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Geology. Age of rock. late– Cretaceous Period. Volcanic arc / belt. Ouachita. Last eruption. 79–83 million years ago [1] Pilot Knob is the eroded core of an extinct volcano located in Austin, Texas, United States. It is near Austin-Bergstrom International Airport and McKinney Falls State Park.
Felsic. In geology, felsic is a modifier describing igneous rocks that are relatively rich in elements that form feldspar and quartz. [1] It is contrasted with mafic rocks, which are relatively richer in magnesium and iron. Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen ...
Today, the Christmas Mountains caldera complex, as well as the dome, is heavily eroded, exposing the deep structure of the complex. The complex is the type location for laccocalderas. Laccocalderas differ from conventional calderas, being relatively small and developing over thin, shallow laccolithic magma chambers rather than deeper bodies ...
Eruptions can last anywhere from hours to days, with longer eruptions being associated with more felsic volcanoes. Although they are usually associated with felsic magma, Plinian eruptions can occur at basaltic volcanoes, if the magma chamber differentiates with upper portions rich in silicon dioxide, [40] or if magma ascends rapidly. [42]
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate ...
Rhyolite (/ ˈraɪ.əlaɪt / RY-ə-lyte) [1][2][3][4] 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 assemblage is predominantly quartz, sanidine, and plagioclase.
Volcanoes with a felsic melt composition produce extremely explosive eruptions that can inject massive quantities of dust and aerosols high into the atmosphere. These particulate emissions are potent climate forcing agents, and can provoke a wide variety of responses including warming, cooling, and rainwater acidification.
Ignimbrite is a type of volcanic rock, consisting of hardened tuff. [1] Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surrounding atmosphere. New Zealand geologist Patrick Marshall (1869–1950) coined the term ignimbrite ...