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Our volcanoes are still a threat and we know it


By Brian Terbush
Volcano Program Coordinator, WA EMD

The news is out… and it’s not surprising. Washington state still has five active volcanoes.

Four of these are considered a “very high” threat based on studies by the U.S. Geological Survey (USGS) Volcano Hazards Program.  The 2018 study is an update to the rankings produced in the National Volcanic Early Warning System Report from 2006, which ranks U.S. Volcanoes in terms of their threat.  These rankings are based on geologic and historical studies of the volcanoes and quantify how likely their eruptions are to impact people and infrastructure.  Some key factors considered to create these ratings were: how many people are exposed to the hazards; how much ash is produced; how much this ash may impact aviation paths; how widespread the hazards are; and how frequently the volcano erupts.

The list ranks Mount St. Helens and Mount Rainier among the top five most dangerous volcanoes in the country. Mount Baker and Glacier Peak are also ranked as a “very high” threat, while Mount Adams is ranked as a “high” threat.

This does not mean there has been any increase in volcanic activity. They've always been a serious threat.

Many Washingtonians were here 38 years ago when Mount St. Helens erupted. They remember exactly how powerful and disruptive an explosive eruption can be, transplanting Spirit Lake, dropping a quarter of a cubic mile of ash downwind from the blast, and dramatically reshaping the area from a scenic landscape into an alien moonscape. Some may also remember in 2004 when the volcano became active again. And while its eruption wasn’t nearly as dramatic, massive amounts of lava flooded the crater floor.

Others may remember the 1975-76 hydrothermal activity at Mount Baker, which didn’t result in any new magma being erupted, but a lot of proactive safety actions such as closing campgrounds and drawing down the Baker Lake reservoir so that it could “catch” any lahars (volcanic mudflows) that came down the sides.

One key principle of geological sciences is studying the past to understand the present and the future. Looking back at deposits from ash fall, pyroclastic flows, lava flows, debris flows and lahars around our volcanoes, it becomes clear. We live in a beautiful state, but its geologic past has been punctuated by occasional episodes of extreme geologic violence.

A graphic from the USGS indicates just how frequently these events have been in the past within the Cascade Range – all four of the “very high threat” volcanoes have had activity within the past 200 years.  Some, like Mount St. Helens, have been quite productive. These volcanoes will erupt again, even if it is not within our lifetimes.


So you live near one of Washington’s “very high threat” volcanoes …what does this mean for your weekend?

If this is the first time that you’ve learned that we have five active volcanoes, it may seem scary at first, but it’s a good thing! It is important to become aware of, and to understand the hazards in your area.  Once you know what the risks are, you can learn how to prepare for them.

Overall, volcanic hazards in the Cascades are not something you need to worry about until one of them begins acting up. The USGS Cascades Volcano Observatory (CVO) closely monitors our volcanoes and keeps an eye out for anything unusual that might be going on – unusual seismic activity, changes in stream chemistry or temperature, gas emissions or geodetic changes (uplift or subsidence). These signs may indicate unrest, precursory signs that a volcano is experiencing internal changes and potentially preparing for an eruption.

This monitoring ensures that Cascade volcanoes will not erupt without warning.

Alert levels will change before the volcano erupts as well: all of Washington’s volcanoes are currently in the “normal” level, but at a sign of unusual activity, USGS CVO may release an information statement, or raise the alert level to “advisory.” Further indication that the volcano unrest is leading to an eruption may lead to a volcano “watch” or “warning.”  

You may have heard these terms before used in weather announcements. The big difference between the weather and volcanic versions of these titles is the length of time that one may be in effect.  A “severe thunderstorm warning” may be in effect for a whole day, while Hawaii’s Kilauea volcano spent early May to mid-August this past year under a “warning.”

These changes in alert level will be widely publicized through traditional media, the USGS Volcanoes social media (and emergency management and other public safety agency accounts will amplify these messages), but if you would like to receive the alerts directly, you can subscribe to the Volcano notification service, or VNS, at:

To help understand volcanic hazards, USGS CVO has published various maps of volcanic hazards.  For example, here is one of Mount Rainier:


Mount Rainier has the potential to cause significant damage when it erupts. However, it is much more likely to have small eruptive events that don’t cause much damage. Large, devastating eruptions are rare at cascade volcanoes, but always a possibility. Still, with the massive amounts of snow and ice on cascade volcanoes, even a small eruption can create far-reaching lahars.

The most important thing is to understand and be aware of the hazards you face in your area, both those are direct and indirect.

For direct hazards, the USGS has developed hazard maps like the one above. The pink area on the mountain’s slopes indicate where near-volcano hazards may occur: these include the most powerful destructive forces, like the heaviest ash-fall, devastating pyroclastic flows, and ejection of what became famous in this summer’s eruption at Kilauea volcano in Hawaii – refrigerator-sized blocks.  The best way to stay safe during volcanic unrest, during a time period where these hazards are likely, is to stay off the slopes of the volcano.

Hazards that are likely to extend beyond the volcano are indicated in the red, orange and yellow areas of the volcano (rivers sourced on the volcano’s glaciers).  These indicate lahar hazards, where heavy flows of glacial meltwater may be mixed with ash, volcanic rocks and whatever other debris they pick up along the way. They are highly destructive and move down the river valleys at 20-40 miles per hour, destroying anything in their path. It is critical to understand these hazards, and to simply be out of their way when they occur. If you’ve ever seen a “Volcano Evacuation route” sign along a road, this is an indication of the fastest way to get off the river valley floor, which is the only way to avoid these hazards.

The vast majority of lahars that occur at cascade volcanoes will be small and will not travel far from the volcano. Only the absolute largest lahars at Mt. Rainier will reach Puget Sound. That being said, if you are potentially in the path of a lahar, it is not worth the gamble that it won’t be a big one; follow “volcano evacuation route” signs to higher ground. Even when a full dense lahar doesn’t reach all the way downstream, flooding is likely in impacted river valleys since the lahar displaces the water in the river when it flows.

If you live in a volcano hazard zone, the best resource for learning more is your local emergency management office. Many cities and counties already have evacuation routes mapped out for their hazard zones. Familiarize yourself with these before your local volcano becomes active. We also have tips at

The other major hazard that may reach long distances from the volcano is ash fall. This is variable from volcano to volcano in the cascades, mainly based on the type of lava that they have. But as we’ve seen from Mount St. Helens, it may have eruptions that produce large amounts of ash (May 18th, 1980), or those that produce smaller amounts of ash (2004-2008 eruptive period). Glacier Peak has also produced massive amounts of ash in the past, but Mount Rainier, Mount Baker and Mount Adams are less explosive. Volcanic ash is a complicated hazard that can cause many issues (e.g., respiratory distress, power outages, abrasion, damage to mechanical parts, etc.). For a detailed description of impacts of volcanic ash, check out USGS’s Ash Hazards web page at

Also, be sure to think about secondary hazards as you get prepared. While you may not live in a lahar zone, do you work in one, or frequently travel through one to visit family or get groceries? Could your local power supply be impacted by an eruption? These indirect impacts are incredibly hard to predict since they often involve multiple systems failing (e.g., a supply chain through a hazard zone will result in medications arriving later than normal). Since these impacts are difficult to predict, it is best to get prepared now for any emergency. Check out tips on how to get “2 weeks ready” at

If this is the first time you’ve heard that four out of Washington’s five active volcanoes are a “very high” threat, congratulations!  Now, while they are all in their background level of activity, is the best time to get to know your volcanoes, their hazards and how to enjoy them safely.
For more details on the rankings and how to learn about how we stack up against other U.S. volcanoes, you can read the full report here:

To learn more about the hazards at your particular volcano (or any other in the U.S.) and the monitoring currently being performed, check out CVO’s web site at: