Mount Edgecumbe description and information

From Wood and Kienle (1990): "The Edgecumbe volcanic field on southern Kruzof Island is on the North American plate 10-15 km inboard of the Queen Charlotte-Fairweather transform fault. The Edgecumbe volcanic field is dominated by the symmetric stratovolcano of Mount Edgecumbe and the domes and crater of adjacent Crater Ridge. Mount Edgecumbe was named by Captain James Cook in 1778. Despite the fresh constructional morphology of the cone, there is no evidence for historic eruptions in Russian documents or in native oral traditions. Thus, the last certain activity of the Edgecumbe volcanic field was two minor tephra-forming eruptions between 4 and 6 ka. The basal shield comprises ~35 cubic km and consists of basalt, basaltic andesite, and andesite lava flows and breccias. The composite cone of Mount Edgecumbe is dominantly of andesite composition and has a volume of ~3.5 cubic km. The low-silica rhyolite domes of Crater Ridge also contain ~3.5 cubic km of magma.

"The latest significant eruptive activity was postglacial and produced voluminous pyroclastic deposits (7.6 cubic km dense-rock equivalent). The main geomorphic features of the Edgecumbe volcanic field were formed during this activity and include basaltic andesite scoria cones, a crater explosively reamed from the Crater Ridge domes during eruptions of rhyolitic pyroclastic flows, and eruption of andesite and dacite tephra during dome emplacement and crater formation on the Mount Edgecumbe cone. Tephra deposits produced by the late Pleistocene-early Holocene activity of the Edgecumbe volcanic field have been found as far away as Juneau and Lituya Bay, 200 km to the north. Vents active during the pyroclastic eruptions have a northeast-southwest alignment that probably marks a regional fissure."