Volcanoes

Question 1

Where in the world do volcanoes occur?

Answer 1

• along the coast lines
• lots of anomalies scattered around the oceans
• around the edge of the Pacific Ocean (pacific ring of fire)
• hardly any in middle of big land masses
• found at constructive and destructive plate margins

Question 2

Why do volcanoes occur at destructive and constructive plates?

Answer 2

This is either due to subduction which causes pressure melting of past crust which rises up through the surface (destructive) or pressure where the plates move apart is low so magma rises (constructive)

Question 3

Why are there some anomalies ?

Answer 3

Mantle plumes (areas of rising hot magma), which causes melting of material in the lithosphere which rises through fissures and causes volcanoes

Question 4

Why do we get chains of volcanoes e.g. Hawaii

Answer 4

As the plates are constantly moving so little volcanoes keep forming… these become dormant as don’t erupt

Question 5

What are the 2 types of volcanoes?

Answer 5

Shield
Composite (cone)

Question 6

Features of shield volcanoes (constructive boundaries)

Answer 6

• gentle slopes and a wide base
• frequent eruptions of basic lava
• lava flows at high speeds and long distances before cooling
• usually non violent eruptions
• non viscous lava due to basaltic composition (runny)

Question 7

Features of composite volcanoes (destructive boundaries)

Answer 7

• steep sided with distinctive cone shape
• tall with a narrow base
• explosive eruptions of lava and ash
• viscous Lava builds in layers and does not flow far from crater
• eruptions occur less frequently

Question 8

What is meant by magma viscosity

Answer 8

Low viscosity = thin magma = flows further and quicker
High viscosity = thick magma = flows shorter distances and slower

Question 9

What effects how viscous magma is?

Answer 9

How much Silica makes up it:
Less silica = low viscosity (gas can easily escape, foam doesn’t form)
More silica = high viscosity (gas can’t easily escape, foam forms)

Question 10

What are the 6 eruption characteristics (from small to large)

Answer 10

Icelandic
Hawaiian
Strombolian
Vulcanian
Pelean
Plinian

Question 11

What does the VEI measure

Answer 11

Measures the explosively, volume of ash and height that the ash cloud reaches into the atmosphere

Question 12

What other information does the VEI show

Answer 12

Gives a description of the eruption, the name of it, and the total number of those eruptions in human history… also allows for comparisons to be made

Question 13

What is the scale of VEI

Answer 13

0-8

Question 14

What are primary effects

Answer 14

Occur immediately along with the event

Question 15

What are secondary effects

Answer 15

Direct consequence of the event but not immediate

Question 16

What is a Lahar

Answer 16

A mixture of hot and cold water and rock fragments which flows down the steep side of a volcano

Question 17

How do Lahar’s form

Answer 17

They form when erupted volcanic material gets saturated during periods of heavy rain. This does not have to be during or immediately after an eruption but may by some time afterwards. Although they may only start small lahars grow as they travel, picking up material as they move down the flanks of the volcano. As a steep slope is required these events are most common on stratovolcanoes due to their greater gradients

Question 18

How are gases a hazard caused by volcanoes

Answer 18

Eruptions release large quantities of gas e.g. sulphur dioxide and carbon dioxide. They are hazardous to human health, can cause respiratory problems and even death. These gases go into the air and can cause short term effects on the climate
E.g. massive release of gas occurred in lake Nyos which is a volcanic crater lake

Question 19

What are Nuees ardentes, and how are they they a hazard caused by volcanic eruptions?

Answer 19

‘Glowing cloud’. A fast moving cloud of hot as and ash erupted from a volcano. Fiery red. Form during explosive eruptions as erupted material collapse. They flow down into valleys at speeds of up to 50 mp. They are usually accompanied by large rocks/bounders.
E.g. 1980 eruption of St.Helens

Question 20

What are mudflows, and how are they a hazard?

Answer 20

A form of mass movement involving the fast moving flow of debris,dirt that has been liquified. Travel up to 5m/s. They contain lots of clay so travel long distances. They can have multiple triggers such as heavy rain flow, snowmelt. They form on volcanoes after an eruption when new, loose, volcanic sediment is formed on the steep slopes is formed on the steep slopes. They can carry cars, trees, even houses. Damage water supplied, gas, waste, and electrical infrastructure.

Question 21

What is pyroclastic flow and how is it a hazard?

Answer 21

Dense, fast moving flow of solidified lava pieces expelled from a volcano during eruption. Occurs when material begins to move down the side of a volcano. Also, when a lava dome collapses on itself as it becomes too steep. They move at up to speeds of 200m/s so are impossible to escape from. Cause secondary flooding as lava block streams

Question 22

What is acid rain and how is it a hazard?

Answer 22

Any other form of precipitation that is unusually acidic, meaning it has elevated levels of hydrogen ions. Acid rain has a ph level lower and the more acidic the rain is, the lower the ph. It effects freshwater supplies, soils, trees, human health, weathering of stone buildings

Question 23

What is ash fallout and how is it a hazard?

Answer 23

It falls to the earths surface from an eruption cloud. Ash and tephra is sent up into the air at incredible heights. The violent ejection contains small fragments of glass ad rock. It can travel many kilometres. Ash can cause health problems, contaminate water and lead to the collapse of structures.

Question 24

What is tephra and how is it a hazard?

Answer 24

Rock fragments and particles ejected by a volcanic eruption grain sized). Airborne fragments are often referred to as pyroclasts. Once these clasts have fallen to the ground, they remain as tephra.
Hot tephra can trigger fires if they fall on ignitable material. Reduces visibility, danger for drivers. Drinking water may also become contaminated by fluorine from tephra

Question 25

What is lava flows and how are they a hazard?

Answer 25

A stream of molten rock that pours out of a volcano during an eruption. As lava is so hot (1,100 degrees), it remains molten and flows across ground until it cools and hardens into rock. They can be very destructive all though they are rarely an effect to human life as they typically move slower than people can walk.

Question 26

How is geological observations a way of PREDICTING/MONITORING volcanoes?

Answer 26

Different techniques exist for measuring the topography (ground shape) of a region. The ground movements occur around an active volcano.
Slope angle- a tilt meter is used to measure changes in the slope of a volcanos side. The shape changes, depending of magma. As more magma rises into the magma chamber, the volcano as a whole expands as magma fills the chamber

Question 27

How is seismic activity a way of PREDICTING/MONITORING volcanos?

Answer 27

This occurs as volcanoes awaken and prepare to erupt. Some volcanoes normally have continued low level seismic activity, but an increased level may signal a volcanic eruption. It’s measured using seismometer/seismograph. Researchers can detect volcanic eruptions by monitoring infra-sound-sub-audible sounds below 20 hz. There are 60 stations around the world that can detect and locate erupting volcanoes.

Question 28

How is measuring gas emissions a way of PREDICTING/MONITORING volcanoes?

Answer 28

As magma nears the surface and its pressure decreases, gases escape. Sulphur dioxide is one of the main components of volcanic gases and increasing amounts of it show the arrival of magma near surface. E.g. on 13th may,1991in the Philippines, and increasing amount of SD was released from mount pinatubo which later erupted on the 12th of June. On many occasions, SD levels have dropped to low levels prior to an eruption, they believe this is caused by the sealing of gas passages by hardened magma.

Question 29

Why are there still deaths from eruptions if these 3 prediction methods exist?

Answer 29

Expensive to do and need highly skilled workers to make sense of the results.
People may have a fatalistic view (they don’t care)
Doesn’t say when and where the volcano will erupt

Question 30

Why is studying past volcanic activity useful for modern day residents?

Answer 30

As they can see what the trends are and look at how well people coped last time, if they would adapt anything if one was to happen agin. If an eruption has taken place, its more likely to happen again

Question 31

Why are there no houses near the immediate surrounding of a volcano?

Answer 31

This is where pyroclastic flow will get to easily (runs down steep slopes), and you will die as you can’t outrun it