The northern face of this 9677ft tall, symmetrical mountain collapsed in a massive debris avalanche. Approximately 230 sq. miles of forest were blown down or buried beneath deposits of volcanic soil. As with most volcanic eruptions, a large mushroom-shaped cloud began to rise, reaching thousands of feet into the air, blotting out the sun. Day was turned to night in moments. Thought the eruption lasted only a matter of nine hours, Mount St. Helen's surrounding landscape, ecosystem, and environment were to be forever changed.
The eruption produced the largest landslide in recoded history, sweeping down the mountain at speeds reaching up to 150 miles an hour, burring parts of the North Fork on the Toutle River. These slides deposited hundreds of feet of debris in some areas, with others recording over 300 feet increase in landmass deposits. In all, an approximate 2/3rd of a square mile of material was removed from the mountain itself.
The lateral blast was something that was not well know of at the time. The blast itself, created a damage path that would reach as far as 17 miles from the crater that was created. Temperatures reaching as high as 660 degrees Fahrenheit, ignited the timber in areas. It is estimated that the blast was equivalent to 24 megatons of energy, enough for it to snap and strip trees, some as old 100 years old.
At its peak, the ash cloud reached an estimated 80,000 ft (15.15 mi) into the atmosphere. This altitude was reached in a matter of 15 minutes. As the ash continued to rise, most of it fell within 300 miles of the blast zone, but some remained air born, circling the globe in approximately 15 days. Some finer particles are believed to have stayed in the air for many years after.
To understand the temperatures that were generated by the blast, snow that was not immediately vaporized, began to form large flows of mud, that would eventually destroy hundreds of homes, hundreds of miles of roadways, scores of bridges and railway lines.
To top this off, pyroclastic flows began rolling out of the crater, lasting hours and hours, covering close to six miles of land, stripping, and destroying the land with temperatures at or near 1300 degrees Fahrenheit.
Because of this eruption, approximately 200 square miles of once pristine, lush, and rich forests, full of trees and wildlife, we completely erased. This blast was so destructive, that now, only 30 years later, the land around the blast is slowly starting to heal itself and return to its once magnificent self.
Because of this one event, President Reagan and the US Congress created the 110,000 acre National Volcanic Monument in 1982. This area was to remain untouched, undisturbed, to allow nature to heal itself naturally. For this reason, the area is used for research, recreation, and educational purposes.
At present (4/1/2011), there is a lava dome that raises 1311 ft above the 1980 crater floor. This "Whaleback," because of its distinctive shape, measures approximately 3725 ft in length, 1900 ft in width, with a volume of 122 million cubic yards. All the lava that has erupted since the 1980 eruption has filled 7% of the crater, to date.
With final estimates, this blast ranked as one of the most costly. Estimates placed include: $1.1 billion for agriculture, timber, and work projects destroyed; 7,000 large game animals; over 10 million Coho and Chinook salmon; and thousands, possible millions of smaller birds and small animals.
The final heartbreak was the lose of 57 people, of which 21 bodies we never recovered, most of them located near the blast zone.
To get credit for this, please venture to the given coordinates. There may or may not be a sign here at times. Please answer the following questions, you can get help at the Johnson Observatory:
1. During the eruption, a debris avalanche occurred at Spirit Lake. How many feet was the lake bed raised.?
2. How many times has the volcano erupted since the 18 May eruption?
3. What type of volcano is Mt. St Helen's and what type of blast occurred on May 18, 1980?
4. What are the names of the two river valleys in front of you?
5. As of 2009, how deep is Loowit Channel?
6. Optional: Please post a pic of yourself and GPS at the coordinates, with the volcano in the background.
As is the nature of nature, signs may become destroyed or damaged. The Johnson Observatory is a wonderful place to ask questions, should these signs go missing. I have contacted the park in the past about this issue and have assured me they attempt to fix them as soon as possible.
Answers with "I dont know; Cant find it; etc..," or failing to answer the first four questions will cause your log to be deleted.
Each person who logs a find must submit their own answers, no group emails.
Please be mindful to remain on all paved and hard surfaces.
Do not go off-roading or damage the natural habitat in any way.
This is a learning opportunity, that many will want to join in on, so CITO and leave no trace when visiting.
I do not reply to correct answers. So please log your find once you have completed the cache and submitted your answers. If there are any concerns, I will contact you.
ALL LOGS THAT DO NOT HAVE ANSWERS SUBMITTED WITH 72 HOURS WILL BE DELETED.