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Tectonic Landscapes Explore the varying impact of both volcanic (extrusive and intrusive) and seismic processes on landscapes Research different locations to draw out the importance of tectonic activity in creating contrasting landscapes Bibliography
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Tectonic Processes and Landscapes

Jun 01, 2015

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Page 1: Tectonic Processes and Landscapes

Tectonic Landscapes

Explore the varying impact of both volcanic (extrusive and intrusive)

and seismic processes on landscapes

Research different locations to draw out the importance of tectonic

activity in creating contrasting landscapes

Bibliography

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Explore – the concepts, theories, models.

Research - case studies + examples to support theories and models.

Landscapes - total surface of any human or natural area. Everything around the landforms as well as the landform itself.

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• Convergent (click for case studies)– Destructive– Collision

• Divergent (click for case studies)

• Transform (click for case studies)

Plates can be...

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Convergent plate boundaries (together)

• The two types of margins that occur here are destructive Margins or Collision Zones.

• Destructive oceanic crust moves towards continental crust. Oceanic crust sinks, and slowly destroyed. Results in deep ocean trenches, island arcs and fold mountains. – Here crust is destroyed and recycled back into the interior of the Earth

as one plate dives under another. These are known as Subduction Zones - mountains and volcanoes are often found where plates converge.

• Collision Zones Two continental crusts meet, neither sinks, fold mountains result. For example, the Alps.

• There are 3 types of convergent boundaries: – Oceanic-Continental Convergence– Oceanic-Oceanic Convergence– Continental-Continental Convergence.

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Convergent boundary of an oceanic plate and a continental plate

DESTRUCTIVE

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Convergent boundary of two continental plates.

COLLISION

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Continental-Continental ConvergenceWhen two continents meet head-on, neither is subducted because the continental rocks are relatively light and, like two colliding icebergs, resist downward motion. Instead, the crust tends to buckle and be pushed upward or sideways. The collision of India into Asia 50 million years ago caused the Eurasian Plate to crumple

up and override the Indian Plate. After the collision, the slow continuous convergence of the two plates over millions of years pushed up the Himalayas and the Tibetan Plateau to their present heights. Most of this growth occurred during the past 10 million years.

Oceanic-Continental Convergence When an oceanic plate pushes into and subducts under a continental plate, the overriding continental plate is lifted up and a mountain range is created. Even though the oceanic plate sinks continuously into the subduction trench, the deepest part of the subducting plate breaks into smaller pieces. These smaller pieces become locked in place for long periods of time before moving suddenly and generating large earthquakes.

Oceanic-Oceanic Convergence When two oceanic plates converge one is usually subducted under the other and in the process a deep oceanic trench is formed. Oceanic-oceanic plate convergence also results in the formation of undersea volcanoes. Over millions of years, however, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form an island volcano. Such volcanoes are typically strung out in chains called island arcs.

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Divergent plate boundaries

• Also known as a Constructive margin.

• Plates move away from each other

• Eg. N. American and Eurasian plates, cresting mid-ocean ridges such as the Mid Atlantic Ridge.

• New material appears at the ocean ridge.

• Sea Floor Spreading

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Transform boundaries • Here plates simply move alongside each other, land is neither created nor

destroyed.

• Transform-Fault Boundaries are where two plates are sliding horizontally past one another.

• Most transform faults are found on the ocean floor and are generally defined by shallow earthquakes.

• A few, however, occur on land. The San Andreas fault zone in California is a transform fault that connects the East Pacific Rise, a divergent boundary to the south, with the South Gorda -- Juan de Fuca -- Explorer Ridge, another divergent boundary to the north.

• Along it, the Pacific Plate has been grinding horizontally past the North American Plate for 10 million years, at an average rate of about 5 cm/yr.

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Divergent/Constructive Boundaries• Earthquakes in these locations are relatively shallow and usually have a magnitude of

less than 8.0 on the Richter scale. • Usually found beneath the oceans, and sometimes underwater volcanoes are formed.

Convergent/convergent Boundaries• Location of the earth’s largest earthquakes.

Transform Boundaries• Crust is neither created nor destroyed, plates slide past each other.

Tectonic activity associated with different types of plate margin

Types of crust involved Landforms

Oceanic Continental Ocean trenches, volcanic mountain ranges

Oceanic Oceanic Ocean trenches, volcanic island arcs

Continental Continental Fold Mountains

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Hotspots • Volcanoes

These occurrences are described either as VOLCANIC or SEISMIC

Plate Margin Earthquake Depth Types of volcano

Constructive Shallow (0-70km below surface) Shield, Cinder

Transform Shallow (0-70km below surface) Rare

convergent Intermediate (70-300km below surface)Deep (300-700km below surface

CompositeCinder

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Igneous – formed from molten rock within the earth

Metamorphic - rocks that have been changed as a result of heat and/or pressure. Eg. Slate/Marble

Extrusive – bigger crystals. Eg. Lava, Giants Causeway

Intrusive – if rock crystals are bigger, it means the magma cooled slower. More defined shape. Eg. Magma, granite.

VOLCANIC

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Volcanic, ExtrusiveVolcanoes∆ Type of explosivity∆ Shape∆ Location in connection with plate boundaries∆ Plate margin + Rock Type

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∆ Lava – when magma flows onto the surface of the earth, it is referred to as lava.

∆ Pyroclasts – fiery, volcanic materials. ∆ Pyroclastic Flow – a mixture of superheated rock

and hot gases that rapidly flows down the side of a volcano.

∆ Lahars – volcanic mud flow. ∆ Volcanic gases – water vapour, carbon dioxide,

sulphur dioxide.

Volcanic Terminology

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Shield Volcano eg. (Mauna Loa, Hawaii)

• Low, wide cone

• Fluid Lava

• Gentle Slope

• Shield volcanoes are usually found at constructive boundaries.

• They are formed by eruptions of thin, runny lava.

• Eruptions tend to be frequent but relatively gentle.

Types of Volcanoes

Composite Volcano eg. (Mt St Helens)• Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just

consist of lava).• They are usually found at convergent or compressional boundaries.• The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow.

A pyroclastic flow is a mixture of hot steam, ash, rock and dust.• A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of

over 400° C.

Fissure Very gentle slope, found at diverging ocean plates, basaltic lava, can flow over large distances.

Cone Symmetrical in shape, A) acid where thick viscous lava, rapidly cools, B) Ash / Cinder.

Crater / Caldera Form when a very violent eruption occurs after a build up of gas beneath the volcano. Can destroy the magma chamber leaving a large crater.

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• Hawaiian Type - Lava slowly and easily escapes from vent. It is runny, basaltic. Gases escape easily & gentle sided volcanoes result.

• Strombolian type - Gas explosions occur more frequently, small but frequent eruptions. Cone shaped volcano.

• Vulcanian type - Gas emissions involved, more violent but less frequent than above. Plugs of cooled lava may be ejected in blast.

• Vesuvian type - Extremely strong explosions, often after volcano has been dormant for a while. Gas and ash clouds, which fall over a large area.

• Krakatoan type - Exceptionally violent.• Plinian type - Usually most violent. Massive amounts of lava,

gas and pyroclastic material emitted. Part of the volcano may be removed.

Eruptions

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Magma Generation

Magma Type Generation Tectonic Setting Hazards

BasalticLow silica, low gas, loc viscosity

Dry partial melting of upper mantle

Oceanic Hot spot (Hawaii)Constructive (Iceland)

Lava flow

AndesiticIntermediate

Wet partial melting of subducting plates

convergent plate margin (Andes)Island arc margin (Montserrat)

Lava flow, ash and tephra, pyroclastic flow, lahar, gas emission

RhyoliticHigh silica, high gas, high viscosity

In situ melting of lower continental crust (very rare eruptions

Continental Hot spot (Yellowstone)Continent collision zone (Himalayas)

Cataclysmic explosion, pyroclastic flow

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• A flood basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava.

Examples:• Deccan Traps• Ethiopian Highlands• Columbia River Basalts• Siberian Traps

Flood Basalts

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Hotspots (Hawaii)• A “plume,” lies at a fixed position under the Pacific Plate.

• As the ocean floor moves over this “hot spot” at about five inches a year, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate - a veritable conveyor belt of volcanic islands.

• Hawaii itself consists of five connected volcanic mountains that were built by this lava plume rising from the mantle.

• Kilauea, the world’s largest active volcano, is still rumbling because the island has yet to move completely off the hot spot. The farther the other islands in the chain are from Hawaii, the greater their age.

• About 2,000 miles from Hawaii, the chain abruptly veers and extends north as a line of submerged volcanoes known as the Emperor Seamounts.

• As it stands today, Loihi rises about 6,000 feet above the sea-floor, which brings it very close to the surface. But you won’t be making any immediate vacation plans to the next Hawaiian Island. At its present rate of ascension, scientists predict that Loihi will poke through the surface in about one million years.

• Similar trails of conveyor-belt volcanoes are found elsewhere in the world, but sometimes a hot spot finds itself under a Mid-Ocean Ridge, a point of sea-floor spreading. When this happens the islands are built on each of the spreading plates, and eventually form a V-shaped pattern as the ocean floors move farther away from the ridge.

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Convergent boundary of two oceanic plates.

Creates an island arc and a tranch.

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• Intrusion: the movement of magma underground into spaces that exist within rock strata. When this magma cools and hardens, intrusive volcanic landforms are created. Weathering and erosion causes these landforms to be exposed.

Volcanic Intrusive

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Pluton∆ An intrusive igneous rock body that crystallised from magma slowly cooling below the

surface of the Earth. Plutons include batholiths, dikes, sills, laccoliths, and other igneous bodies. 

Batholiths∆ Largest of the igneous rocks that form as a result of intrusive activity.∆ Irregular in shape and often composed of granite.∆ Some may be visible, due to weathering but most remain buried because of their

enormous size.Dikes∆ Usually a vertical or near vertical sheet of rock that is created when magma is thrust into a

body of pre-existing rock. Sills∆ A long, thin intrusion of igneous rock through pre-existing strata. They are unlike dikes in

that they intrude between other layers, forming a distinct layer of their own. Laccolith∆ A dome of igneous rock that is formed between two layers of pre-existing sedimentary

rock. Created when slow-flowing, highly viscous magma is forced between the horizontal layers of existing strata. Eventually the magma building up into a dome or mushroom shape.

Vein∆ Magma forced into very small cracks, fractures and openings.

Intrusive

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Earthquakes – shaking of the earth

Internal structure of the earth, plate tectonic theories Ground displacement Liquifaction Faults str k kslk piei , normal, reverse

SEISMIC

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Displacement - when land is moved. The shaking of the ground during earthquakes can also result in landslides and avalanches.

Eg. Before earthquake After earthquake

Liquefaction - occurs when soils are turned into a ‘suspension’ and in soils that are ‘saturated’. Leads to the complete loss of soil strength and stability.

Orogeny - The process of mountain formation, especially by a folding and faulting of the earth's crust

Earthquake Terminology

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Faults• A fault is a break in the crust

where slabs of crust slip past each other. The rocks on both sides of a fault can move up or down or sideways

• When enough stress builds on a rock, the rock shatters, creating faults

• Faults usually occur along plate boundaries, where the forces of plate motion compress, pull, or shear the crust too much so the crust smashes.

• A transform fault actually forms the plate boundary

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Page 31: Tectonic Processes and Landscapes

Strike-Slip Faults

• Shearing creates this fault

• In this fault, rocks on both sides of the fault slide past each other with a little up and down motion

• When a strike-slip fault forms the boundary between two plates, it becomes a transform boundary

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Tectonic Landforms

Faults and Fault LandformsTranscurrent or Strike-slip Faults are produced when tectonic plates move past each other horizontally

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Normal Faults• Tension forces in Earth's crust

causes these types of faults• Normal faults are at an angle, so

one piece of rock is above the fault, while the other is below the fault

• The above rock is called the hanging wall, and the one below is called the footwall

• When movement affects along a normal fault, the hanging wall slips downward

• Normal faults occur along the Rio Grande rift valley in New Mexico, where two pieces of Earth's crust are diverging

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Reverse Faults• Compression forces

produce this fault• This fault has the same

setup as a normal fault, but reversed, which explains it’s name

• Just like the normal fault, one side of the reverse fault is at an angle of the other

• This fault produced part of the Appalachian Mountains in the eastern United States

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Tectonic Landforms

Faults and Fault Landforms

Reverse and overthrust faults are produced by compression in the crust

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Fold Mountains

• Fold mountains are formed when two plates, either continental-continental or oceanic-continental, meet and neither is subducted. Instead, they push together and land is forced upwards, forming mountains.

• Avalanches are a constant threat. Huge amounts of money are spent each year to try and combat the avalanche threat, especially with the large amount of tourists using the mountains.

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Secondary EffectsSecondary effects are the subsequent effects of the quake, and can be

even more devastating then the primary ones. The main secondary effects are:

• Soil liquefaction: Solid material changed into a liquid state. Damages building foundations, resulting in them sinking.

• Landslides: Often as a result of the ground shaking, even if a slope is gentle. Cause burial of people and overrun buildings.

• Tsunami (tidal waves): If the focus of the quake is beneath the sea, tsunami can occur. Ninety percent occur in the Pacific basin. The more movement of the sea floor and the shallower the focus the larger the wave that is created.

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Volcanoes may be associated with creating new land, but we often associate earthquakes with destruction.

Effects of earthquakes on landscapes

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Divergent boundary of two continental plates.

Creates a rift valley.

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Graben• Another name for a Rift Valley is Graben

(German for ditch) A graben is a depressed block of land bordered by parallel faults.

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CONVERGENTcase studies

The Pacific Ring of Fire Montserrat

Mt Pinatubo, Phillipines Krakatau, Indonesia

Mt St. Helens

Kamchatka Aleutian Islands of Alaska

Kobe Earthquake

Andes

Himalayas 2004 Tsunami

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• In a 40,000 km horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements.

• The Ring of Fire has 452 volcanoes and about 90% of the world's earthquakes and 80% of the world's largest earthquakes occur along the Ring of Fire.

The Pacific Ring of Fire

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• Montserrat rests on the boundary of the continental Caribbean plate and the oceanic Atlantic Plate.

• It is a composite volcano• In August 1995, there was a phreatic eruption.• When the major pyroclastic event occurred on 25th June 1997, around 6millionm^3 of

material was dumped onto the island in just a few minutes.

• Farrell's YardThe fine grained pyroclastic surges spread out to each side over the top of the valley ridges travelling north, west and east. They broke and flattened trees on the ridges in the Farrell's Yard.

• As the lava flowed into the sea it warmed up and so many coral reefs died as a result of the change in temperature.

Montserrat

CONVERGENT - DESTRUCTIVEBACK

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Between Northern California and British Columbia, the Pacific, Juan de Fuca,

and Gorda plates have built the Cascades and the infamous Mount Saint Helens which erupted in 1980.

The pressure inside the volcano caused a huge dome to form on the side of the

volcano. When it erupted, due to an earthquake, the dome collapsed and lava ran

down the sides.

Flooding resulting from blocked rivers washed away road and rail bridges

Crops were ruined and livelihoods of loggers were devastated with large areas of trees

being flattened like matchsticks.

Mt St. Helens

CONVERGENT - DESTRUCTIVEBACK

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• The second-largest volcanic eruption of this century, and by far the largest eruption to affect a densely populated area, occurred at Mount Pinatubo in the Philippines on June 15, 1991. The eruption produced high-speed avalanches of hot ash and gas, giant mudflows, and a cloud of volcanic ash hundreds of miles across. The impacts of the eruption continue to this day.

• Huge avalanches of searing hot ash, gas, and pumice fragments (pyroclastic flows) roared down the flanks of Mount Pinatubo, filling once-deep valleys with fresh volcanic deposits as much as 660 feet (200 meters) thick. The eruption removed so much magma and rock from below the volcano that the summit collapsed to form a large volcanic depression (caldera) 1.6 miles (2.5 kilometers) across.

• More than 86,000 hectares of agricultural lands and fishponds were affected by ashfalls and lahars.

• This phenomenon caused the world’s temperature to fall by an average of 1 degree Celsius

Mt Pinatubo, Phillipines

CONVERGENT - DESTRUCTIVEBACK

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• Krakatau is located in the Sunda Strait, 40 km off the west coast of Java on the island of Rakata in Indonesia.

• Krakatoa is part of avolcanic arc. The volcano was formed by the subduction of the Indian-Australia Plate under the Eurasian Plate.

• It erupted on August 26,1883 and the eruption was categorised as ‘colossal’. When it first erupted, the entire northern portion of the island was blown away.

• There was a rain of volcanic ash and pumice from the eruptions. In the nearby islands everything was buried under a thick layer of ash. Plant and animal life did not begin to re-establish itself to any degree in these nearby islands for nearly five years.

• The combined effects of pyroclastic flows, volcanic ashes, and tsunamis had disastrous results in the region.

• Average global temperatures fell by as much as 1.2 degrees Celsius in the year following the eruption. Weather patterns continued to be chaotic for years and temperatures did not return to normal until 1888.

Krakatau, Indonesia

CONVERGENT - DESTRUCTIVEBACK

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Kamchatka

• From Russia's Kamchatka Peninsula to Japan, the subduction of the Pacific plate under the Eurasian plate is responsible for Japanese islands and volcanoes (such as Mt. Fuji).

• It is a continental arc.

CONVERGENT BACK

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Aleutian Islands of Alaska

• Oceanic-Oceanic plate

• Alaska's Aleutian Islands are growing as the Pacific plate hits the North American plate.

• The 300+ islands, with their 57 volcanoes, are in the northern part of the Pacific Ring of Fire. 

• The deep Aleutian Trench has been created at the subduction zone with a maximum depth of 25,194 feet (7679 meters).

CONVERGENT - DESTRUCTIVEBACK

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• Earthquake measuring 7.2 on the Richter Scale. The earthquake lasted 20 seconds.

• Epicentre was under Awaji Island in Osaka Bay, close to the port city of Kobe, Japan.

• Here the ground actually liquefied and acted like thick soup, allowing buildings to topple sideways, resulting in the huge cranes in the harbour toppling over into the sea.

• 17th Jan 1995 at 5.46am.• Located on a destructive plate margin. Pacific Plate and the

Eurasian Plate• 250 000 people left homeless• 5000 people died mostly as a result of fires caused by ruptured gas

mains.• 25 000 injured• Older buildings were worst hit.• Total cost est. $100 billion

Kobe Earthquake

CONVERGENT - DESTRUCTIVEBACK

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The Andes• In South America the Nazca plate is colliding with the South

American plate.• Fold Mountains• At a destructive plate boundary the oceanic plate is subducted

beneath the continental one. The molten material then rises to the surface to form volcanoes, either in an island arc (e.g. the West Indies) or on the continental land mass (e.g. the volcanoes of the Andes). In both cases Fold Mountains can be formed.

• When the Nazca plate dives under the South American one, their motion forward also has been pushing sediment together. This, over millions of years, has been pushed up into huge fold mountains: The Andes. Within them there are also volcanoes as the mountains are above the subduction zone.

• The Andes are a orogenic belt of mountains along the Pacific Ring of Fire. 

CONVERGENT – DESTRUCTIVEBACK

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Himalayas• Fold Mountains• The Himalayas are the result of the collision of two continental plates at

a collision or convergent plate boundary. This type of event is called an orogeny.

• These occur less frequently, but one example is the Himalayas, where the Indian plate is moving North and East towards the stationary European plate.

• Both plates are Continental ones, and so can neither sink nor be destroyed. The material between them is therefore forced upwards to form the mountains.

• For the Himalayas the material that now forms the mountains was originally on the bottom of the non-existent Tethy's Sea. As the Indian plate pushed towards the Eurasian one, the sediments were folded up to form the Himalayas, leaving the only trace of the sea to be the fossilised shells that you can find high up in the mountains.

CONVERGENT – COLLISIONBACK

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• A huge wall under the sea was created when the land was displaced at the fault.

2004 Tsunami

CONVERGENT - DESTRUCTIVE

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DIVERGENT case studies

The Mid-Atlantic Ridge Iceland The Great Rift Valley

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•  It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South American Plate in the South Atlantic.

• Although the Mid-Atlantic Ridge is mostly an underwater feature, portions of it have enough elevation to extend above sea level. (Iceland)

• At Mid-Ocean Ridges, two plates are pulling apart from each other as hot magma emerges from the mantle and oozes forth as lava to fill the crack continuously created by plate separation. The lava cools and attaches itself to the trailing edge of each plate, forming new ocean floor crust in a process commonly known as sea-floor spreading.

• The Mid-Atlantic Ridge includes a deep rift valley which runs along the axis of the ridge along nearly its entire length. This rift marks the actual boundary between adjacent tectonic plates, here magma from the mantle reaches the seafloor, erupting as lava and producing new crustal material for the plates.

The Mid-Atlantic Ridge

DIVERGENTBACK

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• Iceland is part of the Mid-Atlantic Ridge that owes its very existence to the molten rock, or magma, that wells up through the rifts along the ridge. Scientists believe Iceland rose from the sea floor about 20 million years ago. Continuous spreading, accompanied by eruptions along Iceland's section of the ridge, widens the country by about one inch per year.

• Over one third of Iceland's 40,000 square miles is volcanically active and loaded with lava fields. Elsewhere, magma too far below the surface to create volcanoes heats the rock above, sending the heated groundwater percolating to the surface in the form of "hot springs."

• Iceland is far enough north so that it should be entirely covered by ice and snow, like Greenland to the west. The heat generated by the ridge, however, keeps the country in a constant state of thaw, distinguishing it as the Land of Fire and Ice.

Iceland

DIVERGENTBACK

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The Great Rift Valley• The Great Rift Valley is a name given

to the continuous geographic trench, approximately 6,000 kilometres (3,700 mi) in length, that runs from northern Syria in Southwest Asia to central Mozambique in East Africa.

• Upwelling mantle may melt to produce magma, which then rises to the surface, often along normal faults produced by the extensional deformation. 

• Basaltic and rhyolitic volcanism is common in these areas. 

• In the same area, the crust has rifted apart along the Red Sea, and the Gulf of Aden to form new oceanic ridges.  This may also be the fate of the East African Rift Valley at some time in the future

DIVERGENTBACK

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TRANSFORM case studies

Haiti Earthquake New Zealand Earthquake

California Earthquake Kobe Earthquake

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• Magnitude 7.0• Tuesday, January 12, 2010 at 21:53:10• The fault slipped after a pause of 200 years.• Lateral spreading• White sand was forced upwards from the sea bed on top of the tarmac.• The shaking of the earth is believed to have been amplified by the geology of the land

because the rocks were relatively young and soft. • However, the earthquake seems not to have caused any major, immediate damage

to Haiti's ecosystem. • There was one small spill near a coastal oil terminal, some minor warehouse fires

and a few small landslides close to Port-au-Prince, but nothing that required a significant emergency response.

Haiti Earthquake

TRANSFORM – STRIKE/SLIPBACK

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• Occurred Friday, September 03, 2010 at 16:35:46 UTC• Magnitude 7.0 • Occurred as a result of strike-slip faulting caused by the ongoing tensions between the

Pacific and Australian tectonic plates• A new fault line is believed to have been created. One side of the earth has lurched to

the right, up to 11 feet (3.5 meters) and in some places been thrust up.

New Zealand Earthquake

The earthquake struck approximately 50 km to the west-northwest of Christchurch, the largest population center in the region, and about 80-90 km to the south and east of the current expression of the Australia:Pacific plate boundary through the island (the Alpine and Hope Faults). Government seismology agency GNS Science reported that more than 280 aftershocks of magnitude 3.0 or greater have struck the region in five days.No one was killed and only two people were seriously injured _ which authorities attributed to good building codes and the quake's early morning timing.

TRANSFORMBACK

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• Earthquake measuring 6.9 on the Richter Scale.• San Francisco, California, USA• 17th October 1989 at 5.04pm• Located on a conservative plate margin. Juan de

Fuca Plate & North American Plate• 2 000 people left homeless• 67 people died• 3000 injured• Older buildings were worst hit.• Total cost est. over $7 billion

The San Andreas Fault

TRANSFORMBACK

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OTHER LANDSCAPES CREATED BY

TECTONIC ACTIVITY

Dartmoor - Batholith Isle of Arran

The Lulworth CrumpleGiant’s Causeway

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Dartmoor - Batholith

• Dartmoor includes the largest area of granite in Britain. The granite was intruded at depth as a pluton into the surrounding sedimentary rocks.

• Dartmoor is known for its tors – large hills, topped with outcrops of bedrock, which in granite country such as this are usually rounded boulder-like formations.

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Isle of ArranNorth Arran – Batholith formation

• As the granite is harder and more resistant to erosion than the surrounding sedimentary

rocks, it stands up as higher ground forming Arran’s northern hills and mountains.

• Further erosion and chemical weathering of joints in the granite has given rise to Arran’s

rugged highland scenery. (Note: this has lead to the formation of distinctive granite

features such as tors.

Southern Arran: Sills and the Landscape

• The Hills of Southern Arran

They’re normally inclined rather than horizontal due to tilting of Arran’s rock by earth

movements. As the sills are usually harder than the rocks into which they have been

intruded, they have been exposed as the weaker sedimentary rocks have been weathered

and eroded.

• Coastal Cliffs

The exposure of sills has also created coastal cliffs (e.g. Drumadoon Point) and the columnar

characteristics of the joints can clearly be seen.

• Waterfalls

Where rivers have crossed sills, as the harder rock is not eroded as rapidly as the sedimentary

rock, a step in the landscape is formed over which the water will flow as a waterfall. BACK

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Isle of Arran ctd.Southern Arran: Dykes and the Landscape • During the opening of the Atlantic Ocean, the land, including Arran was stretched

which resulted in cracks running North-South through which magma was intruded into the crust.

• The magma solidified underground in the vertical cracks, forming Dykes which cut across the sedimentary rocks. In contrast to sills, as dykes are vertical intrusions, as the rock cooled and shrank horizontal joints were formed. Many of Arran’s dykes radiate from the batholith intrusion.

• Southern Coastline

As the dykes are formed of rocks that in most cases are harder than the surrounding sandstone, along the south coast of Arran, where they have been worn down by erosion they stand a little above the surrounding sandstones. Some form natural breakwaters, trapping sand and forming little beaches between them (separated by the line of the dyke) e.g. Kildonan Shore, Arran.

• Northern Landscape

Where dykes cut through the granite intrusion, it is the dykes that have been worn away to form lower ground as the granite is the more resistant rock. Small gorges have formed where rivers have worn the dyke away and waterfalls and pools result.

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Giant’s Causeway

• Giant’s causeway is an area of about 40,000 interlocking hexagonally shaped basalt columns, the result of an ancient volcanic eruption.

• The fascinating pattern formed as a result of rock crystallization under conditions of accelerated cooling, this usually occurs when  molten lava comes into immediate contact with water, as happens today in Hawaii, the resulting fast accelerated cooling  process causes cracking and results in what we see today at the causeway. 

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The Lulworth Crumple

• Intrusive feature• Changes in climate

147 million years ago produced layered Purbeck rock strata that were later heaved up and folded by the meeting of the continental plates.

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Sources• www.wikipedia.org • www.bbc.co.uk/news• Various powerpoints• www.usgs.gov• http://www.tulane.edu/~sanelson/geol204/volclandforms.htm• www.s-cool.co.uk • Edexcel Student Book : Byrne et al• Edexcel A2 Geography Textbook• http://www.geography-site.co.uk/pages/physical.html

• Krakatoa - http://www.drgeorgepc.com/Volcano1883Krakatoa.html• Isle of Arran http://www.brixworth.demon.co.uk/geography/arran.html)