Forms Of Volcanic Hazards

Question 1

Primary effects

Answer 1

Occur immediately along with the event

Question 2

Secondary Effects

Answer 2

Direct consequence of the event but not immediate

Question 3

Lahars

Answer 3

. Mixture of hot or cold water and rock fragmented which flow down the steep side of a volcano
. Form when erupted volcanic material gets saturated during heavy rain
. Grow as they travel picking up material
. Steep slope needed so most common on strato volcanoes
. When flow stops they set like concrete
. Destroy anything in path

Question 4

Mudflows

Answer 4

. Flow of water that contains large amounts of suspended particles and silt
. Only deposits the coarsest part of its land, causes irreversible sediment entrainment
. High viscosity
. Occur in steep slopes were vegetation does not prevent rapid erosion
. Rain + erodible material increase chance
. Fast as 100km per hour
. Deposits are mixtures of silt, boulders, organic material
. As high as 3-6m high

Question 5

Tephra

Answer 5

. Fragmented material produced by a volcanic eruption
. Unconsolidated pyroclastic material
. Variety of material e.g. crystalline, glassy particles from cooling magma
. Fall to ground and buildings
. Lead to plant burial and strip trees of branches

Question 6

Nueés ardentes

Answer 6

. Turbulent, fast moving cloud of hot gas and ash
. Form during explosive eruptions as columns of erupted material collapse or when volcanic rock collapses
. Flow downslope into valleys
. 80km + per hour
. 200 C - 700 C
. Spread laterally, near group with larger rocks
. Escape by foot or vehicle is nearly impossible

Question 7

Lava flows

Answer 7

. Streams of molten rock that poor from an erupting vent
. Speed depends on viscosity, steepness, lava type rate of production
. Viscosity increases with silica, decrease with water + higher temp
. Flows slowly so rarely causes death
. Destroys everything in path, can’t use land after
. Explodes when interacts with water

Question 8

Gases

Answer 8

. Given off by active and dormant volcanoes
. Most common are water vapour (most abundant) , co2, sulfur dioxide + hydrogen sulfide
. Sources inc. ground water, earth’s atmosphere, absorbed components of the Earth’s crust
. Can kill by acidic corrosion, cause water to be acidic
. Magma contains dissolved gases
. Escape from pyroclastic flows, lahars + lava flows
. Gases separate as magma rises towards surface where pressure decreases
. Gases travel long distances in hemisphere

Question 9

Acid rain

Answer 9

. Rain with high levels of hydrogen ions which can destroy plans, equation life and infrastructure
. Caused by emissions of sulphur dioxide and nitrous oxide which react with water molecules in atmosphere
. Nitrous oxide can be produced naturally by lighting
. Sulphur produced by eruptions
. Makes rivers acidic
.

Question 10

Pyroclastic flows

Answer 10

. Dense, fast moving, flow of solidified lava pieces, volcanic ash and hot gases
. Caused when the the column of lava, ash and gases expelled from a volcano in an eruption loose upward momentum and fall back to the ground
. Or caused when volcanic material from an eruption moves down the volcano sides
. Can form when a lava flow/dome become to steep and collapse
. Very hot, up to 1000 C
. Burns anything in path, as high as 200 m/s
. May = flood as streams are blocked
. Most deadly hazard
. Produce deposits of ash and rock
. Hard to escape, even by car

Question 11

Ash fallout

Answer 11

. Consists of fragments of rock, mineral and volcanic glass from eruptions
. Formed during eruptions when dissolved gasses in magma expand and escape
. Ash piles on roofs causing them to collapse
. Cause fertile soils
. Tiny size and low density means particles travel long distances
. Ash columns moved by wind = ash plume