Description

From Jicha and Singer, 2006 ^[1] : Moundhill is a postglacial monogenetic cone. "Its southeastern flank is built upon 15-20 m of andesitic lavas of unknown age, but the remainder of the cone rises from sea level up to 590 m. The entire cone is composed of numerous 1-3-m-thick, sheet-like, chemically monotonous basalt flows (mvl) distinguished by unusuallylarge (up to 0.7 cm) and abundant plagioclase (40 modal %), clinopyroxene (9%), and olivine (6%) phenocrysts in a glassy matrix. Each flow exhibits pahoehoe structure and extends from near the summit crater all the way to the coast. Levees on several flows descending from the west side of the crater suggest that the inital flow direction was westward, but then shifted to the north or south around the flanks of the stratovolcano. It is possible that the entire cone formed during a single, long-lasting eruption. Several attempts to obtain 40Ar/39Ar ages from Moundhill volcano lavas were unsuccessful due to very low radiogeneic 40AR* yields.