The surface of Mars comprised a number of lava flows and other signs of effusive volcanism. Although models suggest that explosive volcanism should also have produced extensive deposits, direct evidence for large-scale explosive volcanism on Mars has been scarce.
A new investigation by Briony Horgan and James F. Bell III of the mineralogy of dark regions covering more than ten million square kilometers in the northern hemisphere of Mars has revealed that these regions are dominantly composed of glass.
The glass is most likely volcanic glass produced during explosive eruptions, and potential sources include volcano-ice interactions in the northern lowlands as well as ash deposits from the large martian shield volcanoes.
The glass deposits also exhibit signs of weathering, indicating widespread interactions with liquid water.
Under the hyper-arid climatic conditions Mars has experienced over the past three billion years or more, the most likely source of this water is melting ice or snow.
These results suggest that explosive volcanism may be a major source of sediments on Mars, and that limited liquid water has been present at the surface of Mars even under long-term hyper-arid conditions.