Thursday, August 3, 2017

Mount St. Helens, Washington

At one time Mount St. Helens was just another mountain/volcano in the Olympic National Forest. But on May 18, 1980, Mount St. Helens erupted, fracturing the volcano's entire north slope, cutting the summit height by more than 1,300 feet. This caused the largest ever recorded landslide. The resulting ash cloud billowed 15 miles into the air, depositing debris throughout the state.





Landslide
The north flank of the volcano collapsed, forming a landslide that slid into Spirit Lake, up and over Johnston Ridge, and down the North Fork Toutle River Valley.

Lateral Blast
Rapid expansion of volcanic gas and superheated water exploded rocks and ash through the landslide, forming a huge sideways blast that moved faster than 300 miles per hour.

Pyroclastic Flows
Fiery mixtures of volcanic gas and frothy molten rock, known as pumice, erupted from the vent and plummeted down the north side of the volcano.

Ash Column
Within 15 minutes after the eruption began, the boiling ash column rocketed 15 miles skyward. Winds carried the cloud eastward, away from this spot. Ash rained down across four states. Around noon, fresh gas-rich magma erupted from a reservoir about four miles beneath the volcano. Searing, ground hugging flows of pumice, ash and gas boiled out of the crater and on to the landslide deposit. These "pyroclastic flows" swept downward, one on top of another, like waves, creating the smooth Pumice Plain. By early evening, the volcano's pent-up gases had been released. The eruption slowed, then subsided by the next morning. Ash and volcanic gas erupted from the crater for nine hours, ash deposit covered 22,000 square miles. Six square miles of steaming pumice, 120 feet deep in places, lay to the north.

Yakima, Washington
Downtown Yakima, Washington at 1pm on May 18, 1980. Strong, high-altitude winds carried the ash eastward at about 60 mph. Ash turned day into night across eastern Washington.


Picture taken from an old camera a photographer just so happened to find at a Portland, Oregon Goodwill.  She discovered there was still film in the camera and took it to be developed. The pictures were of the erupting volcano, forgotten by the family who took them.

1982



Splintered stumps and downed trees reveal the direction the lateral blast traveled. Hot gasses made the blast flow like a fluid while the weight of ash, rock and fragmented wood held it tight to the ground. The ground-hugging cloud followed the lay of the land, rolling up and over ridge tops. Within 90 seconds, the debris-filled blast struck this forested hillside, pulverizing ancient trees. The nearly 500 mile per hour blast shattered and toppled trees. The blast stripped their bark and branches, carrying them miles away.




Unfortunately, this is how we saw Mount St. Helens the day we were there. As it was when we were leaving the Olympic Peninsula, the fire smoke from Canada has lingered on and is flowing down into southern Washington and into Oregon.

Mount St. Helens was declared a U.S. National Monument in 1982. At the end of the roughly 50 mile drive from Castle Rock to the Visitor Center at the Johnston Ridge Observatory, there are exhibits, movies, and Ranger led walks and talks. We enjoyed our visit, but I sure wish the sky was clearer.










No comments:

Post a Comment