Volcán Tolimán is a large andesitic stratovolcano that rises above the S shore of Lake Atitlán. Tolimán was constructed within the Pleistocene Atitlán III caldera, near its inferred southern margin. A shallow elliptical crater truncates the summit, and a minor subsidiary peak to the SSW also has a shallow crater. In contrast to the tephra-covered surface of its twin volcano to the S, Volcán Atitlán, the surface is draped by prominent thick lava flows. Many of the flows were erupted from vents on the flanks and form a highly irregular shoreline on the S side of Lake Atitlán. No historical eruptions are known. However, a lava flow that entered Lake Atitlán from the parasitic lava dome of Cerro de Oro on the N flank was considered by Newhall et al. (1987) to be less than a few thousand years old based on the thickness of sediment accumulated on the sublacustral part of the flow.