Mount St. Helens

By:Chuck Wolfe

Chris LaPlanteMatt ‘Chang’ Madden

The Biggest Thing To Rock Washington…

Since M

etallica!!!

Since M

etallica!!!

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

…Before

After…