The Pine Canyon Caldera Complex is 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 ...

complex located in

Big Bend National Park Big Bend National Park is an American national park located in West Texas, bordering Mexico. The park has national significance as the largest protected area of Chihuahuan Desert topography and ecology in the United States, and was named after ...

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

. The complex is located in the southern part of the Chisos Mountains in the South Rim Formation. The caldera was formed by several

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

eruptions about 32 million years ago. It is considered a downsag caldera (a type of collapsed caldera), meaning it lacks surficial faulting. The Pine Canyon Caldera also is believed to have been created from crustal stretching during the

Ouachita orogeny The Ouachita orogeny was a mountain-building event that resulted in the folding and faulting of strata currently exposed in the Ouachita Mountains. The more extensive Ouachita system extends from the current range in Arkansas and Oklahoma south ...

. Also in the northern part of the caldera, high

magnetic wave In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...

s are present and are believed to be from a broad

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

, which tends to mean a partial crustal boundary of the Ouachita orogeny. This feature represents the largest intrusion, (, thick, in volume) in an area where laccoliths are ubiquitous in nature. This intrusion may represent a long-lived magma chamber (1 m.y.) that was replenished by smaller batches of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

that varied in viscosity.

References

Big Bend National Park Calderas of Texas Volcanoes of Texas Oligocene calderas {{BrewsterCountyTX-geo-stub