New Eddystone Rock

July 19, 2022


Photographer: John and Ruth Mauel

Summary Author: John and Ruth Mauel

There are many volcanic plugs in the world, of which some are quite spectacular, and many of them in clusters or fields. Shown above is New Eddystone rock located in the Behm Channel, east of Ketchikan, Alaska. This eye-catching landform within the Misty Fjords National Monument is geologically and historically unusual.

Named by Captain George Vancouver in 1793 after a lighthouse near Plymouth, England, 'New' Eddystone rock is the neck of a volcano that erupted approximately 15,000 years ago. Energy from the eruption passed through the ice that carved the steep-sided fjords of the area. The magma erupted near a seam between the granites and gneisses of the Coastal Range Batholith and the Taku terranes. Surrounding rocks were weakened by the isostatic rebound caused by the receding of the ice sheet. Several similar plugs that erupted around the same time, have been eroded and remain below sea level. This difference in form could suggest they were scraped flat by the glaciers.  Studies have also shown these structures are strongly associated with numerous smaller flows and volcanic activity as far east as Mount Edziza in British Columbia.

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