Roadside Geology of Alaska by Connor Cathy

Author:Connor, Cathy [Connor, Cathy]
Language: eng
Format: epub
Publisher: Mountain Press Publishing Company
Published: 2015-07-30T16:00:00+00:00

Late Pleistocene Glacial Lake Ahtna sediments in the Gakona River bluff at the Gakona Junction Roadhouse, near the confluence of the Copper and Gulkana Rivers in the northern Copper River basin.

Wrangell Lava

East of the Richardson Highway the extraordinary Wrangell volcanoes dominate the view from Glennallen and Copper Center. These Pleistocene to Holocene stratocone and shield volcanoes are built on the upland regions of the Wrangell Mountains and produced the Late Miocene to Quaternary Wrangell Lava, which is at least 6,560 feet (2,000 m) thick. The lava beds range from thin to massive. Ash to gravel-sized volcanic particles that fell from the air are also abundant. Flow rocks are mostly andesitic porphyries and are interbedded with glacial tills up to 229 feet (70 m) thick. Gravels, conglomerates, and mudflows also occur, interbedded with the lava flows, and some may have formed as volcanic mudflows, or lahars. The Chetaslina debris flow, further described in the Edgerton Highway section, is a volcanic mass-flow deposit that is an excellent example of volcanic natural hazards.

The Wrangell Lava was generated by the underthrusting of the oceanic crust along the Alaskan Gulf Coast subduction zone in Miocene time, as the Yakutat Plate approached from the south. Currently Mt. Wrangell is the only geothermally active Wrangell volcano. There are also lively mud volcanoes near Mt. Drum and north of the Glenn Highway at Tolsona, with bubbles of methane gas emanating from their mud pots. They show that geothermal anomalies are still generating heat across the basin.

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