Mt. Rainier:

What would happen if it blew its top?


The last time Mount Rainier erupted was in 1852, however the most real danger to people living in the shadow of the volcano is that of large mudflows called lahars. More than 5,000 years ago a large lahar swept down the mountain and out to the Puget Sound, covering an area that is now heavily populated.

PARADISE - Every summer many people from the Lower Yakima Valley make their way west to visit Mount Rainier National Park without giving any thought to the geological wonder they are camping on. According to the National Park Service, Mount Rainier is the highest volcano in the Cascade Range with volcanic activity that began between half a million and a million years ago.

Michael Larson, Mount Rainier's visual information specialist, said the last time the volcano erupted was more than 150 years ago in 1852. He explained that unlike other volcanoes in the Cascade Range, Mount Rainier has no pattern of eruption.

According to the National Park Service, if the volcano were to erupt it would be proceeded by a significant number of small earthquakes, lasting anywhere from weeks to months. The physical appearance of the mountain would also change as pressure built up within the volcano. Information from the park service states the eruption would probably begin with small bursts of gasses from the volcano, followed by a release of magma.

However, Larson said in recent months there has been no increase in seismic activity on the mountain. According to the Pacific Northwest Seismograph Network, the last earthquake measured at Mount Rainier took place Dec. 5, and was a small quake with a 0.2 magnitude that was measured at a depth of 2.5 kilometers.

However, the most immediate concern when visiting Mount Rainier isn't necessarily the issue of the volcano erupting, instead it is the possibility of a lahar or mudflow. Larson said Mount Rainier traditionally has a lot of lahars, which can be caused when snow melts rapidly or rain falls heavily and mixes with earth to form these mudflows.

Larson said one of the real dangers comes from the fact that the area around Mount Rainier is now much more heavily populated than it was the last time the volcano experienced a large lahar 5,600 years ago. He explained that the Osceola mudflow took out a large chunk of the mountain and traveled along the White and Nisqually rivers all the way out to the Puget Sound.

Larson said there are now whole communities that have been built on top of the ancient mudflow, which means if it were to happen again there would be a higher risk of casualties. He noted that the communities of Enumclaw and Bording are located on top of remnants of the old mudflow, as well as parts of the Puyallup area.

Most recently, Larson said the mountain has experienced several debris flows, which are mudflows that do not travel outside the boundaries of the park. He said in 2002 Mount Rainier experienced a small debris flow, and in 2003 the volcano and surrounding area experienced flooding.

In the Lower Yakima Valley, the implications of Mount Rainier erupting would include anything from preparing for ash fallout to following instructions presented through emergency broadcasts. Donna Rahier, a spokesperson for the park, said if an eruption were to take place people in this area would be notified through the media, including emergency broadcasts, and told where to go and what to do.

Rahier said the instructions given to people living in the Lower Valley would depend on the type of eruption. She explained that Mount Rainier could either experience a Mount St. Helens-style blast or the danger could come in the form of a lahar. Rahier said if it was an ash eruption people in the Valley would be dealing with the same issues they faced in 1980 when Mount St. Helens erupted. She said if the eruption comes in the form of a mudslide, the Lower Valley would not likely see any direct effect.

"I don't think there are any major rivers out of the park that lead into the Yakima Valley," Rahier explained.

She said how people in Eastern Washington would receive information about Mount Rainier in case of a blast would be through different forms of the media, depending on how much notice officials had that an eruption was brewing.

"It depends on the circumstances at the time," Rahier said, noting that plans are in place for anything the mountain might present.

. Elena Olmstead can be contacted at (509) 837-4500, or e-mail her at



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