MARTIAN POLAR VOLCANOES: CHARACTERISTICS, IMPLICATIONS FOR EFFUSIVE VS. EXPLOSIVE ERUPTIONS, AND DIFFERENTIATION FROM POLAR IMPACT CRATERS

In this study, we used high-resolution data from the Mars Orbital Laser Altimeter (MOLA) to complete a volcanism landforms survey for the Northern Polar Region of Mars and to characterize topographic differences within the region. Earlier studies of this region using MOLA data identified numerous new volcanic features. A majority of these features were not able to be resolved in pre-MOLA image data (primarily Viking Mission data) because this region is difficult to image due to the presence of dust and frost and because these features have gentle slopes. Using the high-resolution MOLA data, we measured parameters such as basal diameter and area, edifice and cavity volume, flank slope, and crater dimensions. Using these data we were able to identify several types of topographic landforms. Each landform type tends to cluster spatially within the study area.

Some of the volcanic features in the polar region appear to be similar to those of lava shields common in more equatorial latitudes of Mars. However, consistent with earlier studies, the flank slopes tend to be slightly steeper and the summit craters larger at higher latitudes. Also, in the North Polar Region, we identified types of volcanic features that are relatively uncommon or even unseen in more southerly latitudes. These features resemble more explosive terrestrial features such as cinder cones, tuff cones, and other landforms indicative of volatile-rich lava interactions.

We found that in images it is difficult to differentiate between polar volcanic cones and polar impact craters that appear to have been filled and exhumed. Therefore, we developed a preliminary method using topographic signatures to differentiate between these visually similar landforms. Topographic data suggest that the cavity volume normalized by the edifice volume is typically an order of magnitude or more larger for the impact craters than for the volcanic cones. Also, the width of the flanks tends to be greater for volcanic cones than for similar-diameter impact craters. In addition, topographic data were used to differentiate between volcanic cones and fresh impact craters. This differentiation used the relationship between the edifice volume to diameter ratio and the flank slope.