Diagram of a Plinian eruption. Volcanic ash rain 4. Layers of lava and ash 5.
Types of volcanic eruptions Fields Volcanic fields, such as Auckland and Northland, are where small eruptions occur over a wide geographic area, and are spaced over long periods of time thousands of years.
Each eruption builds a new single new volcano, which does not erupt again. Mount Eden and Rangitoto Island are examples in Auckland.
The products from the successive eruptions over thousands of years build the cones. Lake Taupo Caldera Volcanoes Caldera volcanoes, such as Taupo and Okataina which includes Mt Tarawerahave a history of infrequent but moderate-large eruptions.
The caldera forming eruptions create super craters km in diameter and deposit cubic kilometres of ash and pumice. The style of eruption depends on a number of factors, including the magma chemistry and content, temperature, viscosity how runny the magma isvolume and how much water and gas is in it, the presence of groundwater, and the plumbing of the volcano.
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Hydrothermal eruption An eruption driven by the heat in a hydrothermal systems. Hydrothermal eruptions pulverise surrounding rocks and can produce ash, but do not include magma. These are typically very small eruptions Phreatic eruption An eruption driven by the heat from magma interacting with water.
The water can be from groundwater, hydrothermal systems, surface runoff, a lake or the sea.
Phreatic eruptions pulverise surrounding rocks and can produce ash, but do not include new magma. Phreatomagmatic eruption An eruption resulting from the interaction of new magma or lava with water and can be very explosive.
Lava Lava is molten rock erupted at the ground surface. When molten rock is beneath the ground, it is called magma. Lava flows are the effusive non-explosive outpourings of lava, and usually flow slower than walking pace. Lava fountains are a fountain of runny lava fragments from a vent or line of vents a fissure.
They can form spatter piles, and if the fragments accumulate fast enough, they can form lava flows. Lava domes are mounds that form when viscous lava is erupted slowly and piles up over the vent, rather than moving away as a lava flow. They are generally caused by viscous, thick, sticky lava that has lost most of its gas.
They can range in volume from a few cubic metres to cubic kilometres. Strombolian and Hawaiian eruptions These are the least violent types of explosive eruptions.
Hawaiian eruptions have fire fountains and lava flows, whereas Strombolian eruptions have explosions causing a shower of lava fragments.
Vulcanian eruptions Vulcanian eruptions are small to moderate explosive eruptions, lasting seconds to minutes. Ash columns can be up to 20 km in height, and lava blocks and bombs may be ejected from the vent.
Subplinian and Plinian eruptions Eruptions with a high rate of magma discharge, sustained for minutes to hours. They form a tall, convective eruption column of a mixture of gas and rock particles, and can cause wide dispersion of ash. Very rare Ultraplinian eruptions are even larger and have a higher magma discharge rate than Plinian eruptions.The different types of volcanic activity can best be understood by making comparisons, and in this section two specific eruptions are compared—the eruption of Mount Pinatubo (a classic example of explosive volcanism) and the eruption of Mauna Loa (illustrative of effusive volcanism).
Types of Volcanic Eruptions D uring an episode of activity, a volcano commonly displays a distinctive pattern of behavior. Some mild eruptions merely discharge steam and other gases, whereas other eruptions quietly extrude quantities of lava.
There are two predominant types of volcanic eruptions: Effusive eruptions – magma rises through the surface and flows out of the volcano as a viscous liquid called lava.
Explosive eruptions – magma is torn apart as it rises and reaches the surface in pieces known as pyroclasts. Volcanic Eruptions. The most common type of volcanic eruption occurs when magma (the term for lava when it is below the Earth's surface) is released from a volcanic vent.
Eruptions can be effusive, where lava flows like a thick, sticky liquid, or explosive, where fragmented lava explodes out of a vent. Volcanic domes commonly occur within the craters or on the flanks of large composite volcanoes. The nearly circular Novarupta Dome that formed during the eruption of Katmai Volcano, Alaska, measures feet across and feet high.
Volcanoes erupt in many extraordinary ways, depending on the material it is erupting.
Eruptions may be strombolian, vulcanian, vesuvian, hawaiian, phreatic, plinian and others.