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Igneous rock Stratovolcanoes are common at subduction zonesforming chains and clusters along plate tectonic boundaries where oceanic crust is drawn under continental crust continental arc volcanism, e. Cascade Rangecentral AndesCampania or another oceanic plate island arc volcanism, e.
JapanPhilippinesAleutian Islands. 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", and 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 then undergoes partial melting and rises due to its lighter density relative to the surrounding mantle rock, and pools temporarily at the base of the lithosphere.
The magma then rises through the crustincorporating 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 relatively low pressure allows water and other volatiles mainly CO2, SO2, Cl2, and H2O 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 solidified blockage of the volcanic vent is broken, leading to a sudden explosive eruption. In recorded history, explosive eruptions at subduction zone convergent-boundary volcanoes have posed the greatest hazard to civilizations.
HelensMount Etna and Mount Pinatubotypically erupt with explosive force: 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. Although death toll is estimated between 13, to 26, remains, the exact number still remains unknown. Vesuvius is recognized as one of the most dangerous volcanoes, due to its capacity for powerful explosive eruptions combined with the high population density of the surrounding Metropolitan Naples area totaling about 3.
Volcanic ash Apart from possibly affecting the climate, volcanic clouds from explosive eruptions also pose a serious hazard to aviation safety.
During the past two decades, more than 60 airplanes, mostly commercial airliners, have been damaged by in-flight encounters with volcanic ash. Some of these encounters have resulted in the power loss of all engines, necessitating emergency landings.
Luckily, to date no crashes have happened because of jet aircraft flying into volcanic ash. Lava Lava flows from stratovolcanoes are generally not a significant threat to humans and animals because the highly viscous lava moves slowly enough for everyone to flee out of the path of flow.
The lava flows are more of a threat to property.
However, not all stratovolcanoes erupt viscous and sticky lava. Mount Nyiragongo is very dangerous because its magma has an unusually low silica content, making it quite fluid. Rarely, generally fluid lava could also generate a massive lava fountain, while lava of thicker viscosity can solidify within the vent, creating a block which can result in highly explosive eruptions.
Volcanic bombs Main article: Volcanic bomb Volcanic bombs are extrusive igneous rocks ranging from the size of books to small cars, that are explosively ejected from stratovolcanoes during their climactic eruptive phases. Most bombs do not themselves explode on impact, but rather carry enough force so as to have destructive effects as if they exploded.
Lahar Lahars from a Javanese term for volcanic mudflows are mixtures of volcanic debris and water. Lahars usually come from two sources: Depending on the proportion and temperature of water to volcanic material, lahars can range from thick, gooey flows that have the consistency of wet concrete to fast-flowing, soupy floods.
The ensuing lahar flooded the city of Armero and nearby settlements, killing 25, people. Slightly cooler-than-usual temperatures were recorded worldwide, with brilliant sunsets and intense sunrises attributed to the particulates ; this eruption lofted particles high into the stratosphere.
The aerosols that formed from the sulfur dioxide SO2carbon dioxide CO2and other gases dispersed around the world. The SO2 mass in this cloud—about 22 million tons—combined with water both of volcanic and atmospheric origin formed droplets of sulfuric acid, blocking a portion of the sunlight from reaching the troposphere and ground.
The cooling in some regions is thought to have been as much as 0. A similar, but extraordinarily more powerful phenomenon occurred in the cataclysmic April 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 by as much as 3. In parts of Europe, Asia, Africa and North America, was known as the " Year Without a Summer ", which caused considerable agricultural crisis and a brief but bitter famine, which generated a series of distresses across much of the affected continents.Strato volcanoes are usually about half-half lava and pyroclastic material, and the layering of these products gives them their other common name of composite volcanoes.
Left: This is a schematic diagram of a strato volcano, intended to illustrate the different layers of different materials that comprise them. ‹ Shield Volcanoes up. This is the famous "3 types of volcanoes" (shield volcanoes, strato volcanoes, and cinder cones), and it is found in many textbooks from elementary school to college.
Why is this 3-types scheme so bad? Apr 29, · Best Answer: Strato volcanoes and shield volcanoes are different because of their shape and also because of the may they erupt.
Strato volcanoes have steep slopes, shaped like a tall narrow cone.. when a strato volcano erupts vast amounts of gasses such as sulphur dioxide, water and dust are thrown up into the tranceformingnlp.com: Resolved.
A stratovolcano is a tall, conical volcano composed of one layer of hardened lava, tephra, and volcanic ash. These volcanoes are characterized by a steep profile and periodic, explosive eruptions. Strato volcanoes and shield volcanoes are different because of their shape and also because of the may they erupt.
Strato volcanoes have steep slopes, shaped like a tall narrow cone.. when a. A stratovolcano is a tall, conical volcano composed of one layer of hardened lava, tephra, and volcanic ash.
These volcanoes are characterized by a steep profile and periodic, explosive eruptions.