A dramatic calving event triggered outburst flood warnings at Suicide Basin, a glacier-dammed lake adjoining Mendenhall Glacier in Juneau, when a section of ice one-fifth of a mile wide separated ice in the basin from the main glacier. What seemed at first to be the early moments of a glacier outburst flood has since been determined to be a slight drop in water level caused by the massive calving of ice into the basin.
The unprecedented event surprised UAS researchers Eran Hood and Christian Kienholz, US Geological Survey (USGS) scientists Jamie Pierce and Randy Host, and videographer Jonny Antoni who were on site capturing elevation measurements to model the features of the basin and performing routine maintenance on the monitoring equipment. “None of us visualized that scenario happening so rapidly or across such a wide area,” says Hood, who with Kienholz had crossed that very section of ice to deploy equipment only a week before.
Since 2011, an ephemeral glacier-dammed lake has formed in Suicide Basin each summer, fed by melt- and rainwater. The lake drains during outburst flood events, causing flooding along Mendenhall Lake and Mendenhall River in the most heavily populated neighborhood in Juneau. Outburst events have occured in most years since 2011, with the largest event to date occurring in July 2014. Nearly 20,000 cubic feet per second of water flowed through the Mendenhall River. This is greater than the discharge of the Colorado River through the Grand Canyon and nearly ten times greater than the average water flow of the Mendenhall River.
The UAS researchers along with collaborators from the USGS, the National Oceanic and Atmospheric Administration (NOAA), and the City and Borough of Juneau have been monitoring activity in the basin to improve glacial dam forecasting. This spring, water levels measured by sensors installed by the USGS showed that water levels in the basin rose relatively slowly due to cool temperatures, until mid June. In the week leading up to the calving event, the filling rate abruptly increased to more than four feet per day, caused by a combination of rain and relatively warm temperatures both day and night.
While the researchers were on site, the pressure of rising water in the basin caused the ice connecting the Suicide Basin branch to the main glacier to break. Previously held down by the grounded glacier it was connected to, the ice floated to the surface and caused the water levels to drop in the basin by a more than two feet. Hood and Kienholz speculate that the calving event could strengthen the ice dam and further delay an outburst flood.
With the ice dam intact, the water level is expected to continue to rise in the basin. Currently, the team estimates that the volume of water in the basin is about 70 percent of the amount released in an outburst flood in 2016, which caused damage to nearby trails and infrastructure.
Monitoring efforts in Suicide Basin started in 2012, when Hood and Pierce installed a weather station, pressure gage, and timelapse camera in the basin to monitor the water level. Installing and maintaining equipment in the basin requires working in an extreme and quickly changing environment. Pierce, an experienced mountain guide, puts his mountaineering skills to use on the steep terrain that surrounds the basin. Reaching the shores of the lake requires rappelling 150 feet over steep cliffs with equipment in tow, all while combating loose boulders and rocks, and moving ice. This year, the researchers have visited the basin frequently to install and maintain pressure gauges and time lapse cameras that deliver real-time updates via USGS satellites every hour and day, respectively.
In addition to monitoring for outburst events, the researchers are using the Suicide Basin data to better understand the processes that govern the timing and magnitude of outburst floods at Mendenhall Glacier, and create a model that will help predict peak runoff. These tools will help monitor other glacier-dammed lakes in the state as well, including Bear Glacier in the Kenai Mountains, Russell Lake at Hubbard Glacier in the Saint Elias Mountains, Valdez Glacier in the Chugach Mountains. A graduate student from the University of Alaska Fairbanks (Dina Abdel-Fattah), a UAS undergraduate student (Mollie Dwyer) and Gabriel Wolken, a glaciologist at AK CASC and the Alaska Division of Geological & Geophysical Surveys, are also collaborating on the project.
Predicting the exact date of the outburst flood well in advance is challenging, given the number of factors at play (for example, the weather). But with real-time information from the USGS gage and timelapse camera, researchers can detect first signs of an outburst flood and give advance warning to local communities.