DEBRIS FLOWS ON MT. ADAMS, WASHINGTON INITIATED BY THE NOVEMBER, 2006 STORMS: CHARACTERIZATION, INITIATION ZONES AND HAZARD MAPPING

In November of 2006, Mt. Adams experienced debris flows in seven of the eighteen drainages including Adams Creek, Big Muddy Creek, Lewis Creek, Little Muddy Creek, Muddy Fork, Rusk Creek, and Salt Creek. Six debris flows occurred on the northeast side of the mountain. A landslide initiated one debris flow on the inside of a lateral moraine, two were initiated by heavy water flow and in channel landslides and three were initiated by a coalescence of eroded channels (headless debris flows). Four pre-2006 debris flows were found in the Cascade Creek, Crofton Creek, Hellroaring Creek and Morrison Creek drainages. Every 2006 debris flow originated in “Quaternary glacial drift”. The Crofton Ridge Moraine was eroded severely during this event and exposed permafrost in the lower glacial till. Attributes of the drainages were investigated to determine differences between drainages with debris flows and those without (Williams, 2011). The upper basins of drainages with debris flows averaged 37% glacial cover, 29% bedrock, and 35% unconsolidated material. The upper basins of drainages without debris flows averaged 12% glacial coverage, 63% bedrock, and 25% unconsolidated material. All of the drainages with debris flows were directly connected to the glacier, opposed to only 36% of the drainages without debris flows. Drainages with debris flows averaged 18% slopes above 33 degrees, 10% vegetation, a gradient of 0.38, a Melton’s Ruggedness Number of 0.62, an average annual rainfall of 2.16 m, and -52% glacier lost between 1904-2006. The upper basins of drainages without debris flows averaged 11% slopes above 33 degrees, 18% vegetation, a gradient of 0.31, a Melton’s Ruggedness Number of 0.58, an average annual rainfall of 2.38 m, and -41% glacier lost between 1904-2006. Of all of the factors analyzed percent glacial coverage and average annual rainfall predicted the 2006 debris the best.