A few years later, Mount St. Helens experienced a major eruption. Explorers, traders, missionaries, and ethnologists heard reports of the event from various peoples, including the Sanpoil Indians of eastern Washington and a Spokane chief who told of the effects of ash fallout. Later studies determined that the eruption occurred in 1800.
The Lewis and Clark expedition sighted the mountain from the Columbia River in 1805 and 1806 but reported no eruptive events or evidence of recent volcanism. However, their graphic descriptions of the quicksand and channel conditions at the mouth of the Sandy River near Portland, Oregon, suggest that Mount Hood had erupted within a couple decades prior to their arrival.
Meredith Gairdner, a physician at Fort Vancouver, wrote of darkness and haze during possible eruptive activity at Mount St. Helens in 1831 and 1835. He reported seeing what he called lava flows, although it is more likely he would have seen mudflows or perhaps small pyroclastic flows of incandescent rocks.
On November 22, 1842, Reverend Josiah Parrish, while in Champoeg, Oregon, (about 80 miles or 130 kilometers south-southwest of the volcano), witnessed Mount St. Helens in eruption. Ash fallout from this event evidently reached The Dalles, Oregon (48 miles or 80 kilometers southeast of the volcano). Missionaries at The Dalles corroborated Parrish's account. Captain J.C. Fremont recounts the report of a clergyman named Brewer, who gave him a sample of ash a year later (Wilkes, 1845):
"On the 23rd day of the preceding November, St. Helens had scattered its ashes, like a light fall of snow, over the Dalles of the Columbia."
