Decade Volcano: Mount Rainier

First things first: Does Rainier really tower over the city like that?

Yes and no.

Photographers sometimes do bring it closer with a telephoto lens. It’s a spectacular shot. But in real life, Mount Rainier is very impressive, too.

Check out this view of the horizon, taken from the revolving restaurant atop the Space Needle 30-40 miles northwest of the glacier-crowned volcano.

You might want to take some Dramamine before watching this. The volcano was named in honor of an 18th-century British admiral. Native American names for it include Tahoma, Tacoma, and Talol. Many residents of the Seattle-Tacoma metro area simply call it “The Mountain.”

Now, here is Mount Rainier as seen from Tacoma.

The volcano (left) is about 40 miles away. (Image: Real Window Creative/Shutterstock)

In the foreground is the Port of Tacoma.

It sits at the mouth of the Puyallup River, which arises on Rainier’s western slopes (facing us, in this image) and empties into Puget Sound.

Most of the low-lying land between this port and Mount Rainier used to be on top of the mountain.


That part of old Rainier came tumbling down in a series of big lahars — volcanic mudflows — over the last 10,000 years (John et al.; PNSN; Sisson and Valance; Vallance and Scott):

  • The Van Trump Debris Flow, about 10,000 years ago.
  • The Reflection Lake Lahar, some 7,000 years ago.
  • The Paradise Debris Flow, 5,600 to 6,000 years ago.
  • The Osceola Mudflow, 5600 years ago; one of the world’s biggest, this one reached what are now the ports of Seattle and Tacoma after Rainier’s summit and its entire east-northeast flank collapsed.

    Mount Rainier’s top section today, including the new summit with its two overlapping craters, now fills the mile-wide crater left by this collapse and the accompanying lateral blast.

    That’s right — at the time when, in northern Africa, Ancient Egypt was first coming together, Rainier, in North America, resembled mid-1980s Mount St. Helens.

    And much of the region between it and the Sound was a steaming, muddy ruin. (Archaeologists have found at least one buried Native American settlement here.)

    More recent big lahars include:

  • The Round Pass Mudflow, about 2600 years ago.
  • An unnamed flow, 1,000-1100 years ago.
  • The Electron Mudflow, 500 years ago. Beginning at Sunset Ampitheater on Rainier’s west flank, it was still 98 feet deep when it reached Puget Sound at Electron, Washington — after spreading out across the coastal flats!

Believe it or not, real-time news video exists of what Lockhart says is a lahar similar in size to the Electron flow.

The report is in Spanish, since this catastrophic mudflow happened in Colombia (Nevado del Huila, November 2008), but there is amazing footage of the huge flow, particularly around 6:50, and (spoiler) you might someday see a report like this in English from Mount Rainier.

Something like this could happen at Mount Rainier again, during our lifetime. The Puyallup and, to a lesser degree, Nisqually river valleys are most at risk. (Driedger and Scott)

So Decade Volcano work at Rainier focused on:

  • Understanding the risk. In a nutshell, while the rocky walls of the former Osceola Flow crater are strong, there still appears to be enough weak rock on the west flank for a repeat of the Electron Flow. (John et al.; Lockhart; Thelen et al.)
  • Improved warning time. Volcanologists estimate that people in communities downstream from a big lahar like this will have anywhere from 40-50 minutes to a few hours (Lee) to get to higher ground — the only survival option when even a small lahar is on the way. The experts first installed lahar detection equipment in 1998 and have been tweaking the system ever since. See Lockhart for a description of the most recent updates.
  • Public outreach: This involves everything from community information brochures to broad-based volcano response groups that bring together scientists, officials, and other stakeholders. Pierce County has an emergency management plan (PDF download), last updated in 2008, with a newer version coming soon.

    These days, schools in Orting, Washington, and in other towns likely to get the shortest warning time, hold annual lahar drills.

    And Pierce County tests its warning sirens every month — problems that crop up, like a communications glitch in late 2019, can be fixed before the system is needed for a real emergency.

Why are lahars such a problem at Mount Rainier?

Let’s meet the volcano and find out.


46.853° N, 121.76° W, in Pierce County, Washington, US. The GVP Volcano Number is 321030.

Nearby Population:

Per the Global Volcanism Program, not counting the 2 million people drawn to Mount Rainier National Park or the 1.5 million who attend the Western Washington Fair in Puyallup each year:

  • Within 5 km (3 miles): 0
  • Within 10 km (6 miles): 128
  • Within 30 km (19 miles): 3,187
  • Within 100 km (62 miles): 2,667,609

Current Status:

Normal, Aviation Code Green.


What a magnificent mound of lava! (Image: Emily Brouwer/Mount Rainier National Park)

  • Eruption styles: Mount Rainier is a big pile of lava flows, unlike its neighbor to the south — Mount St. Helens, which has somewhat “stickier” magma and tends to build up a series of domes.

    While Rainier did have a subplinian blast some 2,200 years ago, most of its eruptions are, at most, moderate in size. Some of the small ones leave nothing more than a thin layer of fine ash for volcanologists to puzzle over.

    Yet many eruptions are associated with long-distance lahars. (Sisson and Vallance)

    There are two ways that can happen:

    A small lahar — compared to Rainier’s Electron Flow — on snowy Mount St. Helens during a 1982 eruption. (Image: Tom Casadevall, USGS, via Wikimedia, public domain)

    1. Snow and ice melt. Let’s take a simple example. Suppose Rainier erupts, generating a pyroclastic flow. That fiery gray death cloud starts off across extensive glaciers, melting them and their snow cover. Water and ash then mix into a slurry that quickly becomes a cohesive mass as it flows along the ground.

    Water is important because it helps to transform the initial flow into a single entity that gravity can act upon. And since Rainier is both high and steep, the end result is a sizeable lahar that will travel a long way.

    However, the biggest flows — those that have filled in valleys and/or reached the coast — are a little different. They contain a lot of clay. Where did that come from?

    2. Flank collapse. There is water inside most volcanoes, as anyone who has ever seen fumaroles and hot springs knows. Near the magma conduits, it can be acidic enough to turn rock into clay (technically, hydrothermally altered rock), which is likely to collapse. This doesn’t happen at all volcanoes, but it definitely has occurred at Mount Rainier. Geologists say that today’s summit is unaltered, but there’s still a problem with altered rock near the source of the Electron Mudflow — hence all the lahar drills, detection equipment, warning systems, and so forth.

  • Biggest recorded event: A VEI 4 eruption about 2,200 years ago, coming near the end of a 400-year-long bout of activity called the Summerland eruptive episode.

    Rainier tends to cycle through such clusters, with centuries to millennia of dormancy or low-level single eruptions in between. It is in one such quiet period now.

  • Most recent eruption: The last lava flow was a couple thousand years ago during Summerland times.

    Mount Rainier’s last eruption, as listed by the Global Volcanism Program, was in 1450. This was one of those that don’t leave much evidence behind.

    While the timing of roughly 500 years ago works, field work by Sisson and Vallance didn’t uncover any clear connection between the 1450 eruption and the Electron Mudflow.

    This raises the unsettling possibility that a big lahar could happen without any precursors.

  • Past history: See the GVP for details.

    Mount Rainier hasn’t been all that active during recorded history, which only goes back to the early 1800s. Some Native American oral histories mention the volcano, but it isn’t easy to link the stories to geological events.

    There has been a volcano of one sort or another at this location for at least two million years. What we call Mount Rainier first appeared about 500,000 years ago and grew in spurts, with periods of frequent lava flows followed by much quieter spells interrupted now and then by a single eruption. (John et al)

    The last eruptive period — called Fryingpan Creek — was from 1,100 to 1,000 years ago, per the USGS Volcanic Hazards Program. Since then, Rainier has had just a few modest belches.


    The Cascades Volcano Observatory and Pacific Northwest Seismic Network (PNSN).

    Here are some webcams.

    Featured image: Songquan Deng/Shutterstock


    Besides those linked in the text:

    Bernhard, J.
    2019. How a Mount Rainier eruption could impact Seattle vs. the South Sound. Last accessed July 21, 2020.

    Cadag, J. R.; Driedger, C.; Garcia, C.; Duncan, M.; and others. 2017. Fostering participation of local actors in volcanic disaster risk reduction, in Observing the Volcano World, Fearnley, C. F.; Bird, D. K.; Haynes, K.; McGuire, W. J.; and Jolly, G., eds, 481-497. Springer: Cham, Switzerland.

    Cartier, K. M. S. 2020. U.S. readies health response for the next big eruption, Eos, 101, Last accessed July 21, 2020.

    Driedger, C., and Scott, W. E. 2008. Mount Rainier—Living Safely with a Volcano in Your Backyard. U.S. Geological Survey Fact Sheet , 2008-3062, 4 p.

    Driedger, C.; Calvache, M.; Cortés, G. P.; Ewert, J.; and others. 2020. Leveraging lessons learned to prevent future disasters—insights from the 2013 Colombia-US binational exchange. Journal of Applied Volcanology, 9(1): 1-21.

    Hoblitt, R. P.; J.S. Walder, J. S.; Driedger, C. L.; Scott, K. M.; and others. 1998. Volcano hazards from Mount Rainier, Washington, revised 1998 (p. 11). US Department of the Interior, US Geological Survey Open-File Report 98–428.

    John, D. A.; Sisson, T. W.; Breit, G. N.; Rye, R. O.; and Vallance, J. W. 2008. Characteristics, extent and origin of hydrothermal alteration at Mount Rainier Volcano, Cascades Arc, USA: Implications for debris-flow hazards and mineral deposits. Journal of Volcanology and Geothermal Research, 175(3): 289-314.

    King 5. 2019. Hazards at Rainier.

    Klemetti, E. 2020. The 40th anniversary of the Mount St. Helens eruptions reminds us the Cascades are still dangerous. Last accessed July 24, 2020.

    Lee, J. 2017. Mount Rainier to get new digital-warning system for massive mudflows. Last accessed July 21, 2020.

    Lockhart, A. 2020. Lahar detection system developments at Mount Rainier, USGS presentation.

    National Park Service. 2020. Mount Rainier: Geohazards. Last accessed July 21, 2020.

    Newhall, C. 1996. IAVCEI/International Council of Scientific Union’s Decade Volcano projects: Reducing volcanic disaster. status report. US Geological Survey, Washington, DC. Retrieved from

    Oregon State University: Volcano World. 2020. Rainier. Last accessed July 21, 2020.

    Pierce County. 2020. Mount Rainier: An active volcano. Last accessed July 21, 2020.

    ___. 2020. Science and Mount Rainier. Last accessed July 21, 2020.

    Sisson, T. W., and Vallance, J. W. 2009. Frequent eruptions of Mount Rainier over the last∼ 2,600 years. Bulletin of Volcanology, 71(6): 595-618.

    Stanistreet, I. G.; Stollhofen, H.; Njau, J. K.; Farrugia, P.; and others. 2018. Lahar inundated, modified, and preserved 1.88 Ma early hominin (OH24 and OH56) Olduvai DK site. Journal of Human Evolution, 116: 27-42.

    Swanson, D. A.; Cameron, K. A.; Evarts, R.; Pringle, P. T.; and Vance, J. 1989. Cenozoic Volcanism in the Cascade Range and Columbia Plateau, Southern Washington and Northernmost Oregon. AGU Field Trip Guidebook , T106, 60 p. doi:ISBN: 0-87590-604-4

    Thelen, W. A.; Allstadt, K.; Kramer, R.; Lockett, C.; and others. 2019. Current Status of the Mount Rainier (Washington) Lahar Detection System. AGUFM, 2019, V51K-0254. (Abstract only)

    U. S. Geological Survey. 2020. Debris flows at Mount Rainier. Last accessed July 21, 2020.

    ___. 2020. Lahars. Last accessed July 21, 2020.

    ___. 2020. Mount Rainier. Last accessed July 21, 2020.

    Vallance, J. W., and Scott, K. M. 1997. The Osceola Mudflow from Mount Rainier: Sedimentology and hazard implications of a huge clay-rich debris flow. Geological Society of America Bulletin, 109(2): 143-163.

    Vallance, J. W.; Cunico, M. L.; and Schilling, S. P. 2004. Debris-flow hazards caused by hydrologic events at Mount Rainier, Washington. US Department of the Interior, US Geological Survey.

    Washington Military Department, Washington Emergency Management Division. 1999. Mount Rainier Volcanic Hazards Response Plan.

    ___. 2020. New plan coming in 2020 (scroll down).

    Wikipedia. 2020. Mount Rainier. Last accessed July 21, 2020.

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