A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. The process that forms volcanoes is called volcanism.
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 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, with lesser amounts of less viscous mafic magma. Extensive felsic lava flows are uncommon, but can travel as far as 8 km (5 mi).
Lake Nyos is a crater lake in the Northwest Region of Cameroon, located about 315 km (196 mi) northwest of Yaoundé, the capital. Nyos is a deep lake high on the flank of an inactive volcano in the Oku volcanic plain along the Cameroon line of volcanic activity. A volcanic dam impounds the lake waters.
Nevado del Ruiz, also known as La Mesa de Herveo is a volcano on the border of the departments of Caldas and Tolima in Colombia, being the highest point of both. It is located about 130 km (81 mi) west of the capital city Bogotá. It is a stratovolcano composed of many layers of lava alternating with hardened volcanic ash and other pyroclastic rocks. Volcanic activity at Nevado del Ruiz began about two million years ago, during the Early Pleistocene or Late Pliocene, with three major eruptive periods. The current volcanic cone formed during the present eruptive period, which began 150,000 years ago.
The Bromo, or Mount Bromo is an active somma volcano, a Hindu pilgrimage site, and part of the Tengger mountains, in East Java, Indonesia. At 2,329 meters (7,641 ft) it is not the highest peak of the massif, but is the most active and famous. The area is one of the most visited tourist destinations in East Java, and the volcano is included in the Bromo Tengger Semeru National Park. The name Bromo comes from the Javanese pronunciation of Brahma, the Hindu god of creation. At the mouth of the crater, there is an idol of Ganesha, the Hindu god of wisdom which is being worshipped by the Javanese Hindus. Mount Bromo is located in the middle of a plain called "Sea of Sand", a nature reserve that has been protected since 1919.
A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma heats ground water or surface water. The extreme temperature of the magma causes near-instantaneous evaporation of water to steam, resulting in an explosion of steam, water, ash, rock, and volcanic bombs. At Mount St. Helens in Washington state, hundreds of steam explosions preceded the 1980 Plinian eruption of the volcano. A less intense geothermal event may result in a mud volcano.
Santa María Volcano is a large active volcano in the western highlands of Guatemala, in the Quetzaltenango Department near the city of Quetzaltenango. It is part of the mountain range of the Sierra Madre.
Masaya is a caldera located in Masaya, Nicaragua, 20 km (12 mi) south of the capital Managua. It is Nicaragua's first and largest national park, and one of 78 protected areas of Nicaragua. The complex volcano is composed of a nested set of calderas and craters, the largest of which is Las Sierras shield volcano and caldera. Within this caldera lies a sub-vent, which is Masaya Volcano sensu stricto. The vent is a shield type composed of basaltic lavas and tephras and includes a summit crater. This hosts Masaya caldera, formed 2,500 years ago by an 8 km3 (1.9 cu mi) basaltic ignimbrite eruption. Inside this caldera a new basaltic complex has grown from eruptions mainly on a semi-circular set of vents that include the Masaya and Nindiri cones. The latter host the pit craters of Masaya, Santiago, Nindiri and San Pedro. Observations in the walls of the pit craters indicate that there have been several episodes of cone and pit crater formation.
The Sunda Arc is a volcanic arc that produced the volcanoes that form the topographic spine of the islands of Sumatra, Nusa Tenggara, Java, the Sunda Strait, and the Lesser Sunda Islands. The Sunda Arc begins at Sumatra and ends at Flores, and is adjacent to the Banda Arc. The Sunda Arc is formed via the subduction of the Indo-Australian Plate beneath the Sunda and Burma plates at a velocity of 63–70 mm/year.
The Almolonga volcano, also called "Cerro Quemado" or "La Muela" due to its distinct shape, is an andesitic stratovolcano in the south-western department of Quetzaltenango in Guatemala. Part of the mountain range of the Sierra Madre, the volcano is located near the town of Almolonga, just south of Quetzaltenango, Guatemala's second largest city.
Villarrica is one of Chile's most active volcanoes, rising above the lake and town of the same name, 750 km (470 mi) south of Santiago. It is also known as Rucapillán, a Mapuche word meaning "great spirit's house" or " the demon's house". It is the westernmost of three large stratovolcanoes that trend northwest to southeast obliquely perpendicular to the Andean chain along the Mocha-Villarrica Fault Zone, and along with Quetrupillán and the Chilean portion of Lanín, are protected within Villarrica National Park. Guided ascents are popular during summer months.
Kelimutu is a volcano close to the small town of Moni in central Flores island in Indonesia. It is around 50 km (31 mi) to the east of Ende, Indonesia, the capital of Ende regency in East Nusa Tenggara province. It has three volcanic crater lakes that differ in color. Tiwi Ata Mbupu, on the western side of the island is blue in color while Tiwu Nua Muri Kooh Tai and Tiwu Ata Polo are usually colors of green and red. These lakes shift color due to changes that occur within the geology and chemistry of the volcano.
Volcanic gases are gases given off by active volcanoes. These include gases trapped in cavities (vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from lava, from volcanic craters or vents. Volcanic gases can also be emitted through groundwater heated by volcanic action.
Mazuku (Swahili for "evil winds") are pockets of dry, cold carbon dioxide-rich gases released from vents or fissures in volcanically and tectonically active areas, and mixed with dispersed atmospheric air and accumulating in typically low-lying areas. Since CO2 is ~1.5 times heavier than air, it tends to flow downhill, hugging the ground like a low fog and gather in enclosed spaces with poor ventilation, such as lava tubes, ditches, depressions, caves, house basements or in the stratified water layers of meromictic lakes if a water column exists. In high concentrations (≥1vol.%), they can pose a deadly risk to both humans and animals in the surrounding area because they are undetectable by olfactory or visual senses in most conditions.
Prediction of volcanic activity, and volcanic eruption forecasting, is an interdisciplinary monitoring and research effort to predict the time and severity of a volcano's eruption. Of particular importance is the prediction of hazardous eruptions that could lead to catastrophic loss of life, property, and disruption of human activities.
Mount Papandayan is a complex stratovolcano, located in Garut Regency, to the southeast of the city of Bandung in West Java, Indonesia. It is about 15 kilometres (9.3 mi) to the southwest of the town of Garut. At the summit, there are four large craters which contain active fumarole fields. An eruption in 1772 caused the northeast flank to collapse producing a catastrophic debris avalanche that destroyed 40 villages and killed nearly 3,000 people. The eruption truncated the volcano into a broad shape with two peaks and a flat area 1.1 km wide with Alun-Alun crater in the middle, making the mountain appear as a twin volcano; one of the peaks is called Papandayan and the other Mount Puntang.
The Dieng Volcanic Complex is a volcanic complex located on the Dieng Plateau in Central Java, Indonesia, a complex of volcanoes. The volcanic complex consists of two or more stratovolcanoes, more than 20 small craters, and Pleistocene to Holocene-age volcanic cones. It covers a 6 by 14 kilometres area. The Prahu stratovolcano was truncated by a large Pleistocene caldera and then filled by parasitic cones, lava domes, and craters which is 120 °C (248 °F). Some of them are turned into lakes. Toxic volcanic gas has caused fatalities and is a hazard at several craters. On 20 February 1979, 149 people died of gas poisoning in Pekisaran Village on the plateau near the Sinila Crater. The area is also home to a major geothermal project.
On 21 August 1986, a limnic eruption at Lake Nyos in northwestern Cameroon killed 1,746 people and 3,500 livestock.
Ubinas is an active stratovolcano in the Moquegua Region of southern Peru, approximately 60 kilometres (37 mi) east of the city of Arequipa. Part of the Central Volcanic Zone of the Andes, it rises 5,672 metres (18,609 ft) above sea level. The volcano's summit is cut by a 1.4-kilometre-wide (0.87 mi) and 150-metre-deep (490 ft) caldera, which itself contains a smaller crater. Below the summit, Ubinas has the shape of an upwards-steepening cone with a prominent notch on the southern side. The gently sloping lower part of the volcano is also known as Ubinas I and the steeper upper part as Ubinas II; they represent different stages in the volcano's geological history.
On 30 April 1979, Mount Marapi, a complex volcano on the Indonesian island of Sumatra and the most active complex volcano in West Sumatra province, erupted, killing between 80 and 100 people.
