Volcanic Hazards - Formation Of Volcanoes Flashcards
- process of formation
Volcanoes are vents (openings) in the Earth’s crust through which lava,
tephra (ash, dust and fragments of material are produced in a volcanic eruption) and gases erupt.
Molten rock beneath the surface is called magma, but
When it is ejected to the surface it is called lava.
Magma, in addition to molten rock, may also contain suspended
Crystals and dissolved gases and sometimes gas bubbles. Magma often collects in magma chambers that may feel a volcano turn into a pluton.
Underground, the enormous pressure exerted by overlying rocks
Keep the rocks in a semi-detatched state.
Fissures and fragments in the crust create area of low pressure that
Allow some of the rocks to become molten and rise.
If these molten rock reach the surface
They are said to be extrusive.
If they are injected into the crust,
Without reaching the surface they are called intrusive.
Active volcanoes
Have erupted within living memory - present
Dormant volcanoes
Have erupted within historical record - past
Extinct volcanoes
Will never erupt again - never
Pyroclasts - origin
In all explosive eruptions
Pyroclasts - characteristics
Has broken fragments of rock ejected with velocity
Pyroclasts - harmful effects
Large rocks which impact on landing
Tephra - origin
In all explosive volcanoes
Tephra - characteristics
Collective term 4 airborne pyroclasts (including solidifying magma)
- bombs
- Laphilli
- Ash
Tephra - harmful effects
- may spread over distances
- 1500 km
- causes minor/major damage
Pyroclastic flow - origin
- explosive eruptions
- caused by eruption collumn
Pyrochlastic flow - characteristics
- Hot
- Gas charged
- High velocity flows of Tephra
- Composed of mixture of bombs, lapilli, ash, extremely hot gases - high deposits of pumice
Pyroclastic flows - harmful effects
- may extend many kilometres
- high velocity
- lethal mix of bombs, ash, laphilli + hot gases
Atmospheric effects- origin
- Eruption collumns which may extend a few collumns into the atmosphere
- allows ash to be carried by high level winds - pressure of heat drives this
Atmospheric effects - Characteristic
- ash + dust particles (including aerosols) - leads to unusual optical effects
Atmospheric effects - harmful effects
- clouding blocks sun from reaching Earths surface
- cools troposphere
- but gases are released, contributing to troposphere warming
Troposphere
the lowest region of the atmosphere, extending from the earth’s surface to a height of about 6–10 km (the lower boundary of the stratosphere)
Landslides - origin
Dislocation of level and rocks by magmatic pressure
Landslides - characterictics
- huge flows of rocks
- mud
- tephra
Landslides - harmful effects
Destruction of property and land
Lahars - origin
Rain water or meltwater loosen tephra
Lahars - characteristics
- volcanic mudflow
- move downhill
- movement is dependent on topography - almost
- perpenducular (as it is steep) = faster
- gentle slope = slow movement
Lahars - harmful effects
- extensive destruction of property
- loss of life
- e.g. Navado Del Ruiz, Colombia 1985
Mount Pintubo
Lava flows - origin
- any eruptions
Lava flows - characteristics
- the rate of flow depends on temperature
- increased temperature = fast
- decreased temperature = slow
- as lava cools viscosity ☝️and speed 👇 till less than walking speed.
- as it cools a solidified surface is produced
- volume + range are variable - may extend up to 100 km from source
Lava flows - harmful effects
- ignition of fires + burial of land + built environment
- relatively slow rate
- little risk to life
Poisonous gas - origin
Any eruption
Poinsonous gas - characteristics
- ash laden gases
- carbon monoxide, co2, hydrochloric acid, hydrofluric acid, sulfur dioxide
Poisonous gases - harmful effects
- toxic
- contributes to acid rain
- 1700 people suffered from asphyxiation by co2 in 1968 eruption at Lake Monoun Cameroon
- may cause long term starvation and wodespread diseases
Flooding - origin
Submarine explosions = displaced large volumes of rock and hence water
- blockage of river by lahars or lava flows
Characteristics of flooding
Flood of fresh/salt water.
Either gradual or rapid.
Harmful effects of flooding
- dramatic changes in erosion + deposition pattern
- destruction of properties and agricultural land
Beneficial effects of volcanism (BEV)
- Tourism
- Soil
- Volcanic ash
- Industrial materials + chemicals
- Geothermal water
BEV - TOURISM
Scenic landscapes
Increases potential for tourism
BEV - SOIL
Driven from basic/balsaltic lava = fertile
BEV - VOLCANIC ASH
- Rich in K
- phosphorus - rich in natural fertilisers
THIS explains POPULARITY 4 SETTLING around these areas
BEV - INDUSTRIAL MATERIALS + CHEMICALS
- sulfur
- pumice
- boric acid
- ammonia
- silica - cosmetics, hair care etc
BEV - GEOTHERMAL WATER
As water reaches the surface it proves as useful = harnessed for energy
Homes heated by this method
E.g. Italy, US, Mexico, New Zealand and former USSR - naturally occuring heat is used to produce electricity.
