When the mountain blew up physically, it also blew away many false ideas about geology, ideas that were wrong, but had been believed for more than a century.After decades of inactivity, Mount St Helens coughed to life in March 1980, some two months before its explosive eruption.
None of this is credible evidence that something like the Grand Canyon could be formed quickly.
The conventional K-Ar dating method was applied to the 1986 dacite flow from the new lava dome at Mount St. Porphyritic dacite which solidified on the surface of the lava dome in 1986 gives a whole rock K-Ar 'age' of 0.35 ± 0.05 million years (Ma).
Helens, located in southwestern Washington about 50 miles northeast of Portland, Oregon, is one of several lofty volcanic peaks that dominate the Cascade Range of the Pacific Northwest; the range extends from Mount Garibaldi in British Columbia, Canada, to Lassen Peak in northern California. Helens a composite volcano (or stratovolcano), a term for steepsided, often symmetrical cones constructed of alternating layers of lava flows, ash, and other volcanic debris.
Composite volcanoes tend to erupt explosively and pose considerable danger to nearby life and property.
Mount St Helens changed that, which is why I have been so interested in what happened.
The eruption demonstrated that geologic catastrophe can produce in hours and days geologic features previously believed to have taken millions of years.
Helens "Louwala-Clough," or "smoking mountain." The modern name, Mount St.
Helens, was given to the volcanic peak in 1792 by Captain George Vancouver of the British Royal Navy, a seafarer and explorer.
The plume occasionally contains minor ash, which falls in the crater and on the southern flank of the volcano, darkening the new snow.
Seismic activity remains low compared to that observed earlier, and is consistent with a slow but continuous rise of magma driving up the crater floor and feeding a surface extrusion of lava.
These are clear signs of volcanic activity and they are very similar to what was seen before the eruptions of 1980.