Nevado del Ruiz is a stratovolcano. Its summit elevation reaches 5,321 meters (17,457 feet), and covers 200 square km in Colombia. Its structure consists of andesitic and dacitic lavas, as well as andestic pyroclastics. Its modern cone includes a broad cluster of lava domes and calderas. At its summit sits its main crater, the Arenas crater, which is 1 km wide and 240 km deep. Nevado del ruiz's prominent cone is a pyroclastic cone calle La Olleta, and is located at its sw point. Although only 500 km from the equator, the uppermost portion of this volcanoe is covered with 25 square km of snow, ice, and glaciers. As a stratovolcano, is has many layers (strata) of hardened lava and tephra. Its modern cone consits of 5 lava domes: Nevado el Cisne, Alto de Laguna, la Olleta, Alto la Pirana, and Alto de Santano. Other hyrdothermic activity that goes on at Nevado del ruiz includes many hot springs and stream vents located on the volcano. The picture shown, shows the upper slopes of Nevado del Ruiz, where you can see scar paths that lahars have made form the 1985 eruption.
http://www.geology.wisc.edu/~g111/Volcanoes/Nevado_del_Ruiz/sw_10_Fx_Web.jpg Photo by Stan Williams.
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