Volcanic Hazards - Formation Of Volcanoes

Question 1

Volcanoes are vents (openings) in the Earth’s crust through which lava,

Answer 1

tephra (ash, dust and fragments of material are produced in a volcanic eruption) and gases erupt.

Question 2

Molten rock beneath the surface is called magma, but

Answer 2

When it is ejected to the surface it is called lava.

Question 3

Magma, in addition to molten rock, may also contain suspended

Answer 3

Crystals and dissolved gases and sometimes gas bubbles. Magma often collects in magma chambers that may feel a volcano turn into a pluton.

Question 4

Underground, the enormous pressure exerted by overlying rocks

Answer 4

Keep the rocks in a semi-detatched state.

Question 5

Fissures and fragments in the crust create area of low pressure that

Answer 5

Allow some of the rocks to become molten and rise.

Question 6

If these molten rock reach the surface

Answer 6

They are said to be extrusive.

Question 7

If they are injected into the crust,

Answer 7

Without reaching the surface they are called intrusive.

Question 8

Active volcanoes

Answer 8

Have erupted within living memory - present

Question 9

Dormant volcanoes

Answer 9

Have erupted within historical record - past

Question 10

Extinct volcanoes

Answer 10

Will never erupt again - never

Question 11

Pyroclasts - origin

Answer 11

In all explosive eruptions

Question 12

Pyroclasts - characteristics

Answer 12

Has broken fragments of rock ejected with velocity

Question 13

Pyroclasts - harmful effects

Answer 13

Large rocks which impact on landing

Question 14

Tephra - origin

Answer 14

In all explosive volcanoes

Question 15

Tephra - characteristics

Answer 15

Collective term 4 airborne pyroclasts (including solidifying magma)

• bombs
• Laphilli
• Ash

Question 16

Tephra - harmful effects

Answer 16

• may spread over distances
• 1500 km
• causes minor/major damage

Question 17

Pyroclastic flow - origin

Answer 17

• explosive eruptions

- caused by eruption collumn

Question 18

Pyrochlastic flow - characteristics

Answer 18

• Hot
• Gas charged
• High velocity flows of Tephra
• Composed of mixture of bombs, lapilli, ash, extremely hot gases - high deposits of pumice

Question 19

Pyroclastic flows - harmful effects

Answer 19

• may extend many kilometres
• high velocity
• lethal mix of bombs, ash, laphilli + hot gases

Question 20

Atmospheric effects- origin

Answer 20

• 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

Question 21

Atmospheric effects - Characteristic

Answer 21

• ash + dust particles (including aerosols) - leads to unusual optical effects

Question 22

Atmospheric effects - harmful effects

Answer 22

• clouding blocks sun from reaching Earths surface
• cools troposphere
• but gases are released, contributing to troposphere warming

Question 23

Troposphere

Answer 23

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)

Question 24

Landslides - origin

Answer 24

Dislocation of level and rocks by magmatic pressure

Question 25

Landslides - characterictics

Answer 25

• huge flows of rocks
• mud
• tephra

Question 26

Landslides - harmful effects

Answer 26

Destruction of property and land

Question 27

Lahars - origin

Answer 27

Rain water or meltwater loosen tephra

Question 28

Lahars - characteristics

Answer 28

• volcanic mudflow
• move downhill
• movement is dependent on topography - almost
• perpenducular (as it is steep) = faster
• gentle slope = slow movement

Question 29

Lahars - harmful effects

Answer 29

• extensive destruction of property
• loss of life
• e.g. Navado Del Ruiz, Colombia 1985
  Mount Pintubo

Question 30

Lava flows - origin

Answer 30

• any eruptions

Question 31

Lava flows - characteristics

Answer 31

• 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

Question 32

Lava flows - harmful effects

Answer 32

• ignition of fires + burial of land + built environment
• relatively slow rate
• little risk to life

Question 33

Poisonous gas - origin

Answer 33

Any eruption

Question 34

Poinsonous gas - characteristics

Answer 34

• ash laden gases

- carbon monoxide, co2, hydrochloric acid, hydrofluric acid, sulfur dioxide

Question 35

Poisonous gases - harmful effects

Answer 35

• 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

Question 36

Flooding - origin

Answer 36

Submarine explosions = displaced large volumes of rock and hence water
- blockage of river by lahars or lava flows

Question 37

Characteristics of flooding

Answer 37

Flood of fresh/salt water.

Either gradual or rapid.

Question 38

Harmful effects of flooding

Answer 38

• dramatic changes in erosion + deposition pattern

- destruction of properties and agricultural land

Question 39

Beneficial effects of volcanism (BEV)

Answer 39

• Tourism
• Soil
• Volcanic ash
• Industrial materials + chemicals
• Geothermal water

Question 40

BEV - TOURISM

Answer 40

Scenic landscapes

Increases potential for tourism

Question 41

BEV - SOIL

Answer 41

Driven from basic/balsaltic lava = fertile

Question 42

BEV - VOLCANIC ASH

Answer 42

• Rich in K
• phosphorus - rich in natural fertilisers
  THIS explains POPULARITY 4 SETTLING around these areas

Question 43

BEV - INDUSTRIAL MATERIALS + CHEMICALS

Answer 43

• sulfur
• pumice
• boric acid
• ammonia
• silica - cosmetics, hair care etc

Question 44

BEV - GEOTHERMAL WATER

Answer 44

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.