Development of Large Volcanoes on Venus: Constraints from Sif, Gula, and Kunapipi Montes

Abstract

Sif, Gula, and Kunapipi Montes are large volcanoes on Venus. They have differing morphologies reflecting their different eruptive histories and plumbing systems. All have a steeper upper cone surrounded by more shallowly sloping flanks, interpreted as resulting from histories of more frequent, shorter, lower effusion rate summit eruptions accompanied by infrequent, more voluminous flank eruptions. All three volcanoes have multiple flow field types (digitate, sheet, and fan), which probably reflect variations in effusion rate, eruption duration, and vent geometry. Sif Mons' summit has a large caldera, Gula Mons has summit calderas at either end of a summit rift, and the summit of Kunapipi Mons is composed of two volcanic centers on a summit plateau. The summit morphologies of Sif, Gula, and Kunapipi Montes are interpreted to reflect differences in magma chamber location over time, and differing internal plumbing. We find no positive evidence that neutral buoyancy has governed magma chamber position. Instead, magma chambers at the three volcanoes appear to have changed position over time, with lithospheric stresses as well as neutral buoyancy affecting chamber location. All three volcanoes have had episodes of diking at their summits, followed by episodes of extrusion. We interpret this to be caused by variations in either magma supply rate or magma volatile content, or both, over time. Fractures on the flows of the volcano indicate that dike intrusion has occurred throughout the visible history of the volcanoes, indicating that the local stress field within the volcano favored intrusion as well as extrusion over much of its history. The overall shape and history of the venusian volcanoes is similar to the histories of terrestrial volcanoes. However, some aspects of these volcanoes, including the rift at Gula, the large size and very long flows, differ significantly from terrestrial volcanoes.