• A bull elk bugles in Yellowstone National Park

    Yellowstone

    National Park ID,MT,WY

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Geology

photo: Sunset at the Midway Geyser Basin.
A steamy sunset at the Midway Geyser Basin.
NPS/Neal Herbert
 

Yellowstone National Park’s physical landscape has been and is being created by many geological forces. Some of the Earth’s most active volcanic, hydrothermal (water + heat), and earthquake sys­tems make this national park a priceless treasure. In fact, Yellowstone was established as the world’s first national park primarily because of its extraordinary geysers, hot springs, mudpots and steam vents, and other wonders such as the Grand Canyon of the Yellowstone River.

Throughout the Greater Yellowstone Ecosystem, many different geologic processes are occurring at the same time, in different proportions. While these mountains and canyons may appear to change very little during our lifetime, they are still highly dynamic and variable.

Yellowstone’s Geologic Significance

  • One of the most geologically dynamic areas on
    Earth due to shallow source of magma and resulting
    volcanic activity.
  • One of the largest volcanic eruptions known to have
    occurred in the world, creating one of the largest
    known calderas.
  • More than 10,000 hydrothermal features, including
    more than 300 geysers.
  • The largest concentration of active geysers in the
    world—approximately half of the world’s total.
  • The most undisturbed hydrothermal features left in
    the world.
  • One of the few places in the world where active
    travertine terraces are found, at Mammoth Hot
    Springs.
  • Site of many petrified trees formed by a series of
    andesitic volcanic eruptions 45 to 50 million years
    ago.

What Lies Beneath

Yellowstone’s geologic story provides examples of how geologic processes work on a planetary scale. The foundation to understanding this story begins with the structure of the Earth and how this structure gives rise to forces that shape the planet’s surface.

The Earth is frequently depicted as a ball with a central core surrounded by concentric layers that culminate in the crust or surface layer. The distance from the Earth’s surface to its center or core is ap­proximately 4,000 miles. The core of the earth is divided into two parts. The mostly iron and nickel inner core (about 750 miles in diameter) is extremely hot but solid due to immense pressure. The iron and nickel outer core (1,400 miles thick) is hot and molten. The mantle (1,800 miles thick) is dense, hot, semisolid layer of rock. Above this layer is the rela­tively thin crust, three to forty-eight miles thick, on which the continents and ocean floors are found.

The Earth’s crust and upper mantle (lithosphere) is divided into many plates, which are in constant motion. Where plate edges meet and one plate may slide past another, one plate may be driven beneath another (subduction). Upwelling volcanic material pushes plates apart at mid-ocean ridges. Continental plates are made of less dense rocks (granites) that are thicker than oceanic plates (basalts) and thus, "ride" higher than oceanic plates. Many theories have been proposed to explain crustal plate movement. Currently, most evidence supports the theory that convection currents in the partially molten astheno­sphere (the zone of mantle beneath the lithosphere) move the rigid crustal plates above. The volcanism that has so greatly shaped today's Yellowstone is a product of plate movement combined with upwell­ings of molten rock.

At a Glance

Although a cataclysmic eruption of the Yellowstone volcano is unlikely in the foreseeable future, monitor­ing of seismic activity and ground deformation by the Yellowstone Volcano Observatory helps ensure public safety. The University of Utah's seismograph stations detected more than 3,200 earthquakes in the park in 2010, the largest count since 1985. New technology contributed to this increase in detected earthquakes by allowing extensive scientific analysis of small earthquakes. This technology was not avail­able during the 1985 swarm.

From mid-January to mid-February 2010, a swarm of about 2,300 quakes occurred about 10 miles north­west of Old Faithful. The two largest earthquakes, magnitude 3.7 and 3.8, were felt throughout the park and in surrounding communities, but both occurred after 11 pm and had little effect on park visitors.

Beginning in 2004, GPS and InSAR measurements indicated that parts of the Yellowstone caldera were rising up to 7 cm per year, while an area near the northern caldera boundary started to subside. The largest vertical movement was recorded at the White Lake GPS station, inside the caldera's eastern rim, where the total uplift from 2004 to 2010 was about 27 cm. The caldera began to subside during the first half of 2010, about 5 cm at White Lake so far. Episodes of uplift and subsidence have been correlated with the frequency of earthquakes in the park.

Energy and groundwater development outside the park, especially in known geothermal areas in Island Park, Idaho, and Corwin Springs, Montana, could alter the functioning of geothermal systems in the park.

 

Did You Know?

Dog Hooked to Travois for Transporting Goods.

Some groups of Shoshone Indians, who adapted to a mountain existence, chose not to acquire the horse. These included the Sheep Eaters, or Tukudika, who used dogs to transport food, hides, and other provisions. The Sheep Eaters lived in many locations in Yellowstone.