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P. Schenk (LPI, Houston), H Hargitai (Eotvos Lorand Tudoman., Budapest)
Mountain formation on Io is almost certainly related to volcanism or crustal recycling. To understand and constrain models for mountain formation we have surveyed all Voyager and Galileo (G1-G8) images of Io, including limb, terminator and stereo images, to map mountain locations and characterize mountain morphology. Nearly 100 distinct mountainous structures were mapped on Io (although ~20 of these may be outliers of layered plains deposits). Most can be classified as one of 4 major types, plateaus, mesas, ridges, and massifs. The highest, Boosaule Montes, rises 14-16 km. Up to 30 erosion or mass wasting, 20 deposits. Mountains are not uniformly distributed. Although they might be random, at least two concentrations are apparent: at roughly 20N, 45W and 20S, 225W. These concentrations are approx. antipodal to each other, but they are also offset from the sub- and anti-Jovian hemispheres. They may also be 90 deg. offset from the two regions with the greatest concentrations of volcanic centers on Io. The terrain with fewest mountains is within Colchis Regio, a region of smooth bright plains. The morphology and distribution of mountains suggests there may be several mechanisms responsible for their formation and that volcanic activity and mountain formation may be anticorrelated. The morphology of mountains and volcanism is not uniform across the surface of Io, however, and we have not yet taken this into account. (schenk@lpi3.jsc.nasa.gov)