Hecates Tholus is a Martianvolcano, notable for results from the European Space Agency's Mars Express mission which indicate a major eruption took place 350 million years ago. The eruption created a caldera 10 km in diameter. It has been suggested that glacial deposits later partly filled the caldera and an adjacent depression. Crater counts indicate this happened as recently as 5 to 20 million years ago. However climate models show that ice is not stable at Hecates Tholus today, pointing to climate change since the glaciers were active. It has been shown that the age of the glaciers correspond to a period of increased obliquity of Mars' rotational axis.
Hecates Tholus ridges, as seen by HiRISE. Ridges are to the west-northwest of Hecates Tholus. It has been proposed that this region was affected by a volcanic eruption that occurred under a 200 meter-thick ice sheet.