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четверг, 28 февраля 2019 г.

Countdown to Calving at Antarctica’s Brunt Ice Shelf

image

Cracks growing across Antarctica’s Brunt Ice

Shelf are poised to release an iceberg with an area about twice the size of New

York City, (about 604 square miles).

It is not yet clear how the remaining ice shelf will respond following the

break, posing an uncertain future for scientific infrastructure and a human

presence on the shelf that was first established in 1955.


image


NASA

Earth Observatory
image by Joshua Stevens, using Landsat data from the U.S.

Geological Survey
. Story by

Kathryn Hansen, with image interpretation by Chris Shuman (NASA/UMBC).



The above image, from the Operational Land

Imager (OLI) on Landsat 8, shows the area on January 23, 2019. The crack along

the top of the image—the so-called Halloween crack—first appeared in late

October 2016 and continues to grow eastward from an area known as the McDonald

Ice Rumples
.

The rumples are due to the way ice flows over an underwater formation, where

the bedrock rises high enough to reach into the underside of the ice shelf.

This rocky formation impedes the flow of ice and causes pressure waves, crevasses, and rifts to

form at the surface.


The more immediate concern is the rift visible

in the center of the image. Previously stable for about 35 years, this crack

recently started accelerating northward as fast as 4 kilometers per year.


Calving is a normal part of the life cycle of ice shelves, but the recent changes are

unfamiliar in this area. The edge of the Brunt Ice Shelf has evolved slowly

since Ernest Shackleton surveyed the coast in 1915, but it has been speeding up

in the past several years.


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