What will happen if Mount Rainier erupts?

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Answered by: Victor, An Expert in the Seattle and Tacoma - General Category
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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