Volcanoes

Question 1

Benioff zone

Answer 1

The point at which the sun ducted plate melts
As the plate begins to melt it begins to rise up through fissures and cracks in the continental plate and burns their way through overlying rock. Eventually forming explosive volcanoes

Question 2

Andesitic lava

Answer 2

Has a viscous nature (flows less easily) this creates explosive volcanoes

Question 3

Shield volcanoes

Answer 3

Gentle slopes and wide base
Frequent erosion of basaltic lava
Lava flows at high speeds for long distances before cooling
Usually non violent eruptions
Non- viscous lava due to basaltic composition
Found at constructive boundaries

Question 4

Composite volcanoes

Answer 4

Steep sided with distinctive cone shape
High with narrow base
Explosive eruptions of lava and ash
Layers of alternating ash and lava
Viscous lava builds up in layers and does not flow far from the crater
Found at destructive boundaries
Secondly or parasitic cones formed when the main vent gets blocked

Question 5

Manama viscosity; Silica levels

Answer 5

More silica, more viscous, meaning it flows more slowly
High silica- more explosive
Low silica- effusive

Question 6

Viscosity

Answer 6

How easy a liquid flows

A thicker magma means that the gases in the volcano (CO2) can’t escape

Question 7

Eruption styles: pinian

Answer 7

Highly explosive, large eruption column (up to 45km), range of rephrased and pyroclastic fallout, including flows

Question 8

Eruption styles: Pelean

Answer 8

Explosive eruptions with range of tephra with nuee ardent, pyroclastic flows

Question 9

Eruption styles: Icelandic

Answer 9

Low viscosity and highly effusive. ,au have water therefore phreatic

Question 10

Eruption styles: Hawaiian

Answer 10

Effusive, minor explosively, with fire fountain and low viscosity lava flow

Question 11

Eruption styles: Vulcanian

Answer 11

Higher gas build up than Strombolian, highly viscous lava. A series of shots lived explosions, with tephra bombs

Question 12

Eruption styles: Strombolian

Answer 12

Eruption with gas bubbles so eject tephra (ash)

Question 13

Primary effects

Answer 13

Occur immediately along with the event

Question 14

Secondary effects

Answer 14

Direct consequence of the event but not immediately

Question 15

Mudflows

Answer 15

Flows of water than contains large amounts of suspended particles and silt. It has a higher density and viscosity than a streamflow and can only the coarsest part of the load; this causes irreversible sediment entrainment
They may rush down mountainsides at speeds as great as 100km per hour, and can cause great damage to property. Can be 3-6m wide
What to do in case of a mudflow: drive carefully, leave area, watch for patterns in storms water drainage

Question 16

Tephra

Answer 16

Fragment material produced by a volcanic eruption regardless of composition, fragment size
Once clasts have fallen to the ground, they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff
Largest fragments, blocks and bombs have a diameter of 2.5 inches
What to do: stay inside or leave area

Question 17

Lava flows

Answer 17

A mass of flowing or solidified lava
Least hazardous
Streams of molten rock that pour from an erupting vent. The speed at which lava moves across the ground depends on several factors, including type of lava and viscosity, steep end of ground over which it travels.
Happens at shield volcanoes
Can move 1.3km and be 100m thick
Melt snow and ice, causing floods
What to do: get to higher ground or evacuate

Question 18

Gases

Answer 18

The must abundant volcanic gas is water vapour, which is harmless. However significant amount of CO2, sulphur dioxide, hydrogen sulphide and hydrogen halides can also be emitted from volcanoes
These gases are toxic and can harm people
What to do- leave area to avoid breathing in or contact with gases

Question 19

Acid rain

Answer 19

Rainfall made acidic by atmospheric pollution
Can cause environmental harms mainly to forest and lakes
Caused by emissions of sulphur dioxide and nitrogen oxygen, which react with the water molecules in the atmosphere to produce acid
What to do- stay inside or evacuate

Question 20

Ash fallout

Answer 20

Volcanic ash is formed during explosive volcanic eruptions when dissolved gases in magma expand and escape violently into the atmosphere.
Occurs immediately after and eruption
What to do- stay inside or evacuate

Question 21

Pyroclastic flows/ Nuées Ardentes

Answer 21

Fast moving current of hot gas an volcanic matter that moves away from volcano about 100km/h on average but can reach 700 km/h
Destructive and deadly
What to do- evacuate as soon as or before eruption occurs

Question 22

Lanark’s

Answer 22

Mixture of joy or cold water and rock fragments which flows down the steep side of a volcano
For, when eruption volcanic material gets saturated during periods of heavy rain. This does not have to be during or immediately after an eruption but may be some time afterwards
Can grow as they travel
Destroy anything in their path

Question 23

Monitoring volcanoes: seismic activity

Answer 23

Measured using local seismographs . Monitoring infra sound sub audible sound below 20 hertz. As many volcanoes are found at or on plate boundaries, it’s very difficult to observe seismic activity. All volcanoes react differently

Question 24

Monitoring volcanoes: gas emissions

Answer 24

As magma nears the surface, gases escape, SO4 emitted, increasing amounts suggest a rise in magma. Drop in gas before eruptions suggest sealing of gas passage by hardened magma. Measure emissions at volcano or dirtier afield from a safer distance

Question 25

Monitoring volcanoes: geological observations

Answer 25

GPS- calculate vertical movement by satellite
Distance measurement- electronic distance measurement measure horizontal movement
Slope angle- a tilt meter is used to measure changes in the slope on a volcano side. Installed When volcano active, when magma rises to chamber volcano expand