Wednesday, July 23, 2008

Debris flows

On August 15-16, 2006 a small debris flow in the upper Van Trump Creek basin raced down the steep slopes over Comet, Van Trump and Christine Falls into and down the Nisqually river (Seattle PI article). The debris flow started after a period of warm weather caused a portion of the Kautz Creek glacier to calve off over Wapowety Cleaver into the steep wall upper basin, and took ice and debris downstream.

It proceeded to inundate the falls and creek with mud and debris with much of it going into the Nisqually River and carried downstream by the main flow of the river. By the time is reached the USGS streamflow gage at National, the river rose just under 3 inches in minutes, partly from the silt and sediment and partly the increased flow of the melted ice and water from the Van Trump basin.

While this debris flow raised alarms, it was just a small one in the history of mud and debris flows off Mount Rainier, in fact a figurative sneeze of one. But it raised concerns and scientist have renewed their research this year in part from the significantly higher than normal snowpack and late snowmelt (Olympian article).

What does this mean to you the visitor?

It means when you're hiking the trails you should be alert to the signs of upstream debris flows. This is important especially if you're on a trail near a stream, where mud and debris flows can be high and wide through the valley along the stream or creek.

This is especially important this year with the snowpack and in July and August, the warm weather months where the chances of sudden glacier activity and subsequent mud and debris flows increase. And it's important at night if you're in one of the backcountry campground alongside a creek or river. Often the temperature diurnal at night from the warm weather creates the possiblity of glacial activity resulting in mud and debris flows.

It's not something to be in constant anxiety about, but it's worth noting when you hear loud, unusual sounds.

No comments: