DESCRIPTION:
Kautz Creek Mudflow, October 2-3, 1947, Mount Rainier, Washington

The smallest, but most frequent, debris flows at Mount Rainier begin as glacial outburst floods, also called by the Icelandic term "jökulhlaup" (pronounced "yo-kul-h-loip"). Outburst floods at Mount Rainier form from sudden release of water stored at the base of glaciers or within the glacier ice. Outburst floods have been recorded from four glaciers on Mount Rainier: the Nisqually, Kautz, South Tahoma, and Winthrop glaciers. ...

KAUTZ CREEK--The largest debris flow since the establishment of the park occurred October 2-3, 1947, when heavy rains apparently triggered an outburst flood from Kautz Glacier. The flood passed over the lowest part of the glacier, eroding a gorge through the ice, then mobilized sediment and transformed into a debris flow as it continued downvalley. Nine kilometers (5.5 miles) downstream from the glacier, the Nisqually-Longmire Road (equivalent to Highway 706 west of the park entrance) was buried by 9 meters (28 feet) of mud and debris. About 40 million cubic meters (50 million cubic yards) of sediment were moved, including boulders up to 4 meters (13 feet) in diameter. Although Kautz Creek has subsequently cut down through those deposits, visitors to the park will notice that they are driving uphill as they approach the creek. To observe deposits of the 1947 event, along with upright dead trees partly buried by those deposits, stop at the parking lot on the east side of Kautz Creek. Smaller debris flows have moved along Kautz Creek in 1961, 1985, 1986, and perhaps at other times.

From Longmire, hike the Wonderland Trail about 3 kilometers (2 miles) to where it crosses Kautz Creek. Boulders strewn across the valley there were deposited by the 1947 debris flow. Note the splintered trees that lined a former stream channel, and trees that lie buried horizontally in older debris-flow deposits. Above the boulder-strewn region and amid the forest lie moss-covered logs downed by previous debris flows.

During October of 1947, heavy rains and a jökulhlaup racked the lower Kautz Glacier. The resulting torrent ripped away a section of the glacier one mile in length down its center, and gouged a 300-foot-deep canyon once occupied by ice. A 60-foot-deep swath was eroded into the glacial gravels beneath the ice until the power of the flood was rendered ineffective on the hard bedrock. Witnesses observed that as the flood coursed down Kautz Creek it collected enough debris to form a lahar that pooled behind the box canyon and surged to the valley below. The mud toppled some trees and buried others so deeply that they died, then it flowed across the park highway six miles distant!

Debris flows are one of the most common and devastating geologic phenomena in the postglacial history of the volcano. The largest debris flows from Mount Rainier probably originated in volcanic explosions that caused large-scale avalanching of rock debris. Other debris flows were caused by such factors as heavy rainfall and rapid snowmelt, which are unrelated to volcanism; their occurrence at Mount Rainier results from the availability there of large quantities of loose rock debris on steep slopes. ...

Some debris flows form during very heavy rainfall or rapid melting of snow; others are caused by outburst of water from within, under, or on top of glaciers. Flows of these kinds are not directly connected with any king of volcanic activity, unless they result from excessive melting of ice due to volcanic heat. Debris flows caused directly by heavy rainfall pick up rock debris mainly from masses of loose glacial drift. Although these flows are of rather limited size, they occur more often than the vastly larger flows such as the Osceola and Electron. Debris flows occurred in October 1947 in the Kautz Creek valley during a period of very heavy rainfall. As runoff from valley sides and Kautz Glacier swept downvalley, it formed a series of debris flows that came to rest in a broad fan at the lower end of the valley. Grater (1948) estimated that 50 million cubic yards of rock debris was carried by the debris flows. Deposits of at least six pervious but similar debris flows are exposed in the banks of Kautz Creek.

Kautz Creek Mudflow, October 1947 - Crandell, 1971

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