Sumdum Glacier, Endicott Arm

Sumdum Glacier, Endicott Arm

by | Aug 12, 2020

Sumdum Glacier starts on the south slope of Mount Sumdum and flows southwest for 3 miles (4.8 km) to Powers Creek, 89 miles (144 km) northeast of Sitka, and 50 miles (81 km) southeast of Juneau, Alaska. The name is from the Tlingit and reportedly represents the booming sound of the icebergs as they break off from the glacier. The name was first published in 1892 by the U.S. Coast and Geodetic Survey as “Soundon”.

The glacially striated cliffs of Endicott Arm and Tracy Arm show the granite and partially metamorphosed rock associated with the Coast Range Batholith. The Coast Range Episode of mountain building began 115 million years ago when a chain of volcanic islands riding on an oceanic plate collided with the western shoreline of the continental plate in the northeast Pacific. These islands were welded to the edge of the continent by molten rock that cooled deep beneath the Earth’s surface to form the Coast Range Batholith – an enormous body of granitic rocks. This batholith is the largest such body of granitic rocks in North America. Metamorphic rocks form the western margin of the batholith throughout most of southeastern Alaska.

Ore-bearing outcrops occur in a northwest-trending belt of mineralized metamorphic rocks between Tracy Arm and Endicott Arm. The better-known mines and prospects within this belt in the vicinity of Sumdum are at Point Astley and Sanford Cove. Gold was the principal commodity sought by the early prospectors and most of the prospects were developed around 1900 or shortly thereafter. These also yielded significant quantities of silver as a byproduct. Following the heyday of gold mining in the early 1900s, there was little mining activity in the area; however, a titaniferous magnetite deposit was discovered at Port Snettisham in 1918, and a zinc-copper prospect in Tracy Arm was discovered in 1916. In 1958, a copper-zinc prospect was discovered in rugged terrain on Mount Sumdum at elevations between 2,000 feet (610 m) to 6,666 feet (2032 m). Read more here and here. Explore more of Sumdum Glacier and Powers Creek here:

About the background graphic

This ‘warming stripe’ graphic is a visual representation of the change in global temperature from 1850 (top) to 2021 (bottom). Each stripe represents the average global temperature for one year. The average temperature from 1971-2000 is set as the boundary between blue and red. The color scale goes from -0.7°C to +0.7°C. The data are from the UK Met Office HadCRUT4.6 dataset. 

Credit: Professor Ed Hawkins (University of Reading). Click here for more information about the #warmingstripes.

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