ADVANCES IN UNDERSTANDING LAVA FLOW INFLATION ON EARTH AND OTHER PLANETARY SURFACES

Dr. Zimbelman is this year’s recipient of the G. K. Gilbert Award for outstanding contributions to Planetary Geology. In recognition of this honor, this presentation draws extensively from locations where Dr. Zimbelman has worked to inform “the tortoise vs. the hare” debate over rates of planetary flood basalt lava emplacement. Beginning in the 1990s, Dr. Zimbelman’s seminal work investigating long lava flows on Mars, Venus, and the Moon has pointed to similarities between these flows and large lava flows on Earth—particularly those located within the Columbia River Basalt Group (CRBG) and smaller, but analogous flow units in Hawaii. At the time, there was major debate over the timescale of emplacement for large lava flows in the CRBG, with camps favoring extremely rapid emplacement of flow units (i.e., over the course of days to a few weeks) and other camps advocating for more gradual emplacement (i.e., on the order of decades). This debate cascaded into the interpretation of lava flows on other planetary bodies. In recognizing the similarity between inflated lava flows on Earth and extraterrestrial flows, Dr. Zimbelman contributed greatly to understanding the timescales of effusive volcanism on planetary bodies. Specifically, he provided evidence for inflation, which implies longer duration eruptions at lower effusion rates than was initially proposed. This presentation highlights some of Dr. Zimbelman’s important contributions to planetary volcanology as well as recent advances in quantifying the role of inflation within mafic lava flows on Earth and other planetary surfaces. Using terrestrial field observations to inform interpretations of similar flow units on Mars, this study incorporates new approaches to quantifying lava flow morphology using state-of-the-art stereo-photogrammetry and numerical models of flow emplacement. Results demonstrate similarities and differences between large martian lava flows and their counterparts on Earth. Many planetary lava flows exhibit evidence of inflation, but others exhibit evidence of "fill and spill" emplacement, in which lava in-fills craters and valleys before over-topping its confinement to produce local surges in the flow. These dam-breaching events can generate local effusion rates much greater than primary effusion rates at the vent, forming deposits with characteristics that suggest rapid emplacement at high eruption rates—even though the eruption as a whole may have been much longer-lived, with mass-discharge rates similar to terrestrial flood basalt eruptions.