Abstract

Glacier winter velocities are generally slower than summer velocities, that increase early in the season when meltwater runoff reaches the bed. Velocities generally decrease later in the season as the subglacial system becomes channelized. With an innovative ice cave monitoring technique, here we show that a single week-long warm event in the winter triggers an internal drainage system flooding event, leading to velocity doubling for the remainder of the winter, unlike summer speedups when additional meltwater forms efficient drainage channels that reduce glacier velocity. As the climate warms and surface melt and rain events increase during winter months, sustained high winter glacier velocities are likely to occur more often. Increasing glacier velocity near the terminus leads to additional ice entering the fjord, and an increase of sea level rise contribution during these sustained season-long events.