Mount Hood

Summary

Mount Hood has erupted episodically for about 500,000 years and hosted two major eruptive periods during the past 1,500 years. During both recent eruptive periods, growing lava domes high on the southwest flank collapsed repeatedly to form pyroclastic flows and lahars that were distributed primarily to the south and west along the Sandy River and its tributaries. The last eruptive period began in AD 1781 and affected the White River as well as Sandy River valleys. The Lewis and Clark Expedition explored the mouth of the Sandy River in 1805 and 1806 and described a river much different from today's Sandy. At that time the river was choked with sediment generated by erosion of the deposits from the eruption, which had stopped about a decade before their visit. In the mid-1800's, local residents reported minor explosive activity, but since that time the volcano has been quiet.