These images show an identical area on Venus as imaged by the U.S. NASA Magellan spacecraft in 1991 (left) and the U.S.S.R. Venera 15/16 spacecraft in the early 1980's (right). In the area seen here, approximately 200 small volcanoes, ranging in diameter from 2 to 12 kilometers (1.2 to 7.4 miles) can be identified. Volcanoes form from the buildup of cooled lavas and ash on a planetary surface. Solids, liquids, and gases can erupt from a volcano. The amount and makeup of the erupting material affects the volcano’s size and shape. Venus displays the greatest diversity of volcanic features among the rocky worlds.