Volcanic Hazards

Question 1

The explosive of an eruption is determined by …

Answer 1

The viscoity of the lava

Question 2

What is meant by the term viscosity?

Answer 2

viscosity is the level of fluidity of a substance (how thin or thick the substance is).

Question 3

Low viscosity larva produces what kind of eruptions?

Answer 3

Gentle eruptions
(And as the viscosity increases, so does the explosive of the eruption)

Question 4

Explain why the viscosity effects the explositivity of eruptions ?

Answer 4

if the lava is not viscous ( a thin fluid), the gases may escape easily. If the lava is highly viscous (thick and pasty), the gases will not move freely and can build up tremendous pressure within the volcano. Therefore resulting in a more explosive eruption.

Question 5

Explain the nature of vilcanicity at ocean ridges - why is a volcano formed and what are the eruptions like?

Answer 5

in some locations along ocean ridges, where the lava builds up to the plate surface, volcanic islands form. This is because at constructive plate margins where the plates are moving apart, magma is forcing its way to the surface. Volcanoes formed here have fairly gentle sides because of the low viscosity of the basaltic lava. Eruptions are frequent but relatively gentle (effusive)

Question 6

Explain the nature of vulcanicity at subduction zones - why is a volcano formed and what are the eruptions like?

Answer 6

the magma collects in huge subsurface reservoirs called plutons. Eventually, some of the magma reaches the surface and forms volcanoes. The lava which has viscous nature (flows less easily), creates complex, composite and explosive volcanoes (compared with the basaltic emissions or constructive margins)

Question 7

Explain the nature of vulcanicity at rift valleys - why is a volcano formed and what are the eruptions like?

Answer 7

volcanoes also form within continental rift valleys, for example the Great Rift Valley created Kilimanjaro. Volcanoes formed here have fairly gentle sides because of the low viscosity of the basaltic lava. Eruptions are frequent but relatively gentle (effusive).

Question 8

Explain the nature of vulcanicity at hotspots - why is a volcano formed and what are the eruptions like?

Answer 8

The Hawaiian islands in the North Pacific Ocean are examples of shield volcanoes that are located away from plate boundaries over a hot spot. They have low-angled slopes made from viscosity, basaltic lava that flows great distances from the volcano vent itself.

Question 9

Shallow, effusive volcanoes, such as shield volcanoes are associated with what plate boundaries and why?

Answer 9

Constructive
This is because they occur slowly over time due to small amounts of gases. Therefore creating a shallow layer of rock on the ground after the explosion
These volcanoes have a shallow shape because the lava is not viscous which runs over the rock creating a thin layer

Question 10

Steep sided, explosive volcanoes, such as strato- volcanoes are associated with what plate boundary and why?

Answer 10

Destructive

This is because the lava is not viscous and full of gases and the two plates with high pressure collide creating steep sides. These volcanoes have steep sides built from large emissions of ash.

Question 11

Asses the relationship between the nature of volcanism and plate tectonics?

Answer 11

Strong relationship because vast majority of volcanoes are located on plate boundaries, eg. Ring of fire
However - there is some evidence for the relationship not being as strong. As there is significant volcanoes in intra-plate settings. Such as Hawaii

Question 12

What does hazard intensity mean?

Answer 12

hazard intensity measures the scale of the effects on people, human structures, and the natural environment of a hazard

Question 13

What does the areal extent mean?

Answer 13

The size/ scale of the area important by a hazard

Question 14

What are the primary effects (hazards) of a volcano?

Answer 14

primary effects are brought about by materials ejected from the volcano. For example, tephra (volcanic bombs and ash), pyroclastic flows (nuees and ardentes), lava flows and volcanic gases

Question 15

What are the secondary effects (hazards of a volcano)?

Answer 15

a few examples are Lahars (volcanic mudflows), flooding, volcanic landslides, tsunamis, climate change and acid rain

Question 16

Evaluate the impacts of volcanic hazards?

Answer 16

Primary volcanic hazards tend to have a higher intensity but a small areal extent. An Anaomoly is volcanic gasses which have a large areal extent.
Secondary volcanic hazards tend to have a lower intensity but a larger areal extent. An exception is tsunamis which have a high intensity.

Question 17

How can the management response PREDICTION respond to volcanic hazards?

Answer 17

Early prediction means that people can be evacuated from danger zones and lives can be saved.
Signs a volcano may erupt include;
1. An increase in the release of various gases, particularly sulphur dioxide and carbon dioxide
2. A rise in the level of lava lakes in volcanic craters
3. The bulging upwards of surrounding land due to the pressure from below
4. An increasing number of relatively small earthquakes caused by rising magma

Question 18

How can the management response PREPARATION respond to volcanic hazards?

Answer 18

A study of the previous eruptions history of any volcano is important, along with the understanding of the type of activity produced. Ash, lahars and pyroclastic flows leave characteristic deposits around volcanoes. It can be assumed that if this type of hazard appeared once, it can be repeated. It is also possible to identify areas at greatest risk and the frequency of eruptions from the layers of deposits.

Question 19

How can the management response PROTECTION respond to volcanic hazards?

Answer 19

once viscous lava has started to flow, it may be possible to divert it from the built environment
Eg, on Mt Etna in Sicily, trenches are dug, and dropping explosives into the lava was successful in slowing down the flow and in some cases diverting it
In parts of the Hawaii islands, barriers have been built across valleys to protect settlements

Question 20

How can the management response PREVENTION respond to volcanic hazards?

Answer 20

There is no way to prevent a volcanic eruption. Disasters can be prevented or reduced by mitigation, particularly evacuation in advance of an eruption.