Global Volcanism Program | Image GVP-07849
The 84,000-year-old Los Chocoyos Ash from Atitlán caldera is exposed in a quarry near San Juan Ostuncalco, west of Quetzaltenango. The white layer at the base is layer H, a plinian pumice fall unit. The rhyolitic H pumice fall is the largest currently known plinian fall deposit in Central America. Despite its relative thinness, it is preserved over the entire Guatemalan highlands. The thicker overlying unit is the pyroclastic-flow member of the Los Chocoyos. This massive unwelded pyroclastic-flow deposit is up to 200 m thick.
Photo by Bill Rose, 1974 (Michigan Technological University).