2.a. There is a variety of volcanic activity and resultant landforms and landscapes.​

Question 1

What are the 6 types of eruption?

Answer 1

• Icelandic lava eruptions.
• Hawaiian eruptions.
• Strombolian eruptions.
• Vulcanian eruptions.
• Vesuvian eruptions.
• Plinian eruptions.

Question 2

Outline ‘Icelandic lava eruptions’ as a type of eruption.

Answer 2

Characterised by persistent fissure eruption.

Large quantities of basaltic lava build up horizontal plains.

Question 3

Outline ‘Hawaiian eruptions’ as a type of eruption.

Answer 3

Involve more noticeable central activity than the Icelandic type.

Runny, basaltic lava travels down the sides of the volcano in lava flows.

Gases escape easily.

Occasional pyroclastic activity occurs.

Question 4

Outline ‘Strombolian eruptions’ as a type of eruption.

Answer 4

Characterised by frequent gas explosions which blast fragments of runny lava into the air to form cones.

They are very explosive eruptions with large quantities of pyroclastics thrown out.

Question 5

Outline ‘Vulcanian eruptions’ as a type of eruption.

Answer 5

Violent gas explosions blast out plugs of sticky or cooled lava.

Fragments build up into cones of ash and pumice.

Occur when there is very viscous lava which solidifies rapidly.

Often the eruption clears a blocked vent and spews large quantities of volcanic ash into the atmosphere.

Question 6

Outline ‘Vesuvian lava eruptions’ as a type of eruption.

Answer 6

Very powerful blasts of gas creating ash clouds high into the sky.

Lava flows also occur.

Question 6

Outline ‘Plinian lava eruptions’ as a type of eruption.

Answer 6

Gas rushes up through sticky lava and blasts ash and fragments into the sky in a huge explosion.

The violent eruptions create large clouds of gas and pyroclastics.

This lava and clouds can rush down the slopes.

Part of the volcano may be blasted away during the eruption.

Question 7

Outline the location of explosive and effusive eruptions.

Answer 7

Explosive: convergent plate boundaries.

Effusive: divergent plate boundaries.

Question 8

Outline the type of lava at explosive and effusive eruptions.

Answer 8

Explosive: rhyolite (more acid) and andesite (less acid).

Effusive: basalt.

Question 9

Outline the lava characteristics at explosive and effusive eruptions.

Answer 9

Explosive: acid (high % silica), higher viscosity , lower temperature at eruption.

Effusive: basic (low % silica), low viscosity, higher temperature at eruption.

Question 10

Outline the style of eruption at explosive and effusive eruptions.

Answer 10

Explosive: violent bursting of gas bubbles when magma reaches surface, highly explosive, vent and top of cone is often shattered.

Effusive: gas bubbles expand freely, limited explosive force.

Question 11

Outline the materials erupted at explosive and effusive eruptions.

Answer 11

Explosive: gas, dust, ash, lava, bombs, tephra.

Effusive: gas, lava flows.

Question 12

Outline the frequency of explosive and effusive eruptions.

Answer 12

Explosive: tend to have long periods with no activity.

Effusive: tend to be more frequent; an eruption can continue for many months.

Question 13

Outline the shape of explosive and effusive eruptions.

Answer 13

Explosive: steep-sided stratovolcanoes, caldera.

Effusive: gently sloping sides, shield volcanoes, lava plateaux’s when eruptions occur from multiple fissures.

Question 14

Volcanic eruptions produce a varied range of landforms. What is this diversity a result of?

(The nature of volcanicity)

Answer 14

• Where the eruption occurs.
• The type of lava.
• The variety of materials such as ash, pumice, gases produced.
• How the eruption takes place.

Question 15

Give an example as to how volcanic eruptions are able to produce a range of landforms.

(The nature of volcanicity)

Answer 15

Chemical differences within magma (molten rock below the surface) influences the type of eruption and the shape of the volcano.

Once magma is ejected at the surface, its behaviour is affected by its viscosity, which in turn is determined by its chemical composition and temperature, and the changes that take place within the magma chamber.

Question 16

Although classification (effusive/explosive and types of eruptions) are useful, what must be considered?

(The nature of volcanicity)

Answer 16

It is important to remember that every volcano is unique.

Even the same volcano can produce different eruptions over time, depending on the complex chemistry taking place in the volcano magma chamber.

No volcanoes are the same, the eruptions are never the same.

Question 17

What type of eruptions are effusive? Which are explosive?

(The nature of volcanicity)

Answer 17

Effusive:
- Icelandic lava eruptions.
- Hawaiian eruptions.

Explosive:
- Strombolian eruptions.
- Vulcanian eruptions.
- Vesuvian eruptions.
- Plinian eruptions.

Question 18

What are stratovolcanoes? What do most contain?

(Strato-volcanoes)
(The products of Explosive eruptions)

Answer 18

Made up of layers of ash and acidic lava, and have a symmetrical profile.

Most contain complex internal networks of lava flows which form minor igneous features such as sills and dykes.

Question 19

Does acidic magma flow well in strato-volcano vents? Why? What else does this prevent?

(Strato-volcanoes)
(The products of Explosive eruptions)

Answer 19

Acidic magma does not flow easily as the vents are often filled with a mass of solidified magma.

This prevents magma from rising freely from the deep.

Question 20

Masses of solidified magma stuck within strato-volcano vents prevent magma from rising freely from the deep. What can this cause?

(Strato-volcanoes)
(The products of Explosive eruptions)

Answer 20

Enormous pressure can build up inside a volcano until it erupts explosively.

Question 21

Convergent plate boundaries and explosive eruptions often give rise to what?

(Strato-volcanoes)
(The products of Explosive eruptions)

Answer 21

Convergent plate boundaries and explosive eruptions often give rise to chains of strato-volcanoes.

Question 22

Volcanic craters are usually more than how large in diameter.

(Calderas)
(The products of Explosive eruptions)

Answer 22

Volcanic craters, usually more than 2km in diameter.

Question 23

How do calderas form?

(Calderas)
(The products of Explosive eruptions)

Answer 23

They develop when as explosive eruption destroys much of the cone and the underlying magma chamber is largely emptied.

Without the support of this magma, the sides of the volcano collapse, forming a caldera.

Question 24

Give a named example of a caldera.

(Calderas)
(The products of Explosive eruptions)

Answer 24

The 1883 eruption of Krakatoa in Indonesia formed a caldera 7km wide.​

Question 25

How many active strato-volcanoes does Indonesia have along its archipelago?

(Strato-volcanoes)
(The products of Explosive eruptions)

Answer 25

Indonesia has 130 active strato-volcanoes along its archipelago.

Question 26

How many strato-volcanoes have erupted in the Andes?

(Strato-volcanoes)
(The products of Explosive eruptions)

Answer 26

In the Andes, 66 strato-volcanoes have erupted in record history.​

Question 27

How do lava plateaux’s form?

(Lava Plateaux)
(The products of Effusive Eruptions)

Answer 27

Form when basic magma erupts from multiple fissures, vast areas can be covered by free-flowing lava.

These events are known as flood basalts.

Question 28

Outline the Deccan Plateau in central India.

(Lava Plateaux)
(The products of Effusive Eruptions)

Answer 28

Covers more than 500,000 km², known as a large igneous province.

Question 29

Outline the Colombian Plateau.

(Lava Plateaux)
(The products of Effusive Eruptions)

Answer 29

In northwest USA covers 130,000 km².

Millions of years of denudation have created varied relief.

No large-scale flood basalt events have taken place in 50 million years.

When they do occur they have a huge impact on the atmosphere and hydrosphere and consequentially the biosphere.

Question 30

Effusive eruptions are usually found where? Why?

(Shield Volcanoes)
(The products of Effusive Eruptions)

Answer 30

Usually found at divergent plate boundaries.

This is because these boundaries occur with mid-ocean ridges, effusive eruptions are unseen on the ocean floor.

However, Iceland is an exception, it owes its formation to effusive volcanic activity on the ocean floor.

Question 31

Eruptions of basic lava result in what?

(Shield Volcanoes)
(The products of Effusive Eruptions)

Answer 31

Eruptions of basic lava result in volcanoes with gently sloping sides.

Question 32

If successive lava flows accumulate for long enough, what may form? Give an example.

(Shield Volcanoes)
(The products of Effusive Eruptions)

Answer 32

Huge volcanoes, extending horizontally for 10s of kilometres can develop.

E.g. Skjaldbreidur in Iceland.

Question 33

Outline the hot spot of the Hawaiian chain of islands.

(Eruptions at hot spots (not at boundaries))

Answer 33

Located at the centre of the Pacific plate, 1000s of kilometres from the nearest plate boundary.

As the Pacific plate has slowly moved northwest over the Hawaiian hot spot (at an average rate of 10 cm/year), vast amounts of basalt have accumulated on the ocean floor to produce the Hawaiian islands.

Over millions of years, as the Pacific plate moves northwest and away from the hot spot, the volcanoes lose their source of magma and become extinct.

Thus on the older islands in the Hawaiian chain, such as Kauai, volcanism is no longer active.

There, weathering and erosion have broken down the volcanic rocks into deep and fertile soils.

Question 34

Outline East African rift valley.

(Eruptions at hot spots (not at boundaries))

Answer 34

4000km long rift valley containing several active volcanoes.

Over the past 30 million years, the crust has been uplifted and stretched, causing tension within the local rocks.

The result is rifting, with magma forcing its way to the surface and creating a line of active volcanoes.

Mount Kilimanjaro, the highest peak in Africa, was formed in this way.

Question 35

How do eruptions vary? What does this make difficult? What must be considered?

(Measuring and assessing volcanic activity)

Answer 35

The amount of material released, their type (effusive/explosive) and their duration.

It is, therefore, difficult to compare one eruption with another.

However, two key factors need to be considered:

• Magnitude: the amount of material erupted.
• Intensity: the speed at which material is erupted.

Question 36

What is the Volcanic Explosivity Index (VEI)?

(Measuring and assessing volcanic activity)

Answer 36

The most widely used measure of eruption; it is a logarithmic scale.

It combines magnitude and intensity into a single number on a scale from 0, the least explosive, to 8, the most explosive.

Each increase in number represents nearly a ten-fold increase in explosivity.

Question 37

What are the 4 ways of assessing the explosivity of an eruption, according to the VEI?

(Measuring and assessing volcanic activity)

Answer 37

• The volume of erupted material.
• The height ejected material reaches.
• The duration in hours.
• Various qualitative descriptions.

Question 38

State a limitation and a strength of the VEI.

(Measuring and assessing volcanic activity)

Answer 38

The VEI is not that useful for effusive eruptions such as those on Hawaii.

However, it is valuable in suggesting the relative impacts volcanoes might have at different geographical scales.

Question 39

What are super volcanoes?

(Super-volcanoes)

Answer 39

Volcanoes that erupt more than 1000km³ of material in a single eruption event.

Question 40

Where is past super-volcano activity seen? Give an example.

(Super-volcanoes)

Answer 40

In the existence of giant calderas.

E.g. Yellowstone super-volcano (Wyoming) has a caldera that is 75km in diameter.

Question 41

Other than Yellowstone, super-volcanoes that have erupted in the last 2 million years include what two sites?

(Super-volcanoes)

Answer 41

Long Valley in California, and Toba in Indonesia.

Question 42

What was the most recent super-volcano eruption?

(Super-volcanoes)

Answer 42

Occurred 27,000 years ago at Taupo, North Island, New Zealand.

Question 43

How are the impacts of past super-volcano (very-high magnitude) events studied?

(Super-volcanoes)

Answer 43

From the wide extent and depth of the ash layers deposited following the eruption events.

The impact can also be measured by the impact on plant, insect, and animal species (palaeobiology).

Long-term impacts may have a boom of biodiversity, as volcanic soil is preferable to grow in (for some species).

Question 44

What are LIP events? What can they cause?

(Large igneous provinces (LIPs))

Answer 44

Massive effusive outpourings of basalt that commonly erupt intermittently over very long periods of time and typically cover areas between 2000-2500 km across.

Eruptions from LIPs could be the cause of global mass extinction events.

Question 45

The two largest of intra-LIP volcanic features are what? Explain them.

(Large igneous provinces (LIPs))

Answer 45

Continental Flood Basalt: LIP occurring on a continental plate.

Giant Oceanic Plateaus: LIP occurring on an oceanic plate.

Question 46

LIP events are earth shattering, and have been identified as possible causes of at least 4 whats?

(Impacts)
(Large igneous provinces (LIPs))

Answer 46

At least 4 major extinctions, e.g. the Permian extinction.

Question 47

How do LIP events erupt? How does this influence climate?

(Impacts)
(Large igneous provinces (LIPs))

Answer 47

Millions of cubic kilometres of magma ponds up below the lithosphere before periodically breaking through the lithosphere and crust, erupting over several million years.

Given the amount of material produced this might create global cooling initially, as other eruptions have in historic time, but given that CO2 is the most significant gas emitted by most effusive eruptions, the long-term impact is global warming and ocean acidification.

Question 48

Each of the LIP event extinctions has been brought about by what?

(Impacts)
(Large igneous provinces (LIPs))

Answer 48

Brought about by significant peaks in atmospheric CO2.

Question 49

Some Earth scientists propose that what features are the final remnants of past LIP events.

(Impacts)
(Large igneous provinces (LIPs))

Answer 49

Super-volcanoes and hot spots.

Question 50

Outline the Siberian Traps as a named example of a LIP.

(Large igneous provinces (LIPs))

Answer 50

Have a total volume of 3 million km³ which would be enough to bury the whole of western Europe under a 1 km thick sheet of basalt.

It is believed that they are formed by mantle plumes of very hot, but solid, material that rises from the junction between the mantle and the liquid outer core; same as convection currents in the mantle.

Question 51

How were the Columbia River flood-basalts formed?

(Columbia River flood-basalts - product of a LIP event)
(Large igneous provinces (LIPs))

Answer 51

Created about 15 million years ago by a LIP in what is now the north west of the USA - corresponds to where Yellowstone would have been at that time.

In its current hot spot position, volcanic activity began about 2 million years ago when a giant caldera formed.

Two further huge eruptions took place 1.3 million and 640,000 years ago; with dozens of smaller eruptions occurring as well.

Question 52

Why it is not known exactly how often the North-west LIP had erupted, nor the volume of material extruded?

(Columbia River flood-basalts - product of a LIP event)
(Large igneous provinces (LIPs))

Answer 52

The evidence of earlier eruptions may have been either buried or destroyed by later ones.

Question 53

During the largest eruptions of the North-west LIP, what happened? What is this likely to have caused?

(Columbia River flood-basalts - product of a LIP event)
(Large igneous provinces (LIPs))

Answer 53

Ash was spread over much of the western half of North America, while gases and tiny particulates were carried around the globe in the upper atmosphere.

It is likely that this caused a noticeable, though temporary, decrease in global temperatures.