Nevado del Ruiz, a broad, glacier-covered stratovolcano in Colombia, South America, most known for its eruption in 1985 that killed ~25,000 people, has seen recent volcanic activity over the past few weeks. INGEOMINAS, the Colombian goelogical survey is heavily monitoring the volcano in the case of a future eruption. Since March 27th, there have been tremors associated with fluid motion (likely magma), seismic activity and rock fracturing, as well as earthquakes and high SO2 emissions. Above is an image of a small steam plume from the volcano as seen on March 27, 2012. Image from INGEOMINAS Colombia.
The major hazard from Ruiz is the lahars. Melting of the summit icecap during historical eruptions has resulted in ash and other volcanic material mixing with the melted snow and ice at the summit of the volcano, creating devastating lahars. The survey has published a volcanic hazard map that indicates the areas that are at the highest risk of being threatened by volcanic activity, mainly lahars and pyroclastic flows in the case of Ruiz. Left is an image of the volcano's crater seen on March 8, 2012 when scientists flew over the volcano and saw intense steaming from the main crater. Image from INGEOMINAS Colombia.