The Erebus Ice Tongue flow pushes the glacier into Erebus Bay where it butts against seasonal ice pack. This massive but gradual collision of ice against ice creates pressure ridges in the glacier. Portions of the ice tongue become unstable, rupture, and calve icebergs. Such instability in part comes from the flexing and tension the ice beam undergoes from being cantilevered over the sea. Moreover, the river of ice carries with it weaknesses introduced by earlier fractures experienced during its journey down the slopes of Mount Erebus.