Investigating Late-Stage Explosive Eruptions on the Volcanic Rises of Mars and Venus

Abstract

Spacecraft missions to other planets in the inner solar system have led to the identification of evidence for explosive or pyroclastic volcanism in the past. The timing and distribution of explosive activity in the inner solar system has implications for interior magmatic processes, crustal evolution and interior composition, and atmospheric evolution. Investigating occurrences of pyroclastic activity is therefore necessary to develop a comprehensive understanding of a planetary interior and evolution. In this dissertation, we present studies of past explosive activity on the topographic rises of Mars and Venus. Our objectives include characterizing the spatial extent of pyroclastic deposits (on Mars), investigating the emplacement dynamics of pyroclastic deposits (on Venus), and determining the physical properties and structure of pyroclastic deposits (on Venus). We address these objectives primarily using radar remote sensing and theoretical modeling. An introduction to terrestrial and planetary volcanism, and the significance of explosive volcanism is presented in Chapter 1. We also introduce planetary radar instruments and observations in this chapter. In Chapter 2, we discuss late-stage explosive activity in the caldera of Arsia Mons, one of the largest shield volcanoes on Mars. We show how orbital sounding radar observations, together with Bayesian inversion techniques, can be used to map the subsurface and determine the distribution of buried pyroclastic units. In Chapters 3 and 4, we focus on potentially recent explosive activity on the shields and coronae of Venus. Several radar bright deposits in the highlands of Venus have been interpreted as pyroclastic flow deposits. We present a multi-pronged approach to investigate the emplacement and physical structure of these deposits. In Chapter 3, we develop a numerical model for pyroclastic flow transport and deposition on Venus. By comparing the results from the model with orbital observations, we narrow down possible pyroclastic eruption conditions. In Chapter 4, we analyze the scattered and emitted radiation at microwave wavelengths from these deposits to place constraints on the physical properties and shallow-stratigraphy. Lastly, we summarize our findings and discuss avenues for further research in Chapter 5.