New Eddystone Rock

Geology

During the last ice age, Southeast Alaska was covered by a thick ice sheet. The weight of the ice pressed down and compressed the underlying crust, including the area that is now Behm Canal. As the ice melted at the beginning of the current interglacial period, this weight was reduced. The Earth's crust responded by flexing upward, a process known as isostatic rebound. This movement broke the rock and created a New Eddystone volcano that erupted 15,000 to 13,800 years ago.

The volcano rises from the bottom of Behm Canal, about 850 ft below sea level. The island stands to 237 ft above sea level, giving the volcano a total height of over 1000 ft. While the portion of the volcano below sea level is somewhat cone-shaped, wave action over the millennia has eroded all the rock above sea level except the dense, spire-shaped volcanic plug.

Bathymetric studies of the floor of Behm Canal show that New Eddystone was not the only volcano that emerged as the crust buckled. Four other vents have been identified. Two are dome-shaped, suggesting that they erupted below the glacial ice sheet and were rounded off as the ice flowed over them. The other two, and New Eddystone Rock, are more pointed showing that they had never been overridden by ice. Of the five identified volcanic vents in Behm Canal, only New Eddystone Rock rises above sea level.

The tidal range in Behm canal exceeds 20 ft. Since much of New Eddystone Rock is low-lying beach, the size of the island above the water varies considerably with the tides.

History

References

1. Smith, Phillip S.. (1939). "Areal Geology of Alaska". U.S. Government Printing Office.
2. (March 27, 2020). "Eastern Part of Behm Canal - NOAA Chart 17242".
3. (2019). "Sculptures in Granite". US Forest Service.
4. "12 New Alaskan Volcanoes".
5. "Tide Predictions - NOAA Tides & Currents".
6. Vancouver, George. (1798). "A Voyage of Discovery to the North Pacific Ocean, and Round the World". G.G. and J. Robinson ... and J. Edwards.
7. "Proclamation 4623—Misty Fiords National Monument {{!}} The American Presidency Project".
8. Udall, Morris K.. (1980-12-02). "H.R.39 - 96th Congress (1979-1980): Alaska National Interest Lands Conservation Act".