New views of Venus' unusual volcanism.

New radar images of Venus, obtained by the Magellan spacecraft, add details about a planet dominated by volcanoes and rivers of lava. While some of the features shown here resemble geologic activity on Earth, most appear unique.

The far greater atmospheric pressure on Venus can prevent volcanic gases from escaping lava and shooting into the atmosphere as a giant cloud. For example, a large lava flow deposited on the rugged uplands of Venus' Ovda region (bottom photo) may represent a volcanic eruption so powerful that on Earth it would have issued a gas cloud rivaling the one spewed out during the recent eruption of Mt. Pinatubo (SN: 7/6/91, p.7). Instead, the Venusian outburst created a thick, viscious surface flow some 140 kilometers wide and 100 kilometers long, with fingerlike lobes of lava extending in all directions from the central mass of the eruption. Researchers estimate the lava's thickness at about 200 meters. Though unusually thick for Venus, it resembles the depth of silica-rich lavas on Earth.

Each of the flower patterns dotting Venus' Atla region (top photo) reveals evidence of an individual volcano, notes James Head of Brown University in Providence, R.I. This Magelln image, depicting an area about 350 kilometers across, shows petal-shaped lava flows emanating from circular pits or linear fissures in several areas. Surface fractures and valleys crisscrossing the volcanic deposits may have formed after the eruptions.

Lacking Earth's efficient weathering processes, such as wind and rain -- which erase new surface features -- Venus suffers little erosion. Thus it preserves evidence of volcanic activity for long periods, allowing scientists to now begin investigating how the planet's volcanism may have changed over time, explains Head, a geologist on the Magellan scientific team.