18 US Volcanoes as ‘Very High Threat’ (Rainier #3)

Your Favorite Mountain Is Beautiful… And (Very) Dangerous: Mount Rainier is the third most dangerous volcano in the United States.

USGS scientists have classified 18 U.S. volcanoes as “very high threat” (four are in Washington state) because of what’s been happening inside them and how close they are to people.

The U.S. Geological Survey has updated its volcano threat assessments for the first time since 2005. To produce the rankings, the USGS uses a 24-factor hazard and exposure matrix, assessing explosive activity in the past 500 and 5,000 years, frequency of eruptions, and the level of impact an eruption could have on local populations, airplanes, transportation, and power infrastructure. The top five volcanic danger list:

  • Kilauea – Hawaii
  • Mount St. Helens – Washington
  • Mount Rainier – Washington
  • Redoubt Volcano – Alaska
  • Mount Shasta – California

The U.S. Geological Survey has these Washington state volcanoes at the top of their danger list:

  • #2 Mount St Helens
  • #3 Mount Rainier
  • #14 Mount Baker
  • #15 Glacier Peak

The Seattle Times prepared a graphic on volcanic activity in the Cascade Mountains over the past 4,000 years.

Eleven of the 18 at-risk volcanoes are located in Washington, Oregon, or California.

Mount Rainier – Largest Number Of People At Risk: Of the highest threat volcanoes, Washington’s Mount Rainier “has the highest number of people in the downstream hazard zone,” about 300,000 people, said USGS geologist Angie Diefenbach, a report co-author.

“This report may come as a surprise to many, but not to volcanologists,” said Concord University volcano expert Janine Krippner. “The USA is one of the most active countries in the world when it comes to volcanic activity,” she said, noting there have been 120 eruptions in U.S. volcanoes since 1980.

Below are lahar maps for each volcano.

Mount Rainier USGS Lahar Map

 

Mount St. Helens USGS Lahar Map

 

Mount Baker USGS Lahar Map

 

Glacier Peak USGS Lahar Map

Mount Rainier Volcanic History: Mount Rainier is an episodically active composite volcano, also called a stratovolcano. Volcanic activity began between one half and one million years ago, with the most recent eruption cycle ending about 1,000 years ago. Over the past half million years, Mount Rainier has erupted again and again, alternating between quiet lava-producing eruptions and explosive debris-producing eruptions. The eruptions built up layer after layer of lava and loose rubble, eventually forming the tall cone that characterizes composite volcanoes. At one time, lava flows on opposite sides of the mountain probably projected more than 1,000 feet (305 meters) above the present summit at Columbia Crest which rises 14,410 feet (4392 meters) above sea level on the rim of the recent lava cone. The upper portion of the volcano’s cone was likely removed by explosions and landslides. Mount Rainier’s extensive glacier system then carved the volcano’s cone into its current craggy form.

Mount Rainier also sits on a subduction zone where colliding continental and oceanic plates cause regular seismic and geothermal activity. A subduction zone is an area where one continental plate is being forced underneath another into the earth’s mantle. Mount Rainier experiences about 20 small earthquakes a year, making it the second most seismically active volcano in the northern Cascade Range after Mount St. Helens. Learn more about Mount Rainier’s seismicity.

Mount Rainier Hazards: Mount Rainier, the highest (14,410 feet) volcano in the Cascade Range, towers over a population of more than 3.3 million in the Seattle Tacoma metropolitan area, and its drainage system via the Columbia River potentially impacts another 500,000 residents of southwestern Washington and northwestern Oregon. Mount Rainier is the most hazardous volcano in the Cascades not only in terms of its potential for an eruption, but also the risk of producing major debris flows even without an eruption.

The potential hazards posed by Mount Rainier led to its inclusion as one of the sixteen volcanoes worldwide to be designated Decade Volcanoes. The Decade Volcano initiative is part of a United Nations program aimed at better-utilizing science and emergency management to reduce the severity of natural disasters. Mount Rainier was chosen to be studied because it is representative of one or more volcanic hazards: it is geologically active as evidenced by surface manifestation of heat (geothermal activity), it has had recent volcanic events (the last eruption was about 150 years ago), and it is likely to erupt again, based on past history; its location poses significant hazards to a heavily populated area; it is a well-known volcano (a number of research publications have been written on it); it is politically and physically accessible for study; and its volcanic geology is well exposed.

The Washington Emergency Management Twitter page to follow for updates.