MASSIVE DEBRIS FLOW GENERATION ON MOUNT HOOD, OREGON, NOVEMBER, 2006

In November, 2006, a storm unleashed 13.4 inches of precipitation in six days triggering major debris flows in many of the drainages on Mount Hood, Oregon. This volcano is located in the Cascade Range just 80 miles east of Portland, Oregon. The mountain has a long history of debris flow and lahar activity. To date, management response to large climactic events has been limited by a lack of distinction between commonly affected drainages and drainages with little to no response to debris flow generating events. Documentation of this, the most recent event will prove useful for future hazard management practices. Recognition of common factors linked to debris flows at Mount Hood could improve identification of hazard prone areas on other volcanoes. An initial reconnaissance was conducted to survey the primary drainages around the mountain. This assessment was conducted via access points close to major roadways. The November storm triggered multiple known debris flows on all sides of the mountain. Of the eleven primary drainages, five including the White River, Clark Creek, Newton Creek, Eliot Creek, and Sandy River experienced torrents powerful enough to cause major damage to bridges and roadways. Highway 35, a key access route on Mount Hood, was closed in two places. By careful documentation of these flows, we may be able to determine common factors between the drainages which showed a response. This project seeks to answer the question of why some drainage systems responded with debris flows, while others appear to show only mild flooding. A hazard map for debris flows initiated by the November, 2006 storm will result from the project.