National Geographic : 1993 Feb
TECTONICS long with volcanism, tec tonics has shaped the face of Venus. On Earth tectonics involves lateral movements of crustal plates, creating the Himalaya and deep-ocean trenches (diagrams). Magellan has shown that Venus has its own, more localized style of tectonics. Both planets have vast churn ing reservoirs of hot material beneath their crusts. On Earth lava often emerges from the mantle through mid-ocean ridges, creating a new, spread ing seafloor. The seafloor subducts under the continents, generating volcanoes and de forming the continental margin. Venus also has mantle upwelling, which forms high lands such as Beta Regio. Hot spot volcanoes and coronae also form over mantle plumes. Simi lar hot spots on Earth formed the Hawaiian Island chain and are responsible for the thermal activity at Yellowstone. Upwelling can also cause the crust to rupture and spread, forming rift valleys with steep sides and sunken floors.