Mono Craters, California: A New Interpretation of the Eruptive Sequence

Abstract

Recent geologic studies of the Mono Craters in eastern California revealed two types of domal land forms not described in previous investigations: cratered domes and double craters. A pumiceous rhyolite dome in the northern part of the Mono Craters is an example of a cratered dome. This dome has a truncated cone shape and is composed of a funnel-structured rhyolite plug surrounded by a steep talus slope. The summit crater was formed by collapse and explosions. An example of a double crater is West Control Crater (910 m in diameter), which is composed of two funnel-structured pumiceous rhyolite domes, one within the summit crater of the other. Both domes are surrounded by debris and have truncated cone shapes. A four-stage eruptive sequence which includes these two morphologies is: (1) formation of a bowl-shaped rhyolite crater by explosive eruptions, (2) extrusion of a dome of viscous flow-banded rhyolite on the crater floor, (3) formation of a cratered dome by explosion and (or) collapse, and (4) extrusion of a dome in the summit crater of the cratered dome; this dome is cratered, forming a double crater. Flows form during stages 2 and 4 of the sequence. The sequence can be terminated at any stage.