Types of volcanic eruptions
Several types of volcanic eruptions—during which lava and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are named after famous volcanoes where that type of behavior has been observed; some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series. There are three different types of eruptions; the most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity; the third eruptive type is the phreatic eruption, driven by the superheating of steam via contact with magma. Within these wide-defining eruptive types are several subtypes; the weakest are Hawaiian and submarine Strombolian, followed by Vulcanian and Surtseyan.
The stronger eruptive types are Pelean eruptions, followed by Plinian eruptions. Subglacial and phreatic eruptions are defined by their eruptive mechanism, vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index, an order of magnitude scale ranging from 0 to 8 that correlates to eruptive types. Volcanic eruptions arise through three main mechanisms: Gas release under decompression causing magmatic eruptions Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions Ejection of entrained particles during steam eruptions causing phreatic eruptionsThere are two types of eruptions in terms of activity, explosive eruptions and effusive eruptions. Explosive eruptions are characterized by gas-driven explosions that propels tephra. Effusive eruptions, are characterized by the outpouring of lava without significant explosive eruption. Volcanic eruptions vary in strength. On the one extreme there are effusive Hawaiian eruptions, which are characterized by lava fountains and fluid lava flows, which are not dangerous.
On the other extreme, Plinian eruptions are large and dangerous explosive events. Volcanoes are not bound to one eruptive style, display many different types, both passive and explosive in the span of a single eruptive cycle. Volcanoes do not always erupt vertically from a single crater near their peak, either; some volcanoes exhibit lateral and fissure eruptions. Notably, many Hawaiian eruptions start from rift zones, some of the strongest Surtseyan eruptions develop along fracture zones. Scientists believed that pulses of magma mixed together in the chamber before climbing upward—a process estimated to take several thousands of years, but Columbia University volcanologists found that the eruption of Costa Rica’s Irazú Volcano in 1963 was triggered by magma that took a nonstop route from the mantle over just a few months. The Volcanic Explosivity Index is a scale, for measuring the strength of eruptions, it is used by the Smithsonian Institution's Global Volcanism Program in assessing the impact of historic and prehistoric lava flows.
It operates in a way similar to the Richter scale for earthquakes, in that each interval in value represents a tenfold increasing in magnitude. The vast majority of volcanic eruptions are of VEIs between 0 and 2. Volcanic eruptions by VEI index Magmatic eruptions produce juvenile clasts during explosive decompression from gas release, they range in intensity from the small lava fountains on Hawaii to catastrophic Ultra-Plinian eruption columns more than 30 km high, bigger than the eruption of Mount Vesuvius in 79 that buried Pompeii. Hawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of fluid basalt-type lavas with low gaseous content; the volume of ejected material from Hawaiian eruptions is less than half of that found in other eruptive types. Steady production of small amounts of lava builds up the broad form of a shield volcano.
Eruptions are not centralized at the main summit as with other volcanic types, occur at vents around the summit and from fissure vents radiating out of the center. Hawaiian eruptions begin as a line of vent eruptions along a fissure vent, a so-called "curtain of fire." These die down. Central-vent eruptions, meanwhile take the form of large lava fountains, which can reach heights of hundreds of meters or more; the particles from lava fountains cool in the air before hitting the ground, resulting in the accumulation of cindery scoria fragments. If eruptive rates are high enough, they may form splatter-fed lava flows. Hawaiian eruptions are extremely long lived. Another Hawaiian volcanic feature is the formation of active lava lakes, self-maintaining pools of raw lava with a thin crust of semi-cooled rock. Flows from Hawaiian eruptions are basal
A fumarole is an opening in a planet's crust which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrogen chloride, hydrogen sulfide. The steam forms when superheated water condenses as its pressure drops when it emerges from the ground; the name solfatara is given to fumaroles. Fumaroles may occur along long fissure, or in chaotic clusters or fields, they occur on the surface of lava or pyroclastic flows. A fumarole field is an area of thermal springs and gas vents where shallow magma or hot igneous rocks release gases or interact with groundwater; when they occur in freezing environments, fumaroles may cause fumarolic ice towers. Fumaroles may persist for centuries if located above a persistent heat source; the Valley of Ten Thousand Smokes, for example, was formed during the 1912 eruption of Novarupta in Alaska. Thousands of fumaroles occurred in the cooling ash from the eruption, but over time most of them have become extinct. An estimated four thousand fumaroles exist within the boundaries of Yellowstone National Park in the United States.
In April 2006 fumarole emissions killed three ski-patrol workers east of Chair 3 at Mammoth Mountain Ski Area in California. The workers were overpowered by toxic fumes. Another example is an array of fumaroles in the Valley of Desolation in Morne Trois Pitons National Park in Dominica. Fumaroles emitting sulfurous vapors form surface deposits of sulfur-rich minerals. Boiling Lake Cold seep Hydrothermal vent Mazuku Mofetta Mudpot Mud volcano Sulfur Mining on Gunung Welirang Volcano Chisholm, Hugh, ed.. "Fumarole". Encyclopædia Britannica. 11. Cambridge University Press. Pp. 300–301
A summit is a point on a surface, higher in elevation than all points adjacent to it. The topographic terms acme, apex and zenith are synonymous; the term top is used only for a mountain peak, located at some distance from the nearest point of higher elevation. For example, a big massive rock next to the main summit of a mountain is not considered a summit. Summits near a higher peak, with some prominence or isolation, but not reaching a certain cutoff value for the quantities, are considered subsummits of the higher peak, are considered part of the same mountain. A pyramidal peak is an exaggerated form produced by ice erosion of a mountain top. Summit may refer to the highest point along a line, trail, or route; the highest summit in the world is Everest with height of 8844.43 m above sea level. The first official ascent was made by Sir Edmund Hillary, they reached the mountain`s peak in 1953. Whether a highest point is classified as a summit, a sub peak or a separate mountain is subjective; the UIAA definition of a peak is.
Otherwise, it's a subpeak. In many parts of the western United States, the term summit refers to the highest point along a road, highway, or railroad. For example, the highest point along Interstate 80 in California is referred to as Donner Summit and the highest point on Interstate 5 is Siskiyou Mountain Summit. A summit climbing differs from the common mountaineering. Summit expedition requires: 1+ year of training, a good physical shape, a special gear. Although a huge part of climber’s stuff can be left and taken at the base camps or given to porters, there is a long list of personal equipment. In addition to common mountaineers’ gear, Summit climbers need to take Diamox and bottles of oxygen. There are special requirements for crampons, ice axe, rappel device, etc. Geoid Hill – Landform that extends above the surrounding terrain Nadir Summit accordance Peak finder Summit Climbing Gear List
A crater lake is a lake that forms in a volcanic crater or caldera, such as a maar. Sometimes lakes which form inside calderas are called caldera lakes, but this distinction is not made. Crater lakes covering active volcanic vents are sometimes known as volcanic lakes, the water within them is acidic, saturated with volcanic gases, cloudy with a strong greenish color. For example, the crater lake of Kawah Ijen in Indonesia has a pH of under 0.5. Lakes located in dormant or extinct volcanoes tend to have fresh water, the water clarity in such lakes can be exceptional due to the lack of inflowing streams and sediment. Crater lakes form; the water may come from groundwater circulation or melted ice. Its level rises until an equilibrium is reached between the rates of outgoing water. Sources of water loss singly or together may include evaporation, subsurface seepage, and, in places, surface leakage or overflow when the lake level reaches the lowest point on its rim. At such a saddle location, the upper portion of the lake is contained only by its adjacent natural volcanic dam.
If the volcanic dam portion erodes or fails catastrophically, the occurrence produces a breakout or outburst flood. With changes in environmental conditions over time, the occurrence of such floods is common to all natural dam types. A well-known crater lake, which bears the same name as the geological feature, is Crater Lake in Oregon, it is located in the caldera of Mount Mazama. It is the deepest lake in the United States with a depth of 594 m. Crater Lake is fed by falling rain and snow, with no inflow or outflow at the surface, hence is one of the clearest lakes in the world; the highest volcano in the world, 6,893-m Ojos del Salado in Chile, has a permanent crater lake about 100 m in diameter at an elevation of 6,390 m on its eastern side. This is most the highest lake of any kind in the world. Due to their unstable environments, some crater lakes exist only intermittently. Caldera lakes in contrast can be quite long-lasting. For instance, Lake Toba formed after its eruption around 75,000 years ago.
At a size of around 100 km by 30 km in extent and 505 m deep at its deepest point, Lake Toba is the largest crater lake in the world. While many crater lakes are picturesque, they can be deadly. Gas discharges from Lake Nyos suffocated 1,800 people in 1986, crater lakes such as Mount Ruapehu's contribute to destructive lahars. Certain bodies of water, although their formation is directly related to volcanic activity, are not referred to as crater lakes, including: Lakes created by volcanic dams due to lava flowing outside of the volcanic edifice/caldera Closed atoll lagoons, whose formation process implies subsequent biogeomorphologic processes Ponds encountered at the bottom of waterfalls occurring in volcanic canyons in a volcanic context, but not within a volcanic edifice/caldera Lakes can fill impact craters, but these are not referred to as crater lakes. Examples include Lake Bosumtwi in Ghana and Siljan in Sweden. More they can fill craters caused by artificial explosions, such as the radioactive Lake Chagan in Kazakhstan.
Some geomorphological features, when filled with water, can sometimes be confused with crater lakes: Pingos whose summital part has collapsed Sinkholes, such as Otjikoto Lake in NamibiaSome circular open-pit mines can present a similar appearance, such as Big Hole in Kimberley, South Africa, a diamond mine where water has accumulated in the artificially created depression. Lava lake – Molten lava contained in a volcanic crater Volcanic crater – Roughly circular depression in the ground caused by volcanic activity Caldera – Cauldron-like volcanic feature formed by the collapse of a magma chamber Types of volcanic eruptions – Basic mechanisms of eruption and variations Maar – Low-relief volcanic crater Atoll – Ring-shaped coral reef formed over a subsiding oceanic volcano, with a central lagoon and islands around the rim Impact crater – Circular depression on a solid astronomical body formed by a hypervelocity impact of a smaller object Delmelle, Pierre. "Volcanic Lakes". In Sigurdsson, Haraldur.
Encyclopedia of Volcanoes. San Diego: Academic Press. Pp. 877–895. ISBN 978-0-12-643140-7. Varekamp, Johan C.. "Crater Lakes". Journal of Volcanology and Geothermal Research. 97: 1–508. Bibcode:2000JVGR...97....1C. doi:10.1016/S0377-027300167-5. Pasternack, G. B.. C.. "Volcanic lake systematics I. Physical constraints". Bulletin of Volcanology. 58: 526–538. Bibcode:1997BVol...58..528P. Doi:10.1007/s004450050160. Kusakabe, Minoru, ed.. "Geochemistry of Crater Lakes". Geochemical Journal. 28: 137–306. Doi:10.2343/geochemj.28.137. IAVCEI Commission of Volcanic Lakes IAVCEI Commission of
A volcanic crater is a circular depression in the ground caused by volcanic activity. It is a bowl-shaped feature within which occurs a vent or vents. During volcanic eruptions, molten magma and volcanic gases rise from an underground magma chamber, through a tube-shaped conduit, until they reach the crater's vent, from where the gases escape into the atmosphere and the magma is erupted as lava. A volcanic crater can be of large dimensions, sometimes of great depth. During certain types of explosive eruptions, a volcano's magma chamber may empty enough for an area above it to subside, forming a type of larger depression known as a caldera. In most volcanoes, the crater is situated at the top of a mountain formed from the erupted volcanic deposits such as lava flows and tephra. Volcanoes that terminate in such a summit crater are of a conical form. Other volcanic craters may be found on the flanks of volcanoes, these are referred to as flank craters; some volcanic craters may fill either or with rain and/or melted snow, forming a crater lake.
A crater may be breached during an eruption, either by explosions or by lava, or through erosion. Breached craters have a much lower rim on one side; some volcanoes, such as maars, consist of a crater alone, with scarcely any mountain at all. These volcanic explosion craters are formed when magma rises through water-saturated rocks, which causes a phreatic eruption. Volcanic craters from phreatic eruptions occur on plains away from other obvious volcanoes. Not all volcanoes form craters. Caldera – Cauldron-like volcanic feature formed by the collapse of a magma chamber
Bougainville Island is the main island of the Autonomous Region of Bougainville of Papua New Guinea. This region is known as Bougainville Province or the North Solomons, its land area is 9,300 km2. The population of the province is 234,280, which includes the adjacent island of Buka and assorted outlying islands including the Carterets. Mount Balbi at 2,700 m is the highest point. Bougainville Island is the largest of the Solomon Islands archipelago, forming part of the Northern Solomon Islands, politically separate from the sovereign country called Solomon Islands. Bougainville was first settled some 28,000 years ago. Three to four thousand years ago, Austronesian people arrived, bringing with them domesticated pigs, chickens and obsidian tools; the first European contact with Bougainville was in 1768, when the French explorer Louis de Bougainville arrived and named the main island for himself. Germany laid claim to Bougainville in 1899. Christian missionaries arrived on the island in 1902. During World War I, Australia occupied German New Guinea, including Bougainville.
It became part of the Australian Territory of New Guinea under a League of Nations mandate in 1920. In 1942, during World War II, Japan invaded the island, but allied forces launched the Bougainville campaign to regain control of the island in 1943. Despite heavy bombardments, the Japanese garrisons remained on the island until 1945. Following the war, the Territory of New Guinea, including Bougainville, returned to Australian control. In 1949, the Territory of New Guinea, including Bougainville, merged with the Australian Territory of Papua, forming the Territory of Papua and New Guinea, a United Nations Trust Territory under Australian administration. On 9 September 1975, the Parliament of Australia passed the Papua New Guinea Independence Act 1975; the Act set 16 September 1975 as date of independence and terminated all remaining sovereign and legislative powers of Australia over the territory. Bougainville was to become part of an independent Papua New Guinea. However, on 11 September 1975, in a failed bid for self-determination, Bougainville declared itself the Republic of the North Solomons.
The republic failed to achieve any international recognition, a settlement was reached in August 1976. Bougainville was absorbed politically into Papua New Guinea with increased self-governance powers. Between 1988 and 1998, the Bougainville Civil War claimed over 15,000 lives. Peace talks brokered by New Zealand led to autonomy. A multinational Peace Monitoring Group under Australian leadership was deployed. In 2001, a peace agreement was signed including promise of a referendum on independence from Papua New Guinea, which will be held in 2019. Bougainville is the largest island in the Solomon Islands archipelago, it is part of the Solomon Islands rain forests ecoregion. Bougainville and the nearby island of Buka are a single landmass separated by a deep 300-metre-wide strait; the island has an area of 9000 square kilometres, there are several active, dormant or inactive volcanoes which rise to 2400 m. Mount Bagana in the north central part of Bougainville is conspicuously active, spewing out smoke, visible many kilometres distant.
Earthquakes cause little damage. The daily volume of wild rivers appears to be decreasing; this has been affected by deforestation caused by the increased demand for gardens to feed the growing population. Mining with its use of chemicals and its aftereffects poses other environmental issues, e.g. alluvial gold mining and the now decommissioned Rio Tinto-owned Panguna mine. Bougainville has one of the world's largest copper deposits; these have been under development since 1972. The majority of people on Bougainville are Christian, an estimated 70% being Roman Catholic and a substantial minority United Church of Papua New Guinea since 1968. Few non-natives remain. There are many indigenous languages in Bougainville Province, belonging to three language families; the languages of the northern end of the island, some scattered around the coast, belong to the Austronesian family. The languages of the north-central and southern lobes of Bougainville Island belong to the North and South Bougainville families.
The most spoken Austronesian language is Halia and its dialects, spoken in the island of Buka and the Selau peninsula of Northern Bougainville. Other Austronesian languages include Nehan, Solos, Saposa and Tinputz, all spoken in the northern quarter of Bougainville and surrounding islands; these languages are related. Bannoni and Torau are Austronesian languages not related to the former, which are spoken in the coastal areas of central and south Bougainville. On the nearby Takuu Atoll a Polynesian language is spoken, Takuu; the Papuan languages are confined to the main island of Bougainville. These include Rotokas, a language with a small inventory of phonemes, Terei, Nasioi, Siwai, Baitsi and several others; these constitute North Bougainville and South Bougainville. None of the languages are spoken by more than 20% of the population, the larger languages such as Nasioi, Korokoro Motuna and Halia are split into dialects that are not always mutually understandable. For general communication most Bougainvilleans use Tok Pisin as a lingua franca, at least in the coastal areas Tok Pisin is learned by children in a bilingual environment.
English and Tok Pisin are the languages of official government. A 2013 U
A stratovolcano known as a composite volcano, is a conical volcano built up by many layers of hardened lava, tephra and ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas; the lava flowing from stratovolcanoes cools and hardens before spreading far, due to high viscosity. The magma forming this lava is felsic, having high-to-intermediate levels of silica, with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows have travelled as far as 15 km. Stratovolcanoes are sometimes called "composite volcanoes" because of their composite stratified structure built up from sequential outpourings of erupted materials, they are in contrast to the less common shield volcanoes. Two famous examples of stratovolcanoes are Krakatoa, known for its catastrophic eruption in 1883 and Vesuvius, whose eruption in AD79 caused destruction of Pompeii and Herculaneum in 79 AD.
Both eruptions claimed thousands of lives. In modern times, Mount St. Helens and Mount Pinatubo have erupted catastrophically, with lesser losses of lives; the possible existence of stratovolcanoes on other terrestrial bodies of the Solar System has not been conclusively demonstrated. The one feasible exception are the existence of some isolated massifs on Mars, for example the Zephyria Tholus. Stratovolcanoes are common at subduction zones, forming chains and clusters along plate tectonic boundaries where oceanic crust is drawn under continental crust or another oceanic plate; the magma forming stratovolcanoes rises when water trapped both in hydrated minerals and in the porous basalt rock of the upper oceanic crust is released into mantle rock of the asthenosphere above the sinking oceanic slab. The release of water from hydrated minerals is termed "dewatering", occurs at specific pressures and temperatures for each mineral, as the plate descends to greater depths; the water freed from the rock lowers the melting point of the overlying mantle rock, which undergoes partial melting and rises due to its lighter density relative to the surrounding mantle rock, pools temporarily at the base of the lithosphere.
The magma rises through the crust, incorporating silica-rich crustal rock, leading to a final intermediate composition. When the magma nears the top surface, it pools in a magma chamber within the crust below the stratovolcano. There, the low pressure allows water and other volatiles dissolved in the magma to escape from solution, as occurs when a bottle of carbonated water is opened, releasing CO2. Once a critical volume of magma and gas accumulates, the plug of the volcanic vent is broken, leading to a sudden explosive eruption. In recorded history, explosive eruptions at subduction zone volcanoes have posed the greatest hazard to civilizations. Subduction-zone stratovolcanoes, such as Mount St. Helens, Mount Etna and Mount Pinatubo erupt with explosive force: the magma is too stiff 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 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 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 in excess of 160 km/h. Around 30,000 people were killed by pyroclastic flows during the 1902 eruption of Mount Pelée on the island of Martinique in the Caribbean. In March to April 1982, three explosive eruptions of El Chichón in the State of Chiapas in southeastern Mexico, caused the worst volcanic disaster in that country's history. Villages within 8 km of the volcano were destroyed by pyroclastic flows, killing more than 2,000 people. Two Decade Volcanoes that erupted in 1991 provide examples of stratovolcano hazards. On June 15, Mount Pinatubo spewed an ash cloud 40 km into the air and produced huge pyroclastic surges and lahar floods that devastated a large area around the volcano.
Pinatubo, located in Central Luzon just 90 km west-northwest from Manila, had been dormant for 6 centuries before the 1991 eruption, which ranks as one of the largest eruptions in the 20th century. In 1991, Japan's Unzen Volcano, located on the island of Kyushu about 40 km east of Nagasaki, awakened from its 200-year slumber to produce a new lava dome at its summit. Beginning in June, repeated collapse of this erupting dome generated ash flows that swept down the mountain's slopes at speeds as high as 200 km/h. Unzen is one of more than 75 active volcanoes in Japan; the eruption of Mount Vesuvius in 79 smothered the nearby ancient cities of Pompeii and Herculaneum with thick deposits of pyroclastic surges and lava flows. Although death toll is estimated between 13,000 and 26,000 remains, the exact number still remains unknown. Vesuvius is recognized as one of the most dangerous volcanoes, due to its