Minor Outbursts

Day 299: Like most Pacific Northwesterners, when temperatures start edging into the upper 80s and lower 90s, our glacial streams and rivers get a little cranky. Tahoma Creek has a notoriously short temper in this regard, and over the last several days, made its displeasure with the weather known in a set of at least two minor outbursts. When Joe and I drove over the bridge on Wednesday en route to a Team Biota survey, it remained muddy and high despite having had close to 24 hours to calm after its most recent tantrum. It had gone down another two feet by the time we returned to take photos, and new deposits of mud and rock were visible in its bed. It was still pounding hard on the buttresses at either end of the bridge, a reminder that once not too long ago in a major fit of anger, it joined with the larger Nisqually to destroy Sunshine Point Campground. Outburst floods like these two most recent surges may have a number of different initiating factors, including pooled glacial meltwater being released when an ice dam collapses. Tahoma Creek has experienced several outbursts of this nature.

Tahoma Creek

Day 305: And now for the official release concerning yesterday's event, with two views of the creek taken from the main Park road on my way home tonight. As you can see, it is still quite muddy and turbulent. In the upstream view, you can see new deposition of silt on the left side of the image.

Glacial Outburst Flood and Debris Flow Occurs at Mount Rainier National Park

Westside Road Temporarily Closed Through the Weekend

A glacial outburst flood and debris flow occurred at Tahoma Creek in Mount Rainier National Park on Thursday, August 13, 2015 beginning at approximately 9:40 am. The glacial outburst flood originated from the South Tahoma Glacier as a 0.5 acre portion of the terminus of the glacier broke off and quickly released water stored in the glacier.

The outburst flood event was first reported by a park volunteer who was working near Tahoma Creek on an unrelated research project. The volunteer heard a loud roaring sound, followed by the sounds of water moving boulders and the cracks of breaking trees. As the debris flow from the initial outburst crossed the Westside Road, the volunteer hiked to higher ground. Another volunteer at Indian Henry’s Hunting Ground also heard the loud roar coming from the direction of the South Tahoma Glacier and hiked to a safe location near the suspension bridge over Tahoma Creek to report on subsequent outburst surges.

The debris flows was also recorded by seismic monitoring equipment at Emerald Ridge in Mount Rainier National Park at 9:40 am, 10:30 am, 11:30 am and 12:40 pm. The largest event was recorded at 11:30 am and generated a debris flow that reached the Westside Road at approximately 12:00 p.m.

Mount Rainier Park rangers and geologists responded quickly contacting park visitors in the area and assisting them across the area impacted by the debris flow. A Hughes MD530 helicopter from Northwest Helicopters assisted the park with two reconnaissance flights to look for park visitors hiking in the area, check the condition of the trail for possible washouts, and check the South Tahoma Glacier for possible additional outburst geologic hazards. All of the park visitors in the area were accounted for by Thursday evening, but park staff will continue to monitor visitor use in the area.

Some damage to Mount Rainier’s Westside Road was reported on Thursday. The Westside Road will be closed at least through the weekend as the park continues to monitor Tahoma Creek and assess damage to the road and area trails.

“This most recent glacial outburst and debris flow demonstrates again that Mount Rainier is a dynamic landscape,” said Randy King, Mount Rainier Superintendent. “Visitors should be aware of their surroundings when traveling in the park. Remember to remain alert for changes in water levels, unusual sounds or shaking of the ground. If you are near a river or stream, move quickly to higher ground.”

About seven waves of debris flow occurred on Thursday afternoon and evening. As the outburst flood moved down valley, it carried sediment, rocks, and uprooted trees and deposited the debris within the Tahoma Creek valley near Mount Wow in Mount Rainier National Park. A stream gage on the Nisqually River at National registered the 0.5 foot river rise on Thursday afternoon. The debris flow had no impact to properties outside of Mount Rainier National Park.

A glacial outburst flood is a large, abrupt release of water from a glacier. The exact mechanisms through which water moves through glaciers and how these events occur are not well known. Geologists report that stagnant and slow moving ice on the lower part of the glacier combined with faster moving ice on the upper glacier, have been associated with these events in the past.

Since 1985, over 30 debris flows have occurred in the Tahoma Creek valley. Glacial outburst floods from the South Tahoma Glacier during hot, dry weather caused most of the debris flows, but heavy rainstorms in the fall caused several others.

Today's Event

Day 304: This is one of my favourite maps. It was published by the USGS in 1973 and is entitled, "Potential Hazards from Future Eruptions of Mount Rainier, Washington" and covers all the possibilities from flood, mudflow, avalanche and/or tephra (airborne volcanic rock debris). The whole of the upper Nisqually Valley lies in the red and orange zones (areas of highest risk). That's why we get a little nervous around here when the earth shakes, or we hear rumblings on the Mountain.

There's a reason I selected this particular section of the map. Tahoma Creek (labelled just above the more obvious "Satulick Mountain") has turned loose a number of small "outburst floods" over the years, including one which wiped out a large section of the Tahoma Creek Trail and portions of the Westside Road. For this and other reasons, the Park decided to close Westside Road three miles in at Dry Creek. The road is still passable, and official vehicles are allowed beyond the closure, although they must be high-clearance rigs in order to navigate a number of rough washouts and a side stream.

Today, there was an "event" in Tahoma Creek. An outburst flood occurred somewhere up-valley, and the first we heard of it was when a report of a mudflow crossing Westside Road came over the radio. The person reporting the event was on the far side, and took the sensible precaution of moving to higher ground, roughly somewhere between the first W in "Mount Wow" and the M in "Satulick Mountain." She reported a noise like "a couple of helicopters" growing louder and louder as the river swelled and blustered its way over rocks and through forest. By the time the rumbling had subsided, rangers and geologists were on the way to investigate, and to try to locate any hikers who might have been in the area at the time.

I did not find out until a few hours later that the person reporting the event was our intern, Yonit. When she showed up at the office, she was rather visibly shaken but excited to relate the circumstances to us. Later, she showed photos she had taken with her phone of the water and mud breaching the road, and how it had undermined the pavement. She had been escorted to safety by the rangers even as the geologists went up in a helicopter to study the site.

When Kevin and I drove out tonight, Tahoma Creek was still flowing with some ferocity, and as thick as whipping cream with silt and mud. Westside Road has been gated off at the entrance. As outburst floods go, this was minor in terms of resource damage, but as temperatures remain in the 80s and glacial ice melts, the potential is there for more or larger events to occur. The red zone is real. I'm in it, and with full realization of the fact.