Earthquakes + volcanoes

Negative effects of volcanoes

- Kills people and wildlife - Can destroy farms and woodland - Heavy ash can cover area in thick layers and cause roofs to collapse - Destroys communication links and infrastructure - Gases can cause pollution

Negative effects of earthquakes

- Kills people and wildlife - Destroys buildings - Destroys communication links and infrastructure - Can create tsunamis

Continental crust

Continental crust is older, normally thicker, less dense (lighter), can't be made, can't be destroyed.

Positive effects of volcanoes

- Attractive for tourists - Brings in income for locals and country - Minerals - Light ash falls can add nutrients to soil - Can be used for geothermal power

Being prepared for volcanic eruptions

- Diversion channels: It has been attempted to make diversion channels to direct the lava away from settlements. This is very expensive and hard because you can not predict which direction the lava will flow. - Cooling lava: In Iceland in the past they have tried spraying seawater onto lava. The idea was to make the lava go cold and turn into rock before it destroyed nearby settlements. - Sweeping roofs: During ash showers it is very important to regular sweep ask off roofs. If this is not done the ash will get so heavy that it will eventually cause the building to collapse. - Making evacuation routes: It is very important to plan evacuation routes for individual houses and whole settlements. It is also important to regularly practice these evacuation routes. - Exclusion areas: If an eruption is happening or likley to happen it is important to create exclusion zones. This means evacuating everyone that could be effected by the eruption. Because pyroclastic flows can travel up to 30km, these exclusion zones can be very big. - Hazard Mapping: It is very important to map the most dangerous areas near a volcano e.g. areas with the most unstable ground or areas where lava flows are likley to travel. Once you have mapped dangerous areas you can then stop settlements being built on them. - Monitoring volcanoes: Because volcanoes do give warning signs (change in shape, temperature, etc.) it is very important to monitor them carefully so that you can nearby residents warnings. - Looking at volcanic history (previous eruptions and flows): As part of monitoring the volcano you can look at its history and previous flows. You can then try calculate frequencies and areas likely to be effected. - Volcanic Plug: You can attempt to make an artificially volcanic plug by dropping boulders or concrete into a crater or vent. This is dangerous and unlikely to be successful. In fact it might build up the pressure in a volcano and cause a more violent eruption.

Preparedness and Vulnerability in LEDCs

- LEDCs tend to have more informal settlements that don't follow building codes. This makes them more vulnerable when hazards hit. - Many LEDCs suffer from rapid urbanisation and uncontrolled growth of settlements on dangerous marginal land. - Medical care will be poorer in LEDCs and there will be less money spent on search and rescue teams. - Many LEDCs rely on emergency aid during times of natural disasters. Emergency aid always takes several days to mobilise which will usually cost lives. - Transport and communication will be poorer in LEDCs. Much of the population will not have access to phones, television or the internet so will not be warned about forthcoming natural disasters.If they do know, lack of adequate transport may make escape difficult. There will certainly be a shortage of helicopters. - There probably won't be adequate supplies of tents, blankets, food and clean water. - Services like electricity and water will take longer to repair, leading to the secondary hazards of diseases and exposure. - A lot of population will be illiterate and never taught about potential natural disasters and how to respond to the natural disasters. - Less money will be spent on monitoring potential hazards, because countries have less money and less trained scientists. - Evacuation routes may not exist and there may be as shortage of shelters. - Poor LEDC cities often have very high population densities. This causes more people to be effected by the primary and secondary hazard.

Volcanic Hazards

- Lava flow - Pyroclastic flow - Lahars - Ash clouds - Poisonous gases - Lava or Volcanic bombs (tephra) - Acid rain - Landslide

Preparedness and Vulnerability in MEDCs

- Many MEDCs do hazard mapping and zonal planning. They will assess the risk for different areas of the country e.g. is it likely to flood or be in a lava flow. They will then only allow low value and low risk land uses in hazardous areas. - Most MEDCs have fairly strict building codes to protect against earthquake damage. Buildings will have to be reinforced, have shatter proof windows, dampers, sprinklers and escape routes. - In MEDCs the entire population will be educated about hazards. They will know what potential hazards there are and how to respond to them. People will be told evacuation routes and where safe areas are. - Emergency and rescue services will be trained so they know how to find victims and how to treat them. They will have proper equipment and carry out practices. - Hazards will be better monitored in MEDCs, scientists will study volcanoes, track hurricanes and then try and make accurate predictions and inform the public. - Transport and communications are usually much better. The population can be informed and are more easily able to escape. There are likely to be more helicopters which can be essential in search efforts when roads are damaged. - MEDCs are simply richer so they can afford to spend more money on training and preparedness. There will be stockpiles of tents, blankets, food and water for anyone who has lost their home and possessions.

Why people live on tectonically active places

- Poverty: Some people are very poor and are forced to live on marginal land that is very vulnerable to the impacts of earthquakes: - Inertia: Some people have lived in earthquake zones although their life an are unwilling to move - Infrequency: Major earthquakes happen relatively infrequently so some people are prepared to take the risk and don't think that one will occur in their lifetime. - Overpopulation: Some countries are very densely populated so people are forced to live on dangerous and marginal land. - Building Design: Building design has improved and now people are confident that their house or workplace will withstand strong earthquakes. - Education and preparation: Many countries practice earthquake drills and evacuation and prepare their houses so feel confident that they will know what to do in an earthquake. - Economic Opportunities: Many tectonically active locations have good resources and locations e.g. next to the sea. Because of this there are many job opportunities which people move near to take advantage of.

Factors which can affect the damage of an earthquake

- The depth of the earthquake - The magnitude of the earthquake - The duration of the earthquake - The local geology (soft or hard rock, solid or cracked rock) - The location of the epicentre (in a rural or urban area) - The population density around the epicentre. - The building design and hazard mapping near the epicentre. - The time of day (earthquakes at night might trap people in their houses, earthquakes during dinner time might trigger more fires). - The preparedness of the population (evacuation routes, emergency services, etc.)

Cinder cone volcano (caldera)

A cinder cone volcano is simply a steep conical hill of tephra (volcanic debris) that accumulates around and downwind from a volcanic vent. The cinder cones are made from pyroclastic material, which is pretty loose. Cinder cones are commonly found on the flanks of shield volcanoes and stratovolcanoes. Some cinder cones are different than others, in that they only erupt once. However, even the ones that do erupt typically have a lower impact than stratovolcanoes.

Collision plate boundary

A collision or convergent plate boundary happens when two continental plates collide. Because neither plate can be destroyed they are forced upwards and downwards. The upwards section make fold mountains (the Himalayas were made like this) and the downwards section makes mountain roots. You get big earthquakes at collision boundaries because there is a massive build up of friction and pressure. However, because no plate is being destroyed, magma is not being created, so you do not get volcanoes.

Conservative plate boundary

A conservative or transform boundary happens when two continental plates move alongside each other. Because plates are not being forced up or down, there are no major landforms found at these boundaries. Also because crust is not being destroyed, no magma is being created so there are no volcanoes. However, there can be a huge build up of pressure between the two plates so massive earthquakes do occur. The most famous conservative plate boundary is the 'San Andreas Fault' where the North American and Pacific plates are moving past each other.

Volcano

A crack or hole in the earth's surface that allows magma, ash, gas or steam to escape to the surface.

Destructive / convergent plate boundary

A destructive or convergent plate boundary is when oceanic and continental crust collide. The denser oceanic crust is forced (subducted) under the continental plate. Huge amounts of heat from the mantle and also friction cause the oceanic plate to start melting in the subduction zone. The continental plate can not be destroyed so is forced up to make fold mountains e.g. Andes in South America. As the oceanic plate melts, it expands, becoming less dense. This causes some of the magma to rise to the surface through the fold mountains creating volcanoes. Where the oceanic plate subducts under the continental plate a very deep ocean trench is created. This is basically a deep valley in the sea. Ocean trenches are the deepest sections of the world's oceans. Big earthquakes are found at destructive plate boundaries because of the build up of pressure between the two plates. If a destructive plate boundary is found at sea, the continental crust (or less dense oceanic crust) is forced up to make an island arc instead of fold mountains. There are many examples of island arcs including the Caribbean, Indonesia, Japan and New Zealand.

Vent

A long tube or pipe that allows magma to escape to the surface.

Rift valleys

A rift valley is a type of divergent plate boundary. It happens when a continental plate starts pulling itself apart. The most famous rift valley is the Great African Rift Valley. Here the African plate is basically ripping in half along a fault that runs from Syria in the north down to Mozambique in the south. The rift valley is over 6,000km in length. As the plates pull apart the land in between the plates collapses creating a rift valley. Overtime this valley firsts fills up with lakes e.g. Lake Malawi and Lake Tanganyika and then sea e.g Red Sea. Eventually the East of Africa will be separated from mainland Africa by a new sea. As the plates pull apart magma is also able to escape from the mantle below, creating volcanoes e.g. Mount Kenya and Mount Kilimanjaro. Sometimes the rift valleys are called grabens and the remaining higher land horsts or block mountains. When the African plate finally rips in half the two plates will be known as the Somalian plate and the Nubian plate.

Shield volcano

A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They have very gentle slopes and are very developed horizontally. Shield volcanoes are built by effusive eruptions, which flow out in all directions. They almost never have violent eruptions, with basic lava simply flowing out.

Active volcano

A volcano that has erupted recently.

Dormant volcano

A volcano that has not erupted in recent history but may erupt again in the future.

Eruption (Erupting Volcano)

A volcano that is currently releasing lava, ash or gas.

Extinct volcano

A volcano that is unlikely to ever erupt again, because no magma is being produced under it. Often volcanoes that have not erupted for 10,000 years are considered to be extinct.

Magma chamber

An underground store of magma.

Earthquake

Any movement in the earth's crust. Thousands of earthquakes happen everyday, but most are so small they are not felt by humans.

Constructive / divergent plate boundary

At a constructive or divergent plate boundary two oceanic plates are moving apart. Constructive plate boundaries are found under the ocean e.g. Atlantic Ocean and cause the process of sea floor spreading (basically the ocean floor getting wider). The movement apart of the plates allows magma to escape from the mantle below. When the magma touches the ocean it cools and forms new land creating an oceanic ridge. The world's best example of an ocean ridge is the Mid-Atlantic ridge. Overtime ridges can break the surface of the water and form new islands e.g. Iceland. Because the plates are moving apart, there is not a large build of friction so earthquakes tend to be fairly gentle. Volcanoes tend to be less violent than at destructive plate boundaries but can be more constant. Volcanoes can also cause the problems of lahars in Iceland. This is basically the lava melting the snow above and causing a mudslide.

Secondary effects of earthquakes

Earthquakes can cause several secondary hazards, that can often be more damaging than the primary hazard. Secondary hazards caused by earthquakes include: - Tsunamis - Dam failure - Landslides - Fires - Disease - Exposure - Liquefaction Earthquakes are extremely hard to predict because they give no warning and the first earthquake is normally the strongest. Scientists (seismologists) look at earthquake history an attempt to identify plate pressure points to ascertain where earthquakes are likely to happen, but they can not predict how strong they will be or where they will happen.

Distribution of volcanoes and earthquakes

Found mostly on the coastline Especially on tectonic plate boundaries Volcano prone areas: 'The Ring of Fire' Around the Pacific plate. Across the North and South Atlantic ocean There are still anomalies - Hot spots Earthquake prone areas: Around Pacific Ocean Along the Indo-Australian pate boundary Eastern side of Eurasian plate Western side of North American plate Volcanoes and earthquakes are both found on plate boundaries. However, there is a difference between the two since volcanoes are never found on conservative and divergent boundaries because there is no change in crust to allow more magma (molten rock) to be made.

Viscosity

How thick something is. If you describe lave as being viscous, then it means that it is thick.

Magma

Molten (melted) rock under the crust.

Lava

Molten rock on the surface of the earth.

Lava flows

Most traditionally associated with volcanoes, but probably one of the least dangerous hazards to humans. Lava flows only travel up to a couple of km/hr so it is possible to move out of their way. However, they can bury and incinerate any land or property that they travel over.

Ash clouds

Not as fast moving as a pyroclastic flow, but ash clouds can still be very disruptive. The weight of falling ash can collapse buildings and destroy crops. They can reduce sunlight by blocking out the sun and even cause problems for air travel like the recent Iceland volcano.

Oceanic crust

Oceanic crust is younger, normally thinner, denser (heavier), destroyed, can be made

Stratovolcano (composite volcano)

Stratovolcanoes consist of many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. They generally have steep slopes and are the most common type of volcanoes on Earth. They tend to form at subduction zones (where one tectonic plate is sliding beneath the other - the oceanic plate beneath the continental plate). Their eruptions are typically explosive and effusive; the magma is generally rich in volatiles because the magma rises as water trapped both in hydrated minerals and porous basalt rock of the upper oceanic crust is released into mantle rock of the asthenosphere above the sinking oceanic slab. This release of water pushes the magma towards the surface. The chemical composition of the magma is intermediate because it incorporates both basic (from the oceanic plate) and acidic minerals (from the continental plate).

Structure of the earth

The centre of the earth is called the core. This heats the rock around it so it melts (becomes molten). The area of molten rock is called the mantle. The thin surface layer of the Earth is made up of cooled rock and is called the crust. The crust is broken into large pieces called plates. A plate boundary is where plates meet. The plates float on the mantle and the molten rock circulates. The movement of molten rock in the mantle causes convection currents which makes the plates move. The study of these plates is called plate tectonics. Most earthquakes and volcanoes eruptions take place at plate boundaries.

Crust

The crust is solid and is the layer we live on. The crust is usually between 10km and 60km thick. The crust thickness is often referred to as the relative thickness of an apple skin (when compared to the size of an apple).

Tectonic plates

The crust of the earth is broken into giants pieces. These giant pieces are called tectonic plates, or often just plates. There are seven major or primary plates (African, Eurasian, North American, South American, Pacific, Indo-Australian and Antarctica). There are seven smaller secondary plates (Nazca, Cocos, Caribbean, Scotia, Arabian, Philippine and Juan de Fuca). Because the plates are so big they have faults and cracks in them so are sometimes divided into smaller tertiary plates as well. The earth's plates are being constantly moved by convection currents found in the mantle.

Crater

The giant hole left by a volcanic eruption. Craters sometimes fill in with water to make crater lakes.

Lahars

These are a secondary hazard and normally occur on snow covered volcanoes. Hots ash and gas melt the snow and then mix. They then travel down the volcano as a fast moving mudflow which can drown or bury anything in their path.

Pyroclastic Flows

These are giant clouds of ash and gas. They are extremely dangerous because they can travel up to 500 km/hr, reach distances of 30km and can be over 700 degrees centigrade in temperature. They will burn, knock over or bury anything in their path

Aftershock

This is an earthquake that happen after the main earthquake. If the initial earthquake is strong, then the aftershocks can be very strong. Japan has had several aftershocks of over 7.0 since the initial 9.0 earthquake.

Epicentre

This is the location on the surface directly above the hypocentre (focus).

Richter scale

This is the normal scale used to measure the magnitude (strength) of an earthquake. The Richter scale goes up to 10 (although the scale effectively endless). The strongest ever recorded earthquake was a level 9.5 off the coast of Chile in 1960. The recent Japan (2011) earthquake was a 9.0.

Outer core

This layer is believed to be liquid and largely made of iron and nickel. It is extremely hot with temperatures up to 5,500 degrees centigrade.

Inner core

This layer is believed to be solid, because of the immense pressure placed upon it. It contains the centre of the earth which is about 6,378km from the surface. It is also extremely hot at about 5,500 degrees centigrade

Magnitude

This means how strong something is. Earthquakes are normally measured on the Richter scale.

Hypocentre (focus)

This the actually location that an earthquake takes place. The focus is always underground in the crust.

Mantle

This the thickest section of the earth with a diameter of about 2900km. The mantle is often described as being semi-molten, but in reality the top is hard rock and as you near the outer core it is beginning to melt (magma). Convection currents are found in the mantle.

Positive effects of earthquakes

Underground minerals may be brought nearer to the surface

Poisonous Gases

When volcanoes erupt they can release poisonous gases like carbon monoxide and sulphur dioxide. These can kill humans or animals if they are too close, but they can also contribute to the greenhouse effect.

Lava or Volcanic Bombs (tephra)

When volcanoes erupt they often throw out semi molten pieces of rocks. As long as humans are a safe distance they don't really pose any problems. However, because of their heat they can start fires.