Glacial lakes

Outlet glaciers can erode over-deepened troughs, and, as they retreat, water accumulates in the depressions evacuated by the ice and glacial lakes form. These lakes enhance melting, as ice chunks break off the glacier tongue in a process called calving. The largest and most active glacial lake in Iceland is Jökulsárlón on Breiðamerkursandur. The Jökulsárlón glacial lake is the mouth of a 200–300 m deep and 25 km long trough that the glacier has carved out.

Glacial lakes have in recent years formed in front of many outlet glaciers of southeast Vatnajökull. Those in front of Svínafellsjökull and Skaftafellsjökull illustrate the development of such lagoons. Small pools initially form that soon merge into an elongated lake between the glacier moraine and the terminus. The lake grows rapidly when the front of the glacier thins, floats up and breaks into pieces. In the end, a large lake may be formed, into which the glacier calves along a steep front.

 

Svínafellsjökull outlet glacier with several small, separate lakes (front) and Skaftafellsjökull outlet glacier with an elongated lagoon between the glacier moraine and the terminus (back). Photo: Snævarr Guðmundsson, September 13th 2014.

Svínafellsjökull outlet glacier with several small, separate lakes (front) and Skaftafellsjökull outlet glacier with an elongated lagoon between the glacier moraine and the terminus (back). Photo: Snævarr Guðmundsson, September 13th 2014.

 

Fláajökull outlet glacier with a few separate lagoons and another elongated lagoon between the glacier moraine and the terminus. Photo: Snævarr Guðmundsson, September 13th 2014.

Fláajökull outlet glacier with a few separate lagoons and another elongated lagoon between the glacier moraine and the terminus. Photo: Snævarr Guðmundsson, September 13th 2014.

 

The terminus of Heinabergsjökull is floating and ice chunks break off. Photo: Snævarr Guðmundsson, March 3rd 2017.

The terminus of Heinabergsjökull is floating and ice chunks break off. Photo: Snævarr Guðmundsson, March 3rd 2017.

 

Fjallsjökull outlet glacier calves into the terminal lagoon. Photo: Guðmundur Ögmundsson, May 17th 2012.

Fjallsjökull outlet glacier calves into the terminal lagoon. Photo: Guðmundur Ögmundsson, May 17th 2012.