Tupungatito
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Volcán Tupungatito is the northernmost historically active
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 ...
of the southern
Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...
. Part of the Chilean Andes' volcanic segment, it is the northernmost member of the Southern Volcanic Zone (SVZ), which is one of several distinct volcanic belts in the Andes. Over 70
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
or
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
age volcanoes make up this volcanic belt, which on average has one eruption per year. Tupungatito lies in proximity to the border between
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 ...
and
Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...
, 50 miles east of the Chilean capital
Santiago Santiago (, ; ), also known as Santiago de Chile (), is the capital and largest city of Chile and one of the largest cities in the Americas. It is located in the country's central valley and is the center of the Santiago Metropolitan Regi ...
. It is a group of
volcanic crater A volcanic crater is an approximately circular depression in the ground caused by volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During volcanic eruptions, molten magma and volcanic gases rise from an ...
s and a pyroclastic cone associated with a wide
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 ...
, and lies just southwest of the
Tupungato Tupungato, one of the highest mountains in the Americas, is a massive Andes, Andean lava dome dating to Pleistocene times. It lies on the Argentina–Chile border, between the Chilean Metropolitan Region (near a major international highway about ...
volcano. The caldera is filled with
ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...
, and
glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
s on the volcano are important sources of water for the Rio Maipo river and Santiago. Volcanism is caused by the subduction of the
Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...
underneath the South America Plate. Tupungatito formed less than 100,000 years ago and has had a number of historical eruptions, the latest in 1987, which were mostly small
explosive eruption In volcanology, an explosive eruption is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a Viscosity, viscous ...
s. Presently, the volcano features an acidic crater lake and numerous fumaroles. Renewed eruptions could induce
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
falls in Argentina and dangerous mudflows in Chile.


Name and history

The name was assigned to the volcano by , the chair of the Chilean boundary commission, in 1897. It refers to the neighbouring
Tupungato Tupungato, one of the highest mountains in the Americas, is a massive Andes, Andean lava dome dating to Pleistocene times. It lies on the Argentina–Chile border, between the Chilean Metropolitan Region (near a major international highway about ...
volcano; Luis Risopatrón also reported that Tupungatito was an active volcano. The volcano is also known as Volcan Bravard, a name proposed by Argentina but which fell into disuse; it references the French paleontologist Auguste Bravard. There was speculation about the existence of a volcano in the Andes near Santiago already during the Colonial Era, but only by 1890 was there a clear identification and even then it was frequently assumed that Tupungato instead was the only active edifice. The first ascent of the volcano probably took place in 1907, by K. Griebel, H. Gwinner, L. Hanisch, K. Heitmann and J. Philippi.


Geography and geomorphology

Tupungatito is located in the Chilean
Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...
, east from
Santiago de Chile Santiago (, ; ), also known as Santiago de Chile (), is the capital city, capital and largest city of Chile and one of the largest cities in the Americas. It is located in the country's Chilean Central Valley, central valley and is the center ...
. Politically, it is part of the San Jose de Maipo municipality in the Metropolitan Region where about 40% of all Chileans live. East of Tupungatito is Argentina's Mendoza Province. high,
Tupungato Tupungato, one of the highest mountains in the Americas, is a massive Andes, Andean lava dome dating to Pleistocene times. It lies on the Argentina–Chile border, between the Chilean Metropolitan Region (near a major international highway about ...
volcano rises northeast of Tupungatito.
Tourism Tourism is travel for pleasure, and the Commerce, commercial activity of providing and supporting such travel. World Tourism Organization, UN Tourism defines tourism more generally, in terms which go "beyond the common perception of tourism as ...
,
mountaineering Mountaineering, mountain climbing, or alpinism is a set of outdoor activities that involves ascending mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas that have become mounta ...
and hiking are the principal economic activities in the area; in addition, there are mines and hydropower plants in the valleys. Several
protected area Protected areas or conservation areas are locations which receive protection because of their recognized natural or cultural values. Protected areas are those areas in which human presence or the exploitation of natural resources (e.g. firewood ...
s lie in Argentina east of Tupungatito. The volcano features a wide caldera with an erupted volume of and one or two openings to the western flank, and a group of ten craters north of the caldera. Four of these craters overlap and one is located on top of a wide pyroclastic cone northwest of the remaining craters. Three crater lakes are hosted within these craters; one has a turquoise colour and highly acidic water. The total volume of the volcano is estimated to be , and its flows are fresh and uneroded. The caldera may either be of volcanic origin or the product of a giant
landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
. In the past, lava flows have exited the caldera through the northwestern opening.


Glaciers and hydrology

Above elevation, the volcano is covered with
ice Ice is water that is frozen into a solid state, typically forming at or below temperatures of 0 ° C, 32 ° F, or 273.15 K. It occurs naturally on Earth, on other planets, in Oort cloud objects, and as interstellar ice. As a naturally oc ...
. On Tupungatito ice covers an area of about , which is part of a larger ice cover on regional volcanoes. The caldera contains the Tupungatito glacier, with a volume of about it is the most important glacier of the Metropolitana Region. The cold ice lacks internal water pockets and reaches a maximum thickness of . Outlet glaciers of glaciers in the region are typically covered with debris. In 2012, an ice core was drawn from the Tupungatito glacier. The ice and snow cover on Tupungatito is an important source of water for the rivers in the region and Santiago. Meltwater is discharged westwards into the Colorado- Maipo river system that eventually flows through Santiago; the Quebrada Seca, Estero de Tupungatito and Estero de Tupungato originate close to the volcano and are tributaries to the Colorado. Some glaciers drain instead eastward into the Rio Tupungato river, which as a tributary of the Rio Mendoza is an important water source for the inhabitants of Mendoza in Argentina and the surrounding
agricultural Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created f ...
areas.
Arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...
pollution in the Maipo river system may originate from springs associated the volcanoes Tupungatito and San Jose.


Geology


Regional

Off the coast of South America, the
Nazca Plate The Nazca plate or Nasca plate, named after the Nazca region of southern Peru, is an oceanic list of tectonic plates, tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru– ...
subducts beneath the South America Plate at a rate of . Volcanism in the Andes occurs in four separate volcanic belts, the Northern Volcanic Zone, the Central Volcanic Zone, the Southern Volcanic Zone (SVZ) and the Austral Volcanic Zone. The SVZ is a long and, depending on latitude, up to wide chain of
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...
volcanoes, subdivided according to two schemes in two or three sectors. It features over 70
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
or
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
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, as well as
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, maars and scoria cones. About 30-40 were active postglacially and 18-20 in historical times; the SVZ is the most active volcanic zone in Chile with about one eruption per year. Tupungatito is part of the northernmost SVZ, a narrow and short chain which includes Diamante caldera/ Volcan Maipo and San Jose volcano, and is the northernmost active volcano of the SVZ. Tupungato-Tupungatito, San Jose- Marmolejo and Maipo are the highest volcanoes of the SVZ.


Local

The volcano lies on a thick crust, which together with the tectonic regime has influenced the composition of ascending magma. The
basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...
underneath Tupungatito consists of
evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...
s and marine
limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
s of
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
age. Cretaceous conglomerates,
sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...
s and volcaniclastic rocks, as well as
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 ...
sediments. The
Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...
rocks have been deformed during regional tectonic activity and there are numerous reverse faults in the area. Southwest-northeast and north-south trending faults and fractures influence volcanic activity at Tupungatito; the SW-NE trending lineament also includes Tupungato. The volcano forms a volcanic group with Tupungato and another peak, high Nevado Sin Nombre. Tupungato and Nevado Sin Nombre formed during the late and early
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
, respectively, and are presently inactive. The caldera is to a large degree formed by rocks from Nevado Sin Nombre. high Nevado de los Piuquenes is a fourth volcano in this group and overlaps with Nevado Sin Nombre. Below elevation, Tupungatito is underlaid by an eroded volcano whose rocks resemble Tupungato.


Composition

Tupungatito has erupted rocks ranging from basaltic andesite to dacite, which define a
potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
-rich calc-alkaline suite. There has been little compositional variation during its history.
Phenocryst image:montblanc granite phenocrysts.JPG, 300px, Granites often have large feldspar, feldspathic phenocrysts. This granite, from the Switzerland, Swiss side of the Mont Blanc massif, has large white phenocrysts of plagioclase (that have trapezoid sh ...
s include clinopyroxene and
plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...
and less commonly
olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
and orthopyroxene.
Amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...
and biotite occur as xenocrysts. Magma genesis at Tupungatito and other volcanoes in the region appears to involve a small amount of fluids but large amounts of sediments carried down by the slab, with a moderate interaction with the crust. Processes involved are fractional crystallization, low degrees of partial melting and short periods of storage in
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 u ...
s.


Climate

The mean annual temperature on Tupungatito is about and annual
snow Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water througho ...
accumulation is about snow water equivalent. During the winter, the area above elevation is covered with up to of snow. Most precipitation occurs between May and September, when the north-south movement of the South Pacific High and the Westerlies lets frontal systems reach the area. Glaciers have alternatively advanced and retreated during the 20th century. There is some uncertainty as sometimes snow cover is confused for glacial ice. ice covers an area of , down from in 1986; this encompasses the ice cover of Tupungatito and other volcanoes in the area. Volcanic eruptions have not significantly altered the ice extent.


Eruption history

Tupungatito is about 55,000 or less than 80,000 years old. Early activity was effusive, producing
lava flow 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 ...
s up to long as well as
debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented Rock (geology), rock flow down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. ...
s,
lahar A lahar (, from ) is a violent type of mudflow or debris flow composed of a slurry of Pyroclastic rock, pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a valley, river valley. Lahars are o ...
s, and pyroclastic flows which invaded the Rio Colorado valley. Two sequences of volcanic rocks crop out in the valley and its tributaries, both with thicknesses of about . They have been dated to 52,000±23,000 and 31,000±10,000 years ago, respectively. About 30,000 years ago, a change to a more effusive style of volcanic activity took place with shorter lava flows, although with shorter lava flows. Numerous debris avalanches took place on Tupungatito and left deposits in the western valleys. Tupungatito may be the source of late
Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...
rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...
deposits around the city of Mendoza and Pleistocene
tephra Tephra is fragmental material produced by a Volcano, volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, ...
overlying
glacial A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...
deposits in the Rio Mendoza valley.
Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...
activity added an
explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ex ...
component with Vulcanian and phreatomagmatic eruptions, which deposited pyroclastic materials around the volcano. Short lava flows with lengths of on average were also produced and display flow structures such as levees and lobes. Some of the flows are covered with sediments. The decline of the ice cover during the Holocene and an increased distance between glaciers and volcanic vents may have been responsible for this change in eruption style.


Historical activity

Records of activity at Tupungatito go back to 1646 but its eruption record is poorly known, owing to its inaccessible location. Sometimes, eruptions at Tupungatito were incorrectly attributed to Tupungato. With over 19 eruptions between 1829 and 1987, Tupungatito is one of the SVZ's most active volcanoes. The historical eruptions took place in the craters north of the caldera, and involved in total eight craters. The intensity of the eruptions did not exceed a Volcanic Explosivity Index of 2. Many eruptions appear to be linked to tectonic events in Central Chile. In 1835,
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
in his diary mentioned a muleteer telling him that he had seen smoke coming from close to
Tupungato Tupungato, one of the highest mountains in the Americas, is a massive Andes, Andean lava dome dating to Pleistocene times. It lies on the Argentina–Chile border, between the Chilean Metropolitan Region (near a major international highway about ...
although he crossed the Andes close to Portillo de los Piuquenes rather than the Alto Colorado; this is almost certainly a reference to Tupungatito. In 1962 the volcano was reportedly smoking. Eruptions at Tupungatito frequently deposited
volcanic ash Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, produced during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to r ...
in Mendoza. In 1958-1961 the volcano produced a long lava flow in Chile and ash fall in San Martin, Argentina, away. There is also evidence of
ionospheric The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays ...
impacts from this eruption. The 1961 and 1964 eruptions formed one crater each, with the 1964 crater located directly south of the 1961 one. A third crater was the site of the three last eruptions in 1980, 1986 and 1987. The 1986 eruption deposited a thin ash layer over glaciers in the area. The last activity took place in 1987.


Present-day status and threats

The volcano is fumarolically active in four craters, the fumaroles mainly emit
steam Steam is water vapor, often mixed with air or an aerosol of liquid water droplets. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization. Saturated or superheated steam is inv ...
at temperatures of . Gas bubbling has been observed in the crater lakes. The crater lakes and/or fumaroles are visible in
satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...
images, where they appear as temperature anomalies. The gases come from the
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
, ultimately from the downgoing slab, and as they ascend they interact and mix with an overlying
aquifer An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...
and a hydrothermal system. There is also shallow seismicity around the volcano. Since 2012, the volcano is monitored by the Southern Volcanological Observatory of the Andes. Intense eruptions could melt the ice on the volcano through the emission of incandescent rocks and pyroclastic flows, producing medium-sized or long lahars in the Quebrada de Tupungatito and Estero del Azufre valleys. Pyroclastic fallout from high
eruption column An eruption column or eruption plume is a cloud of super-heated Volcanic ash, ash and tephra suspended in volcanic gas, gases emitted during an explosive eruption, explosive volcanic eruption. The volcanic materials form a vertical column or Plu ...
s would most likely occur in Argentina. Future eruptions will most likely be small or medium-sized
Strombolian eruption In volcanology, a Strombolian eruption is a type of volcanic eruption with relatively mild blasts, typically having a Volcanic Explosivity Index of 1 or 2. Strombolian eruptions consist of ejection of incandescent Scoria, cinders, lapilli, and vo ...
s. The nearest towns in Chile are El Alfalfal, El Manzano and Los Maitenes and in Argentina La Consulta, San Carlos, Tunuyan and Tupungato. For Argentina, it is the 4th most dangerous volcano, and for Chile, the 22nd most dangerous volcano. Due to a combination between its relative proximity to population centres, high volume of ice and frequency of eruptions, a 2020 study ranked it the 4th most dangerous volcano on Earth in terms of lava-ice interactions. Eruptions may also endanger tourists.


See also

* List of volcanoes in Argentina * List of volcanoes in Chile


Notes


References


Sources

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Bibliography

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External links

* {{andean volcanoes Active volcanoes Mountains of Chile Mountains of Argentina South Volcanic Zone Polygenetic volcanoes Volcanoes of Santiago Metropolitan Region Stratovolcanoes of Argentina Volcanoes of Mendoza Province Stratovolcanoes of Chile Five-thousanders of the Andes Principal Cordillera Pleistocene stratovolcanoes Holocene stratovolcanoes