Volcanism and tectonism are the dominant geologic processes on Venus. This Magellan 3-D view shows two large volcanic calderas (lower right) on the southern margin of Ovda Regio in the Aphrodite Terra highlands. The largest of these calderas measures 80 × 45 kilometers and is roughly 1.5 kilometers deep. Like most calderas, these probably formed when magma chambers were partially emptied during volcanic eruptions. The roofs of the chambers then sagged downward to fill the void, forming one or more concentric ring faults. Ring faults are clearly preserved in these calderas due to the lack of extensive erosion on Venus.
West of these calderas is a patch of tessera (upper left), a highly fractured terrain type frequently observed on Venus. Tessera is one of the oldest terrain types observed on Venus and formed as a result of complex tectonic forces. The parallel and cross-cutting valleys and ridges formed during periods of extension and compression in the crust of Venus. The dark smooth areas within and near the tessera are volcanic plains that have partially flooded the older tessera.