Lake-Filled Volcanic Calderas of Titan

The methane lakes north of 70°N latitude on Titan occur in two types of depressions. Some lakes have crudely circular to irregular outlines but no visible bounding topography. More interpretable and interesting are the lakes inside depressions that appear to have rims. In some cases a nearly circular radar-dark (smooth) lake is surrounded by a bright (rough) rim; these features could be volcanic or impact craters filled with liquid. It is likely they are volcanic because of their spatial association with the features described next. Many other lakes are within nested bright rims (oval to irregular) that look strikingly like multi-stage collapse calderas. Some have one or more smaller collapse pits within a larger older caldera. Such multi-phase collapse calderas are common on volcanoes on Venus, Earth, Mars and Io. On all of these worlds calderas occur on the summits of low slope shield volcanoes formed by millions of fluid lava flows erupted from central vent areas. On Earth, large shield volcanoes - such as make up the Hawaiian Islands - form over long-lasting hotspots that generate magma by mantle melting. The magma rises diapirically from the mantle to a near surface reservoir that the overlying volcanic mountain collapses into (forming the caldera) following predominantly effusive eruptions that partially drain the reservoir. Hotspot volcanism also has been proposed as the mechanism of formation for caldera-bearing shields on Venus, Mars and Io. The concentration of dozens of possible caldera volcanoes in this northern region of Titan suggests the existence of an extensive hot spot region of heat loss. This differs from the other 8% of Titan so far imaged by radar where volcanic features are infrequent and relatively isolated. We gratefully acknowledge funding from NASA.