The effects of measured slope on Martian lava flow modeling

One of the most frequently used methods for modeling lava flows on Mars is commonly called the “standard rheologic approach” (SRA). This method requires measurements of the flow dimensions (e.g., width, length, thickness) and local topography (e.g., slope), which are used in equations of viscosity and yield strength, for example. Topography is a critical input for most lava flow models, a detailed analysis of how the input slope value affects the results using the SRA is needed. Here we present a topographic sensitivity analysis of SRA modeling, using the minimum, maximum, and one standard deviation of measured slope values. We investigated sixteen lava flows, fourteen south and two north of Arsia Mons, Mars. Depending on the input slope, a 5 % to 60 % change in viscosity, and a 5 % to 70 % change in yield strength was found. This viscosity range produced an inferred composition change from a basalt to an andesite for eight of the sixteen flows. We also tested a single flow using the SRA and derived slopes from MOLA, HRSC, and CTX digital elevation models (DEMs). The same compositional shift from a basalt to an andesite occurred with increasing DEM resolution. These results highlight the importance of testing the full range of possible slopes and using the highest resolution topographic dataset available to avoid inaccurate interpretation of flow composition. If only low to moderate DEM datasets are available, the results should be interpreted with caution.