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Roger Weller, geology instructor

Mt. Rainier
by Adrienne Jones
Physical Geology
Spring 2014

                                                                                 Is Mt. Rainier getting ready to erupt?



     Mount Rainier is a 500,000 year old stratovolcano located in Pierce County, Washington and stands at an elevation of 14,410 feet. The volcano overlooks three cities and can be seen from the top of the space needle.

     Recently many people have been paying attention to this volcano and wondering, Is Mount Rainier getting ready to erupt? The short answer is: itís complicated.

    There are many factors regarding Mt. Rainierís next eruption and here are a few things you need to know. 

What is a stratovolcano?

 A stratovolcano is made of alternate layers of lava and ash. states, ďUsually, these types of volcanoes erupt explosively and violently, sometimes completely blowing their tops!Ē and ďSome of the most powerful and destructive volcanoes in human history have been stratovolcanoes.Ē Although there are many more active and larger volcanoes many experts are saying that it is one of the most dangerous volcanoes in the United States.

Why is Mt. Rainier so dangerous? 

     Mt. Rainier is the largest volcano in the cascade range and towers over 3.3 million people. Also, the inside of the volacano is rotten and could possible collapse at any moment. The interior has a hydrothermal system, which basically means that the insides are being steamed and all of the rock inside transforms into a type of soft clay. The danger of having the inside of this volcano filled with this gooey clay is that it can become too weak and collapse. Although the inside of Mount Rainier is very warm and steamy, the exterior of Rainier is covered in ice which makes up many up glaciers and if it ever erupted the main concern would be mud and ice.

What are some Geological hazards of Mt. Rainier? 

     Rockfall and debris flow are both very hazardous because they can occur with little to no warning.  There are also hazards of floods, volcanic unrest, active steam vents, and periodic earth tremors.


When was the last time Mt. Rainier erupted? 

     Mt. Rainier has not erupted since the first half of the 19th century and has not had a large eruption in over 1,000 years. However, 5,600 years ago the summit (top of the crater of a volcano) collapsed and created a very large mudslide known as a lahar (flow of volcanic debris that has the ability to destroy forests, buildings, bridges, homes, and many other man-made structures), which traveled a minimum of 100 miles before stopping. The last time a lahar of this scale happened was approximately 500 years ago.

     The aftermath of this lahar left deposits 30 feet thick in some places where a great part of Tacoma is built. Most people are familiar with the volcanoes in Hawaii that erupt frequently and spew out hot lava. The difference between those and the future eruption of Mt. Rainier is that the last recorded eruption was hundreds of years ago which means the impact will be much more destructive and have a much greater affect on the 3.3 million people who leave in the Seattle-Tacoma area.

 Mt Rainier vs. Mt. St. Helens 

     Many people are familiar with the Mount St. Helens eruption (also located in Washington) and it is common to try and compare Mt. St. Helensí eruption with Mt. Rainierís future eruption. However, if Mt. Rainier were to erupt it would make the Mt. St. Helens eruption look small by comparison. Because of the large amount of snow, rotten rock, and glaciers, the damage of Mt. Rainierís future eruption would be much more violent and cover much more area. In 1995 there were approximately 100,000 people living in the way of Mt. Rainerís possible path of eruption. It would produce a very rapid lahar at about 30 miles per hour and destroy everything in sight.

 In conclusion

Mt. Rainier is expected to erupt but there is no idea as to when. Washington's director of emergency management told Ultimate Explorer, "It's a low probability it's going to occur in our lifetime. But if and when it does, the consequences are going to be huge." When Mt. Rainer does erupt the greatest threat will be lahars flowing into the Seattle-Tacoma area at rapid speeds. 

Works Cited