Volcanic hazards Flashcards
(81 cards)
1
Q
What is a volcano?
A
A vent in the Earth’s crust where molten rock, gas and heat can escape a magma chamber
2
Q
Lava
A
Molten rock above or on the Earth’s surface, forms extrusive igneous rocks
3
Q
Magma
A
Molten rock below the Earth’s surface, forms intrusive ingneous rock
4
Q
Magma types
A
Mafic
Ultramafic
Intermediate
Felsic
5
Q
Mafic magma
A
Rich in Fe and Mg
Dark colour
Basalt (fine), Dolerite (intermediate) or Gabbo (coarse)
6
Q
Intermediate magma
A
Grey colour
Andesite (fine), Microdolerite (intermediate), Diorite (coarse)
7
Q
Felsic magma
A
Rich in silica
White/pink colour
Rhyolite (fine), Microgranite (intermediate), Granite (coarse)
8
Q
Sill
A
Part of sub volcanic plumbing system that follows sedimentary units and bedding planes
9
Q
Dyke
A
Part of sub volcanic plumbing system that cuts across sedimentary units and bedding planes
10
Q
Batholith
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Part of sub volcanic plumbing system, crystallised magma chamber
11
Q
Volcanic neck
A
Part of sub volcanic plumbing system that connects magma chamber to surface of the Earth
12
Q
Intrusive igneous rocks
A
Cooled slowly, therefore, deeper in the Earth and more insulated
Produces coarser crystals
13
Q
Extrusive igneous rocks
A
Cool quickly
Produce fine crystals or glass
14
Q
Volcanic Explosivity index, VEI
A
- Measures how explosive a volcanic eruption is
- Based on volume of explosive products erupyed and height of eruption cloud
- Logarithmic scale of 0-8
15
Q
Lake Toba
A
Crater lake in Indonesia
- VEI of 8
- Dust and sulphurous gases in the atmosphere cooled the Earth
- Humans almost wiped out
16
Q
Super-volcano affects
A
Severe burning and death Ash collapsing house roofs Suffocation Crop failure Volcanic winter
17
Q
Vesuvius
A
- VEI of 5
- Deadliest in European history
- Petrified the city
18
Q
Mt Tambora - Year without a summer
A
- VEI of 7
- Global temperature dropped by almost 1 degree
- Caused major food shortages and famine
19
Q
Krakatau
A
- VEI of 6
- Volcano tore itself and the island apart
- Landslide exposed magma chamber and water mixed w/ it and generated a huge explosion
- Produced massive pyroclastic density currents
20
Q
Living near a volcano - benefits
A
Energy (e.g. geothermal)
Tourism
Nutrient rich soil
Mineral resources
21
Q
Geothermal energy process
A
- Pump cold water down
- Heat from magma warms the water and produces steam
- Steam turns turbine to generate electricity
22
Q
How do volcanoes assist in fertilising soil?
A
- Volcanic ash and lava weather away and erode
2. Products of erosion introduced key nutrients for plants into the soil (k, Fe, P)
23
Q
Mineral resources provided by volcanoes
A
- Diamond
- Copper
- Nickle
- Aluminium
- Gold
- Lead
- Zinc
24
Q
Fissure volcanoes
A
- Long linear vent
- Effusive eruption producing basaltic lavas
- Fed by dykes that connect the magma chamber to the surface
- Found in rift zones and spreading centres
25
Shield volcanoes
- V. shallow slopes
- Basaltic magma w/ low gas content
- Made of lava flows from effusive eruptions
- Lava is v. hot and runny and so spreads over large distances
- Found at spreading centre and intraplate hotspots
26
Dome volcanoes
- Formed by relatively small bulbous masses of lava
- Viscous basaltic-rhyolite lava that cant travel far from vent as it is cooler
- Grows by slow expansion
- Found on convergent plates
- Mostly effusive but some explosive eruptions
27
Ash-Cinder volcanoes
- Small, grows v. quickly and steep
- Often near or attached to larger volcano
- Gas rich magma
- Made of unconsolidated ash, pyroclastic material, scoria and ejected rock fragments
- Cone-shaped, circular base and crater with a vent
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Composite (stratavolcano) volcanoes
- Consists of altering layers of lava and pyroclastic material
- Felsic-intermediate magma composition
- Explosive type eruptions
- Steep, cone-shaped and w/ crater
- Lava flows from craters or from fissures
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Caldera volcanoes
- Large volcanic eruptions that empty their magma chamber
- Ground above then falls into empty magma chamber to form a caldera
- Steep basin shaped depression
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Effusive eruptions
- Produces lava flows that ooze out of vent
- Magma has low viscosity
- Typically Fe-Mg rich
- Low water/gas content
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Explosive eruptions
- Produces tephra
- Magma has high viscosity
- Typically Si rich
- High water/gas content
- Gas expands rapidly generating an explosion
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Hydrothermal eruptive material
- Just hot water, no magma
- Explosive pulverized rock producing ash
- Generally v. small and short
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Phreatic eruption
- Heat from old magma interacts with water
- No new magma
- Explosive, producing ash
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Phreatomagmatic
- New magma and water
| - V. explosive
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Icelandic (fissure) eruptions
- Effusive eruption
- Flows out of long parallel fissures
- Basaltic lava
- Builds large plateaus of lava
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Characteristic of basaltic lava
Hot
Gas poor
Low viscosity
37
Hawaiian eruptions
- Effusive eruption
- Lava flows out of central vent and radial fissures
- Basaltic lava
- Builds a shield volcano
38
Strombolian eruption
- Explosive, mild sized, regular eruptions
- Magma is more viscous
- Basaltic or andesitic magma
- Caused by bursting slugs in volcanic conduit
- Produces ash and pyroclastic density currents
39
What is a slug?
Large bubble of gas
40
Vulcanian eruption
- Explosive eruption
- Short, violent and small explosion of viscous magma
- Andesite or rhyolite magma
- Caused by fragmentation of plug in volcanic conduit
- Ejection of cinders and lava bombs
- Produces cinder cones
41
Pelean eruption
- Viscous magma produces lava domes that then collapse
- Adesitic or rhyolite magma
- Produces many pyroclastic density currents
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Plinian eruption
- Largest and most explosive
- Fragmentation of gassy and v. viscous magma
- Rhyolitic magma
- Produce large columns of ash and pyroclastic density currents
- Magma chamber completely emptied
43
Characteristics of flood basalt eruption
- Large scale effusive, short and silent
- HUGE lava volume
- Produces thick lava flows that cover huge areas
- Basaltic magma is v. hot and runny causing the lava to flood
- Create lava plateaus and mountain ranges
44
Formation of flood basalt eruptions
Large mantle plumes produce them by
- Hot materials from core-mantle boundary rising
- Plume hits base of the crust and raises the temp.
- Huge amount of melting occurs
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Central Atlantic magmatic province
Flood basalt eruption 200 million yrs ago
Covered 10 million km2 of the Earth's surface
Split the super continent of Pangea
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Flood basalts on the moon
Marias:
| The dark patches on the lunar surface, these are evidence for huge basalt eruptions
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Deccan traps, India
- Successive layers of thick basalt rock from lava flow
- Caused by a deep mantle plume in the reunion island hotspot
- Produced a rift valley
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Deccan traps and the dinosaurs
- Release of large volumes of volcanic gases, like sulphur dioxide, caused an intense climate change
- Global temp. dropped by 2 degrees
- V. toxic world was produced
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Siberian traps, Russia
- 250 million yrs ago
| - Most likely caused by large magma plume
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The great dying, Permian-Triassic mass extinction
Most devastating mass extinction, caused by the volcanic gases, emitted by Siberian traps, causing severe climate change
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Hot water springs and what can they help predict?
- When H2O comes into contact w/ hot rocks heated by magma underground
- Can change temp. or chemistry quickly, CAN signify an impending eruption
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New thermal areas and what do they indicate?
- New areas of hot spring activity or reactivation of old hot springs
- indicate movement of magma
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Geysers
- Underground plumbing systems where a cavity of H2O is heated by magma and hot rock
- This vaporises the H2O and generating a pocket of steam
Steam rapidly rises to surface, displacing H2O on the surface above
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Geysers and predicting eruptions
Geysers can be regular and therefore not a clear sign of an eruption. However, change in geyser behaviuos can be.
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Acidified H2O before an eruption
- Lakes and seas near volcanoes become saturated w/ CO2 and SO2, producing sulphuric and carbonic acid
- pH 0.1 can be reached, causing severe burns and death
- Lake ecology is killed
- Rapid change CAN signify an eruption
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Drying up of springs/wells before an eruption
Movement of magma produces cracks, causing H2O to drain away
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Fumaroles and relation to an eruption
- Heavy and toxic gases released in large amounts from vents
- Sink to ground forming a toxic pocket of gas that travels downhill to into valleys/depressions
- Can be regular, but a change in behaviour could signify an eruption
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Effects of fumaroles
Humans and animals - asphyxiation, respiratory diseases and skin burns
Famine due do crop and vegetation death
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Lake Nyos: Consequences
- Many people and livestock died
- Thousands made ill w/ respiratory diseases, lesions and paralysis
- Lake dropped 1m, turned red and knocked down bank trees
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Lake Nyos: What happened?
- Volcanic gasses became trapped at lake bottom
- Earthquake or landslide released the heavy gases into atmosphere
- Gases hugged the ground and travelled dowm=n valleys and smothered villages
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Lake Nyos: Precautions now takes
- Degassing station penetrates lake bed and releases any trapped gases
- Prevents gas build-up
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Plant dieback in relation to an eruption
- Affect of toxic gases/liquids released from volcano
- Trees/plants yellow and die as a result of increased CO2 in the soil
- New areas of dying plantlife CAN be a sign of an eruption
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Landslides in relation to an eruption
Volcanoes are weak structures and so landslides near summit, w/ no other explanatory cause, could be due to movement of magma FRACTURING EARTH SURFACE or GAS RELEASE
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Soil temp. in relation to an eruption
- Ground near volcanic systems can be v. hot
| - Soil heating up/cooling down indicates activity below surface
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Ground uplift in relation to an eruption
- Ground level rising/falling
| - Can indicate magma, H2O and gas is building up underground causing an uplift
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Volcanic earthquakes in relation to an eruption:
| VOLCANIC TECTONIC EARTHQUAKES
Caused by regional tectonic forces OR injection of new magma
Good indicators of an eruption
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Volcanic earthquakes in relation to an eruption:
| LONG PERIOD EARTHQUAKES
Caused by vibrations from movement of magma/fluid OR pressure build-up causing rocks to break
Good indicators of an eruption
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Harmonic tremors in relation to an eruption:
- Specific type of long-lasting rhythmic seismic signal
- Caused by magma moving through fractures in rock
- V. good indicator of an imminent eruption
69
Changes in wildlife in relation to an eruption:
ANECDOTAL
| Reported that animals behave strangely prior to an eruption and migrate away from volcanic area
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What is ash fall
- Rain of volcanic ash
- Small abrasive particles of glass
- Travels v. far
- Severity depends on layer thickness & grain size
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Ash effects on humans
- Can be irritating or deadly
- Small particles, < 4 micrometres, can be breathed into the lungs alveoli
- Mixes w/ H2O to form a type of concrete in the lungs, resulting in a respiratory disease
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Ash effects on plants
- Ash cloud can block out sun for days-years
- Layer of ash covers leaves
- Plants die
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Ash effects on buildings
- Layers of ash can become v. heavy
- Ash is twice as heavy when wet
- This can cause roofs to collapse
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Ash effects on electrical systems
- Wet volcanic ash is conductive
| - Shorts out electrical systems and damages power lines
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Ash effects on air travel
- Scratches windows obscuring visibility
- Shuts engines down by fusing w/ turbines
- St Elmos fire
76
What is a St Elmos fire
- Type of lightening
- Electrical field is caused by static build-up in a volcanic ash cloud
- Lightening caused by ionisation of the air around sharp objects in the electrical field
- N and O in atmosphere cause blue fluorescence
77
Ash effects: Lahar's
- Volcanic mudflow w/ consistency similar to wet concrete
- Consists of H2O, ash, pyroclastic material and rock
- Solidifies once it stops moving
- Fast moving, can travel up to 10s of m/s
78
Lahar causes
- Melting snow/glaciers come in contact w/ lava or pyroclastic material
- Rainfall or ash deposit after eruption
- Breakout of a crater lake
- Landslides
- Can form during/after an eruption
79
Volcanic explosion aftermath: Sulphurous gases
- Air had eggy smell
- Leaves/fruit fell from trees
- Persistent fog
- Respiratory problems, struggling to breath and death
80
Volcanic winter
- When enough SO2 and ash is released into upper atmosphere and the albedo of the planet increases
- Reflects sunlight back to space
- Cools the planet down (climate change)
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Volcanic explosion aftermath: Erosion of the volcano
- Volcanic structures are not particularly strong, the shape is maintained by volcanic activity
- Once volcanism has ceased, the volcano begins to rapidly erode
- Eventually, only the plug remains
