Monte Andrus

Three coalescing trachytic shield volcanoes with a combined volume of 252 km3 formed during the Miocene along a N-S line in the Ames Range of western Marie Byrd Land. The youngest and best exposed is Mount Andrus, the southernmost volcano, where late-stage volcanic activity resumed during the late-Pleistocene or Holocene (Gonzalez-Ferran and Gonzalez-Bonorino 1972, LeMasurier and Thomson 1990). A distinct 4.5-km-wide caldera truncates the summit of Mount Andrus. Weak fumarolic activity was observed in 1977 at Mount Kauffman, the northernmost volcano, which also has a morphologically distinct 3-km-wide summit caldera.