Glacial earthquakes are moderate earthquakes of (surface-wave) magnitude up to 5 on the Richter scale.
They are closely related to ice motion. They occur only in regions with very high ice flow speeds (in excess of a few km/year); the mechanisms are consistent with, among others, acceleration of massive chunks of ice in the downstream direction. They originate from massive breakups of ice (intense calving events), primarily in Greenland or Antarctica.
Glacial earthquakes occur more often during the summer months, when the most melt is generated. The liquid water at the bottom of the glacier makes its movement easier and faster, making the conditions more favourable for an earthquake to occur. Thus they become more and more common every year, due to climate change.