Jøkullaup
Tracks after a gully collapse from Flatbreen in 2004. Photo: Hallgeir Elvehøy, NVE.
Jøkullaup is an abrupt draining of a lake dammed up by a glacier, leading to a sudden and often catastrophic flood. Similarly, end moraines can act as unstable dams. This can also happen when volcanic eruptions under a glacier rapidly melt large amounts of ice.
Climate change can lead to glacier lake outburst floods
On Blåmannsisen in Sulitjelma, there have been three jøkullaup since 2001. The first was completely unexpected and was discovered when the water level in the dammed Sisovatnet lake rose by 2.5 m over the course of a day and a half. The cause was the emptying of the broad lake Øvre Messingmalmvatn, which actually drains towards Sweden. After draining, it took three years for the lake to fill up again. The lake was abruptly drained again in 2005. The reason for this is believed to be that the glacier has become thinner and therefore cannot withstand the pressure exerted by the water. In 2007, the water was drained again, again completely unexpectedly. This time the water had not been filled up to its original level. It is likely that the ice cover has become even thinner and thus withstood even less pressure. This is an example of how climate change can lead to the draining of wide lakes. NVE is working to find the causes of these depletions so that they can predict them and thus warn when the water is coming. A regulated system can then make room for the water so that it does not cause flooding and expose people to danger.
Here you can read about the Jøkullaup from Flatbreen. There have been several jøkullaup in Norway, some of which are described below:
Demmevatn, Hardangerjøkulen
Perhaps the most famous glacial lake is Demmevatn, which is dammed by the Rembesdalskåki glacier, an arm of Hardangerjøkulen glacier. The lake drained in two ways: either the water melted a channel in the glacier surface, or it melted a tunnel along the bottom of the glacier. The annual floods from Demmevatn were small and lasted 2-3 weeks. The first catastrophic flood occurred in 1896. Two other major floods occurred in 1937 and 1938. After these, tunnels were built to drain Demmevatn, thus preventing it from filling up.
Skaddalsvatnet, Jostefonni
According to written sources, the Vetlefjord valley in Balestrand was ravaged by floods in the first half of the 19th century. The last known flood occurred in 1948. At that time, the Vetlefjord glacier, an arm of the Jostefonni glacier, went 2 km further down the valley. On the west side of the glacier arm, a lake was dammed up in the mouth of Skaddalen, below where Skaddalsvatnet is today. The lake probably behaved very similarly to Demmevatn. Today, the Vetlefjordsbreen glacier has melted so far away that there is no longer any danger of damming and flooding.
Brimkjelen, Jostedalsbreen
Brimkjelen is a wide lake on the west side of the Tunsbergsdalsbreen glacier. Big and devastating floods occurred in 1900, 1903 and 1926. During the 1900 flood, the river Leirdøla carried away a bridge that had been in use for over 100 years. Tunsbergsdalsvatnet lake in front of the glacier is now dammed. The dam is particularly high to catch floods from Brimkjelen.
View towards Brimkjelen in 2010. Photo: Kjersti Moe.
Dammed glacier lakes during the last ice age
At the end of the last ice age, large glacial lakes were dammed up between the watershed and the remains of the melting inland ice. Particularly in Gudbrandsdalen and Østerdalen, traces of the glacial lakes can be seen in the form of shorelines, or seats, that marked the water level. The lakes drained over various passes at the watershed in the north. The very last lakes emptied out in violent jökullaup under the ice to the south.
The most famous lake is "Nedre Glomsjø", which filled Østerdalen valley about 9200 years ago. The 950 km² lake (2.6 times larger than lake Mjøsa) was about 10 miles long, stretching from Røros in the north to Atna and Storsjøen in the south. "Nedre Glomsjø" drained in the form of several jökulhlaups that found their way across Barkaldkjølen, between Østerdalen valley and Tylldalen valley. Calculations show that the maximum water flow during the jökulhlaups may have been 180 million liters per second (32 times the water flow in Niagara Falls). The result was the 250 m deep and 2 km long Jutulhogget gorge.
The word "jøkullaup" comes from Iceland and means "the glacier runs", although it is the water that "runs" out of the glacier we are referring to. The phenomenon often occurs in Iceland and has caused major damage to the island. Particularly in connection with volcanic eruptions, large jökulhlaups have developed. The last major incident occurred in 1996 when a large volcanic eruption under Vatnajökull melted large amounts of water that were collected in a lake under the glacier. In the end, the lake was so large that it lifted the ice dam so that the water was drained into a huge jökull outlet, the largest the world has seen since 1938. The flow was eight times the size of Niagara Falls (45 million liters per second) and it brought with it 100 million tons of sand, gravel and volcanic material. Locally, this led to the coastline being extended by 900 meters and all infrastructure being destroyed.
