1. 3. Volcanic Hazards
1.1. Volcanic Explosivity index
1.1.1. Takes into account magnitude, explosivity and intensity into a single number
1.1.1.1. Each unit represents a 10 fold increase in explosivity, with the scale ranging from 0 to 8
1.1.2. Takes into account height of ejected material reached and duration of eruption
1.1.3. Limitations
1.1.3.1. Not useful in measuring the impact of effusive eruptions due to the little material ejected by them
1.1.3.1.1. Hawaiian eruptions, for example can still have a significant impact despite being low on the scale
1.2. Hazards
1.2.1. Lava Flows
1.2.1.1. Basic lava is free flowing and can run for significant distances
1.2.1.1.1. Everything in its path is destroyed
1.2.1.2. Hawaii July 2015
1.2.1.2.1. 20km lava flow running about 800m a day
1.2.2. Pyroclastic flows
1.2.2.1. Combination of very hot 500 degree celcius gases, ash and rock fragments travelling at a high spreed
1.2.2.1.1. Inhalation of gases cause instant death
1.2.2.2. Pompeii AD79
1.2.2.2.1. Phyroclastic flows overwhelmed the area
1.2.3. Tephra
1.2.3.1. Any material ejected from a volcano into the air
1.2.3.1.1. Ranges from ash to volcanic bombs
1.2.3.2. E15 eruption in Iceland April 2010
1.2.3.2.1. Led to the cancellation of 100,000 flights
1.2.4. Toxic Gases
1.2.4.1. Eruptions emit wide range of toxic gases including CO and SO2
1.2.4.1.1. When SO2 combines with water acid rain is produced enhancing weathering
1.2.4.2. 1986 Lake Nyos disaster
1.2.5. Lahars
1.2.5.1. Type of mudflow with consistency of wet concrete
1.2.5.1.1. Caused by snow and ice on volcano summit melting during the eruption and flowing rapidly
1.2.5.2. 1984 Nevado del Ruiz eruption
1.2.5.2.1. Columbian town of Armero overwhelmed by lahars killing 23,000 people
1.2.6. Floods
1.2.6.1. Volcanic eruptions beneath glacier cause rapid melting
1.2.6.2. Iceland Vatnojokull ice filed
1.2.6.2.1. Eruptions occured beneath it accumulating water until it found an exit causing floods
1.2.7. Tsunami
1.2.7.1. Violent eruption of island volcanoes can cause displacement of ocean water
1.2.7.1.1. Tsunami waves are capable of travelling at 600km/h
1.2.7.2. 1883 Krakatao eruption killed 36,000 people
1.3. Toba Eruption (69,000 to 77,000 years ago)
1.3.1. Most eruptions are short term, but past eruptions of supervolcanoes such as toba in Indonesia led to long term reductions in global temperatures as ash bloicked sunlight from reaching earths surface
1.3.2. Release of SO2 added to global cooling
1.3.2.1. SO2 mixes with water to form sulphuric acid reflecting solar radiation
1.3.2.1.1. Creates a volcanic winter lasting 6 to 10 years
1.4. Mount Pinatubo 1991 eruption
1.4.1. Hazards involved
1.4.1.1. Pyroclastic flows reached 10km either side of volcano
1.4.1.1.1. Wouldve resulted in every building in its path being destroyed having huge local impacts
1.4.1.2. Lahars stretched from pinatubo to oceans and filled valleys
1.4.1.2.1. Would have put a much greater area at risk than pyroclastic flows but may of had less sever impacts on the land they impacted
1.5. 1986 Lake Nyos Disaster
1.5.1. Lake nyos is a deep lake occupying a volcanic crater in Cameroon, West Africa
1.5.2. 1700 people and 3000 cattle died from mass asphyxiation
1.5.2.1. Caused by a leak of co2 from a volcanic crater lake, gas built up at the bottom of the lake
1.5.2.1.1. After being emitted from underlying magma chamber the gas escaped and flowed down volcano slopes
2. 1. Volcanoes: Causes and Features - Eruptions at plate boundaries
2.1. Nature of Vulcanity
2.1.1. Magma
2.1.1.1. Molten rock UNDERGROUND
2.1.2. lava
2.1.2.1. Molten rock that breaks through the surface
2.1.3. Nature of the eruption and the landforms it produces decided by viscosity of lava
2.1.3.1. If lava is viscous it can trap gas resulting in a build up of pressure and more explosive eruptions
2.1.4. Eruptions can be divided into two groups
2.1.4.1. Explosive
2.1.4.1.1. Convergent plate boundaries
2.1.4.1.2. Lava type
2.1.4.1.3. Characteristics of lava
2.1.4.1.4. Often from steep sided/ strato volcanoes
2.1.4.1.5. Style of eruption
2.1.4.2. Effusive
2.1.4.2.1. Divergent plate boundaries
2.1.4.2.2. Lava type
2.1.4.2.3. Characteristics of lava
2.1.4.2.4. Often from gently sloping shield volcanoes
2.1.4.2.5. Style of eruption
2.2. Products of Explosive eruptions
2.2.1. Sratovolcanoes
2.2.1.1. Also known as composite cone volcanoes
2.2.1.1.1. Made up of layers of ash and acid lava
2.2.2. Caldera
2.2.2.1. Volcanic craters usually more than 2km in diameter
2.2.2.2. Formed when an explosive eruption destroys much of the cone and underlying magma chamber is largely emptied
2.2.2.2.1. Without the support of this underlying magma the sides collapse to form a caldera
2.3. Products of Effusive Eruptions
2.3.1. Shield Volcano
2.3.1.1. Because most divergent plate boundaries coincide with mid ocean ridges, most effusive eruptions occur on ocean floor
2.3.1.1.1. Iceland is an exception
2.3.1.2. Eruptions of basic lava result in volcanoes with gently sloping sides
2.3.1.2.1. If successive flows accumulate for long enough huge shield volcanoes form extending horizontally for 10s of kilometers
2.3.2. Lava Plateux
2.3.2.1. Caused by Flood Basalts
2.3.2.1.1. This is where basic magma erupts from multiple fissures covering vast areas by lava
2.3.2.1.2. For example
2.3.2.2. They become more varied in shape overtime by denudation
2.3.2.2.1. This creates more varied relief
3. 2. Hotspots and Super Volcanoes - Eruptions not at plate boundaries
3.1. Hotspots
3.1.1. Hawaii chain of islands
3.1.1.1. Located at the centre of the pacific plate, thousands of miles from the nearest plate boundary
3.1.1.2. The pacific plate is moving at 10cm a year northwest over the hawaiian hotspot
3.1.1.2.1. As a result the volcanoes move away from the hotspot, losing their source of magma
3.1.1.3. Volcano Loihi
3.1.1.3.1. 30km south of main island lies this underwater volcano
3.1.2. East African Rift Valley - Mount Kilimanjaro
3.1.2.1. 4000km long rift valley containing several active volcanoes
3.1.2.1.1. Over 30 million years the crust is stretched, causing tension within local rocks
3.1.3. A hotspot is a fixed area of intense volcanic activity where the magma from a rising mantle plume reaches earths surface
3.2. Super Volcanoes
3.2.1. A volcano that erupts more than 1000km cubed of material in a single eruption
3.2.1.1. Yellowstone volcano
3.2.1.1.1. In Wyoming over 75km in diameter
3.2.1.1.2. Last eruptions were 640,000 and 1.3 million years ago
3.2.1.1.3. Misconceptions surrounding yellowstone