AN OVERVIEW OF MARTIAN SMALL VOLCANIC VENTS AND VENT FIELDS

The volcanic plains of Mars have long been thought to be the product of “plains volcanism” similar to that observed within the Snake River Plains (SRP), Idaho, on Earth. As noted by many authors, the martian plains include the typical plains-style vents features, including fissure eruptions, flow fields, low shields, lava tubes and channels. Some martian regions, such as Tempe Terra, were frequently mentioned as examples of plains volcanism following the Viking Missions. However, typical plains volcanism features are often of relatively modest sizes and subtle relief, it so was not until the recent missions—particularly Mars Global Surveyor (MGS) and Mars Odyssey (MO) that we had sufficient widespread high resolution topographic and image data to map and characterize these smaller vents and associated features is much detail. For example, with Viking image resolutions of ~200 m/pixel, only half a dozen small shield volcanoes were indicated on Syria Planum; The addition of MOLA topography alone allowed mapping of >125 small shields within the same region, and THEMIS data is increasing the total still more as images continue to roll in. A 1-2 orders of magnitude increase in the number of detectable small shields (or lava flows, linear vents, etc…) is common for many regions, and there are additional regions where we can now easily map small volcanic features where we had little or no evidence of their presence previously. Additionally, we are now able to consider regional and global properties—such as the latitude dependence of several shield attributes (e.g. flank slope, summit crater size) proposed several years ago, or the potential interplay between lava and volatiles suggested by possible rootless cones observed in Elysium Planitia and other locations. This newfound abundance of small vents and associated features is allowing new approaches in research techniques that are also applicable to terrestrial fields, increasing the productivity of both research areas. Given the greater observed extent, larger variety, potentially younger ages, and possible water interactions of small volcanic vents, vent fields, and associated features, the impetus for understanding both Martian plains volcanism and its interactions with water have grown significantly.