Surges

Some glaciers, known as surge-type glaciers, have periods of rapid forward movement, during which they advance much faster than normally. The rapid sliding is induced by sustained high water pressure at the glacier bed. During surges the glacier moves at 100 times its normal speed and the front can advance up to several kilometers in a few months. Surge-type glaciers are characterised by gently sloping surfaces (typically 1.5–4°) and they move too slowly to maintain balance with the snow accumulation. The increasing imbalance is periodical­ly “corrected” by a short-term surge forward. During surges, the mass transport can be up to 25% of the total ice flux during the quiescent period and this often affects large areas of the ice cap, including the lo­cation of ice divides, the flow of neighbouring ice basins, the size and shape of the ice cap as well as water flow at the bed of the glacier. Up to 75% of the area of the Vatnajökull ice cap is affected by surges of outlet glaciers, and many of them have a history of regular surges. Since the 1990s, when several outlet glaciers surged, there has only been one surge in Vatnajökull, i.e. in Kverkjökull outlet glacier sometime during the period 2008 to 2011.

 

Surge in Síðujökull outlet glacier in 1994. Photo: Oddur Sigurðsson.

Surge in Síðujökull outlet glacier in 1994. Photo: Oddur Sigurðsson.

 

Surge in Tungnaárjökull outlet glacier in 1994. Photo: Oddur Sigurðsson.

Surge in Tungnaárjökull outlet glacier in 1994. Photo: Oddur Sigurðsson.

 

History of surges of the outlet glaciers of Vatnajökull. Source: Modified from Björnsson et al. (2003).

History of surges of the outlet glaciers of Vatnajökull. Source: Modified from Björnsson et al. (2003).