ARC-1990-AC90-3007

This Magellan image reveals Sacajawea Patera, a large, elongate caldera located in wester Ishtar Terra on the smooth plateau of Lakshmi Planum. The image is centered at 64.5 degrees north latitude adn 337 degrees east longitude. It is approx. 420 km (252 mi.) wide at the base Sacajawea is a depression approx. 1-2 km (0.6-1.2 mi.) deep and 120 by 215 km (74 by 133 mi.) in diameter; it is elongate in a sousthwest-northeast direction. The depression is interpreted to be graben adn fault scarps. These structures are space 0.5 to 4 km (0.3 to 2.5 mi.) apart, are 0.6 to 4 km (0.4 to 2.5 mi.) in width and up to 100 km (62 mi.) in length. Extending up to 140 km (87 mi.) in length from the southeast of the patera is a system of linear structures thought to represent a flanking rift zone along which the lateral injection and eruption of magma may have occurred. A shield edifice 12 km (7 mi.) in diameter with a prominent central pit lies along the trend of one of these features. The impact crater zlata, approx. 6 km (4 mi.) in diameter is located within the zone of graben to the northwest of the patera. Few flow features are observed in association with sacajawea, possibly due to age and state of degradation of the flows. Mottled bright deposits 4 to 20 km (2.5 to 12 mi.) in width are located near the periphery and in the center of the patera floor within local topographic lows. Diffuse patches of dark material approx. 40 km (25 mi.) in width are observed southwest of the patera, superimposed on portions of the surrounding graben. The formation of sacajawea is thought to be related to the drainage and collapse of a large magma chamber. Gravitational relaxation may have caused the resultant caldera to sag, producing the numerous complex, highly deformed tessera-like terrain are located north and east of the patera and are seen in the upper portion of the image. Color has been added to this image to simulate the appearance of the Venus surface.