Interpretations of Lava Flow Properties from Radar Remote Sensing Data

The surface morphology and roughness of a lava flow provides insight on its lava properties and emplacement processes. This is essential information for understanding the eruption history of lava fields, and magmatic processes beneath the surface of Earth and other planetary bodies such as the Moon. The surface morphology is influenced by lava properties such as viscosity, temperature, composition, and rate of shear. In this work, we seek to understand how we can interpret the emplacement processes and lava properties of lava flows using remote sensing data. Craters of the Moon (COTM) National Monument and Preserve in Idaho hosts a suite of compositionally diverse lava flows with a wide range of surface roughness making it the ideal case study. Lava flows there have surface morphologies consistent with smooth pāhoehoe, slabby pāhoehoe, hummocky pāhoehoe, rubbly pāhoehoe, ‘a’ā, block-`a’ā, and blocky textures. The variation in surface roughness across the lava field reflects changes in lava properties and/or emplacement processes over space and time. We investigate geochemical and petrographic variations of the different lava flow morphologies and analyse how they relate to airborne radar data. Results show L-Band (24 cm) radar circular polarization ratios (CPR) distinguish the contrasting surface roughness at COTM, separating the smoother (primitive; low SiO2 and alkali) and rougher (evolved; high SiO2 and alkali) lava flows. However, ambiguities are present when comparing the CPR values for rubbly pāhoehoe and block-`a’ā flow. Even though their CPR values appear similar at the decimetre scale, they have distinct morphologies that formed under different emplacement processes. Without ground-truth information, the rubbly pāhoehoe and block-`a’ā lava flows could therefore be misinterpreted to be the same type of flow morphology, which would lead to false interpretations about their lava properties and emplacement processes. This is important when comparing these flows to lava flows on other planetary bodies that share similar CPR values, such as the Moon. Thus, using terrestrial analogues such as those at COTM can provide an improved understanding of the surface morphology and emplacement processes of lunar lava flows. This will lead to more refined interpretations about past volcanic processes on the Moon