Plate Tectoni Cs

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CARIBBEAN STUDIESCARIBBEAN STUDIES

PLATE TECTONICSPLATE TECTONICSModule 1, Objective 5 (i) (a), (b), (c)Module 1, Objective 5 (i) (a), (b), (c)

The Impact of plate tectonics Caribbean The Impact of plate tectonics Caribbean society and culturesociety and culture

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Plate tectonics theorists:Plate tectonics theorists: 1912 - German geologist, Alfred Wegener observed that 1912 - German geologist, Alfred Wegener observed that the shapes of the continents, fit together like a jigsaw the shapes of the continents, fit together like a jigsaw puzzle. He developed the theory of puzzle. He developed the theory of continental driftcontinental drift - - t the he continents were once joined in one large landmass continents were once joined in one large landmass ( supercontinent), over a long period of time they broke up ( supercontinent), over a long period of time they broke up and drifted apart. and drifted apart.

Canadian geophysicist J. Tuzo Wilson, stated that the Canadian geophysicist J. Tuzo Wilson, stated that the earth’s crust is a dynamic assembly of earth’s crust is a dynamic assembly of moving platesmoving plates whose interactions explain most geological phenomena, whose interactions explain most geological phenomena, including volcanoes and earthquakes. including volcanoes and earthquakes.

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What is plate tectonics?What is plate tectonics?• The theory that the earth’s crust is made

up of a series of rigid plates which float on a soft layer of the mantle and are moved by convection currents in the earth’s interior.

• The study of the movement of the plates on the earth’s surface and the resultant landforms.

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Why plate tectonics is usefulWhy plate tectonics is useful

• Plate tectonics helps to explain many geological events, such as earthquakes and volcanic eruptions as well as mountain building and the formation of the oceans and continents.

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World tectonic plate boundariesWorld tectonic plate boundaries

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•

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Size of platesSize of plates• Largest plates: the Pacific plate, the North

American/Atlantic plate, the Eurasian plate, the Antarctic plate, and the African plate.

• Smaller plates: the Cocos plate, the Nazca plate, the Caribbean plate, and the Gorda plate.

• Plate sizes vary: The Cocos plate is 2000 km (1400 mi) wide; the Pacific plate is almost 14,000 km (nearly 9000 mi) wide.

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Rate of plate movement Rate of plate movement • Tectonic plates move at an average

speed of 2 – 3 inches (4 – 7 cm) per year.

• Movement is slow and continuous and has been taking place for millions of years

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Internal structure of the earthInternal structure of the earth

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Components of the layersComponents of the layers• The inner core is made up of dense iron; the outer core

is made up of liquid iron.

• The lower mantle is made up of molten rock surrounded by partially molten rock in the asthenosphere.

• Part of the upper mantle and crust (lithosphere) is made up of solid rock. It is a rigid layer.

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Why do plates move?Why do plates move?• The upper mantle and crust (lithosphere) lie on

the lower mantle which is fluid. The rocks in the lower mantle (asthenosphere) move in a fluid manner because of the high temperatures and pressures in it.

• Currents in the lower mantle form convection cells which cause the plates to float.

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Types of plate boundaries/movementsTypes of plate boundaries/movementsThe region where plates meet is called a boundary

1. Divergent plate boundaries • Occur where two plates are moving apart from each

other. In the oceanic crust, this process is called seafloor spreading. Magma, or molten rock material, rises to the sea floor surface along the rupture and forms new oceanic crust.

• On land, divergent plate boundaries create rift valleys—deep valley depressions formed as the land slowly splits apart.

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Divergent plate boundary (sea floor Divergent plate boundary (sea floor spreading) – mid Atlanticspreading) – mid Atlantic

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2. Transform plate boundary.

• The plates slide past or slip alongside each other.

• A transform boundary is located where the Caribbean plate and South American plates meet

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Transform and divergent plate boundariesTransform and divergent plate boundaries..

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3. 3. Convergent boundaryConvergent boundary(Also known as destructive boundary or subduction

zone) • Plates move towards one another; the plates are

consumed, or recycled back into the earth’s mantle.

• Earthquakes, volcanoes, oceanic ridges, deep sea trenches, island arcs, (e.g the West Indies, the Japanese islands), and fold mountains occur at convergent boundaries

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Formation of the CaribbeanFormation of the Caribbean

• The eastern Caribbean islands lie on a convergent plate boundary.

• As the Atlantic/America plate sinks beneath the Caribbean plate, magma rises to the surface, it may erupt to form a volcano, resulting in the formation of the islands of the eastern Caribbean, (about 140 million years ago).

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The Caribbean & Atlantic Plate BoundariesThe Caribbean & Atlantic Plate Boundaries

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A convergent boundaryA convergent boundary• Molten material comes to the surface and

forms islands

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A convergent boundaryA convergent boundary

• Formation of volcanoes or fold mountains

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Effects of plate tectonics on the CaribbeanEffects of plate tectonics on the Caribbean• 1) Volcanoes. • A volcano is a vent or opening in the earth’s crust

through which hot molten rock (magma) and gases from the interior of the earth are released.

• Volcanoes occur as the oceanic crust sinks under the continental crust. Magma escapes and rises to the surface and forms volcanoes.

• Eighty percent of the world’s active volcanoes occur at convergent zones.

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Live volcanoes in the Eastern CaribbeanLive volcanoes in the Eastern CaribbeanThere are 19 ‘live’ volcanoes in the Eastern Caribbean

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Major volcanic eruptions in the Eastern Major volcanic eruptions in the Eastern CaribbeanCaribbean

Year Volcano Effects1718 Mt. Soufriere,

St. VincentUnknown number of casualties among Caribs

1812 Mt. Soufriere,St. Vincent

80 killed; major damage to sugar industry

1902 Mt Pele`,Martinique

30 000 killed; St Pierre destroyed; economic cost US$1 000 000 000

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Mt. Soufriere Crater- St VincentMt. Soufriere Crater- St Vincent

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Major volcanic eruptions in the Eastern Major volcanic eruptions in the Eastern CaribbeanCaribbeanYear Volcano Effects


1600 killed; major damage to the sugar industry; economic cost: US$200 000 000

1976 - 77

Soufriere,Guadeloupe

No casualties. Economic cost: US$100 000 000


No casualties. Massive ash fall. Economic cost: US$100 000 000

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MontserratMontserrat

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Soufriere Hills eruption – Montserrat (1995)Soufriere Hills eruption – Montserrat (1995)

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Pyroclastic flow and surgePyroclastic flow and surge• A pyroclastic flow : a hot (100 – 6000C), fast moving

mixture of ash, rock fragments and gas. It usually travels down valleys and cause total destruction of the area over which it flows. This has been the main cause of destruction and loss of life in Montserrat

• A pyroclastic surge is a dilute turbulent cloud of gases and rock debris that moves over the ground at great speeds. It is formed in a similar way to a pyroclastic flow, but the effect is more widespread.

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A pyroclastic flowA pyroclastic flow

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Major volcanic eruptions in the regionMajor volcanic eruptions in the regionYear Volcano Effects

1995 - 1997

Souffriere Hills, Montserrat

19 deaths; destruction of capital, Plymouth; southern portion of island evacuated; relocation of population; mass migration; population reduction from 12, 771 (1996) to about 4000; economy devastated; economic cost: US$500 000 000

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Soufriere Hills volcanic glowSoufriere Hills volcanic glow

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Soufriere Hills ash cloud - MontserratSoufriere Hills ash cloud - Montserrat

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Montserrat- pyroclastic flow damageMontserrat- pyroclastic flow damage

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Damage from Soufriere Hills eruptionDamage from Soufriere Hills eruption

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Plymouth – under ash and mudPlymouth – under ash and mud

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Plymouth MontserratPlymouth Montserrat

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Montserrat – loss of propertyMontserrat – loss of property

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Positive effects of volcanoesPositive effects of volcanoesFeature Location Benefits

Volcanic (igneous) rocks

Antigua, (Greencastle) St. Lucia etc

Road and building construction

Crater Lakes Hot springs, sulphur springs, fumeroles

Grenada, Dominica, Nevis, St Lucia

Tourist attractions

High mountains and fertile soil

Windward Islands, Bendals, Old Road etc.

Relief rainfall -agriculture – food production.

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Effects of plate tectonics on the CaribbeanEffects of plate tectonics on the Caribbean

• 2) Earthquakes • An earthquake results from slow build up of

pressure within the crust at convergent boundaries. If pressure is suddenly released, then the plates jerk past each other resulting in vibrations in the crust.

• Over 600 earthquakes occur in the Caribbean annually.

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Earthquakes for October 17Earthquakes for October 17thth – 24 – 24thth 2005 2005 Red 30 km deep; purple 30 – 70 km deep; blue 70 -100 km

deep; black > 100 km deep

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The Richter ScaleThe Richter Scale

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General effects of earthquakesGeneral effects of earthquakes• loss of life• loss of property• fires from broken gas, or power lines• disruption of transport and other services• exposure due to lack of shelter• shortage of food• shortage of clean water• disease from polluted water supplies.

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Selected Caribbean earthquakesSelected Caribbean earthquakesYear Island Effects

1692 Port Royal, Jamaica

2000 killed, a part of the city was submerged, buildings destroyed.

1842 Haiti More than 700 killed. In addition 200 killed in tsunami in Port-de-Paix.

1843 Antigua, Nevis, Montserrat

Major structural damage; St John’s Cathedral damaged. A tsunami also affected Antigua

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1867 Virgin Islands

20 killed

1907 Kingston,Jamaica

Major destruction by fire and tidal wave

1946 Dominican Republic

100 killed by a tsunami in the town of Mantanzas

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1974 Antigua Structural damage

2004 North of Dominica (6.3 magnitude)

Structural damage to churches in Portsmouth and Vielle Case. One death in Guadeloupe. Also felt in Antigua, St Maarten, Nevis, Montserrat and St. Vincent

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Structural damage – Dominica 2004Structural damage – Dominica 2004

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Structural damage – Dominica 2004Structural damage – Dominica 2004

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Some earthquakes in 2005Some earthquakes in 2005

Date Location Magnitude

Feb 7th North east of Dominica 4.8Feb 14th North of DominicaMarch 22nd Near Trinidad 4.6March 23rd Northwest of Trinidad 3.91st May Northeast of St. Lucia 3.7June 23rd 9 quakes N. of Dominica 3.6 – 4.5Aug 4th Northwest of Trinidad 4.5Aug 30th Northeast of Martinique 5.1Oct 24th Northwest of Trinidad 4.9

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Implications for construction & disaster Implications for construction & disaster preparednesspreparedness• What disaster mitigation methods are in place?• Construction of earthquake resistant buildings?• Restrictions on the height of buildings?• Emergency exits in buildings? • Adequate medical facilities to handle disasters?• Regular public education/awareness?• Earthquake drills in schools?• ARE WE PREPARED TO HANDLE MAJOR

DISASTERS?

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Some landforms formed by plate tectonicsSome landforms formed by plate tectonics

• Landforms: a natural physical feature of the earth’s surface, for example, a valley, mountain, or plain, beaches, marshes, caves, waterfalls.

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Landforms and their useLandforms and their useLandform Territory Benefits

Waterfall Dominica, Jamaica, Guyana

Recreation, tourist attraction

Boiling Lake, Dominica Tourist attraction,

Sulphur springs

Dominica, Nevis Therapeutic

Mountains Windward Islands, Jamaica

Rainfall, agriculture, forestry,

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Landforms and their useLandforms and their useLandform Territory Benefits

MarshesMangroves

All islands Prevents coastal erosion; a spawning area for fish; protection for young marine life

Lagoons Barbuda Fishing, coastal protection

Plains Trinidad etc

Agriculture, settlement

Beaches Leeward Islands

Recreation, fishing, tourism, sand mining

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ReferencesReferences• Reid, Ruel B., (2002), Caribbean Studies, pg. 1 – 4, 21 – 25

• Waugh, David. (2002). Geography An Integrated Approach, Ch. 1

• Microsoft Encarta Reference Library 2005, Articles: Plate Tectonics, Earthquake, Volcano

• www.wikipedia.org, Article: Plate Tectonics

• www.uwiseismic.com (The Seismic Research Unit of the UWI at St Augustine, Trinidad)

http://www.wikipedia.org/

http://www.uwiseismic.com/

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Location of Kick ‘em JennyLocation of Kick ‘em Jenny

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Kick `em JennyKick `em Jenny• A shallow submarine volcano• Located 8km ( 5 miles ) north of Grenada• The summit is 180m (590 ft) below sea level• The only ‘live’ submarine volcano in the Caribbean• Erupted twelve times since 1939• It is actively degassing• Most closely monitored volcano in the Caribbean• It is not growing towards the surface• It is a serious threat to shipping and there is a 1.5 km (approx 1

mile) exclusion zone around it.

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Trenches and TroughsTrenches and Troughs• Trenches/Troughs: Bartlett Trough, between

Cuba and Jamaica, over 20 000 feet deep. • Brownson Trough, north of Puerto Rico and

the Virgin Islands, 30, 000 feet deep

• Anegada Trough, between the Caribbean Sea and the Atlantic Ocean?

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Tsunamis in the CaribbeanTsunamis in the Caribbean• An ocean wave caused by large scale disturbance of the ocean floor or surface

that displaces a large mass of water.

• Waves can reach 15m high (50 ft) and travel 600 kph (372 mph)

• Caused by earthquakes, volcanic eruptions and landslides into the sea.

• Ten earthquake generated tsunamis in the past 500 years, only 450 people have been killed by tsunamis

• Volcanoes, earthquakes and hurricanes have killed 30 000, 15 000, and 15000 people respectively

• In 2003 a major dome collapse of Soufriere Hills Volcano, caused a tsunami 4m high in Montserrat and 1 m high in Guadeloupe.

• Scientists believe that there is a low probability of a major tsunami in the region

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Earthquake terminologyEarthquake terminology• A violent shaking of the Earth’s crust that may cause

destruction to buildings and installations and results from the sudden release of tectonic stress.

• Focus or hypocenter: the point within the earth where an earthquake originates

• Epicenter: the point on the earth’s surface directly above the focus

• Earthquakes also contain surface waves that travel out from the epicenter along the surface of the earth. Two types of these surface waves occur: Rayleigh waves, named after British physicist Lord Rayleigh, and Love waves, named after British geophysicist A. E. H. Love. Surface waves also cause damage to structures, as they shake the ground underneath the foundations of buildings and other structures.

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Piton, St LuciaPiton, St Lucia

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Tectonic plates and volcanoesTectonic plates and volcanoes

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The CaribbeanThe Caribbean

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Divergent boundary – rift valleyDivergent boundary – rift valley

Plate Tectoni Cs

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