Mt. Wrangell volcano, Alaska Photo Information Photograph by R.J. Motyka View to the west across the ice-filled summit caldera of Mt. Wrangell , which is a large shield volcano with a volume of about 900 km 3 . The 4 by 6 km caldera apparently formed when magma withdrew from reservoirs beneath the summit area and not from a violent explosive eruption. Three small post-caldera craters, all geothermally active, occur along the west and north margin of the caldera.
Mt. Drum is in the right background.
Some evidence suggests that increases in the heat flux and concomitant increases in fumarolic and phreatic activity have followed major earthquakes in south-central Alaska. Earlier reports of eruptive activity in 1784 and 1884-85 suspect.