🟠✅Natural Hazards - Volcanic Hazards Flashcards
Magma vs lava
Magma - below ground
Lava - above ground
Extrusive vs intrusive landforms
Extrusive - formed above earths surface
Intrusive - formed below earths surface
Igneous rock
Any rock formed by the cooling of magma / lava
Pyroclastic material
Mixture of hot rock, ash and lava fragments that are thrown from the vent of a volcanoes during an eruption
What’s a volcano
Crack or opening on the earths crust where volcanic materials are ejected
Where do volcanoes occur
On plate boundaries (constructive plate boudnies and destructions subduction zones) and hot spots. There must be a source of magma.
What substances can erupt out of a volcano?
Gases
Nitrogen / sulphur dioxide / steam / carbon monoxide / hydrogen / chlorine
Pyroclastic’s (solid fragments)
Cinders / ash and dust / pumice / volcanic bombs
Lava / liquid rock (made mostly of SO2)
The higher the silica content the…
Stickier
More slow moving
Traps gases better
Violent
Resistant to flow
Viscous
Basic lava
Boundary - constructive
Origin of magma - deep within mantle
Magma name - SIMA (basalt)
Temp of magma - higher
Viscosity - lower
Description - less silica (lower viscosity) more Fe / Mg
Explosively - less
Example - ocean basins (Iceland)
Acid lava
Boundary - destructive
Origin of magma - edge of mantle plate
Magma name - SIAL (acidic)
Temp of magma - lower
Viscosity - higher
Description - more silica, more viscous, more Al / gases
Explosively - more
Example - continents (Indonesia / Philippines)
Fissure volcano
(Fissure or vent / lava type / description / example)
Fissure, constructive plate margin
Basalt
They can flow considerable distances over gentle slops, form flat lava fields with no shape
Heimacy eruption 1973
Basic
(Fissure or vent / lava type / description / example)
Vent
Basaltic
Lava flows of of central vent and spreads over wide distance before it solidifies
Broad base
Mauna Loa in Hawaii
Acid dome
(Fissure or vent / lava type / description / example)
Vent
Acidic
Solidifies quickly on exposure to air, steep sided volcanoes
Mt Pelee
Composite
(Fissure or vent / lava type / description / example)
Vent
Alternate layers of acidic lava (gentle eruption)
Larger classically shaped volcanoes as lava ejected makes cone shape
Mt Etra
Caldera
(Fissure or vent / lava type / description / example)
Fissure
Acidic / some ash
Extreme build up of gas cases large explosions
Krakatoa
VEI scale
The Volcanic Explosivity Index is the volcanic equivalent to the Richter Scale. The VEI is used to identify the magnitude of a volcanic eruption. The VEI combines the magnitude and intensity into a single number of a scale of 0 (least explosive) to 8, the most explosive.
How to predict volcanoes
Changes in shape of volcano
Changes in amount of gas being released
Changes in temperature
Tectonic activity - earthquakes
Animal behaviour
Changes in local hydrology
Mass movements
Frequency of volcanoes
Depends on the locations and the size of the eruption.
Large eruptions are less frequent than smaller eruptions.
High frequency of volcanoes in tectonically active areas with magma source.
Lava flow
Magma that has lost its volatility. Can cause damage to farmland, woodland but it moves too slowly to cause damage to humans
Pyroclastics
Hot dense mixture of materials (ash, rock, solid lava pieces, gas - can be toxic) can move at very high speeds (200m/s). It burns anything in its path.
Ash
Ash fallout to the ground can pose significant disruption and damage to buildings, transportation, water and wastewater, power supply, communications equipment, agriculture, and primary production leading to potentially substantial societal impacts and costs, even at thicknesses of only a few millimetres or inches. Additionally, fine grained ash, when ingested can cause health impacts to humans and animals.
Rarely endangers human lives, but it can have devastating effects on the things that we rely upon from day to day. As a result of its fine-grained abrasive character and widespread distribution by wind, ashfall and volcanic ash clouds are a major hazard to aviation.
Gas
Eg. Sulfur dioxide, carbon dioxide(0.4% of earths atmosphere), water (most abundant but harmless)
Most gases originate in the mantle and are transported to the crust and surface by complex interactions. Usually dissolved in magma. Can be problematic because it can cause respiratory issues as SO2 is toxic.
Tephra
Fragmented material regardless of composition and size it includes ash and stones and volcanic bombs
Lahar
Mudflow containing volcanic material. May form when the rock of the pyroclastic flow mixes with water and becomes a quick moving slurry.
Lahars generally occur on or near stratovolcanoes, such as those of the Aleutian volcanic arc in Alaska and the Cascade Range in the Western U.S.
Tsunami
Sea waves generated by violent volcanic eruptions. Eg. Krakatoa (Indonesia) in 1883 killled 36,000. This tsunami was up to 3.5m high
Flooding
Pyroclastic flows can cause flooding as a secondary effect because all the materials coming down can block rivers and lakes causing swelling. They can also melt glaciers and ice caps that cause flooding.
Acid rain
Volcanoes emit gases which include sulfur. When this combines with atmospheric moisture, acid rain results
Climate change (Pinatubo 1991)
Pinatubo 1991
20 million tonnes of sulfur dioxide and ash
12 miles
Very powerful - reached the lower stratosphere.
Close of ash spread out - reflected incoming radiation back to space which lowers the earths temperature.
Sulfur dioxide converted to sulfur aerosols - reflected radiation back to space - also lowered earths temperature.
Northen hemisphere (1992/1993) lower temperatures.
Absorbs infrared radiation emitted from earth - stopping it reflecting back to earth = cooling
2 years for all ash to be removed from stratosphere (short term).
Which hazards are primary
Lava flow
Pyroclastics
Ash
Gas
Tephra
Which hazards are secondary
Lahar
Tsunami
Flooding
Acid rain
Climate change
Volcanic case study
Eyjafjallajokull (Iceland) April 2010
Mid-Atlantic ridge, divergent (constructive plates) - North American and Eurasian plates.
Hot spot underneath Iceland that feeds the magma changed causing more volcanic activity.
1660m tall / ariel extent - 40Km2 / 2.5km wide caldera opening at the top
Southern part of Iceland.
Case study - Risk and probability of loss
Risk - probability of loss
Vulnerability - reduced by capacity, human + physical profile socec systems
HIC - advanced / industrialised
Disaster preparedness, sophisticated
Effusive eruptions (runny)
Basic lava - lower silica content
South Iceland
Sparsely populated - local impacts minimised
Ash - difficult to manage and control
Case study - social effects
Primary
Ash is carried away from the volcano it disperses and becomes in wisible but it can be sucked into the engines of aircraft endangering their operation / Huge amounts of ice were melted causing floods to rush down the nearby rivers, requiring nearly 1,000 people to be evacuated.
The​ ash contaminated drinking water​ supplies.
Ash caused ​respiratory illnesses​ for some locals.
Cancelled flights left many stranded in different countries.
Secondary
Evacuation of farmers and their livestock due to ash / Visibility decreased
Case study - bad economic effects
Primary
Farmland destroyed / flights stopped.
Secondary
Many European countries were forced to shut down their air space because of the ash; the largest such shut down since World War I. It has been estimated that this cost the airlines £130 million per day for the six days that the airspace was closed. This affected several million people and had knock-on travel effects across the globe.
Estimated £102million loss in London due to less tourists.
Case study - bad environmental effects
Primary
Volcanoes are covered by ice caps feeding glaciers, so when they erupt much ice ice melts so flooding and huge ash clouds. As the magma hits the ice it suddenly cools, forming a glass-like material which instantly disintegrates. Explosions of gas within the main vent pulverise the fragments into very tiny particles. As the gas and steam blown from the vent carry this ash into the atmosphere it can rise to great heights where it is caught in high-altitude winds (jet stream).
Debris flows
Secondary
20 farms were destroyed by flooding and ash / part of main route 1 destroyed / government paid to dredge rivers
Case study - short term responses
Area around the volcano was evacuated - 700 people were evacuated from the disaster zone, more had to evacuate in the middle of the night due to flash floods.
European Red Cross Societies mobilised volunteers, staff and other resources to help people affected directly or indirectly by the eruption of the Eyjafjallajökull glacier volcano. The European Red Cross provided food for the farming population living in the vicinity of the glacier, as well as counselling and psychosocial support, in particular for traumatised children.
Case study - long term responses
Icelandic Met Office / BGS :
On the scientific front, there has been a notable increase in volcanic-cloud research since Eyjafjallajökull. Overall, this eruption has prompted the aviation industry, regulators, and scientists to work more closely together to improve the manner in which hazardous airspace is defined, forecast, and communicated.
International Civil Aviation Organization
A specialized agency of the United Nations. It changes the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth.
ICAO formed the International Volcanic Ash Task Force (IVATF) in May 2010, charging it to examine how best to define hazardous airspace and manage aviation risk. The IVATF included representatives from government and industry groups involved in aviation regulation, operations, and scientific investigations.
Case study - prepardness
Diggers ​were in position to dam rivers.
Texts ​were sent to locals with a ​30 minute warning​.
Case study - good economic effects
The ash made the soil so fertile that farmers could produce rapeseed oil and grapes.
Channel tunnel and ferries did extra business
Case study - good environmental effects
Less aircraft noise and 2.8 million tonnes less CO2 due to flight bans.
Fertiliser for the surrounding land wasn’t needed
Nature of volcanic event - destructive plate boundary
Violent volcanic eruptions
One plate is forced beneath the other, descending plate releases water and other volatiles decreasing the mantle melting point - magma and volcanic eruptions.
Nature of volcanic event - conservative plate boundary
N/A - no magma so no volcano
Nature of volcanic event - constructive plate boundary
Mild volcanic eruptions.
Plates spreading - magma is able to rise up due to gaps in the earths crust.
VEI (volcanic explosively index / Magnitude)
This spheres in the illustration represent the volume of erupted tephra. With each step in the scale representing an exclusivity increase of 10 times, of VEI5 is roughly 10x more explosive than a VEI4, and 100x more explosive than a VEI3.
Frequency
Frequency of eruptions varies per volcano. Volcanoes are classed as either active, dormant or extinct. ​An estimated ​50-60 volcanoes erupt each month​, meaning volcanic eruptions are always frequent (and some volcanoes erupt constantly). Usually, a higher frequency eruption means the eruptions are effusive​ whereas low frequency means the eruptions are ​explosive.
Regularity
Volcanic eruptions are regular in that the eruptions on ​each type of boundary are similar (e.g. eruptions on destructive boundaries will regularly be explosive)
Sometimes eruptions may be irregular and not fit patterns.
Predictability
Regularity of eruptions can help estimate when eruptions will take place (i.e. every 10 years). Seismic activity, gases releasing, elevation etc. can all indicate an imminent eruption, but there is no ​definite​ predictions to a volcanic eruption.
