Earthshots: Satellite Images of Environmental Change

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» Verdi Ice Shelf, Antarctica

Ice shelves surround about three-fourths of Antarctica’s coastline. These floating extensions of glaciers play an important role in stabilizing Antarctica’s mass balance of ice. Ice shelves both grow and shrink. They gain mass from the glaciers that flow into them over land, from snowfall, and from sea water freezing underneath them. They lose mass by calving icebergs or melting from below.

Icebergs regularly break off the ends of ice shelves, but ice shelves can collapse—and this can happen quickly. For example, a large portion of the Larsen B ice shelf, located on the Antarctic Peninsula, collapsed in 2002. Over the course of about one month, 3,250 square kilometers of the ice shelf collapsed. The remains of the ice shelf are weakening.

An ice shelf collapse can make the glaciers that flow into them more unstable, making them flow faster and recede faster. As glaciers accelerate and recede, more ice ends up in the ocean, contributing to sea level rise.

A relatively small ice shelf named Verdi, also located on the Antarctic Peninsula, is showing signs of instability. The rapid development of the rifts seen in these Landsat images suggests that it may be on the verge of collapse.

(Black stripes run through some of the images because of the Scan Line Corrector failure on Landsat 7 in May 2003.)

Map of the featured area.

Ice shelves act as doorstops. They hold back the glaciers that flow to the ocean and slow them down. Even small ice shelves like Verdi help regulate the volume of ice that glaciers deposit into the ocean.

Evidence of ice shelf instability can be seen in Landsat imagery. As ice shelves become thinner, rifts can form in the ice, a sign of structural weakening. In these images of Verdi, the rifts range in length from 2 to 4 kilometers. The entire shelf width is only about 10 kilometers. Landsat 8 can monitor Antarctic ice shelves with enough frequency to see if these rifts expand. The size of these rifts along with their rapid development suggests that Verdi is becoming increasingly unstable.

Another characteristic of thinning seen in Verdi is ice front retreat: the result of this retreat is the front boundary of the shelf bows inward toward the center. The Verdi ice front retreated 1.5–2 kilometers from 1973 to 2001. It retreated another 2 kilometers by 2014.

All of this evidence points to the real possibility of Verdi collapsing. This does not mean that it will happen right away, but scientists suggest that it could happen in the next decade.


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