A debris flow occurred in Tahoma Creek on Monday, Aug. 5, on the southwest side of Mount Rainier National Park. The event occurred between approximately 6:48 p.m. and 7:58 p.m., originating from a sudden and significant change in the primary outlet stream from the terminus of the South Tahoma Glacier. This change caused a surge of water within the glacier and turned into a debris flow.
The park’s Westside Road and Tahoma Creek Trail sustained some damage, so in consultation with the USGS Cascades Volcano Observatory, the park has temporarily closed the Westside Road. No damage is expected outside park from this event. This debris flow may indicate that subsequent events may occur in the coming weeks or months.
“Debris flows are not uncommon during periods of hot weather in the park’s dynamic landscape” said Tracy Swartout, acting superintendent. “Visitor and staff safety are our priority, so limited closures are appropriate at this time.”
Park staff detected the event on Tuesday morning when the Tahoma Creek appeared extremely sediment-rich. Park geologists conducted aerial reconnaissance of the area Tuesday and identified the source and runout areas. They also checked the South Tahoma Glacier for additional outburst geologic hazards. All visitors and staff in the area were accounted for on Tuesday.
Glacial outburst floods and debris flows occur with some regularity in the rivers that drain glaciers within the park. A glacial outburst flood is a large, abrupt release of water from a glacier. Although the mechanism remains unknown, geologists report that stagnant and slow moving ice on the lower part of a glacier combined with faster moving ice on the upper glacier has been associated with such events. The Tahoma Creek valley has had at least 32 outburst floods and debris flows since 1967.
The park reminds all visitors to remain alert for changes in water levels and unusual sounds or shaking ground. In the event of rapidly rising water or a loud roaring sound coming from up valley, move quickly to higher ground at least 200 feet above the valley bottom. Visitors who may have witnessed the event on Monday are encouraged to report observations to Scott Beason, Park Geologist, at email@example.com.