Mount Cameroon is an active volcano in Cameroon near the Gulf of Guinea. Mount Cameroon is known as Cameroon Mountain or Fako or by its native name Mongo ma Ndemi and it is the highest point in sub-Saharan western and central Africa, the fourth most prominent peak in Africa and the 31st most prominent in the world. The mountain is part of the area of volcanic activity known as the Cameroon Volcanic Line, which includes Lake Nyos, the most recent eruption occurred on February 3,2012. Mount Cameroon is one of Africas largest volcanoes, rising to 4,040 metres above the coast of west Cameroon and it rises from the coast through tropical rainforest to a bare summit which is cold and occasionally dusted with snow. More than 100 small cinder cones, often fissure-controlled parallel to the axis of the massive 1, 400-cubic-kilometre volcano, occur on the flanks. A large satellitic peak, Etinde, is located on the southern flank near the coast, Mount Cameroon has the most frequent eruptions of any West African volcano.
The first written account of volcanic activity could be the one from the Carthaginian Hanno the Navigator, moderate explosive and effusive eruptions have occurred throughout history from both summit and flank vents. The peak is frequently ascended by hikers, the annual Mount Cameroon Race of Hope scales the peak in around 4½ hours. Sarah Etonge, who has won the seven times and is a tour operator, has become known as queen of the mountain. English explorer Mary Kingsley, one of the first Europeans to scale the mountain, impatiens etindensis and I. grandisepala are plant species known only from Mount Cameroon. There are no trees in this area, debundscha List of volcanoes in Cameroon DeLancey, M. W. and M. D. DeLancey. Historical Dictionary of the Republic of Cameroon
Sometimes lakes which form inside calderas are called caldera lakes, but often this distinction is not made. Crater lakes covering active volcanic vents are known as volcanic lakes, and the water within them is often acidic, saturated with volcanic gases. For example, the lake of Kawah Ijen in Indonesia has a pH of under 0.5. Lakes located in dormant or extinct volcanoes tend to have water. Crater lakes form as the depression, within the crater rim, is filled by water. The water may come from precipitation, groundwater circulation or melted ice and its level rises until an equilibrium is reached between the rates of incoming and outgoing water. Sources of water loss singly or together may include evaporation, subsurface seepage, if the volcanic dam portion erodes rapidly or fails catastrophically, the occurrence produces a breakout or outburst flood. With changes in environmental conditions over time, the occurrence of floods is common to all natural dam types. A well-known crater lake, which bears the name as the geological feature, is Crater Lake in Oregon.
It is located in the caldera of Mount Mazama and it is the deepest lake in the United States with a depth of 594 m. Crater Lake is fed solely by falling rain and snow, with no inflow or outflow at the surface, and 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 likely the highest lake of any kind in the world, due to their unstable environments, some crater lakes exist only intermittently. Hence, making Lake Toba 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, example of such impact crater lakes include Manicouagan in Canada, Lake Bosumtwi in Ghana and Siljan in Sweden. More rarely they can fill craters caused by artificial explosions, lava lake Volcanic crater Caldera Types of volcanic eruptions Maar Atoll Impact crater Delmelle, Bernard, Alain.
Journal of Volcanology and Geothermal Research, Minoru, ed. Geochemistry of Crater Lakes. California Davis Crater Lake National Park documentation in Building Oregon, Architecture of Oregon & the Pacific Northwest archive World Volcanic Lakes Map
Besides molten rock, magma may contain suspended crystals, dissolved gas and sometimes gas bubbles. Magma often collects in magma chambers that may feed a volcano or solidify underground to form an intrusion, magma is capable of intruding into adjacent rocks, extrusion onto the surface as lava, and explosive ejection as tephra to form pyroclastic rock. Magma is a complex high-temperature fluid substance, temperatures of most magmas are in the range 700 °C to 1300 °C, but very rare carbonatite magmas may be as cool as 600 °C, and komatiite magmas may have been as hot as 1600 °C. Environments of magma formation and compositions are commonly correlated, environments include subduction zones, continental rift zones, mid-ocean ridges and hotspots. Despite being found in such locales, the bulk of the Earths crust. Except for the outer core, most of the Earth takes the form of a rheid. Magma, as liquid, preferentially forms in high temperature, low pressure environments within several kilometers of the Earths surface, magma compositions may evolve after formation by fractional crystallization and magma mixing.
By definition rock formed of solidified magma is called igneous rock, melting of solid rocks to form magma is controlled by three physical parameters, temperature and composition. Mechanisms are discussed in the entry for igneous rock, as a rock melts, its volume changes. When enough rock is melted, the small globules of melt link up, under pressure within the earth, as little as a fraction of a percent partial melting may be sufficient to cause melt to be squeezed from its source. The degree of melting is critical for determining what type of magma is produced. The degree of partial melting required to form a melt can be estimated by considering the relative enrichment of incompatible elements versus compatible elements, incompatible elements commonly include potassium, barium and rubidium. Rock types produced by small degrees of melting in the Earths mantle are typically alkaline. Typically, primitive melts of this composition form lamprophyre, lamproite and sometimes nepheline-bearing mafic rocks such as alkali basalts, pegmatite may be produced by low degrees of partial melting of the crust.
Some granite-composition magmas are eutectic melts, and they may be produced by low to high degrees of melting of the crust. At high degrees of melting of the crust, granitoids such as tonalite and monzonite can be produced. Being only the time in recorded history that magma had been reached, IDDP decided to invest in the hole. A cemented steel case was constructed in the hole with a perforation at the close to the magma
A phreatic eruption, called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, ash, rock, at Mount St. Helens, hundreds of steam explosions preceded a 1980 plinian eruption of the volcano. A less intense geothermal event may result in a mud volcano, phreatic eruptions typically include steam and rock fragments, the inclusion of lava is unusual. The temperature of the fragments can range from cold to incandescent, if molten magma is included, it is classified as a phreatomagmatic eruption. These eruptions occasionally create broad, low-relief craters called maars, phreatic explosions can be accompanied by carbon dioxide or hydrogen sulfide gas emissions. The former can asphyxiate at sufficient concentration, the latter is a broad spectrum poison, a 1979 phreatic eruption on the island of Java killed 140 people, most of whom were overcome by poisonous gases.
Phreatic eruptions are classed as volcanic eruptions because a phreatic eruption could bring juvenile material to the surface and it is believed that the 1883 eruption of Krakatoa, which obliterated most of the volcanic island and created the loudest sound in recorded history, was a phreatic event. Kilauea, in Hawaii, has a record of phreatic explosions. Additional examples are the 1963–65 eruption of Surtsey, the 1965 eruption of Taal Volcano, the 1982 Mount Tarumae eruption, mayon Volcano produced a surprise phreatic eruption lasting 73 seconds
A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption. A maar characteristically fills with water to form a shallow crater lake which may be called a maar. The name comes from a Moselle Franconian dialect word used for the lakes of the Daun area of Germany. Maars range in size from 60 to 8,000 m across and from 10 to 200 m deep, most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme. Maar lakes, referred to simply as maars, occur when groundwater or precipitation fills the funnel-shaped, examples of these types of maar are the three maars at Daun in the Eifel mountains of Germany. A dry maar results when a maar lake dries out, becomes aggraded or silted up, an example of the latter is the Eckfelder Maar. Near Steffeln is the Eichholzmaar which has dried out during the last century and is being renaturalised into a maar, in some cases the underlying rock is so porous that maar lakes are unable to form.
After winters of snow and rainfall many dry maars fill partially and temporarily with water, others contain small bogs or often artificial ponds that, however. The largest known maars are found on the Seward Peninsula in northwest Alaska and these maars range in size from 4,000 to 8,000 m in diameter and a depth up to 300 m. These eruptions occurred in a period of about 100,000 years and their large size is due to the explosive reaction that occurs when magma comes into contact with permafrost. Hydromagmatic eruptions are explosive when the ratio of water to magma is low. Since permafrost melts slowly, it provides a source of water to the eruption while keeping the water to magma ratio low. This produces the prolonged, explosive eruptions that created these large maars, examples of the Seward Peninsula maars include North Killeak Maar, South Killeak Maar, Devil Mountain Maar and Whitefish Maar. Maars occur in western North America, Patagonia in South America, the Eifel region of Germany, elsewhere in Europe, La Vestide du Pal in the Ardèche department of France provides a spectacular example of a maar easily visible from the ground or air.
Kilbourne Hole and Hunts Hole, in southern New Mexico near El Paso, the Crocodile Lake in Los Baños in the Philippines was originally thought of as a volcanic crater is a maar. The notorious, carbon dioxide-saturated Lake Nyos in Africa is another example, an excellent example of a maar is Zuni Salt Lake in New Mexico, a shallow saline lake that occupies a flat-floored crater about 6,500 ft across and 400 ft deep. Its low rim is composed of pieces of basaltic lava and wall rocks of the underlying diatreme. Maars in Canada are found in the Wells Gray-Clearwater volcanic field of east-central British Columbia, a notable field of maars is found in the Pali-Aike Volcanic Field in Patagonia, South America
A caldera is a large cauldron-like depression that forms following the evacuation of a magma chamber/reservoir. When large volumes of magma are erupted over a time period. The ground surface collapses downward into the emptied magma chamber. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence, only seven known caldera-forming collapses have occurred since the start of the 20th century, most recently at Bárðarbunga volcano in Iceland. The word comes from Spanish caldera, and this from Latin caldaria, in some texts the English term cauldron is used. If enough magma is ejected, the chamber is unable to support the weight of the volcanic edifice above it. A roughly circular fracture, the fault, develops around the edge of the chamber. Ring fractures serve as feeders for fault intrusions which are known as ring dykes. Secondary volcanic vents may form above the ring fracture, as the magma chamber empties, the center of the volcano within the ring fracture begins to collapse.
The collapse may occur as the result of a cataclysmic eruption. The total area that collapses may be hundreds or thousands of square kilometers, some calderas are known to host rich ore deposits. One of the worlds best-preserved mineralized calderas is the Sturgeon Lake Caldera in northwestern Ontario, Canada, if the magma is rich in silica, the caldera is often filled in with ignimbrite, tuff and other igneous rocks. Silica-rich magma has a high viscosity, and therefore does not flow easily like basalt, as a result, gases tend to become trapped at high pressure within the magma. Further lava flows may be erupted, if volcanic activity continues, the center of the caldera may be uplifted in the form of a resurgent dome such as is seen at Cerro Galán, Lake Toba, etc. by subsequent intrusion of magma. A silicic or rhyolitic caldera may erupt hundreds or even thousands of kilometers of material in a single event. Even small caldera-forming eruptions, such as Krakatoa in 1883 or Mount Pinatubo in 1991, may result in significant local destruction, large calderas may have even greater effects.
When Yellowstone Caldera last erupted some 650,000 years ago, it released about 1,000 km3 of material, by comparison, when Mount St. Helens erupted in 1980, it released ~1.2 km3 of ejecta. The ecological effects of the eruption of a large caldera can be seen in the record of the Lake Toba eruption in Indonesia, more recently several geneticists, including Lynn Jorde and Henry Harpending have proposed that the human species was reduced to approximately five to ten thousand people
Tangkuban Perahu is a stratovolcano 30 km north of the city of Bandung, the provincial capital of West Java, Indonesia. It erupted in 1826,1829,1842,1846,1896,1910,1926,1929,1952,1957,1961,1965,1967,1969,1983, and 2013. It is a popular tourist attraction where tourists can hike or ride to the edge of the crater to view the hot springs and boiling mud up close. Together with Mount Burangrang and Bukit Tunggul, it is a remnant of the ancient Mount Sunda after the eruption caused the Caldera to collapse. In April 2005 the Directorate of Volcanology and Geological Hazard Mitigation raised an alert, on the mountains northern flank is Death Valley, which derives its name from frequent accumulation of poisonous gases. A study conducted in 2001 determined that Tangkuban Perahu has erupted at least 30 times in the previous 40,750 years, studies of the tephra layers within 3 km of the crater revealed that twenty one were minor eruptions and the remaining nine were major eruptions. The eruptions that occurred prior to approximately 10,000 years ago were magmatic/phreatomagmatic, the eruptions that occurred after 10,000 years ago were phreatic.
The volcano erupted as recently as October 5,2013, the name translates roughly to upturning of boat or upturned boat in Sundanese, referring to the local legend of its creation. The story tells of Dayang Sumbi, a beauty who lived in West Java and she cast away her son Sangkuriang for disobedience, and in her sadness was granted the power of eternal youth by the gods. After many years in exile, Sangkuriang decided to return to his home, Sangkuriang fell in love with Dayang Sumbi and planned to marry her, only for Dayang Sumbi to recognize his birthmark just as he was about to go hunting. In order to prevent the marriage taking place, Dayang Sumbi asked Sangkuriang to build a dam on the river Citarum and to build a large boat to cross the river. Sangkuriang meditated and summoned mythical ogre-like creatures -buto ijo or green giant- to do his bidding, Dayang Sumbi saw that the tasks were almost completed and called on her workers to spread red silk cloths east of the city, to give the impression of impending sunrise.
Sangkuriang was fooled, and upon believing that he had failed, kicked the dam and the boat, resulting in severe flooding. List of volcanoes in Indonesia Sangkuriang Volcano World, Tangkuban Perahu Tangkuban Perahu by JoTravelGuide. com - A main tourist attraction near Bandung
Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism. Volcanologists refer to airborne fragments as pyroclasts, once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff. Tephra mixed in with precipitation can be acidic and cause acid rain, the use of tephra layers, which bear their own unique chemistry and character, as temporal marker horizons in archaeological and geological sites is known as tephrochronology. The word tephra and pyroclast both derive from Greek, τέφρα tephra means ash, while the word pyroclast is derived from the Greek πῦρ, meaning fire, media related to Tephra at Wikimedia Commons How Volcanoes Work Volcanic Materials Identification
Indonesia, officially the Republic of Indonesia, is a unitary sovereign state and transcontinental country located mainly in Southeast Asia with some territories in Oceania. Situated between the Indian and Pacific oceans, it is the worlds largest island country, with more than seventeen thousand islands. At 1,904,569 square kilometres, Indonesia is the worlds 14th-largest country in terms of area and worlds 7th-largest country in terms of combined sea. It has an population of over 260 million people and is the worlds fourth most populous country. The worlds most populous island, contains more than half of the countrys population, Indonesias republican form of government includes an elected legislature and president. Indonesia has 34 provinces, of which five have Special Administrative status and its capital and countrys most populous city is Jakarta, which is the most populous city in Southeast Asia and the second in Asia. The country shares land borders with Papua New Guinea, East Timor, other neighbouring countries include Singapore, the Philippines, Australia and the Indian territory of the Andaman and Nicobar Islands.
Despite its large population and densely populated regions, Indonesia has vast areas of wilderness that support the second highest level of biodiversity. The country has abundant natural resources like oil and natural gas, copper, agriculture mainly produces rice, palm oil, coffee, medicinal plants and rubber. Indonesias major trading partners are Japan, United States, the Indonesian archipelago has been an important region for trade since at least the 7th century, when Srivijaya and later Majapahit traded with China and India. Local rulers gradually absorbed foreign cultural and political models from the early centuries CE, Indonesian history has been influenced by foreign powers drawn to its natural resources. Indonesia consists of hundreds of native ethnic and linguistic groups. The largest – and politically dominant – ethnic group are the Javanese, a shared identity has developed, defined by a national language, ethnic diversity, religious pluralism within a Muslim-majority population, and a history of colonialism and rebellion against it.
Indonesias national motto, Bhinneka Tunggal Ika, articulates the diversity that shapes the country, Indonesias economy is the worlds 16th largest by nominal GDP and the 8th largest by GDP at PPP, the largest in Southeast Asia, and is considered an emerging market and newly industrialised country. Indonesia has been a member of the United Nations since 1950, Indonesia is a member of the G20 major economies and World Trade Organization. The name Indonesia derives from the Greek name of the Indós, the name dates to the 18th century, far predating the formation of independent Indonesia. In 1850, George Windsor Earl, an English ethnologist, proposed the terms Indunesians—and, his preference, in the same publication, one of his students, James Richardson Logan, used Indonesia as a synonym for Indian Archipelago. However, Dutch academics writing in East Indies publications were reluctant to use Indonesia, they preferred Malay Archipelago, the Netherlands East Indies, popularly Indië, the East, and Insulinde
Volcanic gases include a variety of substances given off by active volcanoes. The sources of gases on Earth include and recycled constituents from the Earths mantle, assimilated constituents from the Earths crust, groundwater. Substances that may become gaseous or give off gases when heated are termed volatile substances. The principal components of volcanic gases are water vapor, carbon dioxide, sulfur either as sulfur dioxide or hydrogen sulfide, argon, neon, carbon monoxide and hydrogen. Other compounds detected in volcanic gases are oxygen, hydrogen chloride, hydrogen fluoride, hydrogen bromide, nitrogen oxide, sulfur hexafluoride, carbonyl sulfide, exotic trace compounds include mercury and halogen oxide radicals. The abundance of gases varies considerably from volcano to volcano, water vapor is consistently the most common volcanic gas, normally comprising more than 60% of total emissions. Carbon dioxide typically accounts for 10 to 40% of emissions, volcanoes located at convergent plate boundaries emit more water vapor and chlorine than volcanoes at hot spots or divergent plate boundaries.
This is caused by the addition of seawater into magmas formed at subduction zones, convergent plate boundary volcanoes have higher H2O/H2, H2O/CO2, CO2/He and N2/He ratios than hot spot or divergent plate boundary volcanoes. Magma contains dissolved volatile components, as described above, the solubilities of the different volatile constituents are dependent on pressure and the composition of the magma. As magma ascends towards the surface, the ambient pressure decreases, once the solubility decreases below the volatile concentration, the volatiles will tend to come out of solution within the magma and form a separate gas phase. The gas will initially be distributed throughout the magma as small bubbles, as the magma ascends the bubbles grow through a combination of expansion through decompression and growth as the solubility of volatiles in the magma decreases further causing more gas to exsolve. In the former case, the bubbles may rise through the magma and accumulate at a vertical surface, in volcanoes with an open path to the surface, e. g.
Stromboli in Italy, the bubbles may reach the surface and as they pop small explosions occur. In the latter case, the gas can flow rapidly through the continuous permeable network towards the surface and this mechanism has been used to explain activity at Santiaguito, Santa Maria volcano and Soufrière Hills Volcano, Montserrat. If the gas cannot escape fast enough from the magma, it will fragment the magma into small particles of ash, the fluidised ash has a much lower resistance to motion than the viscous magma, so accelerates, causing further expansion of the gases and acceleration of the mixture. This sequence of events drives explosive volcanism, whether gas can escape gently or not is determined by the total volatile contents of the initial magma and the viscosity of the magma, which is controlled by its composition. The term closed system degassing refers to the case where gas and its parent magma ascend together, the composition of the emitted gas is in equilibrium with the composition of the magma at the pressure, temperature where the gas leaves the system.
In open system degassing, the gas leaves its parent magma, the gas released at the surface has a composition that is a mass-flow average of the magma exsolved at various depths and is not representative of the magma conditions at any one depth. Molten rock near the atmosphere releases high-temperature volcanic gas, in explosive volcanic eruptions, sudden release of gases from magma may cause rapid movements of the molten rock
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example, such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such that expelled lava violently froths into volcanic ash when pressure is suddenly lowered at the vent. Sometimes a lava plug will block the conduit to the summit, Explosive eruptions can send rocks, dust and pyroclastic material up to 20 km into the atmosphere at rate of up to 100,000 tonnes per second, traveling at several hundred meters per second. This cloud will collapse, creating a pyroclastic flow of hot volcanic matter. An explosive eruption always begins with some form of blockage in the crater of a volcano that prevents the release of trapped in highly viscous andesitic or rhyolitic magma. The high viscosity of these forms of magma prevents the release of trapped gases, when this type of magma flows towards the surface pressure builds, eventually causing the blockage to be blasted out in an explosive eruption.
The pressure from the magma and gases are released through the weakest point in the cone, however, in the case of the eruption of Mount St. Helens, pressure was released through the side of the volcano, rather than the crater. The size and duration of the column depends on the volume of magma being released, the eruption column of ash is supported by pressure from the gases being released, and as the gases are depleted, pressure falls and the eruption column begins to collapse. When the column collapses in on itself and rock fall back down to the ground and these flows can travel at up to 80 km per hour, and reach temperatures of 200° to 700° Celsius. The high temperatures can cause combustion of any flammable materials in its path, including wood, when snow and ice melt as a part of an eruption, large amounts of water mixed in with the flow can create lahars. The risk of lahars is particularly high on volcanoes such as Mount Rainier near Seattle and Tacoma, the eruption of supervolcanoes is the rarest of volcanic eruptions but the most destructive.
The timescale between these eruptions is generally marked by hundreds or thousands of years and this type of eruption generally causes destruction on a continental scale, and can result in the lowering of temperatures worldwide. Effusive eruption Volcanic explosivity index Recent Developments in Explosive Volcanism