August 10, 2005
At White River on south flank of Mt Hood. Rick Conrey (Washington State University) explains recent volcanic history of Mt Hood by labeling features on large photographs of the mountain.
Crater rock on the upper part of the south flank of Mt Hood is a lava dome that grew and collapsed during two volcanic episodes of the last 1500 years. The latest volcanic activity occurred in ~1795 about ten years prior to the arrival of Lewis and Clarks’ Corps of Discovery in Oregon. That volcanic activity produced debris flows and volcanic mud flows (lajars) in the Zigzag and Sandy rivers.
The White River continues to transport volcanic material south from Mt Hood into the Deschutes River. The Sandy River transports similar volcanic silt, sand, and gravel from the southwest flank of Mt Hood into the Columbia River. When William Clark stepped from his canoe onto the delta of the Sandy River in October of 1805, he sank to his knees and named the river the “Quicksand River”.