which european explored this area?
George Vancouver.
Mount St. Helens
Royal Navy Commander George Vancouver and the officers of HMS "Discovery" made the Europeans' first recorded sighting of Mount St. Helens on 19 May 1792, while surveying the northern Pacific Ocean coast. 
when did mt st helens erupt before 1980 On April 17, 1857, the "Republican", reported that "Mount St. Helens, or some other mount to the southward, is seen to be in a state of eruption". where is this mountain located? Skamania County, Washington, in the Pacific Northwest region of the United States. is it valuable for the indigenous people? Native American lore contains numerous stories to explain the eruptions of Mount St. Helens.
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Mount St. Helens [SEP] Exploration by Europeans
Alarmed by the "dry snow," the Nespelem tribe of northeastern Washington supposedly danced and prayed rather than collecting food and suffered during that winter from starvation. In late 1805 and early 1806, members of the Lewis and Clark Expedition spotted Mount St. Helens from the Columbia River but did not report either an ongoing eruption or recent evidence of one. They did however report the presence of quicksand and clogged channel conditions at the mouth of the Sandy River near Portland, suggesting an eruption by Mount Hood sometime in the previous decades.