Types of Volcano and ERUPTIONS
There are two types of Volcano, Composite and Shield, both of which generate different types of eruptions and are usually formed in different ways. A composite volcano has the appearance of a steep sided symmetrical cone and is built up of alternating layers of lava and ash. They tend to be tall with a narrow base and they cause violent eruptions. They have viscous magma. A shield volcano has gently sloping sides and a wide base due to the fact that the magma is less viscous meaning that it can travel further before cooling. |
Examples of VolcanoShield Volcano - Manua Loa, Kilavea (Hawaii)
Composite Volcano - Mt St Helens (USA) and Mt Etna (Sicily) |
Composite Volcano
Composite volcanoes are known to be explosive with pyroclastic flows and ash clouds that destroy lots of wildlife and homes that are in its way when it erupts. They are found at destructive plate boundaries and are formed when the Oceanic crust is forced underneath the Continental crust and it melts in the Subduction zone and Benioff zone. This molten rock is less dense than the rock around it so rises up through the Continental plate and erupts on to the surface throwing out clouds of ash which settles in layers of ash and lava. The lava from the eruption is very viscous so cannot move very far before cooling and setting in place. This gives the volcano its shape of a tall cone with a narrow base.
Super Volcanoes
There is one other type of volcano called a super volcano.
eruptions
There are 6 main types of eruptions, mostly named after famous eruptions that have occurred in the past. Before looking at them and their characteristics, it is important to understand what are the main factors that affect the type of eruption.
What Determines Eruption Type? It's all about crystal and gas...
-- Crystals in magma make it more viscous, so magma with a high crystal content is more likely to explode than flow.
-- Gases create explosions if they cannot easily escape from viscous magma, but they can also be released without explosions (or with only minor ones) from fluid magma.
-- High-temperature magmas usually erupt effusively, while low-temperature magmas cannot flow easily and are more likely to erupt explosively.
Slideshow of the 6 types (Hawaiian, Strombolian, Vulcanian, Plinian, Lava Dome and Surtseyan)
What Determines Eruption Type? It's all about crystal and gas...
-- Crystals in magma make it more viscous, so magma with a high crystal content is more likely to explode than flow.
-- Gases create explosions if they cannot easily escape from viscous magma, but they can also be released without explosions (or with only minor ones) from fluid magma.
-- High-temperature magmas usually erupt effusively, while low-temperature magmas cannot flow easily and are more likely to erupt explosively.
Slideshow of the 6 types (Hawaiian, Strombolian, Vulcanian, Plinian, Lava Dome and Surtseyan)
Hawaiian Eruption
In a Hawaiian eruption, jets of basaltic magma propels into the air from a vent or a fissure (line of vents). The nickname fire fountain comes from the fact that these jets of lava can last for hours or even days, the most spectacular fire fountains are produced from the Kilauea volcano on the Big Island of Hawaii. Two excellent examples of these, where lava fountains reached heights of well over a thousand feet, are the 1969-1974 Mauna Ulu eruption on the volcano's flank, and the 1959 eruption of the Kilauea Iki Crater at the summit of Kilauea (seen in photograph below)
The spatter created by bits of hot lava falling out of the fountain can melt together and form lava flows, or build hills called spatter cones. Lava flows may also come from vents at the same time as fountaining occurs, or during periods where fountaining has paused. Because these flows are very fluid, they can travel miles from their source before they cool and harden.
STROMBOLIAN ERUPTION - Strombolian eruptions are named for the volcano that makes up the Italian island of Stromboli, which has several erupting summit vents.
Strombolian eruptions consist of distinct bursts of fluid lava (usually basalt or basaltic andesite) from the mouth of a magma-filled summit. The explosions usually occur every few minutes at regular or irregular intervals. These distinct explosions are caused by the bursting of large bubbles of gas, which travel upward (heat rises) in the magma-filled vent until they reach the open air.
The land formations (or eruptive products) can vary widely, some examples are; spatter, or hardened globs of glassy lava; scoria (which are hardened chunks of bubbly lava); lava bombs, or chunks of lava a few cm to a few m in size; ash; and small lava flows (which form when hot spatter melts together and flows downslope). Products of an explosive eruption are often collectively called tephra.
Strombolian eruptions are often associated with small lava lakes, which can build up in the conduits of volcanoes. They are one of the least violent of the explosive eruptions due to the constant eruptive state, although they can still be very dangerous if bombs or lava flows reach inhabited areas. These eruptions are particularly spectacular at night, when the lava glows brightly.
Below is a video of a recent strombolian eruption
STROMBOLIAN ERUPTION - Strombolian eruptions are named for the volcano that makes up the Italian island of Stromboli, which has several erupting summit vents.
Strombolian eruptions consist of distinct bursts of fluid lava (usually basalt or basaltic andesite) from the mouth of a magma-filled summit. The explosions usually occur every few minutes at regular or irregular intervals. These distinct explosions are caused by the bursting of large bubbles of gas, which travel upward (heat rises) in the magma-filled vent until they reach the open air.
The land formations (or eruptive products) can vary widely, some examples are; spatter, or hardened globs of glassy lava; scoria (which are hardened chunks of bubbly lava); lava bombs, or chunks of lava a few cm to a few m in size; ash; and small lava flows (which form when hot spatter melts together and flows downslope). Products of an explosive eruption are often collectively called tephra.
Strombolian eruptions are often associated with small lava lakes, which can build up in the conduits of volcanoes. They are one of the least violent of the explosive eruptions due to the constant eruptive state, although they can still be very dangerous if bombs or lava flows reach inhabited areas. These eruptions are particularly spectacular at night, when the lava glows brightly.
Below is a video of a recent strombolian eruption
VULCANIAN ERUPTION - named for the Italian island of Vulcano (seen in picture), where a small volcano that experienced this type of explosive eruption was thought to be the vent above the forge of the Roman smith god Vulcan
A Vulcanian eruption is a short, violent, relatively small explosion of viscous magma (usually andesite, dacite, or rhyolite). This type of eruption results from the fragmentation and explosion of a plug of lava in a volcanic conduit, or from the rupture of a lava dome (viscous lava that piles up over a vent). Vulcanian eruptions create powerful explosions in which material can travel faster than 350 meters per second (800 mph) and rise several kilometers into the air. They produce tephra, ash clouds, and pyroclastic density currents (clouds of hot ash, gas and rock that flow almost like fluids). Vulcanian eruptions may be repetitive and go on for days, months, or years, or they may precede even larger explosive eruptions. Plinian Eruption- Mount Vesuvius Mount Vesuvius has experienced numerous Pilinian eruptions since 79 AD. Plinian Eruptions are named after Pliny the younger, a roman historian who was viewing the Mount Vesuvius eruption in 79 AD.
Plinian Eruptions are one of the largest and most violent of all types of volcanic eruptions and are highly destructive. Plinian eruptions produce powerful convection plumes of ash which can rise up to 50km high into the stratosphere. Plinian eruptions are able to sustain eruptive columns because of the thrust of expanding gases and convection forces which can cause the eruptions to last over several days. These eruption columns are able to distribute widespread dispersal deposits of tephra, produce pyroclastic flows and surges and cause extensive ash fall.
This occurs due to the fragmentation of glassy magma which is volatile rich in dacitic to rhyoltitc lava. The eruption columns are often associated with mushroom clouds (like that of a nuclear bomb) Some plinian eruptions inject such large quantities of aerosols into the stratosphere that surface temperatures on earth may decrease slightly Lava dome eruptionsVolcanic domes are formed when sticky, high-silica lava piles up around a vent instead of flowing rapidly away, as in the case of low-silica basaltic lava erupted in Hawai`i.
Erupting domes are commonly associated with fast-moving pyroclastic flows, which form when either blocks of fresh lava break off from the dome and move rapidly downhill or when a lava dome is shattered during strong explosive activity. At the present time, there are 4 major lava dome eruptions taking place in the world - Augustine and Mount St. Helens volcanoes in the U.S., Soufriere Hills Volcano on the Caribbean island of Montserrat, and Santa Maria in Guatemala. The activity is not making headline news now, but the volcanoes deserve close watching, because each is capable of producing powerful explosive activity and dangerous pyroclastic flows. Of the four volcanoes, only Santa Maria is not intensely monitored by scientists. To the right is the lava dome within the crater of Mount Saint Helens. |
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Surtseyan Eruptions
A Surtseyan eruption is a type of volcanic eruption that takes place in shallow seas or lakes. It is named after the island of Surtsey off the southern coast of Iceland.Surtseyan or Phreatic volcanic eruptions are steam-driven explosions that occur when water beneath the ground or on the surface is heated by magma, lava, hot rocks, or new volcanic deposits (for example, tephra and pyroclastic-flow deposits). The intense heat of such material (as high as 1,170° C for basaltic lava) may cause water to boil and flash to steam, thereby generating an explosion of steam, water, ash, blocks, and bombs.
Surtsey erupted off the coast of Iceland between 1963 and 1967.
To the left is an image of the eruption that created the island of Surtsey.
Surtsey erupted off the coast of Iceland between 1963 and 1967.
To the left is an image of the eruption that created the island of Surtsey.