San Jerónimo is a

volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. It is located from

San Antonio de los Cobres San Antonio de los Cobres is a small town of population 5,482 (per the 2001 INDEC census) in northwestern Argentina. It is the capital of the Los Andes Department of the Salta Province. Geography The town is known for its high elevation of appr ...

and the lava flows are visible from the road. Also known as San Gerónimo, it is a

monogenetic volcano A monogenetic volcanic field is a type of volcanic field consisting of a group of small monogenetic volcanoes, each of which erupts only once, as opposed to polygenetic volcanoes, which erupt repeatedly over a period of time. The small monogenetic ...

like Negro de Chorrillos and with it part of the geological Piedras Blancas Formation. The volcano has a cone with three craters and reaches an elevation of , which covers an area of about . It developed on top of

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. 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 surrou ...

s of

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

age of the Aguas Calientes caldera and is formed by

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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

lava bomb A volcanic bomb or lava bomb is a mass of partially molten rock (tephra) larger than 64 mm (2.5 inches) in diameter, formed when a volcano ejects viscosity, viscous fragments of lava during an eruption. Because volcanic bombs cool a ...

s and

scoria Scoria or cinder is a pyroclastic, highly vesicular, dark-colored volcanic rock formed by ejection from a volcano as a molten blob and cooled in the air to form discrete grains called clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackso ...

. The volcano erupted

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron ( mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% ...

- trachyandesitic lava which propagated to distances of from the vent and which dammed a local river, forming a lake. The dating of the eruption is uncertain; an older estimate was 780,000 ± 100,000 years ago but a newer indicates that it formed 144,000 ± 3,000 years ago. The older age was probably a product of rocks contaminated by

xenolith A xenolith ("foreign rock") is a rock (geology), rock fragment (Country rock (geology), country rock) that becomes enveloped in a larger rock during the latter's development and solidification. In geology, the term ''xenolith'' is almost exclusi ...

s. San Jerónimo is part of a long alignment of volcanoes along the Calama-Olacapato-El Toro fault. This string of volcanoes is diverse, including

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

s and

stratovolcano A stratovolcano, also known as a composite volcano, is a typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with ...

es on the one hand and

pluton 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 ...

s and

es on the other hand. This fault zone is represented by fault scarps, ponds and springs that occur in the area of the volcanoes. One volcano that is part of this structure is Aguas Calientes caldera, on whose border the San Jerónimo volcano is constructed. The wider region is part of the Andean

Central Volcanic Zone The Andean Volcanic Belt is a major volcanic belt along the Andean cordillera in Argentina, Bolivia, Chile, Colombia, Ecuador, and Peru. It is formed as a result of subduction of the Nazca plate and Antarctic plate underneath the South Americ ...

, where a number of volcanoes ranging from

es over polygenetic volcanoes to

s developed.

References

Sources

* * Pleistocene volcanoes Volcanoes of Salta Province Monogenetic volcanoes {{Volcanology-stub