Hawaiian - This type of activity is the like of Mauno Loa and Kilauea Volcanoes. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of very fluid basalt-type lavas with low gaseous content. Eruptions are not centralized at the main summit as with other volcanic types, and often occur at vents around the summit. Mount Etna is also known to have Hawaiian activity.
Strombolian- This type of volcanic activity is named after the volcano Stromboli, which has been erupting continuously for centuries. Strombolian eruptions are driven by the bursting of gas bubbles within the magma. These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slugs. These grow large enough to rise through the lava column. Upon reaching the surface, the difference in air pressure causes the bubble to burst with a loud pop, throwing magma in the air in a way similar to a soap bubble. Because of the high gas pressures associated with the lavas, continued activity is generally in the form of episodic explosive eruptions accompanied by the distinctive loud blasts. During eruptions, these blasts occur as often as every few minutes.
Vulcanian - In Vulcanian eruptions, highly viscous magma within the volcano make it difficult for vesiculate gases to escape. Similar to Strombolian eruptions, this leads to the buildup of high gas pressure, eventually popping the cap holding the magma down and resulting in an explosive eruption. However, unlike Strombolian eruptions, ejected lava fragments are no aero dynamical. They are also more explosive than their Strombolian counterparts, with eruptive columns often reaching between 5 and 10km high. Lastly Vulcanian deposits are andesitic rather than basaltic. Example includes Sakurajima, Japan.
Pelean - Is a type of volcanic eruption, named after the volcano Mount Pelee. In Pelean eruptions, a large amount of gas, dust, ash and lava fragments are blown out in the volcano's central crater, and that often creates large eruptive columns. An early sign of a coming eruption is the growth of a lava spine, a bulge in the summit preempting to its total collapse. The material collapses upon itself, forming a fast-moving pyroclastic flow. These massive landslides make Pelean eruptions one of the most dangerous in the world. Volcanoes known to have Pelean activity are Mount Pelee and Mayon Volcano in the Phillippines.
Plinian - High explosive eruptions that occur mostly at stratovolcanoes. Eruptions can last anywhere from hours to days. Plinian eruptions are similar to both Vulcanian and Strombolian eruptions, except that rather than creating discrete explosive events, Plinian eruptions form sustained eruptive columns, which can reach up to 45km in height. The most dangerous feature are pyroclastic flows generated by material collapse, which move down the side of the mountain at up to 435m/ph. The ejection of hot material from the volcano's summit melts snow banks and ice deposits on the volcano, which mixes the tephra to form lahars, fast moving mudslides with the consistency of wet concrete that move at the speed of a river rapid. Major Plinian eruptive events include Mount Vesuvius in AD 79. The 1980 eruption of Mount St. Helens was a Plinian eruption.
Surtseyan - A type of volcanic eruption caused by shallow-water interactions between water and lava, named so after its most famous example, the eruption and formation of the island of Surtsey off the coast of Iceland. Surtseyan eruptions are the "wet" equivalent of ground-based Strombolian eruptions, but because of where they are taking place they are much more explosive.
Fissure eruptions - occur where an elongated crack in the crust allows lava to spill out over a large area. Typically tthese are found around spreading ridges where tension pulls the crust apart - for example, the eruption at Heimaey, Iceland in 1973. When the Eurasian and North American Plates pulled apart, existing topography was drowned in a vast lake of basaltic lava. Fissure eruptions are characterized by a curtain of fire, a curtain of lava spewing out to a small height above the ground.
Source of Info
Shield Volcanoes - are made of basaltic rock and form gently sloping cones from layers of less viscous lava. These volcanoes are known for producing the Hawaiian Islands and are some of the largest in the world, both in height and width. Shield volcanoes are squatty, being lower to the ground, yet having a huge base.
Composite / Stratovolcano - The most common type found on land. They are created by layers of ash from initial explosive phases of eruptions and subsequent layers of lava from the main eruption phases. They are characterized by a fairly symmetrical mountain edifice. They tend to have highly infrequent eruptions hundreds of years apart-- and typically form at subduction zones.
Ciner Cone Volcanoes - These are steep-sided volcanoes formed from very viscous lava. As the lava cnnot travel far, it builds up convex cone-shaped volcanoes. Lava may solidify in the vent and be revealed later by erosion. They usually remain compartively small and are active only for a short time.
Calderas - Form when gasees that have built up beneath a blocked volcanic event result in a catstrophic eruption that destroys the volcano summit, leaving an enormous crater where later eruptions may form smaller cones. In the case of Crater Lake in the US, the caldera has filled with water, while in the case of Krakatoa in Indonesia and Thera/Santorini in Greece, the sea has inundated the broken remains of the volcano.
Calderas - Form when gasees that have built up beneath a blocked volcanic event result in a catstrophic eruption that destroys the volcano summit, leaving an enormous crater where later eruptions may form smaller cones. In the case of Crater Lake in the US, the caldera has filled with water, while in the case of Krakatoa in Indonesia and Thera/Santorini in Greece, the sea has inundated the broken remains of the volcano.
Types of intrusive/extrusive activity
Induced Seismicity
Refers to typically minor earthquakes and tremors that are caused by human activity that alters the stresses and strains on the Earth's crust. Most induced seismicity is of an extremely low magnitude. There are a many of ways in which induced seismicity has been seen to occur. In the past several years, some energy technologies that inject or extract fluid from the Earth, such as oil and gas extraction and geothermal energy development, have been found or suspected to cause seismic events.
The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity. Induced seismicity is usually overlooked due to cost cutting during the geological surveys of the locations for proposed dams. Once the reservoirs are filled, induced seismicity could occur immediately or with a small time lag. The 6.3 magnitude 1967 Koynanagar Earthquake occurred in Maharashtra, India with its epicenter, fore- and aftershocks all located near or under the Koyna Dam reservoir. 180 people died and 1,500 were left injured. The effects of the earthquake were felt 230 km (140 mi) away in Bombay with tremors and power outages.
The 2008 Sichuan earthquake, which caused approximately 68,000 deaths, is another possible example. An article in Science suggested that the construction and filling of the Zipingpu Dam may have triggered the earthquake. However, researchers have been denied access to seismological and geological data to examine the cause of the quake further.
Extraction of fossil fuels and disposal of waste
Fossil fuel extraction can generate earthquakes. Hydraulic fracturing of natural gas wells produces large amounts of waste water. This contaminated water is often pumped into salt water disposal (SWD) wells. The weight and lubricity of this waste water has been shown to trigger earthquakes. As of 2013, the magnitude 5.7 earthquake in Oklahoma in 2011 which occurred after 20 years of injecting waste water into porous deep formations is believed to be the strongest earthquake induced by injection of material.
Induced Seismicity
Refers to typically minor earthquakes and tremors that are caused by human activity that alters the stresses and strains on the Earth's crust. Most induced seismicity is of an extremely low magnitude. There are a many of ways in which induced seismicity has been seen to occur. In the past several years, some energy technologies that inject or extract fluid from the Earth, such as oil and gas extraction and geothermal energy development, have been found or suspected to cause seismic events.
The extra water pressure created by vast reservoirs is the most accepted explanation for the seismic activity. Induced seismicity is usually overlooked due to cost cutting during the geological surveys of the locations for proposed dams. Once the reservoirs are filled, induced seismicity could occur immediately or with a small time lag. The 6.3 magnitude 1967 Koynanagar Earthquake occurred in Maharashtra, India with its epicenter, fore- and aftershocks all located near or under the Koyna Dam reservoir. 180 people died and 1,500 were left injured. The effects of the earthquake were felt 230 km (140 mi) away in Bombay with tremors and power outages.
The 2008 Sichuan earthquake, which caused approximately 68,000 deaths, is another possible example. An article in Science suggested that the construction and filling of the Zipingpu Dam may have triggered the earthquake. However, researchers have been denied access to seismological and geological data to examine the cause of the quake further.
Extraction of fossil fuels and disposal of waste
Fossil fuel extraction can generate earthquakes. Hydraulic fracturing of natural gas wells produces large amounts of waste water. This contaminated water is often pumped into salt water disposal (SWD) wells. The weight and lubricity of this waste water has been shown to trigger earthquakes. As of 2013, the magnitude 5.7 earthquake in Oklahoma in 2011 which occurred after 20 years of injecting waste water into porous deep formations is believed to be the strongest earthquake induced by injection of material.
