HE 1.2

• What are the two groups eruptions can be categorised into - Explosive - Effusive
• Describe the characteristics of explosive eruptions in terms of the nature of vulcanity (4) - Convergent plate boundaries - Rhyolite and Andesite lava type - Highly viscous and acidic lava with high concentration of silica - Erupts tephra and often results in pyroclastic flows - often blowing off top vent
• Describe the characteristics of effusive eruptions in terms of the nature of vulcanity (4) - Divergent plate boundaries - Basaltic lava type - Low viscosity lava - Tend to be more frequent and may continue erupting for months
• What are the two products of explosive eruptions (2) - Stratovolcanoes - Caldera
• Describe stratovolcanoes in terms of the product of explosive eruptions (3) - Made up of layers of ash and acid lava, most contain complex internal networks of lava flows forming minor igneous rocks like sills and dykes - A sill is a igneous rock layer running inbetween beds of rock - A dyke is a layer of igneous rock cutting across beds of rock
• Describe a caldera in terms of the product of explosive eruptions (2) - Volcanic craters usually more than 2km in diameter - formed when an explosive eruption destroys most of the cone and underlying magma chamber is largely emptied - without the support of the chamber, the sides collapse in to form a caldera
• Two products of an effusive eruption (2) - Shield Volcano - Lava Plateux
• Describe a shield volcano in terms of the product of effusive eruptions - Eruptions of basic lava result in volcanoes with gently sloping sides, if successive flows accumulate for long enough huge shield volcanoes form
• Describe a lava plateux in terms of the product of effusive eruptions (2) - Caused by flood basalts where basic magma erupts from multiple fissures covering vast areas with lava - They become more varied in shape over time by denudation, creating more varied relief
• What two elements make up eruptions that dont occur at plate boundaries (2) - Hotspots - Super volcanoes
• Describe Hotspots in terms of eruptions that do not occur at a plate boundary (1) - A hotspot is a fixed area of intense volcanic activity where the magma rising mantly plume reaches earths surface
• Provide an example of a hotspot with regards to eruptions not at plate boundaries (3) - Hawaii is located at the centre of the pacific plate, but located over a hotspot - The pacific plate is moving at 10cm a year, as a result the volcanoes are moving away from the hotspot losing source of magma becoming extinct - Volcano Loihi - Underwater volcanoe 30km south of main island, rising up from the sea floor and will emerge to form a new island in hawaii
• What is a supervolcano - A volcano that erupts more than 1000km cubed of material in a single eruption
• Give an example of a supervolcano (3) - Yellowstone volcano in wyoming, over 75km in diameter - Last eruptions were 640,000 and 1.3 million years ago, the ash spread across much of the wester half of north america - Gases and particulates were carried around the globe in the upper atmosphere - creating a decline in global temperatures
• Describe some misconceptions regarding yellowstone supervolcano in terms of an example of a supervolcano (3) - Yellowstone is overdue a high magnitude event - tectonic events do not actually follow a patten - When yellowstone erupts it will have severe global consequences 0 most probable eruption will be a lava flow, having little except regional impacts - Caldera surface is rising - measurements indicate both rises and falls in ground surfaces within the caldera - this does not indicate an eruption
• Describe the volcanic explosivity index in terms of volcanic hazards - Takes into account magnitude, explosivity and intensity into a single number, each unit represents 10 fold increase in explosivity, ranging from 0 to 8
• Describe limitations of the volcanic explosivity index in terms of volcanic hazards (2) - Not useful in measuring the impact of effusive eruptions due to the little material ejected by them - Hawaiian eruptions, for example, have a significant local impact despite being effusive
• What are the hazards associated with volcanic eruptions (7) - Lava flows - Pyroclastic flows - Tephra - Toxic gases - Lahars - Floods - Tsunami
• Describe Lava flows as a hazard associated with volcanic eruptions, including 1 example (2) - Basic lava is free flowing and can run for significant distances, destroying everything in its path - Hawaii in July 2015 - 20km lava flow running about 800m a day
• Describe Pyroclastic flows as a hazard associated with volcanic eruptions, including 1 example (2) - Combination of very hot 500 degree celcius gases, ash and rock fragments travelling at high speed - inhalation causes instant death - Pompeii/vesuvius in AD79 - pyroclastic flows overwhelmed pompeii
• Describe Tephra as a hazard associated with volcanic eruptions, including 1 example (2) - Any material ejected from a volcano into the air, ranges from ash to volcanic bombs - E15 eruption in Iceland in April 2010, led to the cancellation of 100,000 flights
• Describe toxic gases as a hazard associated with volcanic eruptions, including 1 example (2) - Eruptions emit a wide range of toxic gases including CO and SO2, when SO2 combines with water acid rain is produced enhancing weathering - 1986 Lake Nyos disaster
• Describe Lahars as a hazard associated with volcanic eruptions, including 1 example (2) - Type of mudflow with consistency of wet concrete, caused by snow and ice on the volcano summit melting during the eruption and flowing rapidly, can be up to 50km/h - 1984 Nevado del Ruiz eruption - columbian town of Armero overwhelmed by lahars killing 23,000 people
• Describe floods as a hazard associated with volcanic eruptions, including 1 example (2) - Volcanic eruptions beneath glacier cause rapid melting - Iceland Vatnojokull ice field - eruptions occured beneath it accumulating water until it found an exit causing floods
• Describe tsunamis as a hazard associated with volcanic eruptions, including 1 example (2) - Violent eruption of island volcanoes can cause displacement of ocean water producing tsunami waves capable of traveling at 600km/h - 1883 Krakatao eruption killed 36,000 people in a tsunami
• Describe the Toba eruption (69,000 - to 77,000 years ago) in terms of volcanic hazards (2) - Supervolcanic eruption that led to long term reductions in global temperatures as ash blocked sunlight from reaching earths surface - Release of SO2 mixed with water forming sulphuric acid and reflecting solar radiation, created a volcanic winter lasting 6 years following the eruption
• Describe the hazards involved with the 1991 mount pinatubo eruption in terms of volcanic hazards (2) - Pyroclastic flows reached 10km either side of the volcano, having huge local infrastructural impacts - Lahars stretched from pinatubo to oceans and filled valleys, killed 100 people, impacted a greater area, but had less of a significant impact on the area they hit
• Describe the 1986 Lake Nyos Disaster in terms of volcanic hazards (2) - 1700 people and 3000 cattle died from asphyxiation, caused by a gas leak of co2 from a volcanic crater lake - Gas built up at the bottom of the lake, was emitted from underlying magma chamber and flowed down volcano slopes, 1 billion cubic metres emitted