Bulmer, Mark Howard; (1994) Small volcanic edifices in the plains of Venus: With particular reference to the evolution of scalloped margin domes. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Magellan images show that small volcanoes (< 20 km in diameter) are ubiquitous in the plains of Venus. Three categories are identified: shields, cones and domes. Shields and cones are thought to have been formed by lavas with basaltic rheology. The domes indicate magmas with higher viscosities at the time of emplacement. Small volcanoes often occur in fields similar to those on Earth such as Springerville, in Arizona and fields associated with mid-oceanic ridges. Edifices with scalloped margins are noted to be similar to volcanic domes and fall within a spectrum ranging from unmodified to remnant forms. An extensive database has been compiled from a global survey of volcanic domes on Venus. Over 320 domes have been located of which more than 80% have modified morphologies. Broadly, the modified domes can be described by five sub-categories which are related to three unmodified dome sub-categories. Many modified domes have deposits associated with them that possess characteristics indicative of their having been formed from mass movements. Four morphological sub-categories of debris deposit have been recognised. Data on the debris aprons is compared with mass movements on the Earth, the Moon and Mars. Debris masses on Venus show a tendency to travel further for a given vertical drop and cover greater areas for a given travel distance than mass movements on the Earth, the Moon and Mars. Slope failures on venusian domes appear to have been triggered by explosive and non-explosive events. The deposits in group three are analogous to terrestrial pyroclastic flows and the deposits in groups one and two are analogous to volcanic debris avalanche deposits on Earth. The characteristics of the fourth group of deposits are similar to those resulting from deep-seated slides on Earth. Two models of debris transport provide the most reasonable explanation for the characteristics of large debris masses on Venus.

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