AN INVESTIGATION OF 3D MAAR MORPHOMETRY TO UNDERSTAND THE INFLUENCE OF UNDERLYING TOPOGRAPHY ON CRATER SHAPE

A maar is a volcanic crater formed from magma interaction with groundwater or ice, producing a subsurface explosion. The complexity of maar morphometry reflects complexities of eruption processes and sequences, suggesting changing hazards during an eruptive sequence. Maar shapes have been described in two dimensions in the MaarVLS database. A third dimension of maar morphometry may be helpful for remote identification, such as Mars. An investigation of maar slopes in flat areas compared to those formed interacting with preexisting topography was used to look for diagnostic characteristics of those topographic interactions. Using the MaarVLS database, arid maars with closed rims containing little or no water (n ~ 20), were compared with a subset of maars whose craters cut into preexisting topography (n ~ 29). Using Google Earth, maar morphometry was examined to calculate the slope, rim elevation asymmetry, and the lowest elevation. Of the maars studied, the areas ranged from 0.003 – 3.21 sq. km in the flat maar subset, and 0.046 – 1.31 sq. km in those intersecting preexisting topographies. The slopes of the subset of maars intersecting topography ranges 12 - 50°, while the slopes of the flat subset ranges from 11 - 47°. The rim elevation difference for the subset of maars intersecting topography ranges 49 – 296 m, and for the flat maar subset it ranges 3 – 171 m. Maars that do not intersect with topography can have up to 200 m in rim asymmetry. These results indicate that maar rim elevations are complex even without underlying topographic influences and the range of slopes is similar in both datasets. The observed asymmetry is more common in smaller craters. Detailed comparisons of the maximum slopes observed within these datasets using high resolution data may provide greater insight into factors controlling maar asymmetry. This shape data can be used to help reconstruct eruption histories necessary for understanding maar hazards. Further, this morphometry data is invaluable to the remote recognition of maars on Earth and other planets.