Rappelling down rock cliffs, rafting across glacial lakes, and traversing icy crevasses, all in the presence of a massive, ever-changing glacier—it’s all part of the job for glaciologists monitoring glacial outburst floods (also known as jökulhlaups) in Alaska.
In July 2018, Suicide Basin, a dead ice branch off of the Mendenhall Glacier in Juneau, unleashed more than one billion cubic feet of water (the equivalent of over ten thousand olympic-sized swimming pools) into the Mendenhall River, which flows through the highly populated Mendenhall valley. Such outburst flood events have occurred almost every year since 2011, when the glacier-dammed lake first began forming during the summer months.
Glacier lake outburst floods, which occur when water dammed by a glacier suddenly releases and floods downstream areas, happen across Alaska and in glacial landscapes around the world. Outburst floods can impact infrastructure, such as bridges and roads, and population centers. These floods often catch communities off guard because they often occur in remote locations that are difficult to monitor.
In Juneau, AK CASC scientist Eran Hood, Christian Kienholz, and Gabriel Wolken are collaborating with teams from the National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS) who have been monitoring Suicide Basin for several years. The goal of their work is to better understand and predict the outburst floods that are released from Suicide Basin.
“Combining resources and personnel across agencies allowed us to dramatically expand our campaign of geophysical measurements and flood monitoring in the basin this season,” said Kienholz, who visited the basin more than ten times, mostly with Jamie Pierce from the USGS.
This summer, the evolution of filling and drainage at Suicide Basin took several unusual turns. Fed by rainfall, snow and ice melt the basin filled at a steady rate until the rising waters in the basin caused the tongue extending from the Mendenhall Glacier down into Suicide basin to break off. Previously held down by the weight of the main glacier to which it was connected, the ice floated to the surface and caused the water levels in the basin to drop by 2.5 feet when the ice floated to the surface.
According to Kienholz, who was coincidentally on site with other AK CASC and USGS researchers, “a section of ice one-fifth of a mile wide sprung upwards over 15 feet, and 60 feet into the basin”. The impressive occurrence appeared to be the onset of a drainage event, prompting a flood warning for Mendenhall Valley below before close monitoring showed the ice dam was still intact. The basin continued to fill for several weeks after this event. Juneau residents watched and waited, unsure what the summer would bring.
While the water levels continued to rise, researchers continued to closely monitor the situation and conduct maintenance on their instruments. Doing so became increasingly challenging as the lake continued to grow. During peak lake levels, the researchers had to raft across the water to reach their site—rather than rappelling down cliff faces as they had done earlier in the season.
By mid-July, the amount of water stored in Suicide Basin approached the volume of the 2016 record-breaking flood event that caused extensive flooding in Juneau’s most highly-populated neighborhood. Still short of the 2016 record level, the water started spilling over the top of the glacier dam, which had thinned considerably since 2016. It then ran along the edge of the glacier for several hundred feet before draining beneath the glacier.
The spillover lasted for nearly two days, and the glacier dam started to show signs of erosion. Kienholz, who did a flyover with Tom Mattice (Emergency Manager at the City and Borough of Juneau), described the scene as “spectacular.” “Eventually, the water in the basin found an outlet near the bottom of the glacier dam and the lake drained through this outlet as it had in previous years”, Kienholz elaborated.
The use of time lapse cameras and pressure gauges, along with the extensive aerial imagery the team collected at the basin, allowed the agencies involved to predict potential flood patterns and prepare local authorities for impacts. Flood warnings, evacuations and road closures were put in place along Mendenhall Lake and River with the advance notice given to authorities.
Partly due to the cool and dry weather, the 2018 flooding peaked about a foot below the 2016 record level, but still inundated nearby campgrounds, trails, homes, and roads. Fortunately, no major infrastructure damage or injury occurred. Standing on bridges and nearby vantage points, onlookers watched raging flood waters course through Mendenhall River, eroding river banks along the way. In one spectacular case, the flood waters cut through a large meander, which will have lasting effects on the river’s course and nearby infrastructure.
Following the drainage event, the researchers returned to the basin to conduct surveys and recover some of their instruments. “The water level dropped by 180 feet during drainage”, Kienholz explained. The big calving event earlier in the season had produced many icebergs, some of which were stranded high up on the sides of the basin, burying monitoring instruments under up to 60 feet of unstable ice. Some of this ice may still melt and collapse this season, so the researchers remain optimistic that the instruments may still be recovered.
Using digital images and elevation models from drone surveys, the researchers are currently creating better estimates of the volume of water that accumulated in the basin over the course of the summer. “Refining our estimates of water storage in Suicide basin is crucial for being able to more accurately predict the timing and magnitude of future outburst floods from Suicide Basin and other glacier-dammed lakes in Alaska” said Hood of the University of Alaska Southeast.
The researchers also plan to overlay jökulhlaup and rain-induced high flow events to assess the magnitude of a flood that could be generated if a large rainfall event were to occur at the same time that the outburst flood released. In a complementary effort, a graduate student from the University of Alaska Fairbanks, Dina Abdel-Fattah, has gathered information on the needs of stakeholders, city officials, and local residents. Her work will help improve communication tools and response efforts for future flood events.