entrance of lahars or pyroclastic density currents into surrounding water.On volcanoes, this can occur via a number of mechanisms, for example: Tsunamis form when water, whether in a lake of the sea, is displaced. In fact, tsunamis have caused the most fatalities associated with volcanic eruptions in historical times. Although less common, volcanoes can also cause tsunamis. Tsunamis can form in relation to a wide range of geological activities, from earthquakes to landslides. The Japanese word tsunami means ‘harbour wave’. Thankfully, flood basalt eruptions are very rare! It most likely also increased levels of mortality elsewhere in Europe, through air pollution by sulphur-bearing gas and aerosols. It is now the largest flood basalt in Iceland since the Laki eruption in 1783–1784, which caused the deaths of about 20 per cent of the Icelandic population by environmental pollution and famine. In 2014, the Holuhraun fissure eruption reached flood basalt size. We can learn a lot from flood basalts that happen in Iceland. Such eruptions impact large, up to continental-sized areas (over one million square kilometres), They can have thicknesses up to a kilometre and release large amounts of gas they can cause air pollution and even have an impact on the global climate. These eruptions are rare and our understanding of these events is based on study of past eruptions at places like the Deccan Traps in India, or the Siberian Traps. Flood basaltsįlood basalts are an exceptional form of lava flow. These lava domes are particularly hazardous as they tend to be unstable and can collapse, causing pyroclastic density currents. Because of the high viscosity of the lava, it cannot travel far from the vent and a dome of lava builds up. Lava domes form when high-viscosity lava is slowly erupted from a volcano. The rate of movement of lavas typically ranges from a few metres per hour for high-silica, andesitic lavas to several kilometres per hour for fluid basalts. They form short, thick flows or steep-sided lava domes that don’t travel far from volcanic vents. High-viscosity, silicon-rich andesites are much less fluid than basalt and are erupted at temperatures of around 700–900☌. Low-viscosity, iron/magnesium-rich basalts are the most fluid of the common lava types and are typically erupted at temperatures of 1100–1200☌. The viscosity - how easily a fluid can flow - of lava flows generally increases with silica content and decreases with a rise in temperature and water content. ‘Tephra’ is used as the catch-all term to describe all erupted clasts regardless of size, while the term ‘ash’ describes particles of less than 2 mm in size. Volcanic products are typically named according to clast (particle) size, which can range from metres down to microns in size. For those living alongside volcanoes, knowing about volcanic hazards is just one way that people can reduce their risk. There can be emotional, societal and economic benefits. Such hazards can impact areas hundreds or thousands of kilometres from the volcano, with the potential for significant health and economic impacts (BGS, 2012).Įven though volcanoes can be dangerous, there are lots of reasons why people live alongside them. Volcanic activity also produces hazards that can affect areas far from the volcano, such as tephra or ash falls, releases of gas and tsunamis. Several hazards may affect the area around the volcano, such as lava flows, pyroclastic flows, lahars, jökulhlaups and landslides or debris avalanches.
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