December 5, 2010 - Dust storm off the coast of Alaska

Dust storm off the coast of Alaska

Broad ribbons of dust as well as a plume of near-century-old volcanic ash fill the sky as strong winds blow across the Alaska Peninsula and Kodiak Island, Alaska. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite passed over the region on November 29, 2010, capturing this complex true-color image.

The dust in this image appears very light tan as blows from the Alaska Peninsula toward the southeast. The suspended particles are most likely “glacial flour” - fine-grained, silt-sized particles of rock created by grinding of bedrock by glacial erosion or by the destruction of rock by freeze-and-thaw action. These particles are typically quartz or feldspar, not dirt or clay, and can be carried great distances when the wind is strong.

Glacial flour is also easily suspended in water, often turning rivers a milky color. When the sediment flows into bays or seas, it may turn the waters gray, light tan, iridescent blue-green or a milky white. Extensive flows of glacial flour may form distinct layers of different colors as sediment settles, resulting in a change of light reflectance. In this image, the Nushagak River (upper left corner) appears milky white. Flowing into Nushagak Bay, the silt-laden waters turn tan, then iridescent blue-green as the sediment settles and is carried into the Bering Sea. Patches of airborne sediment also discolors the waters of the Shelikof Strait (between the Alaska Peninsula and Kodiak Island) as well as the Gulf of Alaska.

On November 29, the Anchorage Volcanic Ash Advisory Center reported that strong winds in the Katmai area picked up loose ash deposited during the 1912 eruption and carried it southeast over Kodiak Island. This large ash cloud can be seen near the center of the image as a milky-tan plume arising from the snow-covered mountain range. Katmai is a large stratovolcano whose 1912 eruption was the largest volcanic eruption in the 20th century – ten times the size of the 1980 Mt. St. Helens event. Despite the ash, the volcanic alert level remains at “normal” and the flight aviation code color remained at green, indicating low risk of new volcanic activity from Katmai.

Image Facts
Satellite: Aqua
Date Acquired: 11/29/2010
Resolutions: 1km ( B), 500m ( B), 250m ( B)
Bands Used: 1,4,3
Image Credit: Jeff Schmaltz, MODIS Land Rapid Response Team, NASA GSFC