Rainier's largest glacier is melting. Here's what that means downstream
Scientists are studying the evolution of Emmons Glacier and its implications on watersheds throughout the Pacific Northwest.
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Glaciers are essentially slow-moving rivers of ice and snow that hold water like a storage tank. During summer months, their melt flows into streams and rivers. Emmons — the largest glacier in the continental U.S. — is an important freshwater source for the Puget Sound, feeding into the White River that runs along state Route 410. Although Emmons grew in size each winter for decades, its surface is now melting irregularly, which raises questions about flooding and water supply as the climate warms.
More research is needed to understand what the future could bring, as well as climate policy to significantly lower greenhouse gases and slow climate change. The Inflation Recovery Act, recently passed in the U.S. Senate, is aimed in this direction, including a goal to cut carbon emissions by about 40% by 2030 and invest in clean energy sources.
This July, like every summer for the last 14 years, Todd hiked to Emmons to sample water quality and measure debris ranging from boulders of solidified lava to fragments of talus, or alpine rock. Her fieldwork, currently funded by NASA and the University of Washington, allows for sampling that significantly adds to the information gathered through aerial mapping
When it melts, it pours
Todd shares her findings with the National Park Service, the only government entity closely monitoring the glacier and analyzing changes. National Park Service science technician Mike Larrabee and his team from the park service study Emmons’ snowpack and how much of it has melted compared to past years to better track how the glacier feeds the White River. For the last 20 years, nearly 16% of the glacier’s meltwater flowed into the river, which meanders along the northeast side of the mountain and serves as an unofficial border between King and Pierce counties. In low snowpack years, Larrabee’s team measured as little as 7% of the melt flowing into the river.
Like Todd, Larrabee travels on the glacier to take measurements. When setting out stakes for monitoring during the winter of 2014, Larrabee saw something unusual for the winter season: a deep channel in the snow.
“It was like someone had taken a snowplow and just cut through there,” he said. “It was missing snow. The drainage network of the glacier was just spilling out and funneled down into the canyon, almost like a little stream channel.”
At the lower end of the glacier, Larrabee found 64 million gallons of melted snow — enough water to fill 100 Olympic-size swimming pools.
Scientists call this outburst flooding. This happens when glacier ice melts and abruptly releases water, which then flows downstream and temporarily overflows a river.
Those floods are a normal summertime occurrence, but warmer years are increasing the likelihood for bigger ones. In November 2017, park technicians discovered another outburst flood when it tore out and destroyed monitoring equipment at the White River Bridge near a campground.
The surge of water and sediment usually stays within the park during an outburst flood, but huge flows could have impacts farther downstream at the Mud Mountain Dam, which holds back floods before they can reach nearby towns like Enumclaw.
The dam is essential for flooding control, according to Joanna Curran, a civil hydraulics engineer within the Army Corps of Engineers. Mud Mountain was created in the 1940s to manage heavy rain and snowmelt, when glacial outbursts didn’t happen often.
Emmons gets the least amount of sun compared to Mount Rainier’s other 24 major glaciers. However, its growth is largely attributed to insulation from a 1963 rockfall from Little Tahoma Peak — a craggy, snowy wedge that rises 2,000 feet above Emmons.
While layers of that rocky debris can protect the glacier from the sun, thin spots in its covering can also heat up the ice and accelerate melting. As a result, Emmons is retreating more quickly in the middle than its sides, leaving a horseshoe shape in its wake. As it steepens like a canyon, some areas are losing the rocks shading their ice from the sun. One lower section of the glacier shrunk by nearly 300 feet within just four years of shedding its rock cover.
and more:
https://crosscut.com/environment/2022/08/rainiers-largest-glacier-melting-heres-what-means-downstream
