On a geologic scale, there’s nothing unusual about receding glaciers on Mount Rainier. Over the past 12,000 years, they’ve risen and fallen like the tides.
What is unusual now, scientists say, is how fast it’s happening. Geologic changes that normally take centuries are flitting past like time-lapse photography.
In the past decade, the rate of melting has been six times the historical rate. Geological surveys indicate that the total volume of ice and perennial snow on the mountain decreased as much as 18 percent between 2003 and 2009. The total net loss of water from Mount Rainier’s glaciers since 2003 has been estimated at 200 billion gallons.
“The problem is the rate of change in a short period of time,” Kennard said. “If you look at it on a graph, it’s like a pingpong ball just fell off the edge of the table.”
Temperatures across the Pacific Northwest are averaging about 1.4 degrees warmer now than they were in 1895. The rise sounds minor, but in a natural system as delicately balanced as Mount Rainier, scientists say, the likely consequences of continued warming are enormous.
According to the latest National Climate Assessment report, released this year, temperatures in Washington will continue to rise through the 21st century, increasing somewhere between 3.3 and 9.7 degrees, depending mostly on the rate at which humans continue to produce greenhouse gases.
The Pacific Northwest may get wetter as well as warmer, according to climate models, and precipitation will shift away from snow and toward rain.
Evidence suggests, but is not conclusive, that rain increasingly will arrive in sudden, violent bursts, similar to the “pineapple express” downpours in November 2006, when 18 inches of rain fell on the park in 36 hours.
That’s bad news for Mount Rainier’s glaciers, Kennard says.
The rate of glacial thinning is not directly proportional to rising temperatures, he said. In some cases, it can build exponentially.
“Once it starts, it’s like a feedback mechanism,” Kennard said. Running water beneath the glaciers creates space for warm air, which increases the rate of melting. As the glaciers shrink, they uncover loose material that hasn’t been exposed for thousands of years. Rock walls formerly held in place by ice collapse downward, covering the ice with dark rock that absorbs heat rather than reflecting it.
Aside from the melting caused by warmer temperatures, glacial ice could in some cases disappear faster because of a thinner layer of protective snow on its surface, Kennard said.
Heavier rains would mean an increased likelihood of avalanches, bursts of liquefied mud slurries, and sudden outbursts of trapped water from beneath the glaciers — potentially devastating events called jökulhlaups.
Outburst floods occur without warning, and there’s growing concern at the park that water suddenly released from the Nisqually Glacier could race like a tidal wave through the historic settlement of Longmire, heavily populated by park visitors in summer months.
The more predictable effect of the melting glaciers, though, is the steady accumulation of sediment in the park’s riverbeds, a process called “aggradation.”
“Glaciers act like giant conveyor belts for sediment,” said Scott Beason, a Park Service geologist who works with Kennard at Mount Rainier.
More rocks and gravel in riverbeds means less space for water.
“You can imagine the riverbeds as big bathtubs,” Beason said. “You can fill a bathtub up to a certain level, but when you take a couple of buckets of dirt and dump them into that bathtub, you can’t expect it to carry the same amount of water.”
Sediment from the melting glaciers is filling Mount Rainier’s river drainages at an unprecedented rate, Beason said, up to 3 feet per decade on average.
When riverbeds fill, water finds the next path of least resistance. Lately, that’s been taking it through park roads, campgrounds and trails, causing millions of dollars in damage.
Flooding in 2006 alone cost $36 million in damages.
Roads built in the park in the early 20th century were designed to provide visitors with a stimulating driving experience, not to withstand flooding.
Most were built along old river and stream channels, which now are being filled as glacial meltwater seeks new routes downhill.
Since 2001, Beason said, there have been at least six debris flows in three watersheds where there have not been such flows since the park was founded in 1899.
“Atmospheric river” flooding in 2005 and 2006 set off 10 debris flows in two days, resulting in such extensive damage that the entire park was closed to the public for six months. All of those debris flows began in areas that had been recently exposed by melting glaciers.
“In 2006 after the floods it was like an A-bomb went off there,” Kennard said. “The public is getting kind of squeezed in terms of where they can go.”
The park is spending $26 million to repair the 17.6-mile Nisqually-Paradise Road, which carries half of the 1.7 million park visitors each year.
In November, the first rainstorm of the winter season flooded the road, forcing park officials to shut down the Nisqually entrance and evacuate staff and guests from the National Park Inn at Longmire.
The Carbon River Road, in the northwest corner of the park, was washed out in the 2006 flood and now is closed to vehicles at the park boundary.
The Westside Road, which has the highest concentration of hiking trailheads in the park, is directly in the path of debris flows from the South Tahoma Glacier and has been closed to the public more often than not since the 1980s.
In May of this year, heavy rain sent a barrage of boulders down onto the Westside Road, smashing a pickup truck and leaving several craters, one of them 10 feet across and 3 feet deep.
On the other side of the park, increased sedimentation has raised the elevation of the White River 14 feet above heavily traveled state Route 410 for a distance of 3 miles. In 2006, a portion of the White jumped its banks and inundated the highway for several miles. A larger shift could send the entire mainstem of the river flowing down Route 410, said Roger Andrascik, the park’s Chief of Natural and Cultural Resources. “Once a river finds a road, it loves it,” he said.
Historic park buildings are also at risk, most notably at Longmire, the collection of 1920s era buildings along the Nisqually that are collectively protected as a National Historic Landmark District.
The cascade of rock tumbling down the Nisqually valley has filled the river channel to a point where the riverbed is now perched more than 30 feet above the buildings.
Most of Longmire’s 57 buildings are below the level of the river, including the park’s emergency operations center. Park managers consider the danger of flooding at Longmire so high that in 2002 they moved most administrative offices and permanent employee residences out of Longmire and onto safer ground outside the park.
The scale of some of the possible consequences of global warming is so large at Mount Rainier, it’s forcing a reexamination of traditional park policies and values once held nearly sacred.
More than a cubic mile of snow and ice remains on top of Mount Rainier, high above sea level, and as climate change intensifies it will continue to come down, scientists say, occasionally with extreme force.
“At some point, there may come a time when you just can’t do any more,” Andrascik said “But at what point do you stop trying?”