This Magellan image, centered at 10 degrees north latitude, 188 east longitude shows the volcano Sapas Mons located in the broad equatorial rise known as Atla Regio (8 degrees north latitude, 188 degrees east longitude). Sapas Mons is about 400 kilometers (250 miles) across and rises 1.5 kilometers (0.9 miles) above the local terrain. It is about 4.5 km above the mean planetary radius. The flanks of the volcano are composed of numerous overlapping lava flows. The dark flows on the lower right are thought to be smoother than the brighter flows near the central part of the volcano. Many of the flows appear to have erupted along the flanks of the volcano, rather than from the summit. This type of flank eruption is common on large volcanoes on the Earth, such as the Hawaiian volcanoes. The summit area consists of a pair of flat-topped mesas, whose smooth tops give a relatively dark appearance in the radar image. Also seen near the summit are groups of pits, some as large as 1 kilometer (0.6 miles) across. These are thought to have formed when underground chambers of magma were drained through other subsurface tubes, leading to a collapse at the surface. A 20-kilometer (12.5-mile) diameter impact crater northeast of the volcano is partially buried by the lava flows. Little was known about the Atla Regio rise prior to Magellan. The new data, taken in February 1991, show the region to be composed of at least five large volcanic edifices such as Sapas Mons, which are commonly linked by complex systems of fractures or rift zones. By analogy with similar features on the Earth, Atla Regio is thought to result from upwellings of large volumes of molten rock from the interior of Venus known as "hot spots."
