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Question What will happen if Mount Rainier erupts? (Posted by: Anonymous )

Victor Answered by: Victor, an
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Since the eruption of Mount Saint Helens in 1980, people both locally and internationally have hypothesized as to how much destruction would occur should Mount Rainier erupt. As the largest mountain and volcano in the lower 48 states, an eruption would be catastrophic, not only due to the size of the mountain itself, but also because of the sheer number of people who call the surrounding valley home.

Mount Rainier is part of the Cascade Range, a string of mountains and foothills, including Mount Saint Helens, that march from southern British Columbia in Canada to northern California. Many of the volcanoes in this range are active and concern nearby communities, but a Rainier eruption would be the most devastating of them all.

The destruction that would follow should Mount Rainier erupt would come not from the blast itself, but from the tsunami-like mud flow that would follow. This flow, called a lahar, would be enhanced by glacier melt caused by the steaming hot volcano. Traveling at immense speeds, the lahar would collect everything in its path, from trees to boulders to cars and buildings, adding all to its growing wave of destruction.

The numerous towns and cities that occupy the surrounding valley would all be at risk for not only severe destruction, but complete annihilation. Residents of cities like Orting, Sumner, Buckley, and Enumclaw are estimated to have no more than 30 minutes before the lahar, speeding down from the many rivers that flow from Mount Rainier, buries their homes and businesses beneath as much as 30 feet of mud and debris. Even the larger cities like Auburn, Puyallup, and Tacoma itself are not safe. Auburn and Puyallup, with nearly 80,000 residents between them, would be covered in 20 feet of mud in less than an hour, and Tacoma, at almost 200,000, is estimated to be hit with nearly 10 feet from the lahar.

One of the features that makes this valley attractive and prosperous could also spell doom for the people should Mount Rainier erupt. The many rivers, creeks, and tributaries that provide irrigation for the fertile farmland and recreation for fishermen could act as a deathtrap for the locals. In order to reach higher ground, a large percentage of the valley's populace must cross at least one of the bridges that traverse these many waterways. While the lahar may take 30 minutes to reach the population centers, the strain that the lahar will place on these rivers will cause nearly instant flooding along the entirety of the riverbanks. Should people not leave immediately, they could easily find the bridges washed out, and their hopes for survival dashed.

As terrible as the prospect of an eruption sounds, you will be hard pressed to find a resident of the valley who is overly concerned with an eruption. Most who worry about it don't move to the valley in the first place, and those who do live there are familiar with the lahar early warning system. A traveler to any of the towns will soon spot one of the many blue "Lahar Evacuation Route" signs. In addition, the cities have all adopted an alarm that is similar to the bomb raid warnings of World War 2. All who live in the valley know that if they hear the siren, they are to find high ground as soon as they can.

In the end, however, these warning systems are merely a backup; a fail safe in the unlikely event an eruption occurs that catches everyone off guard. Scientists have learned much from the 1980 eruption of Mount Saint Helens, and with the myriad of monitoring devices on the mountain itself, it is unlikely that anyone would be surprised when Mount Rainier erupts. All who desire to live in the area would do well to keep that in mind.

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Thanks for your information. Being as I am not familiar with the area....my husband wants to relocate there. My concern is for my children being at school during an imminent problem. I understand the warning system has been found so far to save lives...that is reassuring. What I don't understand is your terminology when you say mudflow...does that mean mud, rock and such or does that include lava...and how would people in a city like Seattle most likely die? The mud, air, Lamar and how soon would it reach there? The surrounding area of the mountains would be within 30 minutes, but does it slow and take days to reach Puget sound. Forgive me for my ignorance, but I have until the 8th. to let him have my answer as to whether or not to apply for the job. I am excited to go to a place that is green, but a bit apprehensive. We live in the desert...on five acres, but I want my homeschooled son to experience more of the outdoors...and Seattle seems perfect for that. Thankyou for this post. It has been the most helpful!;) Jenny By Jenny on 04-12-12 at 12:51pm
Iwas curious if you knew if Eatonville would be effected? I am thinking about moving there and would like to make sure I am ok. By john on 27-01-13 at 12:22pm
I would just like to say that at least some of those killed at Mt St Helens were outside of the zone that scientists had deemed unsafe. They died because the blast came from the side of the volcano, not the top, and so the actual danger zone exceded the predicted zone. They did not refuse to leave, they were given the green light to be where they were. By Marta on 29-03-13 at 12:52am
What would the chances be of a Mt St helens like lateral blast and lahar and how far would a mt rainier lateral blast reach? By Jeff D. on 23-09-13 at 10:24am
Thanks so much for your answers. I think they give much more information than some other sites. At least, after reading these posts, I know what direction I would head. Just hope we never have to put these plans to use. By Diane on 13-03-14 at 09:59pm
Even if you managed to avoid the Lahar wouldn't you still have to worry about the ash,lava and pyroclastic cloud full of deadly chemicals?. When Vesuvius erupted it effected areas as far away as Heculaneum and parts of Naples. By Kat on 16-04-14 at 10:46am

Follow-Up Question I was looking at a map of if a lahar happened. It only shows that it would go down river flows. Is it thought that it would cover everything? I am looking to move down that direction, towards Roy. (Posted by: Anonymous )

Victor-12518 Answered by: Victor-12518, an
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The rivers in the area originate on Mt. Rainier, so they provide the path of least resistance for a lahar to travel. Communities in the valley areas (Puyallup, Auburn, Sumner, Orting, Tacoma) will be the ones that are hit by the lahar and will suffer the devastation.

The further away from the mountain you are located, the less the lahar will affect you. For example, Orting is theorized to get a 30 foot wave of the lahar, whereas Tacoma is thought to get 10 feet or less. The lahar will travel down the rivers, flood the surrounding areas, and empty into Puget Sound.

All of the valley residents are familar with the "Volcano Evacuation Route" signs that are scattered around the area. Puyallup and Orting residents are supposed to head up the hills to South Hill and Graham, while Sumner and Auburn residents will flee up toward the Bonney Lake/Lake Tapps area. It's essentially a "head for the hills scenario."

Even though towns like Orting and Sumner will most likely be completely wiped out by the lahar, South Hill and Bonney Lake will be unaffected, even though they are located just a few miles from Orting and the other valley communities. Their elevation will keep them safe.

Roy isn't located in a valley or near any of the rivers that would be affected, and so it should be untouched by the lahar. Rest assured that a resident of Roy will definitely hear the blast if Mt. Rainier erupts!

I have lived my entire life in the shadow of Mt. Rainier, and my home would be one of those destroyed should Rainier ever erupt. I also sold real estate for 8 years, with many of my home sales occurring in the valley area where I live.

While I understand that people would be concerned for the safety of their family and themselves, I believe there is no reason to worry. If you look at the eruption of Mt. St. Helens in 1980, people knew for weeks that the mountain was going to erupt. The small communities and tourist sites in that area were evacuated, and those who died were people who refused to heed the warnings and leave their homes.

As a historian, I have never heard of a mountain spontaneously erupting on such a massive scale as what would create the lahar that would destroy the valley communities. Even then, Mt. Rainier has so many sensors on the mountain that are monitored by seismologists that nobody should live in fear of an eruption.

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