This once-in-a-lifetime spectacular image was shot from the International Space Station on June 12, 2009 and shows an early stage of one of the larger eruptions at Sarychev Volcano.
The eruption plume is composed of  brown ash and white steam. The vigorously rising plume gives the steam a bubble-like appearance; the surrounding atmosphere has been shoved up by the shock wave of the eruption. The smooth white cloud on top may be water condensation that resulted from rapid rising and cooling of the air mass above the ash column.
Caption credit: M. Justin Wilkinson, NASA-JSC.
Image credit: Expedition 20 crew, NASA's Earth Observatory
http://earthobservatory.nasa.gov/IOTD/view.php?id=38985 Eruption of Sarychev from space photo: Nasa's Earth Observatory with detailed interpretation of the above picture.