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40-552: The village of Tejeda is situated 6 km (4 mi) north-west of the Pico de las Nieves and 23 km (14 mi) south-west of the island capital Las Palmas . The municipality's area is 103.3 km (39.9 sq mi), spreading near the centre of the island, on the latter's west side. The south-eastern part of its territory includes the second highest point of Gran Canaria island, Pico de las Nieves ("Snows Peak") - 1,949 m (6,394 ft). Other remarkable summits in

80-747: A 4-inch thick ash layer can weigh 120-200 pounds and can get twice as heavy when wet. Wet ash also poses a risk to electronics due to its conductive nature. Dense clouds of hot volcanic ash can be expelled due to the collapse of an eruptive column , or laterally due to the partial collapse of a volcanic edifice or lava dome during explosive eruptions . These clouds are known as pyroclastic surges and in addition to ash , they contain hot lava , pumice , rock , and volcanic gas . Pyroclastic surges flow at speeds over 50 mph and are at temperatures between 200 °C – 700 °C. These surges can cause major damage to property and people in their path. Lava flows from stratovolcanoes are generally not

120-510: A car, as there is a road used by the army. The peak is located between the municipalities of Tejeda , Vega de San Mateo and San Bartolome de Tirajana . This Canary Islands location article is a stub . You can help Misplaced Pages by expanding it . Stratovolcano A stratovolcano , also known as a composite volcano , is a conical volcano built up by many alternating layers ( strata ) of hardened lava and tephra . Unlike shield volcanoes , stratovolcanoes are characterized by

160-479: A fast moving mudflow . Lahars are typically about 60% sediment and 40% water. Depending on the abundance of volcanic debris the lahar can be fluid or thick like concrete. Lahars have the strength and speed to flatten structures and cause great bodily harm, gaining speeds up to dozens of kilometers per hour. In the 1985 eruption of Nevado del Ruiz in Colombia , Pyroclastic surges melted snow and ice atop

200-515: A final intermediate composition . When the magma nears the top surface, it pools in a magma chamber within the crust below the stratovolcano. The processes that trigger the final eruption remain a question for further research. Possible mechanisms include: These internal triggers may be modified by external triggers such as sector collapse , earthquakes , or interactions with groundwater . Some of these triggers operate only under limited conditions. For example, sector collapse (where part of

240-468: A focal point located roughly 2 km under sea level, at what was in the past the center of the island. New magma would then tend to also take the same conical shape. Conical dykes of this size are not found in other islands; Vallehermoso on La Gomera island has some smaller ones. Biologist Juan Sergio Socorro considers this crater to be one of the few clear examples in the world of a very large collapsed volcanic crater , particularly in comparison to

280-769: A result of intraplate volcanism on oceanic islands far from plate boundaries. Examples are Teide in the Canary Islands , and Pico do Fogo in Cape Verde . Stratovolcanoes in the East African Rift include Ol Doinyo Lengai in Tanzania, and Longonot in Kenya. Subduction zone volcanoes form when hydrous minerals are pulled down into the mantle on the slab. These hydrous minerals, such as chlorite and serpentine , release their water into

320-461: A significant threat to humans or animals because the highly viscous lava moves slowly enough for everyone to evacuate. Most deaths attributed to lava are due to related causes such as explosions and asphyxiation from toxic gas . Lava flows can bury homes and farms in thick volcanic rock which greatly reduces property value. However, not all stratovolcanoes erupt viscous and sticky lava . Nyiragongo , near Lake Kivu in central Africa ,

360-552: A steep profile with a summit crater and explosive eruptions. Some have collapsed summit craters called calderas . The lava flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high viscosity . The magma forming this lava is often felsic , having high to intermediate levels of silica (as in rhyolite , dacite , or andesite ), with lesser amounts of less viscous mafic magma . Extensive felsic lava flows are uncommon, but can travel as far as 8 km (5 mi). The term composite volcano

400-531: Is a passive release of gas during periods of dormancy. As per the above examples, while eruptions like Mount Unzen have caused deaths and local damage, the impact of the June 1991 eruption of Mount Pinatubo was seen globally. The eruptive columns reached heights of 40 km and dumped 17 megatons of SO 2 into the lower stratosphere . The aerosols that formed from the sulfur dioxide (SO 2 ), carbon dioxide (CO 2 ), and other gases dispersed around

440-519: Is impressive. All those black walls of the great caldera, with its crests, which look like battlements, with its erect rocks, offer a Dantesque vision. The cauldrons of Hell that the Florentine visited can be no different. It is a tremendous commotion of the entrails of the earth; it looks quite like a petrified storm, but a storm of fire, of lava, more than of water. ") Its population was 2,028 in 2013. Pico de las Nieves Pico de las Nieves

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480-452: Is left of it are found a few green-bluish peaks (such as "azulejos" de Veneguera - "Veneguera's tiles") and below these are the oldest basalts of the island, primitive substrate of Grand Canary. The caldera was produced in probably less than two hours, by the explosion of the residual magma chambers During the collapse of the caldera de Tejera ignimbrite rock was produced, with a pink matrix dotted with white crystals. It exists because

520-550: Is the highest peak and a stratovolcano on the island of Gran Canaria , Canary Islands , Spain . Its height is 1,949 metres (6,394 ft) above sea level. On its slopes, Canary Islands Pine was reintroduced in the 1950s. Traditionally, Pico de las Nieves has been considered the highest peak on the island of Gran Canaria; however, this is uncertain since Morro de la Agujereada stands at 1,956 metres (6,417 ft), which would make it higher than Pico de las Nieves. The two mountains stand next to each other. Gran Canaria has

560-451: Is the most famous example of a hazardous stratovolcano eruption. It completely smothered the nearby ancient cities of Pompeii and Herculaneum with thick deposits of pyroclastic surges and pumice ranging from 6–7 meters deep. Pompeii had 10,000-20,000 inhabitants at the time of eruption. Mount Vesuvius is recognized as one of the most dangerous of the world's volcanoes, due to its capacity for powerful explosive eruptions coupled with

600-450: Is typically between 700 and 1,200 °C (1,300-2,200 °F). Volcanic bombs are masses of unconsolidated rock and lava that are ejected during an eruption. Volcanic bombs are classified as larger than 64mm (2.5 inches). Anything below 64mm is classified as a volcanic block . When erupted Bombs are still molten and partially cool and solidify on their descent. They can form ribbon or oval shapes that can also flatten on impact with

640-1014: Is used because the strata are usually mixed and uneven instead of neat layers. They are among the most common types of volcanoes; more than 700 stratovolcanoes have erupted lava during the Holocene Epoch (the last 11,700 years), and many older, now extinct, stratovolcanoes erupted lava as far back as Archean times. Stratovolcanoes are typically found in subduction zones but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are Krakatoa in Indonesia (which erupted in 1883 claiming 36,000 lives) and Mount Vesuvius in Italy (which erupted in 79 A.D killing an estimated 2,000 people). In modern times, Mount St. Helens (1980) in Washington State , US, and Mount Pinatubo (1991) in

680-403: Is very dangerous because its magma has an unusually low silica content , making it much less viscous than other stratovolcanoes. Low viscosity lava can generate massive lava fountains , while lava of thicker viscosity can solidify within the vent, creating a volcanic plug . Volcanic plugs can trap gas and create pressure in the magma chamber, resulting in violent eruptions. Lava

720-575: The Cañadas del Teide for which several theories are held regarding its formation. "El espectáculo es imponente. Todas aquellas negras murallas de la gran caldera, con sus crestas, que parecen almenas, con sus roques enhiestos, ofrecen el aspecto de una visión dantesca. No otra cosa pueden ser las calderas del Infierno que visitó el florentino. Es una tremenda conmoción de las entrañas de la tierra; parece todo una tempestad petrificada, pero una tempestad de fuego, de lava, más que de agua." (" The spectacle

760-579: The Philippines have erupted catastrophically, but with fewer deaths. Stratovolcanoes are common at subduction zones , forming chains and clusters along plate tectonic boundaries where an oceanic crust plate is drawn under a continental crust plate (continental arc volcanism, e.g. Cascade Range , Andes , Campania ) or another oceanic crust plate ( island arc volcanism, e.g. Japan , Philippines , Aleutian Islands ). Stratovolcanoes also occur in some other geological settings, for example as

800-649: The explosive eruption by which the caldera collapsed was so powerful that the magma was pulverized in a very fine spray and created almost microscopic structures in the matrix rock. Ignimbrita is found on the outside of the periphery of the caldera . The caldera also bears traces of a 2 million year period of evolution. This is especially notable at the heads of the Agaete ravine ( barranco de Agaete ) and Mogan ravine ( barranco de Mogan ), where we can see horizontal basaltic lavas in their lower parts and, above, thicker material in sloping layers. Another rare feature of

840-891: The magma is too viscous to allow easy escape of volcanic gases . As a consequence, the tremendous internal pressures of the trapped volcanic gases remain and intermingle in the pasty magma . Following the breaching of the vent and the opening of the crater, the magma degasses explosively. The magma and gases blast out with high speed and full force. Since 1600 CE , nearly 300,000 people have been killed by volcanic eruptions . Most deaths were caused by pyroclastic flows and lahars , deadly hazards that often accompany explosive eruptions of subduction-zone stratovolcanoes. Pyroclastic flows are swift, avalanche-like, ground-sweeping, incandescent mixtures of hot volcanic debris, fine ash , fragmented lava , and superheated gases that can travel at speeds over 150 km/h (90 mph). Around 30,000 people were killed by pyroclastic flows during

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880-443: The mantle which decreases its melting point by 60 to 100 °C. The release of water from hydrated minerals is termed " dewatering ", and occurs at specific pressures and temperatures for each mineral, as the plate descends to greater depths. This allows the mantle to partially melt and generate magma . This is called flux melting . The magma then rises through the crust , incorporating silica-rich crustal rock, leading to

920-616: The 1902 eruption of Mount Pelée on the island of Martinique in the Caribbean . During March and April 1982, El Chichón in the State of Chiapas in southeastern Mexico , erupted 3 times, causing the worst volcanic disaster in that country's history and killied more than 2,000 people in pyroclastic flows . Two Decade Volcanoes that erupted in 1991 provide examples of stratovolcano hazards. On 15 June, Mount Pinatubo erupted and caused an ash cloud to shoot 40 km (25 mi) into

960-485: The 1982 eruption of Galunggung in Java , British Airways Flight 9 flew into the ash cloud, causing it to sustain temporary engine failure and structural damage. Although no crashes have happened due to ash, more than 60, mostly commercial aircraft , have been damaged. Some of these incidents resulted in emergency landings. Ashfalls are a threat to health when inhaled and are also a threat to property. A square yard of

1000-585: The 5,321 m (17,457 ft) high Andean volcano. The ensuing lahar killed 25,000 people and flooded the city of Armero and nearby settlements. As a volcano forms, several different gases mix with magma in the volcanic chamber. During an eruption the gases are then released into the atmosphere which can lead to toxic human exposure. The most abundant of these gases is H 2 O ( water ) followed by CO 2 ( carbon dioxide ), SO 2 ( sulfur dioxide ), H 2 S ( hydrogen sulfide ), and HF ( hydrogen fluoride ). If at concentrations of more than 3% in

1040-819: The air, when breathed in CO 2 can cause dizziness and difficulty breathing. At more than 15% concentration CO 2 causes death. CO 2 can settle into depressions in the land, leading to deadly, odorless pockets of gas. SO 2 classified as a respiratory, skin, and eye irritant if come into contact with. It is known for its pungent egg smell and role in ozone depletion and has the potential to cause acid rain downwind of an eruption. H 2 S has an even stronger odor than SO 2 as well as being even more toxic. Exposure for less than an hour at concentrations of over 500 ppm causes death. HF and similar species can coat ash particles and once deposited can poison soil and water. Gases are also emitted during volcanic degassing, which

1080-748: The air. It produced large pyroclastic surges and lahar floods that caused a lot of damage to the surrounding area. Pinatubo , located in Central Luzon just 90 km (56 mi) west-northwest of Manila , had been dormant for six centuries before the 1991 eruption. This eruption was one of the 2nd largest in the 20th century. It produced a large volcanic ash cloud that affected global temperatures, lowering them in areas as much as .5 °C. The volcanic ash cloud consisted of 22 million tons of SO 2 which combined with water droplets to create sulfuric acid . In 1991 Japan's Unzen Volcano also erupted, after 200 years of inactivity. It's located on

1120-424: The caldera is its system of conical dykes in its center, that were damaged by the eruptions and determined the structure of the island by their own structure. The lava passed through these dykes during some eruptions, in particular basaltic eruptions ; this created a crack in the surrounding channels where the lava was injected, and from them the volcano arose. In Grand Canary these conical dykes were centered on

1160-457: The eastern edge of a volcanic basin or crater that bears its name ( caldera de Tejeda ). The caldera ’s dimensions are 28 km x 18 km, with a surface that extends from the head of Agaete's ravine ( barranco de Agaete ) near Artenara, to Verde Andén ("Green Platform") in the west, Veneguera and the head of Mogán ravine ( barranco de Mogán ) up to Arguineguín's ravine ( barranco de Arguineguin ). Only half of its perimeter remains standing; on what

1200-540: The flank of a volcano collapses in a massive landslide) can only trigger the eruption of a very shallow magma chamber . Magma differentiation and thermal expansion also are ineffective as triggers for eruptions from deep magma chambers . In recorded history , explosive eruptions at subduction zone ( convergent-boundary ) volcanoes have posed the greatest hazard to civilizations. Subduction-zone stratovolcanoes, such as Mount St. Helens , Mount Etna and Mount Pinatubo , typically erupt with explosive force because

1240-478: The ground. Volcanic Bombs are associated with Strombolian and Vulcanian eruptions and basaltic lava . Ejection velocities ranging from 200 to 400 m/s have been recorded causing volcanic bombs to be destructive. Lahars (from a Javanese term for volcanic mudflows) are a mixture of volcanic debris and water. Lahars can result from heavy rainfall during or before the eruption or interaction with ice and snow. Meltwater mixes with volcanic debris causing

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1280-458: The high population density of the surrounding Metropolitan Naples area (totaling about 3.6 million inhabitants). In addition to potentially affecting the climate, volcanic ash clouds from explosive eruptions pose a serious hazard to aviation . Volcanic ash clouds consist of ash which is made of silt or sand sized pieces of rock, mineral, volcanic glass . Ash grains are jagged, abrasive, and don't dissolve in water. For example, during

1320-589: The highest elevation of the province of Las Palmas and the third highest in the Canary Islands. Of the other Canary Islands, only Tenerife and La Palma have higher peaks. The name means 'peak of the snows' in Spanish and refers to the fact that several covered pits (neveras in Spanish) for holding snow were built directly into the mountainsides. (An alternative theory states that the name came about as

1360-459: The highest plateau is occupied by a military base, including a large ball-shaped radar. Civilian visitors are allowed to enter a platform somewhat below the base, from which half of the island as well as Tenerife's Pico del Teide is visible, in case of good weather. The most distinctive feature is the Roque Nublo monolith, the second highest peak of the island. The peak could be accessed by

1400-475: The ice cream shop in the Cathedral of Las Palmas (the capital of the island) on horseback, which took five or six hours. The snow was used for alleviating disease, to lower the temperature in the epidemics of yellow fever and cholera, as well as an anti-inflammatory and analgesic. It was also used for cooling water or beverages for the upper class. Water from the pools was used for irrigation purposes. Most of

1440-504: The island of Kyushu about 40 km (25 mi) east of Nagasaki . Beginning in June, a newly formed lava dome repeatedly collapsed. This generated a pyroclastic flow that flowed down the mountain's slopes at speeds as high as 200 km/h (120 mph). The 1991 eruption of Mount Unzen was one of the worst volcanic disasters in Japan's history, once killing more than 15,000 people in 1792. The eruption of Mount Vesuvius in 79 AD

1480-588: The mountain had the highest frequency of snowfalls on the island.) The first of the neveras was constructed in 1694 by order of the Catholic Church. The snow was collected by laborers using wooden shovels and wicker baskets, making real mountains of snow. The snow was placed into the pits by the "paleros" in rows, and packed in rectangular boxes of wood or cork separated by layers of straw. There were many blocks of ice, called "sabanada", which in June would be carried in panniers of straw covered with blankets to

1520-596: The municipality are Roque Nublo ("Cloud Rock") 813 m (2,667 ft) and Roque Bentayga (" Bentayga Rock ") with its ritual place ( almogarén ) and other features. Close by are the cuevas del Rey ("the King's caves", 1 km to the west of Rock Bentayga), an antique cave house village with granaries; and 2 km further west the antique cave house village of Acusa Seca . All these sites are listed Spanish Heritage as Properties of cultural interest (" Bien de Interés Cultural "). The village of Tejeda sits on

1560-464: The size of Mount Pinatubo affected the weather for a few years; with warmer winters and cooler summers observed. A similar phenomenon occurred in the April 1815, the eruption of Mount Tambora on Sumbawa island in Indonesia . The Mount Tambora eruption is recognized as the most powerful eruption in recorded history. Its eruption cloud lowered global temperatures as much as 0.4 to 0.7 °C. In

1600-412: The world. The SO 2 in this cloud combined with water (both of volcanic and atmospheric origin) and formed sulfuric acid , blocking a portion of the sunlight from reaching the troposphere . This caused the global temperature to decrease by about 0.4 °C (0.72 °F) from 1992 to 1993. These aerosols caused the ozone layer to reach the lowest concentrations recorded at that time. An eruption

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