Oceanic crust forms by eruptions along the Juan de Fuca ridge. As the Juan de Fuca plate drifts eastward, it cools, becomes more dense, and eventually dives under the less dense continental plate at the Cascadia trench.
Images
Volcano Hazard Program images.
![Subduction of the Juan de Fuca plate beneath the North American pla...](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/vhp_img946.jpg?itok=96_bC3ZF)
Oceanic crust forms by eruptions along the Juan de Fuca ridge. As the Juan de Fuca plate drifts eastward, it cools, becomes more dense, and eventually dives under the less dense continental plate at the Cascadia trench.
![Location of magma formation, accumulation, and storage beneath Moun...](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/vhp_img947.jpg?itok=YYY6Obnl)
Magma forms above the subducting slab of oceanic crust and accumulates at the base of Earth's rigid crust before collecting in a storage zone 13 km (8 mi) beneath the volcano prior to eruption.
Magma forms above the subducting slab of oceanic crust and accumulates at the base of Earth's rigid crust before collecting in a storage zone 13 km (8 mi) beneath the volcano prior to eruption.
![Kalama age, dark andesite flows include a lava-flow complex on the ...](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/vhp_img994.jpg?itok=zVyib8YX)
Aerial view of Mount St. Helens, taken from the southwest.
Aerial view of Mount St. Helens, taken from the southwest.
![The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps pose on Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park.](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/media/images/H-03614%20copy.jpg?itok=aeZ4aUBP)
The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps pose on Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park. Pvt. John Findley, front left, was the primary bicycle mechanic for the unit, and so carried a heavy toolbox attached to his handlebars. Photo by F.
The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps pose on Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park. Pvt. John Findley, front left, was the primary bicycle mechanic for the unit, and so carried a heavy toolbox attached to his handlebars. Photo by F.
![The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps walk their cycles up Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/media/images/H-03615%20copy.jpg?itok=9BPLfCo6)
The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps walk their cycles up Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park. Photo by F. Jay Haynes, 1896. Montana Historical Society Research Center, Haynes Foundation Photograph Collection, H-3615. Used with permission from the Montana Historical Society.
The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps walk their cycles up Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park. Photo by F. Jay Haynes, 1896. Montana Historical Society Research Center, Haynes Foundation Photograph Collection, H-3615. Used with permission from the Montana Historical Society.
![The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps ride on an inactive portion of Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/media/images/H-03616%20copy.jpg?itok=4JrV5QjW)
The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps ride on an inactive portion of Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park. Photo by F. Jay Haynes, 1896. Montana Historical Society Research Center, Haynes Foundation Photograph Collection, H-3616. Used with permission from the Montana Historical Society.
The Buffalo Soldiers of the 25th Infantry Regiment Bicycle Corps ride on an inactive portion of Minerva Terrace, Mammoth Hot Springs, Yellowstone National Park. Photo by F. Jay Haynes, 1896. Montana Historical Society Research Center, Haynes Foundation Photograph Collection, H-3616. Used with permission from the Montana Historical Society.
![Volcano Art at Hawai`i Volcanoes National Park—A Science Perspectiv...](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/vhp_img5952.jpg?itok=MXf196xY)
The painting by Jules Tavernier, depicting the 1880-81 lava flow from Mauna Loa as it enters a stream near Hilo, Hawaii on July 20, 1881, provided courtesy of the National Park Service, Hawaii Volcanoes National Park (catalog number HAVO 806).
The painting by Jules Tavernier, depicting the 1880-81 lava flow from Mauna Loa as it enters a stream near Hilo, Hawaii on July 20, 1881, provided courtesy of the National Park Service, Hawaii Volcanoes National Park (catalog number HAVO 806).
![Painting by Henry Wood Elliott (1846-1930), Yellowstone Lake, 1871, watercolor.](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/thumbnails/image/elliott%27s%20painting%20of%20YLake%20from%20Pelican%20Ck.jpg?itok=MjXgQhNn)
Painting by Henry Wood Elliott (1846-1930), Yellowstone Lake, 1871, watercolor (Phoenix Art Museum). The view is from northern Yellowstone Lake looking to the south. In the foreground, one can see the Annie in the northern lake and the three largest of the lake’s islands: Stevenson Island, with Frank Island and the smaller Dot
Painting by Henry Wood Elliott (1846-1930), Yellowstone Lake, 1871, watercolor (Phoenix Art Museum). The view is from northern Yellowstone Lake looking to the south. In the foreground, one can see the Annie in the northern lake and the three largest of the lake’s islands: Stevenson Island, with Frank Island and the smaller Dot
Henry Elliott’s 1871 map of Yellowstone Lake (https://hdylake.org/about/history-of-mapping-yellowstone-lake/). The headwaters of the Snake River, Upper Valley of the Yellowstone River, and Pelican River are shown.
Henry Elliott’s 1871 map of Yellowstone Lake (https://hdylake.org/about/history-of-mapping-yellowstone-lake/). The headwaters of the Snake River, Upper Valley of the Yellowstone River, and Pelican River are shown.
![Henry Wood Elliott during a geological expedition in 1870](https://d9-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/masonry/public/thumbnails/image/HenryWoodElliotUSGS-WHJackson1870.jpg?itok=liHstI93)
Henry Wood Elliott during a geological expedition in 1870. Photo by William Henry Jackson.
Henry Wood Elliott during a geological expedition in 1870. Photo by William Henry Jackson.