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52-450: Nightingale Island is the smallest of the four main islands of the Tristan da Cunha Group, measuring only 4 square kilometres (1.5 sq mi), and lies 30 kilometres (18.6 mi) away from Tristan and 22 kilometres (13.7 mi) from Inaccessible. Stoltenhoff and Middle (also known as Alex Island), are really two large islets rather than conventional islands. The Nightingale Islands are

104-484: A volcanic vent , piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types of volcanic cones include stratocones , spatter cones , tuff cones , and cinder cones . Stratocones are large cone-shaped volcanoes made up of lava flows , explosively erupted pyroclastic rocks, and igneous intrusives that are typically centered around

156-747: 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

208-416: A cylindrical vent. Unlike shield volcanoes , they are characterized by a steep profile and periodic, often alternating, explosive eruptions and effusive eruptions . Some have collapsed craters called calderas . The central core of a stratocone is commonly dominated by a central core of intrusive rocks that range from around 500 meters (1,600 ft) to over several kilometers in diameter. This central core

260-458: A density of around 1.3 pairs per square metre; almost the entire vegetated island is occupied. The Nightingale Island finch is found nowhere else in the world. The Nightingale Islands group has been recognised internationally as part of the Tristan da Cunha Endemic Bird Area (EBA). It has also been identified as an Important Bird Area (IBA) by BirdLife International as a breeding site for seabirds and its endemic landbirds. Birds for which

312-474: 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

364-430: A few days to a few years. Of observed cinder cone eruptions, 50% have lasted for less than 30 days, and 95% stopped within one year. In case of Parícutin, its eruption lasted for nine years from 1943 to 1952. Rarely do they erupt either two, three, or more times. Later eruptions typically produce new cones within a volcanic field at separation distances of a few kilometers and separate by periods of 100 to 1,000 years. Within

416-515: 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

468-738: 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

520-461: 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 ,

572-1026: A single, typically cylindrical, vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as either cinders, clinkers, or scoria around the vent to form a cone that often is noticeably symmetrical; with slopes between 30 and 40°; and a nearly circular ground plan. Most cinder cones have a bowl-shaped crater at the summit. The basal diameters of cinder cones average about 800 meters (2,600 ft) and range from 250 to 2,500 meters (820 to 8,200 ft). The diameter of their craters ranges between 50 and 600 meters (160 and 1,970 ft). Cinder cones rarely rise more than 50–350 meters (160–1,150 ft) or so above their surroundings. Cinder cones most commonly occur as isolated cones in large basaltic volcanic fields. They also occur in nested clusters in association with complex tuff ring and maar complexes. Finally, they are also common as parasitic and monogenetic cones on complex shield and stratovolcanoes. Globally, cinder cones are

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624-552: 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

676-399: A tuff cone have commonly been altered, palagonitized , by either its interaction with groundwater or when it was deposited warm and wet. The pyroclastic deposits of tuff cones differ from the pyroclastic deposits of spatter cones by their lack or paucity of lava spatter, smaller grain-size, and excellent bedding. Typically, but not always, tuff cones lack associated lava flows. A tuff ring

728-525: A volcanic field, eruptions can occur over a period of a million years. Once eruptions cease, being unconsolidated, cinder cones tend to erode rapidly unless further eruptions occur. Rootless cones , also called pseudocraters , are volcanic cones that are not directly associated with a conduit that brought magma to the surface from a deep-seated magma reservoir. Generally, three types of rootless cones, littoral cones , explosion craters , and hornitos are recognized. Littoral cones and explosion craters are

780-637: Is a low, steep-sided hill or mound that consists of welded lava fragments, called spatter, which has formed around a lava fountain issuing from a central vent. Typically, spatter cones are about 3–5 meters (9.8–16.4 ft) high. In case of a linear fissure, lava fountaining will create broad embankments of spatter, called spatter ramparts, along both sides of the fissure. Spatter cones are more circular and cone shaped, while spatter ramparts are linear wall-like features. Spatter cones and spatter ramparts are typically formed by lava fountaining associated with mafic , highly fluid lavas, such as those erupted in

832-527: 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

884-408: Is a related type of small monogenetic volcano that is also produced by phreatic (hydrovolcanic) explosions directly associated with magma brought to the surface through a conduit from a deep-seated magma reservoir. They are characterized by rims that have a low, broad topographic profiles and gentle topographic slopes that are 25 degrees or less. The maximum thickness of the pyroclastic debris comprising

936-666: Is a small monogenetic volcanic cone produced by phreatic (hydrovolcanic) explosions directly associated with magma brought to the surface through a conduit from a deep-seated magma reservoir. They are characterized by high rims that have a maximum relief of 100–800 meters (330–2,620 ft) above the crater floor and steep slopes that are greater than 25 degrees. They typically have a rim to rim diameter of 300–5,000 meters (980–16,400 ft). A tuff cone consists typically of thick-bedded pyroclastic flow and surge deposits created by eruption-fed density currents and bomb-scoria beds derived from fallout from its eruption column. The tuffs composing

988-414: Is surrounded by multiple generations of lava flows, many of which are brecciated , and a wide range of pyroclastic rocks and reworked volcanic debris. The typical stratocone is an andesitic to dacitic volcano that is associated with subduction zones . They are also known as either stratified volcano, composite cone, bedded volcano, cone of mixed type or Vesuvian-type volcano. A spatter cone

1040-451: 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

1092-450: 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

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1144-990: 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

1196-403: 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

1248-572: 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

1300-466: The Ramsar Convention . The islanders of Tristan da Cunha depend on the fish resource to a large extent for food and for bait for the local rock lobster industry. Approximately 61.5 tons of linefish are harvested each year for these purposes. The insular nature of the island ecosystem renders it vulnerable to over-exploitation from commercial fishing operations. Most of the fish species are bound to

1352-891: 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

1404-443: 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

1456-607: 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

1508-481: 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

1560-585: 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

1612-571: The Hawaiian Islands. As blobs of molten lava, spatter, are erupted into the air by a lava fountain, they can lack the time needed to cool completely before hitting the ground. Consequently, the spatter are not fully solid, like taffy , as they land and they bind to the underlying spatter as both often slowly ooze down the side of the cone. As a result, the spatter builds up a cone that is composed of spatter either agglutinated or welded to each other. A tuff cone , sometimes called an ash cone ,

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1664-708: The IBA is significant include northern rockhopper penguins (up to 125,000 breeding pairs), sooty albatrosses (up to 250 pairs), Atlantic yellow-nosed albatrosses (5000 pairs), broad-billed prions (10,000 pairs), soft-plumaged petrels (up to 1000 pairs), great shearwaters (up to 3 million pairs), white-faced storm petrels (10,000 pairs), white-bellied storm petrels (1000 pairs), Antarctic terns (up to 400 pairs), southern skuas (up to 500 pairs), Tristan thrushes , Wilkins's buntings and Nightingale buntings . The nearby islands of Gough and Inaccessible Island have been recognised as Wetlands of International Importance under

1716-816: 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

1768-741: 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

1820-426: The calderas and volcanic cones of Ulysses Patera , Ulysses Colles and Hydraotes Chaos are argued to be cinder cones. Cinder cones typically only erupt once like Parícutin. As a result, they are considered to be monogenetic volcanoes and most of them form monogenetic volcanic fields . Cinder cones are typically active for very brief periods of time before becoming inactive. Their eruptions range in duration from

1872-422: The crater of a tuff ring generally has been excavated below the existing ground surface. As a result, water commonly fills a tuff ring's crater to form a lake once eruptions cease. Both tuff cones and their associated tuff rings were created by explosive eruptions from a vent where the magma is interacting with either groundwater or a shallow body of water as found within a lake or sea. The interaction between

1924-540: 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

1976-478: 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

2028-436: The heavily eroded remnant once much larger stratovolcano . The oldest potassium–argon dating from the island is 18 ± 4  Ma . The most recent submarine eruption was in 2004. On August 29-30, 2004, earthquake swarms from the south flank of Nightingale island were recorded in Tristan da Cunha. This was subsequently followed by pumice rafting up on the shores of Tristan da Cunha. The youngest subaereal volcanic activity on

2080-458: 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

2132-600: The island in September 1767. Nightingale was renamed after British captain Gamaliel Nightingale in 1760. Jonathan Lambert temporarily changed the name to "Lovel Island" in his 1811 proclamation in the Boston Gazette , but as with his other proposed changes (i.e. Tristan da Cunha Group to "Isles of Refreshment"), the name did not last. Nightingale, a tiny island, is home to more than three million pairs of seabirds at

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2184-558: The island is indirectly dated to 39,160 −3,410 uncalibrated years BP by radiocarbon dates on peat overlain by volcanic tuff. Originally named "Gebrooken (Broken) island" by the Dutch under Jan Jacobszoon in January 1656, they found no safe anchorage and did not make the first landing until 1696 (most likely by Willem de Vlamingh in August of that year). Frenchman D'Etchevery also visited

2236-500: 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

2288-524: The islands for the completion of their life cycles; hence, the populations are more or less isolated and not supplemented by recruits from outside of the system. 37°25′16″S 12°28′52″W  /  37.421°S 12.481°W  / -37.421; -12.481 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

2340-638: The magma, expanding steam, and volcanic gases resulted in the production and ejection of fine-grained pyroclastic debris called ash with the consistency of flour . The volcanic ash comprising a tuff cone accumulated either as fallout from eruption columns, from low-density volcanic surges and pyroclastic flows, or combination of these. Tuff cones are typically associated with volcanic eruptions within shallow bodies of water and tuff rings are associated with eruptions within either water saturated sediments and bedrock or permafrost . Next to spatter (scoria) cones, tuff cones and their associated tuff rings are among

2392-748: The most common types of volcanoes on Earth. An example of a tuff cone is Diamond Head at Waikīkī in Hawaiʻi . Clusters of pitted cones observed in the Nephentes/Amenthes region of Mars at the southern margin of the ancient Utopia impact basin are currently interpreted as being tuff cones and rings. Cinder cones , also known as scoria cones and less commonly scoria mounds , are small, steep-sided volcanic cones built of loose pyroclastic fragments, such as either volcanic clinkers, cinders, volcanic ash, or scoria . They consist of loose pyroclastic debris formed by explosive eruptions or lava fountains from

2444-687: The most typical volcanic landform found within continental intraplate volcanic fields and also occur in some subduction zone settings as well. Parícutin , the Mexican cinder cone which was born in a cornfield on February 20, 1943, and Sunset Crater in Northern Arizona in the US Southwest are classic examples of cinder cones, as are ancient volcanic cones found in New Mexico's Petroglyph National Monument . Cone-shaped hills observed in satellite imagery of

2496-494: The result of mild explosions that were generated locally by the interaction of either hot lava or pyroclastic flows with water. Littoral cones typically form on the surface of a basaltic lava flow where it has entered into a body of water, usually a sea or ocean. Explosion craters form where either hot lava or pyroclastic flows have covered either marshy ground or water-saturated ground of some sort. Hornitos are rootless cones that are composed of welded lava fragments and were formed on

2548-421: The rim of a typical tuff ring is generally thin, less than 50 meters (160 ft) to 100 meters (330 ft) thick. The pyroclastic materials that comprise their rim consist primarily of relatively fresh and unaltered, distinctly and thin-bedded volcanic surge and air fall deposits. Their rims also can contain variable amounts of local country rock (bedrock) blasted out of their crater. In contrast to tuff cones,

2600-460: 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

2652-412: 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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2704-518: The year following the eruption, most of the Northern Hemisphere experienced cooler temperatures during the summer. In the northern hemisphere , 1816 was known as the " Year Without a Summer ". The eruption caused crop failures, food shortages, and floods that killed over 100,000 people across Europe , Asia , and North America . Volcanic cone Volcanic cones are among the simplest volcanic landforms . They are built by ejecta from

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