DEBRIS FLOW INITIATION ON MT. RAINIER AS A RESULT OF RECORD PRECIPITATION FROM THE NOVEMBER 2006 PINEAPPLE EXPRESS RAINSTORM

In November 2006, a Pineapple Express system moved through the Pacific Northwest dropping record amounts of rain. Debris flows were recorded on Mt. Hood, Mt. Adams, Mt. St. Helens, Mt. Jefferson, and Mt. Rainier. Thirty-four drainages around Mt. Rainier have been examined using orthophotos, LiDAR, previous reports, and field verification in order to determine if a debris flow was initiated as a result of the 2006 storm. Previous studies have identified seven drainages that produced debris flows: Inter Fork, Kautz Creek, Ohanapecosh, Pyramid Creek, Tahoma River, and Van Trump Falls Creek. So far, five other drainages have been determined to have had a debris flow during the 2006 event: Carbon River, Fryingpan Creek, Muddy Fork Cowlitz River, South Mowich River, and South Puyallup River. Two other drainages are still under examination: North Puyallup and White River. Characteristics like changes in vegetation coverage, stream channel patterns, in some instances a landslide in the upper drainage, and levees were used to determine if a debris flow occurred. Twenty-seven total drainage basin attributes related to glacier area and change, percent vegetation, bedrock, and surficial geology coverage in the upper basin, topography, initiation zones, and rainfall were collected for each drainage. Currently, these drainages and data provide a complete database for basin characteristics and changes due to the rainstorm. These attributes will be evaluated to help determine why some drainages had debris flows and others did not. A regression analysis will be done on the data that do not have repeated components and are measureable across all basins in order to determine which attributes are most influential on debris flow initiation. From this, a prediction model and susceptibility map can be produced for debris flow occurrence Mt. Rainier due to a high precipitation rainfall event like the November 2006 storm.