A broad plume of dust rose from the Copper River in Alaska in early December, 2012 and blew hundreds of kilometers southward over the Gulf of Alaska. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite captured this stunning true-color image of the event at 2105 UTC (12:50 p.m. local time) on December 3, a day that was sunny, cold and windy. Temperatures in nearby Anchorage topped out at 12°F, and the low hit -5°F, with winds gusting up to 18 mph. Sustained winds and gusts in the Copper River basin – a channel that is prone to high winds - were likely much higher.
The Copper River rises from the Copper Glacier, located well inland atop Mount Wrangell in the Wrangell Mountains. The river winds through steep, glacier-carved terrain for approximately 287 miles (462 km) before reaching the broad delta at the Gulf of Alaska, and drops an average of 12 feet per mile (2.3 m/km) over that extent.
The Copper River is choked with silt and lined with sand, most of which was created from the heavy glaciers grinding rock into sediment, sand and gravel. This sediment washes into the rivers, and is either carried into the ocean or deposited on the river bank. In some places, sand has accumulated into broad fields of dunes along the Copper River. When the river runs low and the winds blow fast, the deposited sediment is lofted into the air in great quantities, and the plumes of dust can be carried far over the Gulf of Alaska.