From Miller and others (1998): "Mount Wrangell is a large
andesitic shield volcano with a volume of about 900 cubic kilometers (Nye, 1983). Its top is capped by a 4 by 6 km, ice-filled summit
caldera whose depth may exceed 1 km (Benson and Motyka, 1979). The caldera is apparently of non-explosive origin (Richter and others, 1984) formed in response to the withdrawal of
magma from high-level reservoirs beneath the summit area. Three small (<1 km in diameter) post-caldera craters, all geothermally active, occur along the west and north margin of the caldera. Mt. Zanetti (3965 m) a large (450 m high) steep-sided, relatively undissected cinder-
spatter cone occurs high on the northwest flank of the shield and may be the source of some
lava flows. Lavas on the southwest flank have flowed as much as 58 km from their source despite being
phenocryst-rich andesite, a mobility attributed to a very high eruption rate (Nye, 1983)."