Shield Volcano Slope Distributions: an Approach for Characterizing Martian

Introduction: Terrain analyses are commonly used to study the geomorphic processes that have modified surfaces [1]. Our approach is based on analysis of slopes, which are the irregular surface expressions of the processes responsible for shaping landscapes [2]. Slope distributions likely represent unique surface forming processes and can be used to characterize entire landscapes at a given scale [3]. Because terrestrial slopes are constantly changing due to the influence of exogenic agents this approach is typically used to examine erosional processes. However, it is reasonable to utilize slope distributions to identify different lava flow emplacement processes and therefore volcanic style, when the overall surface construction rate is higher than the surface modification rate or when the opposing processes are separable upon analysis. The final form of a lava flow is dependent, in part, on the physical properties of the lava and the effusion conditions [4]. Thus the slope distributions displayed by different volcanic terrains should be unique to their emplacement conditions. We present slope distributions for the shield volcanoes on the island of Hawaii as a possible comparative approach to characterize martian volcanic provinces. Background: The volcanoes of Hawaii satisfy the criteria presented above allowing quantitative characterization of their constructional processes based on slope distributions. The island of Hawaii consists of five Quaternary shield volcanoes at various stages of their eruptive sequence [5]. Kohala and Mauna Kea are thought to be extinct and have undergone some erosion, Hualalai is likely dormant, and both Mauna Loa and Kilauea are active [5]. The general shield morphology of Hawaiian volcanoes evolves from a broad, gently sloping structure composed of long, thin, overlapping tholeiitic basalts, to a steeper structure surrounding the vent when lavas become more silicic [5] and eruption volumes and duration diminish as the volcano becomes inactive [6,7]. With a range of eruptive stages and emplacement conditions present, Hawaii presents an ideal location to test the validity of characterizing terrestrial basaltic shields according to slope distributions. The availability of the MOLA topographic dataset [8] provides the opportunity for comparisons between terrestrial slope distribution trends and trends displayed by martian volcanoes. Results: The complete Hawaiian USGS 10 m/pixel DEM grid (mosaiced in ArcView GIS 3.2 by ESRI) is used to calculate slopes over each volcano.