Small debris flows observed in Tahoma Creek at Mount Rainier National Park.

On August 13, a series of small debris flows rumbled down Tahoma Creek, in Mount Rainier National Park. No one was injured and damage was limited to the stream channel inside the Park.

Observations and photos taken by National Park Service geologists during an overflight in the afternoon indicate that the debris flows appear to have started at the terminus of South Tahoma Glacier. Some sediment from the debris flow was visible 8 miles downstream at the Highway 706 crossing.

Looking at seismic data from the Pacific Northwest Seismic Network, the vibrations from the debris flow are recorded on seismograms from Rainier station RER, located at Emerald Ridge overlooking Tahoma Creek. The debris flow signal starts at ~9:50 AM PDT. Signals are emergent, pulsatory, and relatively high-frequency, all characteristics of debris flows. There was a period of time from ~9:50 AM through to ~12:45 PM where signals were occurring relatively continuously, with several tens-of-minutes-long higher-amplitude bursts at 10:15-11:10, 11:25-11:50, and 12:30-12:40 that probably correspond to major debris-flow pulses. No debris-flow-like signals showed up overnight.

This event is similar to numerous debris flows that have occurred at Mount Rainier in past decades. Water stored in the glacier was released and quickly gathered up loose mud, sand, soil, and rock to form a debris flow. Small flows are common at Mount Rainier during late summer and early fall; a second group of debris flows commonly develops from torrential rainfall during early winter storms. Between 1985 and now, more than 30 debris flows have rushed down the Tahoma Creek valley.

The visiting public is reminded to stay clear of valley floors during debris flows and to the safety of higher ground when a debris flow is passing.

Visit the Mount Rainier National Park for information on the event and any closures. Follow the Mount Rainier debris flows link for more information on these events.