On September 15, 1990, the Magellan spacecraft started radar operations for its mapping mission at Venus. This image is taken from the first set of radar data collected in the normal operating mode. This Magellan radar image is part of the southern Lavinia Planitia region of Venus obtained during orbit 377. The center of the image is at 356 degrees east longitude, 68.7 degrees south latitude. The image is 30 kilometers (18 miles) wide and 70 kilometers (43 miles) long. On the basis of Arecibo data it is known that these features are located near the center of a large oval-shaped deformation structure, known as a corona, 775 kilometers (480 miles) in diameter adjacent to east-northeast trending linear features. The center of this corona is the focus of abundant lava flows extending hundreds of kilometers into the surrounding plains. The Magellan image reveals the details of this central volcanic source region. The Magellan image is characterized by an egg-shaped fault-bounded depression (center left of the image) interpreted to be a volcanic caldera, a radar-bright lobate deposit interpreted to be a volcanic flow, and multiple east-west trending bright linear structures interpreted to be fault scarps and troughs. Calderas form from the withdrawal of molten rock from a chamber below the surface and collapse of the overlying rocks. The egg-shaped caldera shows evidence of two stages of collapse. The outer boundary, which appears to have a slightly raised rim, is 8 x 10 kilometers (5 x 6 miles) in diameter; the inner boundary is 5 x 6 kilometers (3 x 4 miles) in diameter. The floor of the caldera is 4 x 6 kilometers (2.5 x 4 miles) in diameter and appears smooth. The part of the bright lava flow seen in this image (just south of the caldera) is 30 kilometers (18 miles) long and 2-12 kilometers (1.25-7.5 miles) wide. Various features often associated with lava flows are observed. Features resembling raised levees are observed along the edges of the flow in the western part of the image. Lobate extensions of the flow are observed in a direction towards the caldera. A variety of cross-cutting relationships of linear structures and the flow are observed. On Earth, such linear features are often the sources of flows. The linear feature north of the caldera extends across the width of the image, is approximately 2 kilometers (1.25 miles) wide, and appears to be a trough that tapers to the east. The linear features to the south of the caldera extend from 13 to at least 30 kilometers (8-18 miles) across the image and are 1-2 kilometers (.62-1.24 mile) wide. These features may represent fault scarps or troughs, and are likely associated with the movement of subsurface magma and the formation of the large corona in which these features occur.
