Jökulhlaup season is back.
Juneau city officials announced Thursday afternoon that Suicide Basin, a depression above the Mendenhall Lake, has started filling with rain and melt water and a glacier outburst flood is soon to follow.
But predicting the time and size of that flood, known by its Icelandic word jökulhlaup, is tricky business.
The city is working with the U.S. Geological Survey and the National Weather service to monitor the situation as best it can, according to a press release. The most revealing pieces of information, however, which could help the determine when the jökulhlaup might happen, are buried under several feet of ice.
Jökulhlaups are a recent annual phenomenon and begin when water fills Suicide Basin, adjacent to Mendenhall Glacier. As the water level rises in the basin, pressure builds until it eventually becomes great enough to lift the glacier.
Without the ability to see what is happening beneath the glacier, it’s difficult to know the exactly when there will be enough pressure to lift the glacier. Once this happens, though. the water in Suicide Basin rapidly drains into the Mendenhall Lake, which causes the lake and the Mendenhall River to flood.
During the past five years jökulhlaups have taken place at the glacier, there have been a few big floods. In 2011, the first time a jökulhlaup was observed in Juneau, the Mendenhall Lake rose to 10.92 feet, according to past Empire reports. The minor flood stage starts at 9 feet. There was also a large flood in 2014.
Last season was fairly mild. There were several glacier outburst floods during June and July, but most of them were hardly noticeable to tourists and people living along the Mendenhall River.
Though city officials don’t yet know how the predicted jökulhlaup may stack up to past floods, they are urging those who live along the river to be prepared.