#volcano week

Mount Rainier is a type of volcano called a stratovolcano. 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 stratovolcanoes. The most recent eruption cycle ended about 1,000 years ago, but Mount Rainier is still considered an active volcano.

Mount Rainier is one of several volcanoes along the Cascade Range. Learn more about volcanoes across the National Park Service at https://go.nps.gov/NPSVolcanoes

Mount Rainier is an active volcano with the potential for future eruptions, but eruptions do not happen without warning. The USGS Cascades Volcano Observatory (CVO) carefully monitors Mount Rainier and other Cascade Range volcanoes. Follow the link for Current Alerts for U.S. Volcanos and click the "CVO" tab for Cascade Range volcano updates: https://www.usgs.gov/programs/VHP/volcano-updates#cvo

Mount Rainier is not the only volcano in the park. There are also several satellite volcanoes surrounding it. A couple of these satellite volcanoes formed about 105,000 years ago when new vents opened on the lower northwest flank of Mount Rainier. Lava flows of basaltic andesite (hotter, more fluid magmas than typical for Mount Rainier) spread across the Spray Park and Mist Park areas from cinder cones preserved as Echo and Observation Rocks. The vents were probably fed from a great depth rather than laterally from the same system that fueled Mount Rainier’s eruptions. Have you noticed these two two volcanic features when hiking in the area?

Volcano Week

Be Geohazard Aware! Eruptions on volcanoes like Mount Rainier are complicated by the glaciers covering them. During an eruption, glacial ice can melt and mix with rock, ash, and other volcanic materials to form powerful flows of mud and debris. Lahars (volcanic mudflows), post-lahar sedimentation, and flooding can have greater effects on downstream populations than the eruptions themselves, and these hazards can persist for years after the eruption is over. These geohazards can occur during eruptions, after large landslides, even without an active volcanic eruption.

Smaller seasonal debris flows can also be caused by sudden outbursts of glacial water, by intense precipitation, or embankment failure. While detection and warning models are improving, it is important to always be aware of your surroundings. Remember, if you notice a sudden change in water levels, feel the ground rumble, or hear a loud roaring sound, move to higher ground immediately! If you see signs of a debris flow or other geohazard activity, please report it to a ranger.

Mount Rainier is an active volcano with the potential for future eruptions, but eruptions do not happen without warning. The USGS Cascades Volcano Observatory (CVO) carefully monitors Mount Rainier and other Cascade Range volcanoes. Follow the link for Current Alerts for U.S. Volcanos and click the "CVO" tab for Cascade Range volcano updates.

Volcano Week

Mount Rainier is a type of volcano called a stratovolcano. 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 stratovolcanoes. The most recent eruption cycle ended about 1,000 years ago, but Mount Rainier is still considered an active volcano. 

Stratovolcanoes have highly viscous or “sticky” lava that does not flow easily, causing pressure to build up until there is an explosive eruption. Some volcanoes, like the ones in Hawaii, have low-viscous lava that does flow easily forming gently sloping shield volcanoes.

However, each volcano is different. While more viscous than Hawaiian volcanoes’ lava, Mount Rainier’s primarily andesite lava flows are less viscous than the stickier dacite magmas of Mount St. Helens. Learn more about volcanoes across the National Park Service.

Mount Rainier is an active volcano with the potential for future eruptions, but eruptions do not happen without warning. The USGS Cascades Volcano Observatory (CVO) carefully monitors Mount Rainier and other Cascade Range volcanoes. Follow the link for Current Alerts for U.S. Volcanos and click the "CVO" tab for Cascade Range volcano updates.

Lava fountain at Halemaʻumaʻu Crater, Hawai'i Volcanoes National Park, Janiary 2021