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Vulcanicity

Vulcanicity

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a-levl-vulcanicity

Specification

Variations in the type and frequency of volcanic activity in relation to types of plate margin and types of lava.
Forms of intrusive activity – dykes, sills, batholiths. The above paragraph has been added.
Minor forms of extrusive activity – geysers, hot springs and boiling mud.
Major forms of extrusive activity – types of volcanoes.
Two case studies of recent (ideally within the last 30 years) volcanic events should be undertaken from contrasting areas of the world. In each case, the following should be examined:


• the nature of the volcanic hazard
• the impact of the event
management of the hazard and responses to the event.

What you need to know:

http://www.slideshare.net/mobile/anicholls1234/geography-notes-volcanoes-earthquakes-aqa

Volcanic activity and plate margins:

 

Constructive plate margins: These form chains of volcanoes that follow the line of mid-ocean ridges. Basaltic lava is produced, sometimes from fissure eruptions. Basalt has low viscosity and so plateaux of basalt can form. Volcanoes in Iceland typically start with the eruption of volcanic ash, which is then followed by basaltic lava flows. Where the eruptions are under the sea, pillow lavas form. Iceland is also well-known for having other minor forms of volcanic activity such as geysers and hot springs.

Destructive plate margins: These tend to be more explosive because the lava has a higher silica and water content (andesite lava) than constructive margins. This forms chains of composite volcanoes made of alternating layers of ash deposits and lava. Eruptions can be very explosive (e.g. Mt St Helens 1980), blowing large volumes of rock in the atmosphere, leaving behind a huge crater or caldera e.g. that left behind after the Krakatoa eruption in 1883. Some eruptions are in the form of pyroclastic flows. These are fast-moving currents of extremely hot (1000⁰C+) gas and rock which travel away downhill from a volcano at speeds generally as great as 700 km/hour.

• Kilauea is one of the most active volcanoes on the planet and has been continuously erupting since 1983, making it the longest eruption of the last 200 years. It makes up part of the Hawaian Islands in the middle of Pacific plate. Here the eruptions tend to be relatively gentle because the basalt lava is not very viscous. Low angled shield volcanoes are formed.

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Forms of intrusive activity:

Only a small amount of magma actually reaches the surface, most is intruded into the crust where it solidifies and produces intrusive features. Intrusive activity has little or often no impact on the surface until overlying rocks are later worn away, leaving landforms produced by their exposure on the surface. During intrusive activity, magma cools slowly allowing the mineral crystals to grow. This produces a coarsely crystalline rock e.g. granite. Types of intrusions include:

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• Batholiths.                                                                              Yosemite

These are large dome-shaped features intruded deep underground. They cut across the sedimentary rocks they intrude into. They are created by the injection of large amounts of magma into the crust. They cool very slowly and are coarse grained, usually granites. The best known example in the British Isles is the batholith that underlies the southwest of England. Parts have been exposed to form the granite moorlands of Dartmoor and Bodmin.

 

• Dykes

These are much smaller, vertical or near vertical intrusions that cut across layers of sedimentary rock. They form by being forced into existing weaknesses in rocks. On the surface they are often more resistant than the surrounding rock and form small ridges across the landscape. If there are a large number of them radiating out from a central batholith, they are called dyke swarms.

• Sills

These are intrusions that are injected parallel to the layers of the surrounding ‘country rock’. In the British Isles the best known is The Great Whin Sill that outcrops across much of NE England. Because it is much more resistant than the surrounding rock it forms escarpments e.g. Peel Crags on Hadrian’s Wall.

Minor forms of extrusive activity

• Geysers:

These are natural fountains that throw up jets of hot water and steam at regular intervals through a vent in the surface. They are caused by rainwater seeping through cracks in the rocks and draining into a deep chamber where it reaches hot rocks. This water is boiled and turns into steam. This increases the pressure in the chamber until it shoots upwards through a vent and then high in the air. The process repeats itself.

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• Hot Springs:

These are surface pools of hot water fed from below. The water comes from cooling magma deep below the surface. When it reaches the surface it is often rich in mineral salts dissolved from the rocks it has passed through on its way to the surface. Evaporation at the edge of the pools often allows minerals to crystallise. Hot springs can be found in Japan, New Zealand, Kenya and Iceland.

• Boiling mud:

Boiling mud, (or mudpots), can be found where there are hot springs in areas where surface water is in short supply. The water rises to the surface as with hot springs, passing through layers of volcanic ash. The mud takes the form of a viscous, often bubbling, slurry. As the boiling mud is often squirted over the brims of the mudpot, a sort of mini-volcano of mud starts to build up, sometimes reaching heights of 1.5 m.

Major forms of extrusive activity – types of volcanoes:

 

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Geologists generally group volcanoes into four main kinds–cinder cones, composite volcanoes, shield volcanoes, and lava domes. Their form depends upon the type of lava and the amount of water vapour contained in the magma. Generally, the more viscous acidic (silica rich) lavas form steep sided volcanoes whereas the less viscous basic lavas (e.g. basalt) for low angled volcanoes. The more water vapour there is present, the more explosive the eruption. Both the type of lava and water vapour depend in turn on the volcano’s position in relation to plate boundaries.

• Cinder cones:

Cinder cones are the simplest type of volcano. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than 300m above their surroundings. E.g Paracutin, Mexico

Cinder cone

Cinder cone

• Composite Volcanoes (Stratovolcanoes)

These are typically steep-sided, symmetrical cones of large dimension. They are built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 3000m above their bases. Examples of composite volcanoes include Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California and Mount St. Helens in Washington State, USA.

Most composite volcanoes have a crater at the summit which contains a central vent or a clustered group of vents. Lavas either flow through breaks in the crater wall or issue from fissures on the flanks of the cone. Lava, solidified within the fissures, forms dykes that act as ribs which greatly strengthen the cone.

The essential feature of a composite volcano is a conduit system through which magma from a reservoir deep in the Earth’s crust rises to the surface. The volcano is built up by the accumulation of material erupted through the conduit and increases in size as lava, cinders, ash, etc., are added to its slopes.

This is the type of volcano which produces calderas. These are giant craters left behind when the eruption is so violent that much of the top of the volcano is blown off. E.g. Crater Lake, Oregon, USA.

Composite cone

Composite cone

• Shield Volcanoes:

This type of volcano is built from low viscosity basalt lavas that flow long distances out of a central vent building a broad, gently sloping cone. Some of the largest volcanoes in the world are shield volcanoes. The Hawaiian Islands are composed of a chain of these volcanoes including Kilauea and Mauna Loa on the island of Hawaii– two of the world’s most active volcanoes.

Shield volcano

Shield volcano

• Lava Domes:

Lava domes are formed by relatively small, bulbous masses of lava too viscous to flow any great distance; consequently, on extrusion, the lava piles over and around its vent and a dome grows largely by expansion from within. As it grows its outer surface cools and hardens, then shatters, spilling loose fragments down its sides. Lava domes commonly occur within the craters or on the flanks of large composite volcanoes. E.g.Mont Pelée in Martinique.

Lava dome (Mt St Hel)

Lava dome (Mt St Hel)

Case Studies

The video below contains more information on the primary and secondary effects of a volcano

The eruption of Nyiragongo, Congo, January 2002

 

Montserrat (West Indies) Soufriere Hills 1995-97

Mount St Helens

http://http://www.slideshare.net/donotreply16/montserrat-ledc-case-study

The specification demands 2 case studies. For each one:
• Nature of the hazard
This should include a clear location, a description of the eruption itself, including the amount and nature of the material erupted.

• The impact of the hazard. This can be divided into:
– Environmental impacts
– Social impacts (deaths, property destroyed etc)
– Economic impacts (costs, loss of earnings etc)

• The management of the hazard

What did the authorities do to mitigate the effect of the hazard (e.g. evacuation of an area of 20km around Mt Pinatubo prior to the eruption)

• The responses to the hazard

What did the authorities and individuals do following the initial management phase (e.g. Planes grounded in many European airports following the 2010 Icelandic eruption).

Case study: Eyjafjallajökull

Eyjafjallajökull

Eyjafjallajökull

Iceland – eruption from slideshare: http://www.slideshare.net/geography101/eyjafjallajkull-icelandic-eruption-2010

Eyjafjallajokull is in Iceland, and is an example of a major volcanic eruption. The name is a description of the characteristics of the volcano, namely Eyja meaning island; fjalla meaning mountain; and jokull meaning glacier.

This volcano (pronounced as ay-yah-fyah-lah-yoh-kuul ) is located on a spreading ridge on the Island of Iceland. Here, convection currents are driving apart the North American plate (moving West) and the Eurasian Plate (moving East) along a constructive or divergent plate boundary. This is creating the Mid Atlantic ridge, along which the age of the rocks either side of the ridge and paleomagnetism have been used as evidence of Plate Tectonics theory. The plates are moving apart at a rate of 1cm to 5 cm per year. This has created a chain of volcanoes along the SE Rift zone of Iceland, which runs from NE to SW across Iceland, even passing underneath some of the countries Ice caps.

Eyjafjallajökull

Eyjafjallajökull

Eyjafjallajökull is a small volcano (about 40km2) within the chain of volcanoes in the SE Rift Zone. It is the most southerly volcano on mainland Iceland before Surtsey in the sea to the south west.  It is a relatively small volcano, and is located W of Katla volcano. Eyjafjallajökull consists of an elongated ice-covered strato volcano with a 2.5-km-wide summit caldera.

The nature of the volcanic hazard – type, frequency, magnitude

The major problem with this volcano was volcanic ash and the ash plume that resulted from the eruption. This ash plume reached 11,000m into the air, high enough to reach into the Stratosphere and also to be distributed by high velocity jet streams between the Troposphere and the Stratosphere. The problem with the ash was that it was very fine grained, a sample taken by the Environment Agency on Mýrdalssandur (50 km away from the eruption site) after the ash fall 14-16 April was analysed by Institute of Earth Sciences and is very fine grained:

24% of the sample is under 10 μm (as aerosol)

33% of the sample is in the range of 10-50 μm

20% of the sample is in the range of 50-146 μm

23% of the sample is in the range of 146-294 μm

This fine grained ash poses a problem to airplanes, as it can affect many systems when it enters the engines and even turn to a glassy substance because of the heat of the jet engine. Britain had fine anticyclonic weather for a lot of the time that the Ash cloud existed. This was a problem because winds would have dispersed the cloud better.

The other complicating factor is that the volcano is covered by the Eyjafjallajokull glacier. This caused a flood (a jökulhlaups – glacier outburst flood) on the 14th of April, when an eruption partly melted a glacier and set off a major flood which prompted authorities to order 700 people to evacuate. This flood had huge discharges of 2000-3000 m3/sec.

The volcano also emitted lava from a 500m long fissure, spewing the 1,000°C lava 150m into the air.  The volcano was classified with a VEI of 4, with greater than 1.4 ± 0.1 x 107 m3 (100 million cubic meters) of lava erupted and > 1.4 x 108 m3 (1,000million cubic meters!) of Tephra erupted.  It was also categorised as both a fissure and explosive eruption.

Ash cloud

Ash cloud

Vulnerability

Before the eruption in 2010 the volcano is known to have erupted in 920, 1612, 1821 and 1823. Between March the 3rd and 5th of 2010 there were plenty of warning signs of an eruption, as there were over 3,000 recorded earthquakes, the vast majority of these being less than 2 on the Richter scale and only some large enough to be felt in nearby towns.

The vent for the volcano is 1.8 to 2.5 miles across, and is located close to a much more active volcano, Katla. Scientists were very concerned at the time of the eruption that this eruption could be a precursor or warning sign of a much larger eruption of the historically more active and dangerous Katla. This volcano erupts more often and is known to be more violent. This area is therefore incredibly vulnerable to this sort of activity, but weather conditions made the effects of the ash must worse.

Capacity to cope and institutional capacity (prediction, preparation, prevention)

The Icelandic Meteorological Office monitors earth movements, water conditions and weather and issues warnings. Many kinds of measurements are carried out by the IMO and other agencies that provide valuable information used to warn of impending danger, for example potential eruptions and floods. The IMO’s weather radar on the southwest tip of the country showed the height of the ash plume, which is important for calculating the distribution of the ash. There was a 24/7 watch at the IMO, where a meteorologist is present and a seismologist and hydrologist are on call. The IMO worked closely with the National Emergency Agency, the University of Iceland and the British Meteorological Office, where the London VAAC (Volcanic Ash Advisory Centre) is stationed. The London office gave information on ash which is based on information from the Icelandic Met Office. This event was therefore tracked and prepared for, and the ash cloud was tracked by satellite by many nations. In addition, all of the countries in Europe have bodies which determine the safety of conditions to fly in. This means that many of the countries have great capacity to cope in terms of making predictions and preparing alternatives for companies and people stuck by the restrictions on air travel.

The European Union is a trading block which has a very large combined GDP of $24400; this means it has the collective financial capacity to cope with emergencies like this eruption.  In addition, the EU has other transport mechanisms such as extensive road and motorway networks, rail networks (including the Channel tunnel) and boat networks (which were particularly important for the transportation of food goods etc.). In addition, the EU’s CAP means that the EU is largely self-sufficient in food production and could cope if imports from outside of the EU could not arrive. Finally, in legal and insurance terms the EU is well prepared. Travellers stuck by the ash cloud were entitled to legal compensation from their airlines and their airlines were also legally responsible for the well-being of stranded passengers. Also, the EU’s insurance system means that many people (but not all) would have been able to claim back any losses, as could many companies. Finally, many companies had contingency plans in place for an emergency such as this, so could cope better, Tesco circumvented the ash cloud by flying Kenyan produce into Spain and then using road haulage for example.

The impact of the event (social, economic, environmental), in the short and longer term

Within Iceland many people were very lucky as the volcano is on the south coast and the wind carried the ash southeast towards Europe: away from the most inhabited areas of Iceland. However, the people living in the rural areas ‘down wind’ of the volcano had to wear goggles and facemasks as the ash was so thick. Indeed, visibility was down to a few metres and local cattle farmers suffered. 500 farmers and their families had to be evacuated from the area around the volcano, and many of the roads surrounding the volcano where shut down. The ash contaminated local water supplies and farmers near the volcano were warned not to let their livestock drink from contaminated streams and water sources, as high concentrations of fluoride from the ash mixed with river water can have deadly effects, particularly in sheep.

The major impact was Internationally however, as winds redistributed the ash that was pumped high into the atmosphere over Northern and western Europe and stopped flights from taking off. The map shows the extent of the ash cloud, note it interrupts not just European flights but also Trans Atlantic fights. Although the ash cloud was invisible to the naked eye, as it is made up of very fine particles and substances. These particles clog up the engines of aircraft that attempt to fly through them, and this is the reason for aviation disruption.

Ash cloud

Ash cloud

This also has a knock on effect on International flights globally as they could not land or take off from Europe.  This is thought to have cost Airlines and associated businesses were losing about £130 million a day (according to the IATA), whilst hundreds of thousands of people (including me!) were stranded in other countries. Hire car companies and other forms of transport Hiked their prices as people sought other ways to get home, on my way back from France I met people who had paid thousands of pounds to hire a car to get them to Northern France to take a ferry.

This also has a huge impact on public institutions (such as schools) and businesses, particularly those who rely on air freight or those whose workers were stranded overseas. During the main 8 day travel ban around 107,000 flights were cancelled accounting for 48% of total air traffic and roughly 10 million passengers.

LEDCs were also badly affected, with Kenya being a great example. 20% of the Kenyan economy is based on the export of green vegetables (beans, sugar-snap peas and okra) and cut flowers to Europe. These are perishable goods and they are transported by plane to keep them fresh but the flight ban meant that products returned unsold and destroyed. Over 1 million flower stalks were unsold in the first two days and over 50,000 farmers were temporarily unemployed as their beans and peas could not be sold.

There were many environmental impacts of this eruption, and scientists feared a climatic impact.  However, despite the Eyjafjallajökull eruption putting up to a maximum 30000 tonnes per day of CO2 in to the air, it is thought this will not make a substantial addition to global anthropogenic atmospheric CO2 emissions .The main risks were to soils and water courses.  The main risks are to livestock through fluoride ingestion from volcanic ash on pasture.

Responses to the event.

Many of the responses have been covered above, but it is important to recognize that unlike in LEDCs and LDCs the responses were entirely DOMESTIC. That means that the countries affected by this hazard responded by themselves or collectively, and had the capacity to do so. Their legal, technical and infrastructure systems can cope with hazards such as this eruption, even if there are economic impacts. Their actions also limited the impact in terms of casualties, and tests have taken place since to see if planes can fly in ash clouds, in what type of ash or around ash clouds.

(Source http://www.coolgeography.co.uk/A-level/AQA/Year%2013/Plate%20Tectonics/Volcanoes/MEDC%20case%20study.htm)

 

Questions:

4. Discuss the ways in which people and organisations have attempted to minimise the effect of volcanic eruptions. [10 marks]

5. Describe the effects that a major volcanic eruption can have on the population of an area.[8 marks]

6. Discuss the ways in which people and organisations respond to volcanic eruptions and their effects. [10 marks]

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