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Dust storm off Alaska
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Dust storm off Alaska

January 1, 2011
Strong winds carried plumes of glacial sediment over the Gulf of Alaska on an early winter day, when the Moderate Resolution Spectroradiometer (MODIS) aboard the Aqua satellite passed overhead. This image was captured on December 23, 2010. On that day Valdez, a town located at the head of a deep fjord in Prince William Sound, reported maximum wind speeds of 37 miles per hour (60 km/hr) with gusts to 63 mph (101 km/hr). In this image, Prince William Sound can be seen as the large round bay on the coast.

The largest plume of light tan dust arises from the Copper River, near the center of the coastline. The Copper River is formed from the Copper Glacier, which has slowly carved a landscape of steep mountains and has created fields of fine sand from constant grinding and erosion of stone. High winds often blow through this valley lifting the glacial silt and blowing it hundreds of miles out into the Gulf of Alaska.

Copper River is just one of many glaciers fringing the coastline of Alaska, remnants of a vast icefield that was predominant during the Pleistocene age, when the climate was 3 to 9 degrees Farenheit colder than it is today.

In some areas of coastal Alaska today, winter accumulation of snow may exceed summer snowmelt, which allows for formation or expansion of glaciers. New snow layers create pressure on existing layers of snow and ice. After the first season's melt, snow becomes firn, a dense granular snow. As new snow accumulates and places pressure on firn, the compressed firn slowly becomes ice.

Glaciers often form in the highest elevations, where the temperatures remain coldest throughout the year. They slowly move downslope, carving steep valleys and move sediment of all sizes downslope. They also grind rocks into glacial silt and glacial flour - fine sediments, as the names suggest. The sediment is often left behind, and meltwater percolating through glaciers often deposits glacial flour in mud plains. When the mud plains dry out, wind easily lifts it aloft, creating the dust storms seen in this image.


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