Severe flooding from Alaska glacial break would not have happened without climate change, scientists say

(JUNEAU, Alaska) — The glacier lake outburst that sent an unprecedented amount of water rushing towards Alaska’s capital, destroying homes, would not have happened without climate change, according to the National Oceanic and Atmospheric Administration.

An outburst flood from a meltwater lake on the Mendenhall Glacier, located about 12 miles north of Juneau, Alaska, sent record amounts of water into Mendenhall Lake and down the Mendenhall River between Aug. 4 and Aug. 6, according to NOAA.

Significant flooding was reported in areas along the river that have not seen flooding from these types of events in the past, the National Weather Service office in Juneau said. Floodwaters swept trees and buildings into the river as significant erosion occurred.

Decades worth of erosion happened in one weekend, Rick Thoman, Alaska Climate Specialist at the Alaska Center for Climate Assessment and Policy told Climate.gov.

The Mendenhall Lake crested at 14.97 feet the night of Aug. 5, smashing the previous record of 11.99 feet set in July 2016 and exceeding the initial forecast of 12.3 feet by the Alaska-Pacific River Forecast Center.

At the height of the flooding event, a streamflow of about 25,000 cubic feet per second was recorded, National Weather Service Juneau hydrologist Aaron Jacobs told ABC News earlier this month.

Andrew Park, a Meteorologist at NWS Juneau, described the fast-moving flow to Climate.gov as “historic.” The previous maximum streamflow, set in 2015, was 16,300 cubic feet per second, according to USGS records.

The Federal Emergency Management Agency created flood maps for the Mendenhall Glacier, defining a 100-year flooding event as a discharge of 17,000 cubic feet per second, with less than a 1% chance of occurring in any given year, and a 500-year flooding event as a discharge of 26,000 cubic feet per second, or a .2% of occurring in any given year, Jacobs said.

“Without climate change, there is no reason to think that this would be happening on the Mendenhall Glacier, then in the lake, and downriver,” Thoman said.

The flooding occurred after a break from the Mendenhall Glacier’s Suicide Basin, which has changed drastically due to thinning, melting and glacial retreat, according to NOAA. Suicide Glacier was once a much larger frozen tributary, which flowed into and merged with the Mendenhall Glacier.

The flooding destroyed several structures along the Mendenhall River, according to the National Weather Service.

The buildings that fell into the river and those that are uninhabitable now were not right next to the river on Friday afternoon before the flooding started, Thoman said.

Mendenhall Valley, where the floodwaters went once the river and lake overflowed, is Juneau’s most heavily populated neighborhood, according to the Alaska Coastal Rainforest Center.

Scientists are concerned that a similar event, although considered extremely rare in the past, could happen again.

Alaska has warmed twice as fast as the rest of the United States over the last several decades, according to NOAA’s National Centers for Environmental Information. Alaska’s average annual temperature has risen 3.1 degrees Fahrenheit over the last century, and the overall trend continues to increase.

The retreat, melting and thinning of glaciers over the last century has been attributed by climate scientists to Earth’s warming climate. Alaska’s glaciers been experiencing a steep decline since the late 1980s, according to the Alaska Department of Geological and Geophysical Surveys

Before 2011, when the first lake outburst in the Mendenhall occurred, glacial lake outburst floods were a relatively new phenomenon. Suicide Basin has been releasing glacier lake outburst floods that cause inundation along Mendenhall Lake and Mendenhall River since 2011, according to the National Weather Service.

Those in charge of monitoring the Mendenhall Glacier and the lakes within it can tell when a flooding event is gearing up, Jacobs said.

The National Weather Service in Juneau has a “well-versed” monitoring program, which involves elevation marks on Suicide Basin and a camera pointed in its direction, to see how much the water levels are falling and rising.

Suicide Basin began to refill on Aug. 9 but remains at very low levels, making another lake outburst before the fall season unlikely, according to NOAA.

ABC News’ Dan Manzo contributed to this report.