Do volcanoes be classified according to a record of eruption except?
Answers
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.
Types of eruptions
Multiple types of eruptions can occur at each of New Zealand’s volcanoes - the eruption type can vary minute to minute. The style of eruption depends on a number of factors, including the magma chemistry and content, temperature, viscosity (how runny the magma is), volume and how much water and gas is in it, the presence of groundwater, and the plumbing of the volcano. For information on volcanic hazards which can be produced by our volcanoes, click here.
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. The water can be from groundwater, hydrothermal systems, surface runoff, a lake or the sea.
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 flow types include a’a, blocky and pahoehoe.
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.
Sub Plinian 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. Sub Plinian eruption columns are up to 20 km high, and are relatively unsteady, whereas Plinian eruptions have 20 to 35 km tall columns which may collapse to form pyroclastic density currents (PDC’s). Very rare Ultra Plinian eruptions are even larger and have a higher magma discharge rate than Plinian eruptions.
Q. what determine the nature of eruption?
Ans. The three factors that determine the nature of a volcanic eruption are magma composition, temperature, and the amount of dissolved gases. To varying degrees, these factors affect or control the viscosity of magma.
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