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Mount St. Helens

Most everyone is familiar with Mount St. Helens. She is the most active volcano in the Cascade Range, and the most likely volcano in the contiguous U.S. to erupt again.

The activity that led to the May 18, 1980 eruption began with earthquakes in March of that year. The mountain experienced it's first eruption in over 100 years on March 27. Eruptions continued at a rapid clip of around one per hour to one per day through late April. By May 17, 10,000 small earthquakes had shaken the mountain, and a big bulge had formed and was growing around six feet per day.

The big eruption on May 18 kicked off with the 5-point earthquake. In the event, the bulge and summit slid off the mountain leading to the largest debris avalanche in recorded history. All this was accompanied by a lateral blast and a nine-hour plinian eruption featuring a large plume of ash.

There was some renewed activity on the mountain from 2004-2008 with earthquakes and several explosions. The USGS says the two recent eruptive episodes show a high probability of more eruptive activity. That is why they have what they call a "robust" monitoring system at the site. See data from current monitoring.

Mount Rainier

Mount Rainier is an active volcano and the highest peak in the Cascade Range. The USGS says due to its close proximity to populated areas it is also the most threatening.

The most recent lava flows occurred at Mount Rainier around 2,200 years ago, with pyroclastic flow eruptions, which is a hot mix of rocks, gas and ash, recorded around 1,100 years ago. Rainier has been an active volcano for the last 500,000 years.

The USGS says an eruption at the mountain will likely be preceded by a period of small earthquakes beneath the volcano. Whether a lava flow eruption or pyroclastic flow, an eruption could create lahars that could reach populated areas. As a result of this possibility, the mountain is closely monitored.

Indian Heaven
Indian Heaven is located around 19 miles southwest of Mount Adams. There are 50 known vents on the site that runs parallel to Cascades.

The most recent eruption in the area 9,000 years ago created Big Lava Bed which can be found at the south end of the field. Lava from that event traveled about 25 miles.

Mount Baker

Mount Baker is an active volcano that last erupted in 1843. Its most recent major eruption was 6,700 years ago and resulted in a major flank collapse that caused lahars to rush into the Nooksack River and Baker Lake.

The USGS says more and more people live and play in areas downstream that might be impacted by a big event in the future.

There was recent volcanic activity recorded 1975-1976 with evidence of magma intruding into the volcano in the Sherman Crater, south of the summit, but it did not erupt. Increased steam emission has been recorded at that site since 1975.

The USGS says monitoring at Mount Baker is insufficient considering the risk an event could pose to nearby communities. They say it's listed as high priority to have monitoring systems enhanced.

West Crater Volcanic Field

This is a 12-mile wide volcanic field south of Mount St. Helens that spans from Marble Mountain to south of Trout Creek Hill. The area includes West Crater, a small lava dome, small cinder cones, which are steep conical hills formed by lava around the vent of an eruption, and shield volcanoes, which are marked by a wider, not very steep hill.

The USGS says the Trout Creek Hill shield volcano produced a lava flow about 340,000 years ago that went a distance of 20 km and temporarily dammed the Columbia River. The last eruptions in this area were about 8,000 years ago.

Mount Adams
This is the largest active volcano in the state. It hasn't erupted in 1,000 years, but the USGS says it surely will again.

Mount Adams lies on a 500 square mile volcanic field that houses "at least" 120 volcanoes. Ten vents in the area have been the sites of eruptions in the last 15,000 years.

Around 300 years ago, debris avalanches created big lahars off the mountain that covered 11 square miles. The threat of debris avalanches and lahars remain today as there is a good deal of unstable rock at the summit. The USGS says such an event could be catastrophic and may not be tied to an eruption.

The most likely type of eruption at the site, according to the USGS, is a lava flow. The annual probability of a lava flow impacting one of the neighboring communities is around 0.001 to 0.0001 percent. The probability of future lahars impacting the nearby Trout Lake area is about 0.1 to 1 percent.

Volcanoes in Washington

Seattle, Washington, USA

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