Glacial earthquakes are moderate earthquakes of (surface-wave) magnitude ~ 5 on the Richter scale, first detected in 2003.
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 acceleration of massive chunks of ice in the downstream direction. They originate from massive breakup 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, and they become more and more common every year, due to climate change.