Nevado del Ruiz volcano in Colombia is featured in this image photographed by an Expedition 23 crew member on the International Space Station. The large Nevado del Ruiz volcano (center) is located approximately 140 kilometers to the northwest of the capital city of Bogota and covers an area of over 200 square kilometers. Nevado del Ruiz is a stratovolcano — a type of volcano built from successive layers of lava, ash, and pyroclastic flow deposits — formed by magma generated above the boundary between the subducting Nazca and overriding South American tectonic plates. The historical record of eruptions extends back to 1570, but the most damaging eruption in recent times took place in 1985. On Nov. 13, 1985, an explosive eruption at the Arenas Crater (center) melted ice and snow at the summit of the volcano. This lead to the formation of mudflows (or lahars) that swept tens of kilometers down river valleys along the volcano’s flanks, resulting in the deaths of at least 23,000 people. Most of the fatalities occurred in the town of Armero which was completely inundated by lahars. Eruptive activity at Nevado del Ruiz may have occurred in 1994, but this is not confirmed. The volcano’s summit and upper flanks are covered by several glaciers that appear as a white mass surrounding the one-kilometer-wide Arenas Crater; meltwater from these glaciers has incised the gray to tan ash and pyroclastic flow deposits mantling the lower slopes. A well-defined lava flow is visible at lower right. This photograph was taken at approximately 7:45 a.m. local time when the sun was still fairly low above the horizon, leading to shadowing to the west of topographic high points.