A stratovolcano, also known as a composite volcano, is a typically 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).
Volcanology is the study of volcanoes, lava, magma and related geological, geophysical and geochemical phenomena (volcanism). The term volcanology is derived from the Latin word vulcan. Vulcan was the ancient Roman god of fire.
A lahar is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley.
Novarupta is a volcano that was formed in 1912, located on the Alaska Peninsula on a slope of Trident Volcano in Katmai National Park and Preserve, about 290 miles (470 km) southwest of Anchorage. Formed during the largest volcanic eruption of the 20th century, Novarupta released 30 times the volume of magma of the 1980 eruption of Mount St. Helens.
Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism.
Mount Pinatubo is an active stratovolcano in the Zambales Mountains in Luzon in the Philippines. Located on the tripoint of Zambales, Tarlac and Pampanga provinces, most people were unaware of its eruptive history before the pre-eruption volcanic activity in early 1991. Dense forests, which supported a population of several thousand indigenous Aetas, heavily eroded and obscured Pinatubo.
Cerro Negro is an active volcano in the Cordillera de los Maribios mountain range in Nicaragua, about 10 km (6.2 mi) from the village of Malpaisillo. It is a very new volcano, the youngest in Central America, having first appeared in April 1850. It consists of a gravelly basaltic cinder cone, which contrasts greatly with the surrounding verdant hillsides, and gives rise to its name, which means Black Hill. Cerro Negro has erupted frequently since its first eruption. One unusual aspect of several eruptions has been the emission of ash from the top of the cone, while lava erupts from fractures at the base.
Plinian eruptions or Vesuvian eruptions are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in 79 AD, which destroyed the ancient Roman cities of Herculaneum and Pompeii. The eruption was described in a letter written by Pliny the Younger, after the death of his uncle Pliny the Elder.
USS Ingraham (FFG-61), the last American Oliver Hazard Perry-class guided missile frigate to be built, was the fourth ship of the United States Navy to be named for Captain Duncan Ingraham (1802–1891).
An eruption column or eruption plume is a cloud of super-heated ash and tephra suspended in gases emitted during an explosive volcanic eruption. The volcanic materials form a vertical column or plume that may rise many kilometers into the air above the vent of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km (25 mi), penetrating the stratosphere. Stratospheric injection of aerosols by volcanoes is a major cause of short-term climate change.
Cerro Azul, sometimes referred to as Quizapu, is an active stratovolcano in the Maule Region of central Chile, immediately south of Descabezado Grande. Part of the South Volcanic Zone of the Andes, its summit is 3,788 meters (12,428 ft) above sea level, and is capped by a summit crater that is 500 meters (1,600 ft) wide and opens to the north. Beneath the summit, the volcano features numerous scoria cones and flank vents.
Typhoon Yunya, known in the Philippines as Typhoon Diding, was a strong tropical cyclone whose landfall in the Philippines coincided with the 1991 eruption of Mount Pinatubo. A small tropical cyclone, Yunya rapidly developed from a tropical disturbance near East Samar on June 11. By June 13 the storm had reached typhoon status as it moved west-northwest near the Philippines. Yunya attained its peak intensity the following day with estimated winds of 145 km/h (90 mph); however, strong wind shear soon impacted the typhoon and caused it to rapidly decay. The storm struck southern Luzon early on June 15 as a minimal typhoon before moving over the South China Sea later that day. After turning north and weakening to a tropical depression, the system brushed the southern tip of Taiwan on June 16 before dissipating the following day.
Mount Bulusan, also known as Bulusan Volcano, is a stratovolcano on the island of Luzon in the Philippines. Located in the province of Sorsogon in the Bicol Region, it is 70 kilometres (43 mi) southeast of Mayon Volcano and approximately 390 kilometres (240 mi) southeast of Manila. Bulusan is one of the active volcanoes in the Philippines.
Kanlaon, also known as Mount Kanlaon and Kanlaon Volcano, is an active andesitic stratovolcano and the highest mountain on the island of Negros in the Philippines, as well as the highest peak in the Visayas, with an elevation of 2,465 m (8,087 ft) above sea level. Mount Kanlaon ranks as the 42nd-highest peak of an island in the world.
Phreatomagmatic eruptions are volcanic eruptions resulting from interaction between magma and water. They differ from exclusively magmatic eruptions and phreatic eruptions. Unlike phreatic eruptions, the products of phreatomagmatic eruptions contain juvenile (magmatic) clasts. It is common for a large explosive eruption to have magmatic and phreatomagmatic components.
The 1991 eruption of Mount Pinatubo in the Philippines' Luzon Volcanic Arc was the second-largest volcanic eruption of the 20th century, behind only the 1912 eruption of Novarupta in Alaska. Eruptive activity began on April 2 as a series of phreatic explosions from a fissure that opened on the north side of Mount Pinatubo. Seismographs were set up and began monitoring the volcano for earthquakes. In late May, the number of seismic events under the volcano fluctuated from day-to-day. Beginning June 6, a swarm of progressively shallower earthquakes accompanied by inflationary tilt on the upper east flank of the mountain, culminated in the extrusion of a small lava dome.
This timeline of volcanism on Earth includes a list of major volcanic eruptions of approximately at least magnitude 6 on the Volcanic explosivity index (VEI) or equivalent sulfur dioxide emission during the Quaternary period. Other volcanic eruptions are also listed.
Between March and June 2010 a series of volcanic events at Eyjafjallajökull in Iceland caused enormous disruption to air travel across Western Europe.
1991 in the Philippines details events of note that happened in the Philippines in the year 1991.
Naval Base Subic Bay was a major ship-repair, supply, and rest and recreation facility of the Spanish Navy and subsequently the United States Navy located in Zambales, Philippines. The base was 262 square miles (680 km2), about the size of Singapore. The Navy Exchange had the largest volume of sales of any exchange in the world, and the Naval Supply Depot handled the largest volume of fuel oil of any navy facility in the world. The naval base was the largest overseas military installation of the United States Armed Forces, after Clark Air Base in Angeles City was closed in 1991. Following its closure in 1992, it was transformed into the Subic Bay Freeport Zone by the Philippine government.
