Debris avalanches can result, which are fast-moving slurries of rock, water and debris. Rarely, very large landslides can occur on the flanks of volcanoes, called sector collapse. Landslides The down-slope movement of rock and soil under the influence of gravity. They are also highly erosive, and can cause a lot of damage to bridges and other infrastructure, entraining all material in their paths. Due to the large amount of sediment carried by a lahar, water channels (and other nearby flat land) can rapidly fill with deposited sediment, causing long-term flooding issues. Lahars can travel well over 100 km from the source, and can be dangerous to downstream populations who are unaware of the approaching hazard. It may also be unaccompanied by an eruption, such as by the collapse of a crater lake wall, or through remobilisation of volcanic material due to heavy rain. A lahar may be caused by the rapid melting of ice/snow by an eruption or from an eruption ejecting crater lake water. valleys), however, they may overtop banks. Lahars usually flow down topographical lows (i.e. Lahar A volcanic mudflow – a flow of water-saturated, typically dense volcanic material that resembles a flow of wet concrete. Hydrothermal activity may include hydrothermal eruptions, fumaroles, gas/steam emissions, steaming ground, geysers, hot springs and streams, and hot pools (including mud pools). Hydrothermal activity Manifestations seen at the surface of geothermal systems. Hot springs A surface feature of a geothermal system, where warm or hot water flows out of the ground.
#DEFINITION OF VISCOSITY IN GEOLOGY CRACK#
Fįissure A large crack in the ground allowing magma to travel up and erupt onto the surface.
Explosions are typically accompanied by the ejection of ballistics, gas and steam from the vent.
#DEFINITION OF VISCOSITY IN GEOLOGY WINDOWS#
A shock wave is often caused, which on rare occasions can blow down trees and break windows at nearby buildings, and is usually accompanied by a loud boom. Explosions During a volcanic eruption, the sudden decompression of hot, pressurised volcanic gas can cause a volcanic explosion, or blast. Eruption plume A cloud of volcanic ash emitted from a volcanic vent or volcano. Eruption hazards Eruption hazards depend on the volcano and eruption style, and may include explosions, ballistics, pyroclastic density currents, lava flows, lava domes, landslides, ash, volcanic gases, lightning, lahars, tsunami, and/or earthquakes. Eruption The arrival of fragmented material, the effusion of lava, or both, to the surface of the Earth (or other planetary bodies) by a volcano. Earthquakes can occur in swarms, where the largest magnitude earthquakes are all of a similar size. Different types of earthquakes or seismicity include low frequency, high frequency (or ‘volcano tectonic’ earthquakes) and hybrid earthquakes and tremor. EĮarthquakes A sudden motion or trembling in the crust caused by the abrupt release of accumulated stress along a fault. Debris avalanches can move rapidly, and commonly occur on volcanoes. Debris avalanche An avalanche or slurry consisting of unsorted rock, water and other material (such as fragmented cold and hot volcanic rocks, snow/ice and trees). Dĭacite A type of volcanic rock intermediate between andesite and rhyolite Mount Edgecumbe is an example of this. The diameter of a caldera many be times larger than the size of the individual vents. CĬaldera A volcanic depression formed by the collapse of the ground above a magma chamber, which empties during very large volcanic eruptions. Forms dark coloured rock (often red or black), such as the scoria cones of Auckland. Basalt A type of fluid magma with low silica content. They rarely reach more than about 3 kilometres radius from the vent. Bīallistics Tephra particles larger than 64 mm (including solid ‘blocks’ and molten ‘bombs’) that are ejected from a volcanic vent in any direction without being affected by wind. Particles smaller than 2 mm in diameter are termed ‘ash’. Ash Fine particles of pulverized rock (tephra) erupted from the vent of a volcano. Andesite is also the name given to the volcanic rock formed from andesite magma. Forms large composite volcanoes, sometimes called stratovolcanoes, made up of alternating ash and lava layers, such as Mount Ruapehu. Andesite A type of magma with intermediate viscosity and silica content.
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