The Pacific Northwest of the United States has a variety of active tectonic settings, including plate convergence at the Cascadia Subduction Zone and divergence in the Basin and Range Continental Rift Zone. But superimposed on these active tectonic features is a line of volcanic activity stretching from the Columbia Plateau of eastern Oregon and Washington all the way to the Yellowstone Plateau at the intersection of Wyoming, Idaho and Montana.
Shaded relief map of United States, highlighting National Park Service sites at a Continental Hotspot. Letters are abbreviations for NPS sites listed below. Sites in the the Columbia Plateau of Oregon and Washington, the Snake River Plain of Idaho, and the Yellowstone Plateau of Wyoming lie along the track of the Yellowstone Hotspot that is currently beneath Yellowstone National Park.
Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.
Continental Hotspot
- CRMO—Craters of the Moon National Monument, Idaho—[Geodiversity Atlas] [Park Home]
- HAFE—Hagerman Fossil Beds National Monument, Idaho—[Geodiversity Atlas] [Park Home]
- JODA—John Day Fossil Beds National Monument, Oregon—[Geodiversity Atlas] [Park Home]
- YELL—Yellowstone National Park, Wyoming, Idaho & Montana—[Geodiversity Atlas] [Park Home]
The Greater Pacific Northwest Has all Three Types of Plate Boundaries and a Hotspot
The Yellowstone Hotspot track is superimposed on other tectonic provinces of the Pacific Northwest. The hotspot first surfaced 17 million years ago as massive outpourings of fluid basalt lava in the Columbia Plateau and Steens Basalt region. Surfacing of the hotspot was affected by subduction that is now manifest as the Cascadia Subduction Zone where the Juan de Fuca Plate descends beneath the edge of the continent. Since then the North American Plate has been moving west-southwest over the hotspot, so that a chain of explosive rhyolite volcanic centers (pink blobs) extends across the Snake River Plain to Yellowstone. This line of supervolcanoes is concurrent with continental rifting forming the Basin and Range Province.
Modified from “Oregon's Island in the Sky: Geology Road Guide to Marys Peak, by Robert J. Lillie, Wells Creek Publishers, 75 pp., 2017, www.amazon.com/dp/1540611965.
Volcanic Activity along Columbia Plateau – Yellowstone Hotspot Track
The Columbia Plateau has been the site of enormous volcanic eruptions, unsurpassed anywhere on Earth during the past 17 million years. Lava from large fissures in northeastern Oregon and southeastern Washington was so fluid that it flowed considerable distances, forming the numerous layers of basalt familiar to visitors to the Columbia Gorge. Some of the lava traveled more than 300 miles (500 kilometers) all the way to the Pacific Ocean. This vast volcanism resulted from the rise of hot material from deep within Earth’s mantle. Over the past 17 million years the North American continent has continued to drift west-southwest over this hotspot. The spectacular hot springs, geysers, and other hydrothermal features of Yellowstone National Park are the current manifestation of the hotspot activity.
Columbia Plateau, Oregon
Photo courtesy of Robert J. Lillie.
Yellowstone Plateau, Wyoming
Photo courtesy of Robert J. Lillie.
NPS Sites along Columbia Plateau – Yellowstone Hotspot Track
A rising mantle plume has a massive head as much as 500 miles (800 kilometers) in diameter. The volume of basaltic magma that rises initially through the overriding plate can be so enormous that it matters little what kind of crust is capping the plate – huge volumes of basaltic lava pour out on the surface. The numerous lava flows that poured out in the Columbia Plateau and the Steens Basalt region of southeastern Oregon are thought to represent the original surfacing of the Yellowstone Hotspot that began 17 million years ago. Since then the North American Plate has continued to move in a west-southwestward direction over the Yellowstone Hotspot. Starting near the Oregon/Nevada/Idaho juncture 16 million years ago, a line of rhyolite magma centers—supervolcanoes—formed across what is now the Snake River Plain of southern Idaho. Yellowstone National Park today lies directly over the hotspot.
Shaded relief map of the Pacific Northwest highlighting National Park Service sites along the Yellowstone Hotspot track. Letters are abbreviations for NPS sites listed near the top of this page. The Yellowstone Hotspot surfaced 17 million years ago as massive outpourings of basalt lava in the Columbia Plateau–Steens Basalt region. Since then the North American Plate has moved west-southwestward, forming a chain of supervolcanoes across southern Idaho to Yellowstone National Park. The Yellowstone Plateau is a broad region of high elevation directly above the hotspot, while the Snake River Plain has gradually subsided as that portion of the plate moved away from the hotspot.
Modified from “Parks and Plates: The Geology of our National Parks, Monuments and Seashores,” by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.
Columbia Plateau —Yellowstone Hotspot Track
Volcanic rocks in the Pacific Northwest show the effects of a tectonic plate riding over a deep-mantle hotspot.
A hotspot is like the hot wax rising in a lava lamp.
- When the lamp is off, the cold wax is more dense than the oil.
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When you turn the lamp on the heated wax rises because it expands and becomes less dense than the oil.
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A broad “head” developes, connected to the vat of wax by a narrow “stem.”
Illustrations above modified from “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest,” by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015, www.amazon.com/dp/1512211893.
When only the stem remains, the magma mixes with melted continental crust and is enriched in silica, forming the rhyolite lavas that poured out across southern Idaho and Yellowstone.
Along with black lights and hookahs, lava lamps are iconic fixtures of the psychedelic 1960’s. Observing what happens when we turn on a lava lamp can help us understand the evolution of the Columbia Plateau–Yellowstone Hotspot track. It’s not clear exactly why deep mantle material heats up. But when it does it expands like the hot wax in a lava lamp. The wax rises as it becomes less dense than the surrounding oil. At times the rising wax develops a mushroom shape, with a large head and narrow stem. Similarly, deep within the Earth heated mantle becomes less dense than the surrounding material. Although it is still solid, the heated mantle can rise slowly toward the surface. And like the wax in a lava lamp, it can develop a mushroom shape. The magma melting off the mantle at a hotspot initially has a low-silica, basalt composition. When the Yellowstone Hotspot initially reached the surface 17 million years ago, it was shaped like a mushroom, with a large head and narrow stem. The massive outpourings of basalt lava covered the Columbia Plateau and Steens Basalt regions.
After a few million years, the mushroom head of the hotspot dissipates, leaving only a thin stem. Plate motion carries the region of extensive basalt lava away, but the magma rising from the stem must somehow work its way to the surface. That’s when the thickness and composition of continental crust come into play. The basaltic melt from the hotspot stem may, in fact, form two levels of magma chambers within the overriding plate. The lowest is at the base of the crust, retaining a low-silica (basalt/gabbro) composition. Magma rising from that level melts its way through thick, silica-rich continental crust, forming high-silica (rhyolite/granite) magma chambers in the upper part of the crust. A narrow chain of explosive, rhyolite volcanoes forms on the surface of the moving plate.
The areas of rhyolite underlying the Snake River Plain form discrete areas of volcanic activity, rather than one long ridge. This situation is analogous to that seen in the Pacific Ocean, where discrete islands form over the Hawaiian Hotspot. “Islands” of rhyolite, progressively younger to the northeast, extend across the Snake River Plain of southern Idaho. Similar to the Big Island of Hawaii, a very high region, the Yellowstone Plateau, lies directly above the hotspot.
John Day Fossil Beds
John Day Fossil Beds National Monument in northeastern Oregon contains incredible examples of mammal, plant, and other fossils. Those fossils are preserved in sedimentary layers that were deposited from 54 to 6 million years ago. Within the fossil beds are lava flows—part of the enormous volume of basalt that formed the Columbia Plateau of northeastern Oregon and southeastern Washington. The fluid lavas poured out of long fissures, much like those seen erupting from rift zones on the flanks of shield volcanoes in Hawaii and Iceland. More than 20 such flows, totaling about 1,600 feet (500 meters) thickness, can be seen in Picture Gorge within the monument.
Hard Lava Flows form the Caprock of many Buttes and Mesas in the Columbia Plateau Region
John Day Fossil Beds National Monument, Oregon
Left image
Sheep Rock.
Credit: Photo Courtesy of Robert J. Lillie.
Right image
Feature labels. (Click on arrows and slide left and right to see labels.)
One of the many outstanding murals at the Thomas Condon Visitor Center at John Day Fossil Beds National Monument depicts ancient life on the Columbia Plateau landscape. Note the columnar basalt columns in the foreground.
NPS photo.
Columbia Plateau Basalt often forms columns that are ideally six-sided (hexagons).
Photo courtesy of Robert J. Lillie.
Development of hexagonal columns
As a lava flow cools it shrinks, putting the surface of the flow under tensional forces that form cracks, known as “joints.” If the cooling is uniform, circular columns try to form, but there are spaces between the cracks. Octagonal (eight-sided) columns also have spaces. The most efficient form develops hexagonal (six-sided) columns, with no spaces between the cracks.
Modified from “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest,” by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015, www.amazon.com/dp/1512211893.
Yellowstone Plateau Development
The Yellowstone region is a bit like Hawaii—it’s part of a chain of volcanoes that get progressively older in one direction. Only the “islands” southwest of Yellowstone are part of the North American continent. In fact, standing in the middle of Yellowstone National Park is much like standing on top of the Big Island of Hawaii. The Yellowstone region, at 8,000 feet (2,500 meters) elevation, is about 2,000 to 3,000 feet (600 to 1,000 meters) higher than the surrounding territory. Like Hawaii, the Yellowstone region lies directly above a hotspot.
Modified from “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest,” by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015, www.amazon.com/dp/1512211893.
As the Yellowstone Hotspot rises, it expands like a hot-air balloon, causing the Yellowstone Plateau to elevate to great height. Eruptions of silica-rich (rhyolite) lava formed the Yellowstone Caldera on the crest of the plateau. The region is so high that a small ice cap—similar to the one that currently covers the island of Iceland—formed during ice ages. The combination of silica-rich soil, high elevations, glacial deposits, and hydrothermal features creates a unique ecosystem on the Yellowstone Plateau.
As the plate moves away from the hotspot it cools and contracts, forming lower elevations in the Snake River Plain of southern Idaho. This is similar to Hawaii, where islands get shorter in a northwestward direction, eventually sinking beneath the sea as atolls and seamounts. Likewise, the Snake River Plain of southern Idaho is a depression in the landscape where the North American Plate has moved off the Yellowstone Hotspot. Younger basalt lava flows (some from Basin and Range continental rifting) cover much of the earlier rhyolite supervolcanic centers.
Yellowstone: A Truly Super Volcano!
Very large eruptions occurred in the Yellowstone region three different times: about 2 million years ago, 1.3 million years ago, and then 640,000 years ago. Those eruptions were similar to the explosion and collapse that formed the Crater Lake Caldera in Oregon 7,700 years ago, only much bigger. The latest large eruption at Yellowstone produced about 1,000 to 2,000 times the volume of material as the 1980 eruption of Mt. St. Helens in Washington. As happened at Crater Lake, volcanic material poured out onto the floor of the Yellowstone Caldera. Rhyolite lava erupted intermittently from 640,000 years to 70,000 years ago. The Yellowstone River has carved through the younger flows, exposing them along the walls of the Grand Canyon of the Yellowstone River.
The giant crater (“caldera”) formed by the eruption and collapse of Yellowstone Supervolcano 640,000 years ago dwarfs the crater on top of Mt. St. Helens and the caldera of Mt. Mazama.
Modified from “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest,” by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015, www.amazon.com/dp/1512211893.
Development of Yellowstone Hydrothermal Features
Yellowstone National Park is a dazzling display of geysers, hot springs, mud pots, and other hydrothermal features. But where does the hot water come from? How does it make its way to the surface? And what causes geysers to erupt, often at such regular intervals? The answers to all of those questions relate to the presence of the hotspot directly beneath Yellowstone. The hotspot results in pockets of partially molten rock, or magma chambers, at various levels within the crust. But the hot water that surfaces as Yellowstone’s thermal features does not originate from those magma chambers. Rather, the water is rainfall and snowmelt that enters the ground from above. The magma chambers are essential, though, because they heat the overlying rock.
1. Hot material rises from deep within Earth’s mantle and melts, forming basalt magma at the base of the crust.
2. Magma that encounters silica-rich continental crust on its journey upward forms a rhyolite magma chamber only 5 to 10 miles (8 to 16 kilometers) beneath Yellowstone National Park.
3. Water from rainfall and snowmelt seeps into the ground.
4. The water circulates 1 to 2 miles (2 to 3 kilometers) underground, where it encounters hot rock above the rhyolite magma chamber.
5. Hot water reaches the surface as geysers, hot springs, mudpots, and fumaroles.
Modified from “Beauty from the Beast: Plate Tectonics and the Landscapes of the Pacific Northwest,” by Robert J. Lillie, Wells Creek Publishers, 92 pp., 2015, www.amazon.com/dp/1512211893.
As the rain and snow falls, some of the water moves down through the cracks and pore spaces of the shallow rock layers. The groundwater descends to a depth of one-to-two miles (1½ to 3 kilometers), where it encounters hot rocks heated from below by a shallow, upper-crustal magma chamber. The hot water expands, rising to the surface as hot springs. The water sometimes incorporates a lot of solid material on its way up, forming mud pots. At depth within the Earth, the water is under great pressure. If it becomes superheated, the water may suddenly expand to gas, forcing the overlying water column out of a geyser.
Yellowstone Hydrothermal Features: Hot Springs and Geysers
Photo courtesy of Robert J. Lillie.
Fishing Cone Spring
Hot Springs develop where the geothermal waters flow freely to the surface.
Photo courtesy of Robert J.Lillie.
Heart Spring
Photo courtesy of Robert J. Lillie.
Mammoth Hot Springs
Mammoth Hot Springs form in the northern part of the park where the hot water flows through limestone. Dissolved calcium carbonate is deposited on the surface as beautiful terraces.
Photo courtesy of Robert J. Lillie.
Mammoth Hot Springs Terrace
Photo courtesy of Robert J. Lillie.
Old Faithful geyser
Geysers form where dissolved silica from rhyolite volcanic rocks constricts flow. Under pressure, the superheated water flashes from liquid to gas, propelling the column of water upward through the narrow constriction.
Photo courtesy of Robert J. Lillie.
Sawmill Geyser
Yellowstone Hydrothermal Features: Fumaroles, Mudpots, Paint Pots and Mud Volcanoes
Photo courtesy of Robert J. Lillie.
Dragon's Cauldron
Mudpots, paint pots and mud volcanoes develop where a lot of fine rock material is incorporated into the hot water. Fumaroles are eruptions of steam on the surface. Dazzling colors occur where steam and hot water alter minerals.
Photo courtesy of Robert J. Lillie.
Mud Volcano
Photo courtesy of Robert J. Lillie.
Artists Paint Pots
Life Above a Hotspot
The overall plant and animal community, or ecosystem, is influenced by the local geology and climate conditions. The plants and animals found in Yellowstone National Park are there because the landscape developed over a hotspot. Rising, hot mantle has elevated the Yellowstone Plateau to 8,000 feet (2,500 meters) above sea level, resulting in long winters with deep snow cover. The rhyolite lava flows found throughout the park weather to very acidic soil. The high elevation, poor soil and long winters mean high stress for plants in Yellowstone. The dominant tree found in the park is the Lodgepole Pine, a tree that thrives in such stressful environments.
Yellowstone’s high elevations and silica-rich volcanic soils favor lodgepole pine forests. Glacial lake deposits in Hayden Valley form wetland meadows ideal for bison and other wildlife. Bison, elk and grizzly bears thrive in the forests and meadows.
Bison hang around open areas near hydrothermal features.
Photo courtesy of Robert J. Lillie.
The rich yellow and orange colors around many hot springs are microscopic thermophiles—special forms of life that survive at very high temperatures.
Photos courtesy of Robert J. Lillie.
During recent ice ages, the Yellowstone Plateau was covered by a 3,000-foot (1,000-meter) layer of ice, similar to the modern ice cap that covers part of Iceland. Yellowstone’s ice cap scoured the landscape and left behind deposits of sand, silt and gravel. These deposits provide just the right soil and drainages conditions for meadows like Hayden Valley, in the heart of Yellowstone, where bison, elk, bear, waterfowl and other wildlife thrive.
Figures Used
Related Links
Site Index & Credits
Plate Tectonics and Our National Parks
- Plate Tectonics—The Unifying Theory of Geology
- Inner Earth Model
- Evidence of Plate Motions
- Types of Plate Boundaries
- Tectonic Settings of NPS Sites—Master List
Teaching Resources—Plate Tectonics
Photos and Multimedia—Plate Tectonics
Geological Monitoring—Plate Tectonics
Plate Tectonics and Our National Parks (2020)
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Text and Illustrations by Robert J. Lillie, Emeritus Professor of Geosciences, Oregon State University [E-mail]
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Produced under a Cooperative Agreement for earth science education between the National Park Service's Geologic Resources Division and the American Geosciences Institute.
Last updated: December 5, 2022