ISS021-E-005555 (11 Oct. 2009) --- This picture of the active Soufriere Hills volcano on Montserrat Island was photographed on Oct. 11, 2009 by the Expedition 21 crew members onboard the International Space Station. Meteorologists and other scientists note that this area is nearly always cloudy so it is considered rare when astronauts get good images of the plumes or volcanic activity. Soufriere Hills is identified as a "stratovolcano" by geologists because it is built of layers (the "strato" part of the name) of both lavas and pyroclastic flows from older eruptions. Another name for this kind of volcano is a "composite volcano" referring to the fact that when it erupts it produces both lava and fragmented deposits during explosive eruptions. Scientists point out that the magma feeding the Soufriere Hills volcano is created by the subduction of local tectonic plates -- stratovolcanoes are commonly associated with this type of geologic environment. Photo credit: NASA