How does the structure of a volcano affect its type of activity?
Answers
Answer:
Volcanic 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.
Cone Volcanoes
Cone volcanoes (also called composite cone or stratovolcanoes) such as Ruapehu, Taranaki / Egmont and Ngauruhoe, are characterised by a succession of small-moderate eruptions from one location. The products from the successive eruptions over thousands of years build the cones.
Caldera Volcanoes
Caldera volcanoes, such as Taupo and Okataina (which includes Mt Tarawera), have a history of infrequent but moderate-large eruptions. The caldera forming eruptions create super craters 10-25 km in diameter and deposit cubic kilometres of ash and pumice.
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.
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. Subplinian 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 Ultraplinian eruptions are even larger and have a higher magma discharge rate than Plinian eruptions.