFW