title: Discovery of a flank caldera and very young glacial activity at Hecates Tholus, Mars.
abstract: The majority of volcanic products on Mars are thought to be mafic and effusive. Explosive eruptions of basic to ultrabasic chemistry are expected to be common, but evidence for them is rare and mostly confined to very old surface features. 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 degrees N and 149 degrees E on the northwestern flank of the shield volcano Hecates Tholus. The eruption created a large, 10-km-diameter caldera approximately 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 today, 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 axis.
authors.affiliation: Institute of Planetary Research, German Aerospace Center (DLR), 12489 Berlin, Germany. Ernst.Hauber@dlr.de
authors.forename: Ernst
authors.initials: E
authors.lastname: Hauber
authors.forename: Stephan
authors.initials: S
authors.lastname: van Gasselt
authors.forename: Boris
authors.initials: B
authors.lastname: Ivanov
authors.forename: Stephanie
authors.initials: S
authors.lastname: Werner
authors.forename: James W
authors.initials: JW
authors.lastname: Head
authors.forename: Gerhard
authors.initials: G
authors.lastname: Neukum
authors.forename: Ralf
authors.initials: R
authors.lastname: Jaumann
authors.forename: Ronald
authors.initials: R
authors.lastname: Greeley
authors.forename: Karl L
authors.initials: KL
authors.lastname: Mitchell
authors.forename: Peter
authors.initials: P
authors.lastname: Muller
mesh_terms: D002980:Climate; D005118:Extraterrestrial Environment / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry; D046448:Ice Cover; D018535:Mars; D010781:Photography; D013997:Time Factors