Journey on the Cowlitz: Glacial Beginnings

Imagine prehistoric glaciers carving the land we call Lewis County almost like a child scraping a groove through a sandbox. 

Roughly 35,000 years ago, long valley-filling glaciers extended from the Mount Rainier area into what is now Silver Creek near Mayfield Lake. 

In that area, one can still see layers of silt and sand known as lacustrine layers, which were laid down by water that was dammed by a wall of ice. As the climate changed over the course of about 20,000 years, the ice receded during what’s called the Evans Creek Period. The glaciers in the Cowlitz Basin shrunk away from where Mossyrock is now and ended just a little ways east of today’s Riffe Lake. 

“(There was) more than 1,000 feet of ice all the way down to ... about a mile east of Riffe Lake,” said Carolyn Driedger, a U.S. Geological Survey hydrologist. “(Drive east on U.S. Highway 12) and you’re going to see a lot of rock that’s been deposited when the glaciers melted.”

Although those formations melted thousands of years ago, massive sediment piles are all over the county. 

Those massive glaciers are long gone, but people of Western Washington rely heavily on those that are still left for freshwater needs. Though still impressive in providing cold, fresh meltwater, the glaciers in Mount Rainier National Park are a shadow of what they once were. 

As the world gets warmer, Mount Rainier’s glaciers are shrinking at an alarming rate,  and the sediment they’re leaving behind is often creating serious problems for life below. 

There are 143 glaciers and permanent snowfields on Mount Rainier, 27 of which have names. 

According to park documents, “Glacier area and cumulative net mass balance (volume) are decreasing rapidly at (Mount Rainier) due to increasing temperature and decreasing snowfall.” 

Indeed, in less than 100 years, about 21 percent of the park’s ice has melted away. Within the last 10 years, the trend has accelerated, park officials say. 

“(The glaciers) are all at their historic minimums,” said Paul Kennard, a regional geomorphologist stationed at Mount Rainier National Park. “The equilibrium line, where accumulation equals the melt, is about 10,000 feet. If a glacier starts below that, it’s going to be in trouble.” 

Glaciers above the 10,000-foot line are staying cool and getting snow.  

The stereotype of glaciers as pristinely white, massive ice formations is far from reality. 

“They’re conveyer belts of rock, especially around volcanoes,” Driedger said. 

As the glaciers melt, they leave huge deposits of rock that wash downstream and threaten everything from old-growth forests to roads and buildings in the developed sections of the national park. As sediment moves downstream out of the park, it chokes waterways and can leave communities vulnerable to flooding. 

“Sediment is causing problems in the park and it’s causing problems outside the park,” Kennard said. “The Cowlitz (Glacier) is one of the few that doesn’t seem to be overwhelming the Cowlitz River (with sediment), so that’s good for Packwood and Randle.”

While communities along the Puyallup and White rivers are dealing with massive deposits of gravel and boulders being washed downstream, the upper Cowlitz Basin is actually incising. 

“To me, it’s somewhat consistent with the fact that you have significant clearwater tributaries to the Upper Cowlitz that you don’t have in these other watersheds,” said Ben Wright, a biological science technician for the park. 

Along with several other watersheds in Western Washington, the Cowlitz River traces much of its origins to the glaciers on Mount Rainier. 

But the Cowlitz is somewhat unique compared to other watersheds starting in the park in that it isn’t accumulating deposits of glacial material.

The Muddy Fork of the Cowlitz starts at the Ingraham Glacier and significantly thinning Cowlitz Glacier. The Muddy and the smaller streams it connects with carry huge amounts of glacial silt downstream and, at certain points, are widening into gravelly braided channels, but that process stops when they travel through hard rock canyons.

 Areas such as Box Canyon, for example, move water with so much force that little, if any, sediment can be deposited until the Muddy Fork meets with the Cowlitz outside of Packwood. The Muddy’s confluence has caused sediment issues in the past, but further downstream its contents are diluted by the clean combination of the Ohanapecosh River and the Clear Fork of the Cowlitz.

“You’ve got the big Cowlitz Glacier that’s dumping all this sediment, but it is being buffered by the Ohanapecosh and the Clear Fork of the Cowlitz, which are both significant clearwater tributaries. They’re probably contributing about 60 percent of the flow.”

Due to climate change, lower elevation glaciers and snow fields are melting away, park officials say. Tributaries of the Cowlitz River system that rely on other lower elevation glaciers, such as the Ohanapecosh, will likely have less water should the melt continue. 

The Cowlitz Glacier, for example, is retreating at an average of 4.4 meters per year. According to Kennard, its decline may cause occasional episodes of huge water and sediment flows to wash downstream, but even if it were to go away, the Muddy Fork would still get water from the higher, and thus safer, Ingraham Glacier. 

So as the world warms, the water sources may change, but the Cowlitz will continue to flow from Mount Rainier.  

“You’re going to continue to have that. I don’t think you're going to have the problems of the summer water supply,” Kennard said. “I can’t imagine a credible scenario where the upper glaciers would go away.”