The Restless Earth

Volcanoes, Earthquakes and Fold Mountains

Distribution of plates

Oceanic crust: newer – less than 200 million years old; denser; can sink; can be renewed or destroyed.

Continental crust: older – most over 1500 million years old; less dense; cannot sink; cannot be destroyed or renewed.

Plates – Pacific Plate covers most of Pacific Ocean – ‘Ring of Fire’.

Plate marginsDestructive plate margins: plates move together. A subduction zone forms where the denser oceanic crust sinks under the lighter continental crust. Great pressure is exerted and the oceanic crust is destroyed as it melts to form magma. If two continental plates meet, they collide rather than one sinking beneath the other. This collision boundary is a different type of destructive margin.

Constructive plate margins: When plates move apart – usually under oceans. As the plates pull apart, cracks form and magma wells up these cracks, forming volcanoes.

Conservative plate margins: the plates slide past each other. They often get stuck and this builds up pressure, resulting in earthquakes.

Landforms

Fold mountains: large mountain ranges where rock layers have been crumpled as they have been forced together.

Ocean trenches: deep sections of the ocean, usually where an oceanic plate is sinking below a continental plate.

Composite volcano: a steep sided volcano that is made up of a variety of materials, such as lava and ash.

Shield volcano: a broad volcano that is made up of lava.

Case Study of Fold Mountains: The Alps

Farming: The fold mountains of the Alps are used for pastoral farming – sheep, goats, cattle. They practice transhumance – the movement of the animals up the slopes to the summer pastures.

The melt waters from the melting snow is used to generate hydro-electric power (HEP).

Tourism is a key industry in the Alps. In the winter, many people come for the skiing and other winter sports.

Life in the mountains can be difficult due to inaccessibility, the threat of avalanches, steep slopes and poor soils. Tunnels have been built through the mountains to make travelling easier.

Countries – Austria, Italy, France,

Switzerland.

Volcanoes Shield volcanoes: so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lavas that can flow a great distance from a vent, but not generally explode catastrophically. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland, as well.

Composite volcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. Composite volcanoes are aso known as stratovolcanoes. Strato/composite volcanoes are made of cinders, ash and lava. The volcanoes are made by another volcano. Cinders and ash pile on top of each other, then lava flows on top and dries and then the process begins again. Classic examples include Mt. Fuji in Japan, Mount Mayon in the Philippines, and Mount Vesuvius and Stromboli in Italy.

Case Study: Volcanic eruption – Montserrat, Caribbean

Secondary effects: Small eruptions continued. Infrequent ventings of ash into the uninhabited areas. People still haven’t been able to go home.

Cause: On a destructive plate margin. 1995 Soufriere Hills volcano erupted.

Primary effects: Plymouth the capital was buried in 40m of mud. The port & airport were destroyed. Many homes were destroyed. Half the population had to flee. Death & destruction.

Immediate responses: British navy sent to evacuate island; emergency services rescued people. People moved from homes. Helicopters. Ash cleared.

Long term responses: Better monitoring of volcano; restricted access. Rebuilding of roads and bridges. Trees replanted.

Monitoring and predicting volcanoes: observation of ‘bulges’; use tiltmeters to identify changes in the landscape. Use GPS (Global Positioning Systems) and satellite imaging – detect temperature changes. Use robots to collect gases being emitted. Warn people & evacuate.

Supervolcanoes

Characteristics - Much bigger than other volcanoes. Only a few.An eruption would have global consequences. The explosion will be heard around the world. The sky will darken, black rain will fall, and the Earth will be plunged into the equivalent of a nuclear winter.

Yellowstone National Park - Is one of the largest supervolcanoes in the world. Scientists have revealed that it has been on a regular eruption cycle of 600,000 years. The last eruption was 640,000 years ago... so the next is overdue.

Location and causes of earthquakes

Location : along plate boundaries.

Causes: when pressure and tension built up along a fault line or plate margin is suddenly released.

Features of earthquakesEpicentre the point at the earth’s surface directly above the focus.Focus – the point in the earth’s crust where the earthquake originates.Shock waves – seismic waves generated by an earthquake that pass through the earth’s crust.

Measuring earthquakes

Richter Scale - a logarithmic scale used for measuring earthquakes, based on scientific recordings of the amount of movement

Mercalli Scale – a means of measuring earthquakes by describing and comparing he damge done on a scale of I to XII.

Case Study of earthquakes –Haiti 2010 – poorer area of the world

Location, features and size: The epicentre of the magnitude 7.0 quake was near the densely populated Haitian capital, Port-au-Prince. Strong aftershocks rocked Haiti.Causes: The earthquake was caused by pressure and tension along the boundary of the Caribbean Plate and the North American Plate being suddenly released. Primary effects: 100,000

deaths; widespread damage to buildings and infrastructure.

Secondary effects: UN had to enforce law and order; outbreak of disease (cholera); homelessness; emergency health care.

Immediate responses: International rescue teams and emergency doctors and aid (tents). Charities and governments.

Long term responses:The International Community will be working in Haiti for many years to come trying to rebuild what was already a very poor country. This catastrophe will set the country back a whole generation.

Case Study of earthquakes Kobe, Japan, 1995 – richer area of world

Causes: the Philippine Plate shifted beneath the Eurasian Plate along the Nojima fault that runs under Kobe.

Primary effects: death (6,434 died); serious injuries (40,000); homelessness (300,000); gases mains erupted; water pipes leaked; roads and bridges collapsed) railway lines buckled; homes without water and electricity; fire.

Immediate responses: rescue of trapped people; emergency operations; telecommunications restored; rebuilding of roads, bridges and the port.

Long term responses: new building have to be earthquake proof; all citizens have to be prepared for earthquakes; earthquake drills; emergency services prepared; media used to warn people.

Tsunami Case Study – Indian Ocean 2004

A tsunami is a special type of wave where the entire depth of the sea or ocean is set in motion by an event, often an earthquake, which displaces the water above it and creates a huge wave.

Cause: the Indo-Australian Plate subducted beneath the Eurasian Plate. The Earthquake measured 9.1 on the Richter scale.

Effects: Waves of 25m first hit Sumatra in Banda Aceh and then Sri Lanka and Thailand. 220,000 died. 650,000 were seriously injured. 2 million were made homeless. Many buildings were destroyed. 1,500 villages were wiped out. Many people were missing feared dead.

Responses: rescue services & emergency teams were overwhelmed with the scale of the disaster. The international community responded with fresh water, food, sheeting and tents. Charities and governments raised millions. The UK Disasters Emergency Committee co-ordinated the British response. The affected areas were rebuilt and a tsunami early warning system set up.