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IGCSE Geography - Revision guide: Plate Tectonics

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Layers of the earth, plates, faults, tectonic landscapes, convergent, divergent plate margins, fold mountains

Volcanoes - types, dangers of volcanic eruptions, advantages of volcanic activity, primary, secondary effects, Mount Merapi Indonesia   

Earthquakes - effects, responses, living in an earthquake zone, 

Tectonic Plates - Main features (scroll)

Plate tectonics

click image to access quick revision of tectonic plates and continental movement

  • The Earth's surface is made up of a series of large plates (like pieces of a giant jigsaw puzzle).
  • These plates are in constant motion travelling at a few centimetres per year.
  • The ocean floors are continually moving, spreading from the centre and sinking at the edges.
  • Convection currents beneath the plates move the plates in different directions.
  • The source of heat driving the convection currents is radioactive decay which is happening deep in the Earth.

Test Interactive

Click on this image to access a quick recap and test your 'tectonic plates' skills!!

San Andreas fault

The Pacific Plate (on the west) moves northwestward relative to the North American Plate (on the east)these moving plates meet in western California; the boundary between them is the San Andreas fault, causing earthquakes along the fault. The San Andreas is the "master" fault of an intricate fault network that cuts through rocks of the California coastal region. The entire San Andreas fault system is more than 800 miles long and extends to depths of at least 10 miles within the Earth.

The presence of the San Andreas fault was brought dramatically to world attention on April 18, 1906, when sudden displacement along the fault produced the great San Francisco earthquake and fire. Read more from the USGS webpage HERE

Earthquakes - how do they happen ?

What is an earthquake?

An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter. Read MORE

What factors determine the destructiveness of an earthquake?

Location, Magnitude, Depth, distance from epicenter, Geologic condition, secondary effects, architecture. Read more details from the Smithsonian blog

Impact of an earthquake

Economic development of the location

Urban or rural area

Distance from epicentre

Weather and season

Time of day and Day of week

Emergency services and earthquake response plans

Landscape and rock type

Damages from earthquakes

• Shaking: moves the ground in place. This does not usually cause significant damage to the ground itself, but often results in major damage to structures in or on the ground. This can include, not only buildings, but water, gas and sewer lines, train tracks, and roads. 

• Landslides: ground is moved (displaced) to somewhere else .

• Liquefaction: strength of the ground is removed, causing the ground and objects on it to sink. Any heavy objects sitting on liquefied ground will rapidly sink. This includes all types of natural features as well as structures. Liquefaction can result in depressions, a type of landslide called a lateral spread, and the formation of sand blows

MEDC and LEDC disaster management

PORT-AU-PRINCE v CANTERBURY

Wealth: NZ much better resourced to cope.

Building codes/standards: Haiti's lacking.

Ground motion: Significantly less in Christchurch due to faulting distance.

Readiness: NZ's history of earthquakes meant Cantabrians knew what to do.

Emergency response: The comparatively minimal damage meant services could respond quickly, hospitals stay open.

Luck: The Christchurch quake struck at night when people were asleep, businesses shut.

Dynamic Earth - Interactive

click on image to access Interactive's Dynamic Earth

Plate Boundaries

Earth's outer layer, the crust, is divided into a set of large moving plates. The lines where they meet are called plate boundaries.

There are three main types of plate boundary: divergent, convergent and transform. Plates move away from one another at divergent boundaries. This happens at mid-ocean ridges.

Plates move towards one another at convergent boundaries; one plate is forced below another in a process called subduction. Earthquakes and composite volcanoes are common at this type of boundary.

Plates move past on another at transform boundaries. The most famous example of this type of boundary is the San Andreas Fault in California. Read more about this from BBC

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Tectonic Plates - NatGeo

There are a few handfuls of major plates and dozens of smaller, or minor, plates.

Six of the majors are named for the continents embedded within them, such as the North American, African, and Antarctic plates. Though smaller in size, the minors are no less important when it comes to shaping the Earth.

The tiny Juan de Fuca plate is largely responsible for the volcanoes that dot the Pacific Northwest of the United States. Read more from NatGeo

Fold Mountain

Fold mountains are created when two of the Earth’s tectonic plates crash together – like in a head-on car crash. The edges of the two plates buckle and fold, and the peaks of these folds are mountains. Entire mountain ranges, thousands of kilometers long, are created during these slow motion collisions between tectonic plates. Some famous examples of fold mountains are the Himalayan mountains in Asia and the Rocky Mountains in North America. 

How do scientists measure earthquakes?

Magnitude is a measure of the energy released during an earthquake, and it's related to the size of its waves on a seismogram. Seismologists use several different magnitude scales to desribe the size of a quake. The Richter scale is the one most commonly referred to. For mathematical reasons, Richter is accurate only up to about 6.5. For larger quakes, scientists use the newer moment magnitude scale. source

How do scientists measure jolts such as the recent disaster in Japan? Hint: They don’t use the Richter scale.

Instead, scientists use the moment magnitude scale, developed in the 1970s. An earthquake produces many types of waves, which radiate from its epicenter and move with a wide variety of frequencies. Compared to the Richter scale, the moment magnitude scale can account for more types of these waves, and at more frequencies. Read more about the 'moment magnitude' scale HERE

Haiti and Christchurch earthquakes

At first blush, the earthquake that struck Christchurch, New Zealand on Saturday was the spitting image of the one that ravaged Haiti in January. Each was a powerful magnitude 7.0 quake, and each occurred on a strike-slip fault near a major population center.

Reports out of Christchurch have been almost miraculous: Though the city suffered extensive damage, not a single person out of nearly 400,000 appears to have died. By contrast, the Haitian capital city of Port-au-Prince was flattened, and a quarter of a million people were killed.

What are the reasons for such a stark contrast ? Read from these two news articles to find out

BBC videos on Volcanoes

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Can Volcano eruptions be predicted?

How do volcanoes form?

How do volcanoes form?
Deep inside Earth, between the molten iron core and the thin crust at the surface, there is the mantle, a large layer of rock that is largely solid, but flows like plastic. When, for various reasons, rock from the mantle melts, it sometimes moves to the Earth?s surface through weak spots in the crust, releasing heat, gasses, and rock--a volcanic eruption. source

Volcano Glossary

Volcano - a vent (opening) at the Earth's crust through which magma (molten rock) and associated gases erupt.
Magma - molten rock beneath the surface of the Earth.
Lava - magma that has reached the surface.
Cinders - lava fragments about 1 centimeter in diameter.
Pyroclastics (“fire fragments”) - ash, cinders, angular blocks, and rounded bombs (block and bomb fragments can be over 1 meter in diameter).
Explosive eruptions – eject lava and pyroclastics.
Quiet eruptions
 – fluid lava flows out of a volcano's vent.

Types of Volcanoes (use scroll bar)

Click on image to read about Volcano types from Utah geological survey

Geologists have identified 3 major types of volcanoes:
There’s the shield volcano, formed from low viscosity lava that can flow long distances.
There are cinder cone volcanoes, which are made by the eruption of lava, ash and rocks that build up around a volcanic vent.
But the last type is the composite (strato) volcano, and these are some of the most famous volcanoes (and most dangerous) in the world. A composite volcano is formed over hundreds of thousands of years through multiple eruptions. The eruptions build up the composite volcano, layer upon layer until it towers thousands of meters tall. Some layers might be formed from lava, while others might be ash, rock and pyroclastic flows. 
Some of the most famous volcanoes in the world are composite volcanoes. And some of the most devastating eruptions in history came from them. For example, Mount St. Helens, Mount Pinatubo, and Krakatoa are just examples of composite volcanoes that have erupted. Famous landmarks like Mount Fuji in Japan, Mount Ranier in Washington State, and Mount Kilimanjaro in Africa are composite volcanoes. From Universe Today

Volcanoes - Animation

Volcano Hazards

Volcanic eruptions are one of Earth's most dramatic and violent agents of change. Not only can powerful explosive eruptions drastically alter land and water for tens of kilometers around a volcano, but tiny liquid droplets of sulfuric acid erupted into the stratosphere can change our planet's climate temporarily.

click on image to read full details

Mount Merapi - Indonesia

Mount Merapi, which looms on the horizon north of the major city of Yogyakarta, is located on the island of Java.

A total of "380,049 people are still displaced in around Yogyakarta and Central Java." The death toll from the volcano's latest round of eruptions, which started October 26, has reached 206, and nearly 400,000 people have had to flee their homes...