1. Institute of Planetary Research, German Aerospace Center (DLR), 12489 Berlin, Germany
2. Institute of Geosciences, FU Berlin, 12249 Berlin, Germany
3. Institute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow, 117334, Russia
4. Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA
5. Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287-1404, USA
6. Environmental Science Department, Lancaster University, Lancaster LA1 4YQ, UK
7. Department of Geomatic Engineering, University College London, Gower Street, London WC1E 6BT, UK
8. A list of all members of The HRSC Co-Investigator Team and their affiliations appears at the end of the paper

Correspondence to: Ernst Hauber¹ Correspondence and requests for materials should be addressed to E.H. (Email: Ernst.Hauber@dlr.de).

Abstract

The majority of volcanic products on Mars are thought to be mafic and effusive^{1, 2}. Explosive eruptions of basic to ultrabasic chemistry are expected to be common^{3, 4}, but evidence for them is rare and mostly confined to very old surface features⁵. Here we present new image and topographic data from the High Resolution Stereo Camera that reveal previously unknown traces of an explosive eruption at 30° N and 149° E on the northwestern flank of the shield volcano Hecates Tholus. The eruption created a large, 10-km-diameter caldera 350 million years ago. We interpret these observations to mean that large-scale explosive volcanism on Mars was not confined to the planet's early evolution. We also show that glacial deposits partly fill the caldera and an adjacent depression. Their age, derived from crater counts, is about 5 to 24 million years. Climate models predict that near-surface ice is not stable at mid-latitudes today⁶, assuming a thermo-dynamic steady state. Therefore, the discovery of very young glacial features at Hecates Tholus suggests recent climate changes. We show that the absolute ages of these very recent glacial deposits correspond very well to a period of increased obliquity of the planet's rotational axis⁷.

1. Institute of Planetary Research, German Aerospace Center (DLR), 12489 Berlin, Germany
2. Institute of Geosciences, FU Berlin, 12249 Berlin, Germany
3. Institute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow, 117334, Russia
4. Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA
5. Department of Geological Sciences, Arizona State University, Tempe, Arizona 85287-1404, USA
6. Environmental Science Department, Lancaster University, Lancaster LA1 4YQ, UK
7. Department of Geomatic Engineering, University College London, Gower Street, London WC1E 6BT, UK
8. A list of all members of The HRSC Co-Investigator Team and their affiliations appears at the end of the paper

Correspondence to: Ernst Hauber¹ Correspondence and requests for materials should be addressed to E.H. (Email: Ernst.Hauber@dlr.de).

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