Post-glacial lahars of the Sandy River Basin, Mount Hood, Oregon.

Within the last 10 000 years, three significant lahar-producing periods have occurred at Mount Hood, Oregon. The Timberline eruptive period occurred between 1400 and 1800 years BP. It was by far the most voluminous of the three periods, producing enough clastic debris to bury the glacial topography of the southwest face of the mountain beneath a smooth debris fan. Timberline-age lahars traveled the length of the Zigzag and Sandy Rivers, a distance in excess of 90 km. Between 400 and 600 years BP, the Zigzag eruptive period produced deposits along the middle reaches of the Zigzag River and the upper Sandy River. The Old Maid eruptive period occurred between 180 and 270 years BP. A single lahar flowed down the Sandy River at least as far as Brightwood, 30 km from Crater Rock. -from Authors