The Creation of the Beast Created 40,000 years ago Created from decite and andesite eruptions Most of the Volcano’s bulk was created over the last 2500 years
What, When, Where… What: –Mt. St. Helens; a majestic stratovolcano that drew tourists from thousands of miles When: –Erupted on May 18, 1980 Where: –Washington State; 46.2N 122.18W
The Point is…. Pre-eruption –Early effects of the volcano –The explosion of the Summit Dome Pyroclastic activity –The establishment of pyroclastic activity –The effect on the land surrounding the volcano
Taking One to the “Dome” Geothermic activity heated underground water –Steam gradually built up which resulted in a phreatic explosion –Summit Dome exploded from the pressure, hurling material across the landscape
She called out a warning… University of Washington deployed portable seismographs. So well known that people came to observe volcano for pleasure. Despite warnings, some people didn’t want to leave.
Active History Mt. St. Helens has been dormant for a century. –Months before the 1980 eruption, seismic activity has been recorded. –Out of the Cascade Volcanic range, St. Helens is presently the most active.
The Warning Signs To Doom Early Effects –Earthquakes began to increase in quantity and intensity. This led to the breakup of St. Helens icecaps –The intrusion of the Goat Rock Dome
The Beginning of the Calamity Predictions come true with the occurrence of a 5.1 earthquake –Causes biggest landslide in recorded history Second largest eruption in U.S. history
Pyroclastic Pyroclastic flows –Hot mixtures of volcanic gas, pumice, and ash Pyroclastic surge –Low density surge of pyroclastic material –Carries less material, but travels at much faster rates
Spirit Lake Created by previous volcanic activity thousands of years ago A heavily forested area before 1980 eruption
The Destruction of Spirit Lake Post-Eruption –Barren land scattered with ash, tree trunks scattered across the area, empty waterbed
Powerful Nature of the Surge The pyroclastic material is capable of traveling up to 300 mph The temperature of the rocks reach 200°C to 700°C Follow indentations of crust (i.e. valleys & canyons)
Range and Effect of the Flow The Mount St. Helens pyroclastic flow created a 15 mile radius of destruction around the base of the volcano
The Conclusion The destruction –Flooding –Pyroclastic flows; Melted icecaps –Mudslides –Falling debris