geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...

, a resurgent dome is a dome formed by swelling or rising of a

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

floor due to movement in the

magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it up ...

beneath it. Unlike a lava dome, a resurgent dome is not formed by the extrusion of highly viscous

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

onto the surface, but rather by the uplift and

deformation Deformation can refer to: * Deformation (engineering), changes in an object's shape or form due to the application of a force or forces. ** Deformation (physics), such changes considered and analyzed as displacements of continuum bodies. * Defor ...

of the surface itself by magma movement underground. Resurgent domes are typically found near the center of very large open calderas such as

Yellowstone Caldera The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northwest corn ...

Valles Caldera Valles Caldera (or Jemez Caldera) is a wide volcanic caldera in the Jemez Mountains of northern New Mexico. Hot springs, streams, fumaroles, natural gas seeps and volcanic domes dot the caldera floor landscape. The highest point in the calde ...

, and in turn such calderas are often referred to as "resurgent-type" calderas to distinguish them from the more common (but much smaller) calderas found on shield volcanoes and stratovolcanoes. The structure that makes a resurgent dome possible is a fracture zone made up of ring faults surrounded by concentric normal faults around the outside of the rings. During initial formation of the caldera these ring faults provide vents for ash-flow eruptions and are the point at which subsidence of the cauldron block occurs. Subsequent magma flows then push the cauldron block back up creating the dome. In the monitoring of

volcanic hazards A volcanic hazard is the probability a volcanic eruption or related geophysical event will occur in a given geographic area and within a specified window of time. The risk that can be associated with a volcanic hazard depends on the proximity and ...

, resurgent domes are often intensively monitored, as an ongoing increase in elevation accompanied by seismic activity is certain evidence for magma rising beneath the surface.

Examples of calderas with resurgent domes

* Ko'olau Caldera *

Long Valley Caldera Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the Earth's largest calderas, measuring about long (east-west), wide (north-south), and up to deep. Long Valley was formed ...

Lake Toba Lake Toba ( id, Danau Toba) ( Toba Batak: ᯖᯀᯬ ᯖᯬᯅ; romanized: ''Tao Toba'') is a large natural lake in North Sumatra, Indonesia, occupying the caldera of a supervolcano. The lake is located in the middle of the northern part of the i ...

Bennett Lake Volcanic Complex The Bennett Lake Volcanic Complex (BLVC) is a huge 50-million-year-old extinct caldera complex that spans across the British Columbia-Yukon border in Canada. It is located near the western end of the West Arm of Bennett Lake. The caldera complex ...

* Blake River Megacaldera Complex *

Lake Taupō Lake Taupō (also spelled Taupo; mi, Taupō-nui-a-Tia or ) is a large crater lake in New Zealand's North Island, located in the caldera of the Taupō Volcano. The lake is the namesake of the town of Taupō, which sits on a bay in the lake's no ...

* Iwo Jima *

La Garita Caldera La Garita Caldera is a large caldera in the San Juan volcanic field in the San Juan Mountains near the town of Creede in southwestern Colorado, United States. It is west of La Garita, Colorado. The eruption that created the La Garita Calde ...

in Colorado * Timber Mountain Caldera in Nevada

References

Geologic domes Volcanology {{Volcanology-stub