Volcanoes Flashcards
What is magma?
Molten rock below the surface
What is lava?
Molten rock above the surface
What does extrusive mean?
When lava and other materials reach the surface
What does intrusive mean?
Material that is injected into the crust
What is igneous rock?
Rocks formed from cooled magma
What is pyroclastic material?
Material ejected from the volcano as fragments
What are fissure eruptions?
1) Lava erupts from an elongated fissure of the main central vent
2) Lava fills up hollows creating a dome shape
3) Cooling produces columnar jointing
•Comprised of basalt
•E.g. Giants causeway, N Ireland
What are dome volcanoes?
1) Lava from central vent and acid lava quickly solidifies forming a steep sided convex cone with many layers
•E.g. Mt St Helens, USA
What are shield volcanoes?
1) Lava flows from central vent and spreads over a large area before solidifying giving it a cone-like appearance with long, gentle sloping sides with many layers
•E.g. Mauna Loa, Hawaii
What are ash and cinder cones?
1) Fine ash and cinder are ejected from central vent, layering up creating a shallow sided, concave cone
•E.g. Mt Etna, Italy
What is caldera volcano?
1) Gas builds up in the magma chamber causing an explosion
2) Sides of the crater subside
3) Craters can be flooded by the sea creating lagoons
What are magma plumes?
•Vertical columns of extra-hot magma that rises up from the mantle
• Volcanoes can form above magma plumes
•Can create chains of island e.g. Hawaii
How are magma plumes formed?
1) Radioactive decay in the Earth’s core heats the lower mantle, creating plumes of magma with thermal currents
2) These currents can cause plate movement or burn through the lithosphere, creating a hotspot volcano
3) The hotspots stay fixed whilst the plate above moves causing a chain of extinct volcano -> Bends in the chain can show plate movement
What do active volcanoes mean?
Erupted in living memory like Mt Etna, Italy
What do dormant volcanoes mean?
Erupted in historic record like Mt Kilimanjaro, Tanzania
What do extinct volcanoes mean?
Will not erupt ever again like Ben Nevis, Scotland
How to measure volcanic eruptions?
Measured using volcanic explosivity index which measures the volume of ejected material
-No characteristic mark on the scale
-Low end -> Hawaii and Icelandic eruptions
-High end -> Super volcanic eruptions
Info bout Basaltic lava:
-Found at constructive margins
-Hot 1200°C, runny and low viscosity -> Flows for a long time
-Low silica content 45-52%
-Flows like rivers of molten rock as it takes longer to cool
-Keeps it’s gas content so it’s more mobile
-Produces extensive, gently sloping landforms
-Volcanoes erupting basaltic lava do so frequently and continuously
-Relatively gentle but frequent eruptions
-Not violet
-Lava and steam erupts
-Underwater = ocean ridges formed e.g. disused along mid-Atlantic ridge
-On land = rift valleys, magma can rise making land thinner so it can break the surface
-Hot spots = Maura Loa, Hawaii - forming gentle sided shield volcanoes
Info about Andesitic lava:
-Found at destructive margins
-Cooler (800 °C) and high viscosity so flows more slowly over shorter distance
-High silica content 52-63%
-Erupt intermittently and are short-lived
-Flows short distances as soon cools and solidifies
-Steep-sided, localised features
-Less frequent eruptions but are violent because of gas build up
-Pyroclastic - as, rock, gases and steam + lava ejected
-Subduction zones = melting of the plates forms magma, which rises to volcano surface. Because this lava is viscous it forms blockages in the volcano vents, causing pressure to build which is cleared by violent eruptions
-Island arcs = Mt. Pelee, Martinique
How do you predict volcanoes?
-Measure seismic activity and ground deformations
-Changes in CO2 and O2 signify imminent eruptions
-Bulges on volcano sides
Pyroclastic flow
-Mixture of super-heated gas, ash, lava and volcanic rock
-Travels downslope
-High speeds of 80-200Km/h
-Travels around 10-15Km
-Relatively little warning due to speeds which can cause widespread death and destruction
-Temperatures of 350-1000°C
- occurring at subduction zones, commonly with andesitic lava
Pyroclastic flow impacts:
-Widespread destruction and death due to high speeds e.g. burning and burial under debris as it carries away anything in its path
-Extreme temperatures can ignite fires
-Ice and snow can melt due to extreme temperatures
-Risk of serious burns
-Causes floods and lahars
Nuee ardente
-Means glowing cloud
-Contains more dense material
-Normally found 50Km from source
Tephra
-Rock fragments ejected during an eruption, large fragments land close to the source whereas small fragments can travel great distances
-Ash can cause breathing difficulties, block sunlight and alter temperatures
Tephra and nuee ardente: impacts
-Endangers aviation + infrastructure
-Damage crops
-Can cause health problems to humans and animals
-Can interrupt communication n
Mudflows/Lahars
Occurs when ash and volcanic material mix with water
-Flows at speeds upto 60Km/h
-Highly erosive
-Engulf anything they pass over
-Occurs in glaciated areas due to rapid ice melting
Mudflows/Lahars: Impacts
-Crushes, abrades or carries away anything in its path
-Can melt snow and ice
-Destroys bridges and roads
-Silts up rivers causing future flooding
-Can cause flooding
-Trap people in hazardous areas
Lava flows
-Lava flowing down the volcano sides
-Slow flow rates allow evacuation
-Low viscosity lava travels at 10Km/h and may cover thousands of Kms
-Destroys anything it passes over
Lava flows: Impacts
-Knocks over, hurries or surrounds anything
-Can trigger a lahar
-Can cause water to evaporate immediately creating a molten shower
-Can cause methane gas build from vegetation creating explosions
Volcanic gases and acid rain
-CO2 and SO2 released upon eruption
-Can be harmful to humans and animals -> breathing difficulties + harm wildlife
-Gases released react with water vapour creating acid rain e.g. SO2 forms weak sulfuric acid
-This damages ecosystems and infrastructure like metal and stone start to deteriorate
3 Volcano case studies
•Nevado del ruiz eruption and lahar, Columbia 1985
-25,000 dead in Armero
-$218 million worth of damage
•Mt St Helens. Washington State, USA may 1980
-57 dead
-Pyroclastic flows and lahars formed
-Destructive plate boundary =
Stratovolcano
•Mt Kilauea, Hawaii
-Hot spot chain -> Basaltic lava
- Low viscosity so it has frequent,
predictable eruptions
Environmental impacts of volcanic hazards
-Ecosystems damaged and destroyed due to fallout and flows
-Acid rain can cause acidification of aquatic ecosystems killing some plants and animals, damages tree leaves and removes nutrients from soil which damages forests
-Volcanic gases contribute to enhanced greenhouse effect and add to global warming
Clouds of ash reduce amount of sunlight reaching earth, decreasing temps over large areas
-Changes in weather periods (adds tk point above)
-Crop damage
Social impacts of volcanic hazards
-Deaths and injuries
-Infrastructure and buildings destroyed -> Homes, places of work, roads (to transport trade)
-Wildfires starting due to pyroclastic and lava flows damaging buildings
-Mudflows and flooring from ice melts can cause further damage and deaths
Economic impacts of volcanic hazards
-Eruptions can destroy businesses, ash clouds prevents aviation and damaged crops which damages the economy of the region and the country
-Expensive repair costs
-Eruptions and scenery can attract tourists, boosting the economy
political impacts of volcanic hazards
-Damages crops can cause food shortages, leading to conflict and political unrest
-Governments spending money on repairing damaged roads and building rather than hospitals and schools, the country may not develop as quick
Short term responses to volcanic hazards (in mediating before, during or after)
-Evacuating people at risk
-Emergency supplies
-International aid and deployment of emergency services
Long term responses to volcanic hazards (before, during and after)
-Alert systems
-Risk managements
-Storage of emergency food and water + aid supplies
-Creation of Hazard maps to aid evacuation
What is preparedness?
About what happens before an eruption to minimise risk or vulnerability
Examples of preparedness for volcanic hazards
-Monitoring systems to predict an eruption might occur and evacuation plans
-Authorities stopping people accessing the area around a volcano
-Emergency kits and knowing where local emergency shelters are
-Search and rescue teams set up
What is mitigation/prevention?
Authorities stopping land surrounding the volcano being developed
What is adaption?
The action of changing peoples behaviour or surrounding to minimise risks and maximise benefits of living near a volcano
How do they monitor gas emissions?
-Main basis sulphur dioxide
-Increase in gas quantity can signal the start of volcanic activity
-Gas levels drop rapidly hours before the eruption
What is ground deformation?
-Magma moving in the lithosphere can deform the ground above
-Volcanoes swell prior to eruption due to the gathering of magma
What is thermal monitoring?
-Magma movement and gas changes can alter temperatures
-Magma heats up groundwater
What is satellite and remote sensing?
-Monitoring changes in volcanoes from surface
-Images can be used to compare to previous times
What is mass movement and mass failures?
-Can happen before, during and after eruptions
-Evidence of past activity and deformation
What is seismic activity?
-An increased frequency and intensity of earthquakes can signal an imminent eruptions
-Detected by seismometers producing seismographs
What is a short period quake?
Caused by breaking and fracturing of rock as magma is forced up
What is a long period quake?
Increase in gas pressure throughout the vents and chambers
What are harmonic tremors?
Magma pushing against rock below surface creating a humming effect
Examples of adaption for volcanic hazards
-Buildings strengthened to reduce the chance of collapsing
-Fertile soil great for farming
-Increased tourism, a tourist spot
Examples of mitigation/prevention for volcanic hazards
-Authorities preventing land surrounding the volcano
