Several craters in Arabia Terra seen by NASA’s Mars Reconnaissance Orbiter are suspected to be volcanic calderas and are filled with layered rock consistent with altered volcanic ash. Credit: NASA/JPL-Caltech/University of Arizona.

Volcanism is a fundamental geologic process on the terrestrial planets, including Mars. It has been suggested that several large, circular depressions in the northern region of Mars called Arabia Terra are calderas produced by explosive volcanic supereruptions about four billion years ago. If these features truly are explosive calderas, they would have released vast amounts of volcanic ash that would have been transported and deposited as thick layers across Arabia Terra. However, such extensive ash deposits had never been identified.

A research team led by Patrick Whelley at NASA Goddard Space Flight Center studied the mineralogy and morphology of exposed layered deposits in Arabia Terra. They used data from the Mars Reconnaissance Orbiter instruments CRISM (Compact Reconnaissance Imaging Spectrometer for Mars), HiRISE (High Resolution Imaging Science Experiment), and CTX (Context Camera). The team found altered ash deposits that are likely related to early martian supereruptions are widely distributed across Arabia Terra, showing thicknesses from 1 kilometer to 100 meters as far away as 3,400 kilometers from the potential caldera sites. The minerals observed include hydrated sulfates, hydrated silicas, and phyllosilicates such as montmorillonite, imogolite, and allophane, all of which are consistent with or diagnostic of altered volcanic ash. The volume of ash in the observed deposits across Arabia Terra would require 1,000 to 2,000 individual explosive eruptions in the late Noachian to early Hesperian epochs. The total volume of erupted magma needed to produce the observed volcanic ash deposits is estimated to be 30% to 60% of the total volume of Olympus Mons, the largest volcano in the solar system. Through the combination of mineralogic and topographic analyses, this research supports the hypothesis that volcanic supereruptions occurred in Arabia Terra in ancient times. It also motivates future studies of how such extensive volcanism was possible on Mars. READ MORE