Volcanoes and Lahars
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Washington has five major volcanoes: Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams. These volcanoes are part of the Cascade Range, a 1,200-mile line of volcanoes from British Columbia to northern California.

Each of Washington’s volcanoes is still active. In fact, all of them except for Mount Adams have erupted in the last 250 years. Volcanoes do not erupt at regular intervals, so it is difficult to know exactly when or where the next eruption will happen.

Many hazards come with living near volcanoes. Volcanic eruptions can send ash and volcanic debris into the air. Heat from the volcano can melt snow or ice and cause dangerous mudslides called lahars. Molten rock called lava can erupt and flow downhill, destroying everything in its path.

Volcanoes are also beautiful mountains that many people visit each year for recreation. Volcanoes are also the most visual result of plate tectonics, and are one of the few places on Earth where molten rock can reach the surface. There are even old volcanoes on other planets, like Venus and Mars.

Click below to learn more about volcanoes, their hazards, who is at risk, and how to prepare for an emergency.


The mission of the Washington Division of Geology and Earth Resources is to collect, develop, use, distribute, and preserve geologic information to promote the safety, health, and welfare of the citizens, protect the environment, and support the economy of Washington.

Develop hazard response plans

The Division of Geology and Earth Resources works with an inter-agency team of counties, the U.S. Geological Survey, and the Washington Emergency Management Division to develop response plans to volcanic events. This effort includes:

  • Evacuation routes and information based on comprehensive hazard assessments. As of 2015, these products have been completed for the Mount Rainier and Glacier Peak areas.
  • Loss estimation analysis for areas near volcanoes. As of 2015, we have completed this analysis for areas near Mount Rainier.
  • Loss estimation and multi-hazard analysis for all other areas near volcanoes and for all counties in Washington. These analyses are currently underway.

Work to increase public understanding

The Division works to increase public and scientific understanding of volcanic hazards in our state through efforts such as this website, field guides, and other public outreach. We work closely with the Washington Emergency Management Division, the U.S. Geological Survey, and local counties to develop and publish educational material and information about evacuation.

Please visit our Geologic Information Portal and Geologic Hazard Maps page for the most up-to-date listing of all of our hazard maps.

Check out our Field Trip guides for Mount Rainier and Mount St. Helens


Consider subscribing to our blog, Washington State Geology News, to receive notifications when new information is published. Also check out Ear to the Ground, published by the Department of Natural Resources.

Assist during times of emergency

The Division is the lead science agency for the State during times of geologic emergency. During these times we assist other emergency planners and responders, such as the Washington Emergency Management Division, in making geologically sound decisions.


  • Who is at risk?
  • Hazard types
  • Prediction
  • Who is at Risk?

    Residents throughout the state of Washington are at risk of volcanic hazards. There are five active volcanoes in Washington, and more than seven others in the rest of the Pacific Northwest. These volcanoes tend to erupt explosively and can cause significant damage both near and far. High-speed flows of hot ash and rock, lava flows, and landslides can destroy homes and infrastructure within ~10 miles of the eruption. Enormous mudflows of ash, debris, and melted ice—called lahars—can devastate low-lying areas more than 50 miles away.

    Know your risk! Learn what volcanic hazards exist near your home, place of work, or where you recreate. Visit our Geologic Hazards Map page for the most up-to-date reports and maps.

  • Types of Volcanic Hazards

    There are 5 main types of volcanic hazards. Most of these hazards are associated with eruptions, but some, such as lahars, landslides, and volcanic gas can occur at any time.

    Eruption Columns and Clouds

    When a volcano erupts, the blast sends gas and pieces of molten rock into the air. Lighter pieces, such as volcanic glass, minerals, and ash can rise high into the air and form a massive cloud called an eruption column. The larger pieces—called volcanic bombs—usually fall quickly to the ground with a few miles of the volcanic vent.

    When eruption columns become large, they pose a serious hazard to health and aviation. The small particles of dust, rock, and volcanic glass—called ash—can be inhaled and cause lung damage. Ash is also damaging to airplanes if they fly through the ash cloud.

    Eruption columns and ash clouds can become enormous and extend for hundreds of miles. The 1980 eruption of Mount St. Helens covered over 22,000 square miles with ash. This is considered to be a relatively small volcanic eruption. Larger eruptions, such as the 1883 eruption of Krakatoa in the south Pacific, produced enough ash to slightly lower the temperature of the entire earth for several years.

    This diagram shows the sizes of a few volcanic eruptions. Smaller eruptions are much more common than larger ones. Diagram from the U.S. Geological Survey at http://volcanoes.usgs.gov/images/pglossary/eruptionsize.php.

    Lava Flows and Domes

    Molten rock that reaches the Earth's surface is called lava. Some types of lava (such as basalt) have low viscosity, move very quickly downhill, and can travel great distances. Other types of lava (such as rhyolite) have high viscosity, move very slowly, and cannot travel very far.

    Many volcanoes in the Cascade Range can erupt different types of lavas. For example, the Ape Caves near Mount St. Helens were created about 2,000 years ago by low-viscosity basalt that travelled many miles from their vent on the slope of the mountain. Later, during the 1980 eruption, Mount St. Helens created a high-viscosity dacite dome over 1,000 feet tall.

    Pyroclastic Flows

    A pyroclastic flow is a very dangerous and fast-moving mixture of ash, rock, and gas. The root word 'pyro' means fire and 'clastic' means rock. These flows can reach temperatures of more than 1,500°F and reach speeds of 100–150 miles per hour. They often occur as hot ash and rock move down the slope of the volcano, or as a result of volcanic collapse during an eruption.

    Pyroclastic flows will destroy nearly everything in their path. During the 1980 eruption of Mount St. Helens, pyroclastic flows destroyed nearly 230 square miles of forest. Trees 6 feet across were knocked down like twigs over 15 miles from the volcano.


    When enough water mixes with loose volcanic ash and rock on the side of a volcano, the mixture flows downhill and forms a lahar. These mudflows can travel more than 50 miles from the volcano (sometimes reaching the Pacific Ocean!) at speeds up to 40 miles per hour. Some lahars can contain so much solid material that they look more like rivers of concrete.

    Lahars can occur at almost any time and do not need a volcanic eruption. The water that forms lahars can come from snow and ice that were melted by heat from the volcano or from hot pyroclastic flows. The water can also come from intense rain events.

    Lahars have typically been the deadliest volcanic hazard because they can happen at any time and affect people far downstream of the volcano. For this reason the Division of Geology and Earth Resources works with the U.S. Geological Survey to provide lahar hazard maps for all of the Washington volcanoes. These can be found on our Geologic Hazard Maps page:

    Volcanic Landslides

    Landslides and debris avalanches can occur on the slopes of volcanoes at any time. Since volcanoes are built of layers of ash and rock, their slopes can be relatively loose and weak. Groundwater and the circulation of hot acidic water from the volcano can alter minerals and make the rocks even weaker. Strong ground shaking during an earthquake, a volcanic eruption, or simply heavy rain or melting snow can trigger landslides on volcanoes.

    Landslides can also occur during an eruption if a part of the volcano collapses. For example, part of Mount Shasta in northern California collapsed about 300,000 years ago and created a giant landslide over 30 miles long. The deposits of this landslide are where the cities of Weed and Yreka are now built.

    Volcanic Gas

    Volcanoes release gas both during eruptions and between eruptions. During eruptions this release can be very explosive and is often what propels the ash and rock into the air. As magma is formed deep in the earth it contains small amounts of gas under very high pressure. As the magma moves towards the surface it is so thick that the gas cannot expand. When the volcano erupts it is like opening a soda can that has been shaken up!

    Between eruptions, much of the gas a volcano creates is steam. This steam is made when groundwater interacts with the hot interior of the volcano. The steam rises through cracks and can eventually reach the surface. At the surface it can form fumaroles, mud pots, or hot springs. The rising steam can also melt snow or ice, potentially causing lahars or landslides.

    In addition to steam, volcanoes can also release more dangerous gas, such as carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen, and fluorine. These gases can react with water in the air to create acid rain. Heavy gas, such as carbon dioxide, can be trapped in low-lying areas and suffocate animals or people.

  • Predicting Volcanic Eruptions

    With increasing numbers of people living near volcanoes in the Pacific Northwest, it is important to be able to give adequate warning before a major eruption.

    Volcanoes are part of a complex geologic system that operates on a time scale of tens to thousands of years. We know that all of the Cascade Range volcanoes are active and have had major eruptions in the past 400 years, but many lie dormant for centuries. It is certain that they will erupt again, but we cannot predict exactly which one will erupt next.

    Volcanoes have been erupting in the Cascade Range for millions of years. During the past 4,000 years eruptions have occurred at an average rate of about two per century. This chart shows 13 volcanoes on a map of Washington, Oregon, and northern California and time lines for each showing the ages of their eruptions. Figure modified from USGS General Information Product 63.

    Our best defense against volcanic hazards is through careful monitoring. Large numbers (10s to 1,000s) of small earthquakes sometimes happen right beneath a volcano as magma moves through the interior plumbing. Sometimes these earthquakes are a warning sign that an eruption may occur. Sometimes they are simply reminders that volcanoes are constantly changing. Not all earthquakes near a volcano mean that it will erupt. Some volcanoes have erupted without any seismic warning.

    Geologists at the Pacific Northwest Seismic Network and Cascade Volcano Observatory use the increase in earthquakes to continuously monitor the volcanoes of the Pacific Northwest. When there is enough data to cause concern, scientists deploy mobile monitoring instruments to more closely watch the volcano. Monitor the volcanoes yourself at the Cascade Volcano Observatory and the Pacific Northwest Seismic Network:

    These efforts enable early detection of possible eruptions. Close monitoring of Mount St. Helens enabled evacuation notices to be issued prior to the major eruption.


Volcanic eruptions and lahars are frightening natural disasters. It is important to prepare ahead of time.

The eruption of Mount St. Helens on May 18, 1980 killed 57 people, destroyed 27 bridges and almost 200 homes, and caused disruption for thousands of people. You can minimize damage and loss of life by being prepared for a volcanic emergency. One of the most important things you can do is learn about your risks.

The following information is synthesized from the Cascade Volcano Observatory, Washington Emergency Management Division, and Ready.gov web sites.

Before an Eruption

  • Learn about your risks—Know the danger and hazards you face at home, at work, and where you recreate or travel.
  • Plan ahead. Have emergency supplies, food, and water stored.
  • Plan an evacuation route away from streams that may carry lahars or landslide debris.
  • Make sure your emergency provisions contain a pair of goggles and disposable breathing masks for ash and dust.
  • Make a family emergency plan so that you know how to contact your family members in case of an emergency.
  • Stay informed: Listen to media outlets for warnings and evacuations. Listen for All Hazard Alert Broadcast sirens that warn of lahars. Check out the Volcano Notification Service to subscribe to alerts about specific volcanoes.
  • Ask local and state emergency offices and schools about their response plans. Be prepared to follow official guidance.

Be informed. Make a plan. Build a kit. Educate and protect your family, neighbors, and friends.

During an Eruption

  • Follow evacuation orders issued by authorities. Evacuate immediately from an erupting volcano!
  • Be aware that lahars and other types of landslides or debris flows can travel great distances from the volcano. Avoid river valleys and other low-lying areas that may be prone to these hazards.
  • If you are in a lahar hazard zone and become aware of an oncoming lahar, get to high ground and then shelter in place. If there are signed evacuation routes, follow them.
  • Stay informed: Watch and/or listen for additional information.
  • Listen for All Hazard Alert Broadcast sirens that warn of lahars.
  • Do your part to remain safe and help others in need.

If There is Ashfall...

Protect your lungs!

Volcanic ash is made of microscopic shards of glass and other fine-grained material. Ash can can cause significant damage to animals, including significant damage to lungs or asphyxiation if inhaled.

  • If there is falling ash and you cannot evacuate, remain indoors with doors, windows, and ventilation systems closed until the ash settles.
  • Help infants, the elderly, and those with respiratory conditions.
  • Wear a respirator, face mask, or a use a damp cloth across your mouth to protect your lungs.
  • Use goggles, and wear eyeglasses instead of contact lenses.
  • Avoid driving in heavy ash fall unless absolutely required. If you must drive, reduce your speed significantly.
  • Avoid operating engines of any kind. Ash can clog engines, damage parts, and stall vehicles.
  • Wear long-sleeved shirts and long pants.
  • Keep roofs free of ash in excess of 4 inches.
  • Limit outdoor activity. Remove outdoor clothing before entering a building.
  • Check to ensure that ash does not contaminate your water. If it does, use a different source, such as bottled water.
  • For more information about ash fall, check out the USGS Volcanic Ash website.

After an Eruption

  • Go to a designated public shelter or evacuation area if you have been told to evacuate or you feel it is unsafe to remain in your home. Text SHELTER + your ZIP code to 43362 (4FEMA) to find the nearest shelter in your area (example: shelter 98506)
  • Stay informed: Watch and/or listen for additional information. Listen to NOAA Weather Radio, watch TV, listen to the radio, or check the internet for official instructions and information.
  • Do not approach the eruption area.
  • Be prepared to stay indoors and avoid downwind areas.
  • Be aware of lahars and landslides. These hazards can occur long after the main eruption.


This table provides a quick summary of the most recent eruptions for each of the volcanoes in Washington.

increased steam
and heatflow
ash eruption
ash eruptions and lahars
ash eruptions and lahars
Around 1700
ash and steam eruptions, small lahars
steam and ash eruptions
steam and ash eruptions
steam and ash eruptions
steam and ash eruptions
Last eruption ~1,000 years ago
landslides and small lahars in 20th century
lava dome slowly builds, steam and ash eruptions
steam and ash eruptions
ash eruptions and lava-dome building
ash eruption, catastrophic landslide, lahars
steam eruptions
ash eruptions and lava-dome building
ash eruptions, lava flows


The information in this table was modified from the Volcano Awareness Month poster, produced as a collaborative effort between the Washington Emergency Management Division, U.S. Geological Survey, USDA Forest Service, and National Park Service.