Planetology

On the Cover: Space shuttle astronauts took this optical photo of Russia's Kliuchevskoi volcano in the early hours of its eruption on September 30, 1994. The ash plume, which reached a height of more than 18 kilometers (about 11 miles), is emerging from a vent on the north flank of Kliuchevskoi, which is partially hiddenin this view by the plume and its shadow. The small, whitish steam plume near the photo's center is emanating from the dome of a companion volcano, Bezymianny. This is part of a sequence of photos that first allowed scientists to image through ash and cloud. To see a radar version of this photo, go to <i><a href="http://jpl.nasa.gov/radar/sircxsar/kliucomp.html">jpl.nasa.gov/radar/sircxsar/kliucomp.html</a></i>.