Impact of Geographical Phenomena- Form 6

IMPACT OF GEOGRAPHICAL PHENOMENA

Caribbean Studies- Module 1

Objectives

Plate tectonics:

(i) definition

(ii) location and movement of the Caribbean plate and its interaction with other plates

(iii) earthquakes and volcanoes: threat of tsunami, social displacement.

Hurricanes social and economic consequences.

Soils erosion, conservation.

Coral reefs coastal protection, sustainability of fishing industry.

Droughts and Floods social and economic impact.

PLATE TECTONICS

Objectives

Overview of Plate tectonics:

Definition of Plate Tectonics

Location and movement of the Caribbean plate and

its interaction with other plates

Earthquakes and volcanoes: threat of tsunami, social

displacement.

The Earths Structure

The Earths Structure

The earth is made up of three distinct layers:

1. The core

2. The mantle

3. The crust

The Core

12% of the Earths density

3480 km thick

4300C

The core is composed of iron and nickel with a liquid

outer region and a solid core.

The core is about half the diameter of the Earth.

The inner core is made of solid iron and nickel and the

outer core is molten iron

The Mantle


2900 km thick

3800C

The mantle is composed of very hot, dense rock, rich

in iron and magnesium.

The movement of the mantle is the reason that the

plates of the Earth move.

The Crust


5-50 km thick

870C

The outer brittle shell of the Earth is the crust that forms

the "skin" of the lithosphere.

The crust is primarily composed of silicate rocks. These

plates ride atop the mantle beneath.

The Crust

The crust is broken into several continental and

oceanic tectonic (lithospheric) plates:

The more dense oceanic crust is primarily

composed of Silica and Magnesium (SIMA).

The less dense continental crust is primarily

composed of Silica and Aluminium (SIAL).

Mohorovicic Discontinuity

Separating the upper mantle from the oceanic crust is

the Mohorovicic Discontinuity or the Moho.

It marks the lower limit of Earth's crust and occurs at

an average depth of about 8 kilometres beneath the

ocean basins and 32 kilometres beneath continental

surfaces.

FYI: The word "discontinuity" is used for a surface at

which seismic waves change velocity. At this

discontinuity, seismic waves accelerate.

Asthenosphere

The Asthenosphere is the thin semifluid layer of the

earth (100-200 km thick), below the outer rigid

lithosphere, forming part of the mantle

Lithosphere

The lithosphere is the rigid cool layer composed of

the crust and the uppermost mantle

Plate Movements

Continental Drift

Continental drift describes the movements of continents over the Earth's surface.

The theory was developed by Alfred Wegener in the early 1900's .

The concept stated that the "shell" of the Earth's surface was fractured and these "pieces" drifted about.

He concluded that the present configuration of the continents is not the same as it was in the past and in fact the continents were one "super-continent" called Pangea.

Continental Drift

Pangaea then started to break up into two smaller

supercontinents, called Laurasia and

Gondwanaland.

The continents were separated by the Tethys Sea.

Over time, the continents were separating into land

masses that look like our modern-day continents.

Continental Drift- Evidence

Continental Drift- Criticism

Alfred Wegeners hypothesis that the continents

drifted to their present day locations was rejected

by scientists because they couldnt think of a force

strong enough to move the continents.

Convection Currents

In 1928 Scottish geologist called Arthur Holmes proposed a mechanism to drive continental drift.

He believed a fluid mantle possessed convection currents created by heat trapped beneath the Earth's surface.

Holmes hypothesized that convection currents moved up toward the surface and then dragged continents across the surface.

Convection Currents

Sea- Floor Spreading

Sea-floor spreading refers to

the creation new oceanic

plate material and movement

away from the mid-ocean

ridge.

It was a hypothesis created

by Harry Hess in 1960.

Sea- Floor Spreading

On the basis of new discoveries about the deep-ocean floor, Hess postulated that molten material from the Earths mantle continuously wells up along the crests of the mid-ocean ridges that wind for nearly 80,000 km through all the worlds oceans.

As the magma cools, it is pushed away from the flanks of the ridges.

This spreading creates a successively younger ocean floor, and the flow of material is thought to bring about the migration, or drifting apart, of the continents.

The continents bordering the Atlantic Ocean, for example, are believed to be moving away from the Mid- Atlantic Ridge at a rate of 12 cm per year, thus increasing the breadth of the ocean basin by twice that amount.

Plate Tectonics

Both of the previous hypotheses and the information

discovered from them led to another theory, called

Plate Tectonics.

Plate Tectonics Theory

The surface of the lithosphere is fractured into a number

of rigid of rocks or crustal plates (also known as

lithospheric or tectonic plates) which are in constant

motion.

As these plates move and collide, the lithosphere

buckles, warps and is torn apart.

Plate Tectonics Theory

Plate Tectonics proposes that the Earths crust

consists of a number of mobile rigid elements or

plates, that overtime move relative to each other,

resulting in various landforms.

How do Plates Move??

How Do Plates Move?

The movement of lithospheric plates referred to

as continental drift, is believed to be caused by the

radioactive decay of elements in the core and mantle

that produces heat.

The heat in turn creates convection currents in the mantle

which "drive" the plates along their path of movement.

Plates at our planets surface move because of the

intense heat in the Earths core that causes molten rock in

the mantle layer to move.

How Do Plates Move?

It moves in a pattern called a convection cell (in a circular

motion) that forms when warm material rises, cools, and eventually sink down.

As the cooled material sinks down, it is warmed and rises again.

The upward movement of the currents causes the plates to be forced apart, resulting in new crust being formed.

The downward movement of the currents causes the plates to be forced together, resulting in plate material being destroyed.

How Do Plates Move?

PLATE

MARGINS/BOUNDARIES

Objectives

1. Define plate margins

2. Identify and explain the three types of plate

margins

3. Identify the different landforms/features and

geographical events at each type of plate

margins

4. Illustrate the plate margins using diagrams

Plate Margins/Boundaries

Plate Margins/Boundaries: the place where one or more

plates meet or interact

There are 3 types of plate boundaries/margins:

1. Divergent (Constructive) boundaries

2. Convergent (Destructive) boundaries

3. Transform Fault (Conservative) boundaries

Divergent boundaries

Divergent boundaries occur where plates are moving

apart and new crust is created by magma pushing up

from the mantle.

Magma (molten rock) is slowly forced upwards

between the two plates and new crust is created

when the magma hardens.

Divergent boundaries

Features/Landforms formed:

Sea Floor Spreading (ocean growth)

Mid Ocean Ridges (Mid-Atlantic Ridge)

Submarine volcanoes

Islands (Iceland)

Rift Valleys (over land)

Earthquakes

Mid-Atlantic Ridge

This submerged mountain range runs the entire length of the

Atlantic Ocean, extending from the Arctic Ocean to beyond the

southern tip of Africa

The rate of spreading along the Mid-Atlantic Ridge averages

about 2.5 centimetres per year.

Convergent boundaries

The size of the Earth has not changed significantly during the past

600 million years and very likely not since shortly after its

formation 4.6 billion years ago.

The Earth's unchanging size implies that the crust must be

destroyed at about the same rate as it is being created.

Such destruction (recycling) of crust takes place along convergent

boundaries.


Convergent boundaries are where plates move toward

each other (pushed together).

In some cases one plate sinks (is subducted) under

another (the location where sinking of a plate occurs is

called a subduction zone).


The type of convergence that takes place between plates depends

on the kind of lithosphere (crust) involved (continental or oceanic).

There are 3 types of convergent boundaries:

1. Oceanic-Continental Convergence (Subduction)

2. Oceanic-Oceanic Convergence

3. Continental-Continental Convergence (Collision Zone)

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 as a whole sinks smoothly and 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.

Such earthquakes are often accompanied by uplift of the land by as much as a few meters.

Oceanic-continental convergence

Features/Events:

Earthquakes

Ocean Trenches

Mountains

Volcanoes

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.

The Marianas Trench, for example, is a deep trench

created as the result of the Phillipine Plate subducting

under the Pacific Plate.

Oceanic-oceanic convergence

The subduction processes in oceanic-oceanic plate

convergence also result in the formation of undersea

volcanoes.

Over millions of years, 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 (example the Lesser Antilles)

Oceanic-oceanic convergence

Magmas that form island arcs are produced by the partial melting of the descending plate and/or the overlying oceanic lithosphere.

The descending plate also provides a source of stress as the two plates interact, leading to frequent moderate to strong earthquakes.

Features:

Ocean Trenches

Island Arcs

Earthquakes

Continental-continental convergence

(Collision Margin)

When two continental plates meet head-on, neither plate

is subducted because the continental rocks are relatively

light and resist any downward motion.

Instead, the crust tends to buckle and be pushed upward

or sideways, creating mountains.

Continental-continental convergence

Features:

Fold Mountains

Earthquakes

Transform Fault boundaries

Transform-Fault Boundaries are where two plates are

sliding horizontally past one another.

These are also known as transform boundaries or more

commonly as faults.

Most transform faults are found on the ocean floor.

They produce zig-zag plate margins and are generally

defined by shallow earthquakes.

A few, however, occur on land. For example, 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.

Transform boundaries

Features/Events:

Earthquakes

The Earths Tectonic Plates

Objectives

1. Identify the major crustal plates in the world

2. Identify the crustal plates adjacent to the

Caribbean Plate

Earthquakes

Earthquakes

An earthquake is a sudden vibration or trembling in the

Earth as a result of crustal movement.

Earthquake motion is caused by the quick release of

stored potential energy into the kinetic energy of

motion.

Earthquakes

Most earthquakes are produced along faults, tectonic

plate boundary zones, or along the mid-oceanic

ridges.

At these areas, large masses of rock that are moving

past each other can become locked due to friction.

Friction is overcome when the accumulating stress has

enough force to cause a sudden slippage of the rock

masses.

Earthquakes

The magnitude of the shock wave released into the

surrounding rocks is controlled by:

1. the quantity of stress built up because of friction,

2. the distance the rock moved when the slippage

occurred

3. ability of the rock to transmit the energy contained in

the seismic waves

Earthquakes

Sometime after the main shock wave, aftershocks

can occur because of the continued release of

frictional stress.

Most aftershocks are smaller than the main

earthquake, but they can still cause considerable

damage to already weakened natural and human

constructed features.

Distribution of earthquake epicentres from 1975 to 1995. Depth of the earthquake focus

is indicated by colour. Deep earthquakes occur in areas where oceanic crust is being

actively subducted. About 90% of all earthquakes occur at a depth between 0 and 100

kilometres.

Distribution of earthquakes with a magnitude less than 5.0 relative to the various tectonic

plates found on the Earth's surface. Each tectonic plate has been given a unique colour. This

illustration indicates that the majority of small earthquakes occur along plate boundaries.

Earthquake Waves

Earthquakes are a form of wave energy that is

transferred through bedrock.

Motion is transmitted from the point of sudden

energy release, the earthquake focus, as spherical

seismic waves that travel in all directions outward.

The point on the Earth's surface directly above the

focus is termed the epicentre.

Movement of body waves away from the focus of the earthquake. The epicentre is

the location on the surface directly above the earthquake's focus.

How are earthquakes recorded?

Earthquakes are recorded by instruments

called seismographs.

The recording they make is called a seismogram.

Richter scale

When an earthquake occurs the seismograph

converts the wave energy into a standard unit of

measurement like the Richter scale.

In the Richter scale, units of measurement are

referred to as magnitudes.

The Richter scale is logarithmic. Thus, each unit

increase in magnitude represents 10 times more

energy released.

Relationship between Richter Scale magnitude and energy

released.

The spatial distribution of small and large

earthquakes

Distribution of earthquakes with a magnitude less than 5 on the

Richter Scale.

Distribution of earthquakes with a magnitude greater than 7 on the Richter

Scale.

Earthquake Damage and Destruction-

Factors

Earthquakes are a considerable hazard to humans.

Earthquakes can cause destruction by structurally

damaging buildings and dwellings, fires, tsunamis and

mass wasting. Earthquakes can also take human lives.

The amount of damage and loss of life depends on a

number of factors. Some of the more important factors

are:


Factors

The amount of damage and loss of life depends on a

number of factors. Some of the more important factors

are:


Factors

1. Time of day: Higher losses of life tend to occur on

weekdays between the hours of 9:00 AM to 4:00 PM.

During this time interval many people are in large

buildings because of work or school. Large structures

are often less safe than smaller homes in an

earthquake.

2. Magnitude of the earthquake and duration of the

event.


Factors

3. Distance from the earthquake's focus. The strength of the

shock waves diminishes with distance from the focus.

4. Geology of the area effected and soil type. Some rock

types transmit seismic wave energy more readily. Buildings

on solid bedrock tend to receive less damage.

Unconsolidated rock and sediments have a tendency to

increase the amplitude and duration of the seismic waves

increasing the potential for damage. Some soil types when

saturated become liquefied.


Factors

5. Type of building construction. Some building

materials and designs are more susceptible to

earthquake damage.

6. Population density: More people often mean

greater chance of injury and death.

Loss of Life

The greatest loss of life because of an earthquake this century occurred in Tangshan, China in 1976

when an estimated 250,000 people died.

In 1556, a large earthquake in the Shanxi Province of China was estimated to have caused the death of

about 1,000,000 people.

Loss of Life

The UWI Seimic Research Unit stated in June 2014

that

current estimates of seismic hazard suggest that the

likelihood of a person being killed in Trinidad by an

earthquake in the next 50 years is comparable to the

likelihood of being murdered in that same period given

the current murder rate and current estimate of the

seismic hazard.

Property & Infrastructure Damage

Economic Damage

The UWI Seismic Research Unit indicated in June

2014 that if a 7.5 magintude earthquake hit

Trinidad , the economic damage for Port of Spain

will cost US$5 billion (TT$32 billion) and US$6

billion (TT$39 billion) for San Fernando.

Fires

A common problem associated with earthquakes in

urban areas is fire.

Shaking and ground displacement often causes the

severing of electrical and gas lines leading to the

development of many localized fires.

Response to this problem is usually not effective because

shock waves also rupture pipes carrying water.

In the San Francisco earthquake of 1906, almost 90% of the damage to buildings was caused by fire.

Downtown Kobe, Japan at about noon on the day of the 1995 earthquake. Many

areas of downtown Kobe were on fire and there was no water pressure to put out

the flames.

Landslides

In mountainous regions, earthquake provoked

landslides can cause many deaths and severe

damage to built structures.

The town of Yungay, Peru was buried by a debris flow that was triggered by an earthquake that occurred

on May 31, 1970. This disaster engulfed the town in seconds with mud, rock, ice, and water and took the

lives of about 20,000 people.

The Guatemala earthquake of February 4, 1976 had a magnitude of 7.5. This

earthquake killed about 23,000 people, injured 76,000, and caused just over

1 billion dollars in property damage. The earthquake also caused a number of

landslides.

Tsunamis

Another consequence of earthquakes is the generation of

tsunamis.

Tsunamis form when an earthquake causes a sudden

movement of the seafloor.

This movement creates a wave in the water body which

radiates outward in concentric shells.

On the open ocean, these waves are usually no higher

than one to three meters in height and travel at speed of

about 750 kilometres per hour.

Tsunamis

Tsunamis become dangerous when they approach

land.

Frictional interaction of the waves with the ocean

floor, as they near shore, causes the waves to slow

down and collide into each other.

This amalgamation of waves then produces a super

wave that can be as tall as 65 meters in height.

Tsunami

Tsunamis in the Caribbean??

In October 1918, a 7.2 magnitude earthquake on

the north coast of Puerto Rico killed 116 persons

and caused a tsunami.

The active underwater Kick em Jenny volcano

located north of Grenada has the potential to

cause a tsunami if it erupts.

Compare

The 2010, 7.0 magnitude earthquake hit Haiti

killed almost 300,000 persons.

The same year, the 8.0 magnitude earthquake that

hit Chile resulted in the deaths of almost 200

persons.

Why the contrasts??

Social Displacement in Haiti

Check website for journal files.

Volcanoes

A volcano is an opening in the surface of the Earth from

which magma (molten subsurface rock ) and associated

gases and ash erupt.

Volcanoes vary in their structure - some are cracks in the

earth's crust where magma erupts, while some are

domes, shields or mountain-like (conical shaped)

structures with a crater at the summit (built by

accumulations of lava flows, tephra and volcanic ash)

What is a Volcano?

About 95% of active volcanoes occur at the plate subduction zones and at the mid-oceanic ridges.

The other 5% occur in areas associated with lithospheric hot spots.

These hot spots have no direct relationships with areas of crustal creation or subduction zones and it is believed that hot spots are caused by plumes of rising magma that have their origin within the asthenosphere.

Location of Volcanos

Volcanoes are most likely to occur along the margins of tectonic plates, especially in subduction zones where oceanic plates dive under continental plates.

As the oceanic plate subducts beneath the surface, intense heat and pressure melts the rock. Molten rock material, magma, can then ooze its way toward the surface where it accumulates at the surface to create a volcano.

Volcanic activity can be found along the Mid-ocean ridge system as well. Here, oceanic plates are diverging and magma spreads across the ocean floor, ultimately being exposed at the surface.

Volcanoes along Plate Margins

The Pacific Ring of Fire is an area of frequent

earthquakes and volcanic eruptions encircling the basin

of the Pacific Ocean.

The Ring of Fire has 452 volcanoes and is home to over

50% of the world's active and dormant volcanoes.

90% of the world's earthquakes and 81% of the world's

largest earthquakes occur along the Ring of Fire.

Pacific Ring of Fire

Hot spots are places where a chamber of magma has

accumulated at depth beneath the surface.

The volcanic islands of Hawaii are a notable example of

this.

The Hawaiian Islands ride atop the Pacific plate as it

moves in a north-westerly direction over the hot spot that

creates the volcanoes. Therefore, the oldest volcanic island

is found at the northwest end of the chain and the

youngest to the southeast. Volcanic activity ceases as the

older islands move off the hot spot.

Hot spots

Scientists have categorized volcanoes into three main

categories: active, dormant, and extinct.

An active volcano is one which has recently erupted and

there is a possibility that it may erupt soon.

A dormant volcano is one which has not erupted in a long

time but there is a possibility it can erupt in the future.

An extinct volcano is one which has erupted thousands of

years ago and theres no possibility of eruption.

What are the different stages of

volcanoes?

Volcanic Features/Landforms

Volcanic features/landforms can be either intrusive

or extrusive.

Intrusive features are formed by magma beneath

the Earths surface while extrusive features are

formed at the Earths surface (mainly by lava)

Volcanic Features/Landforms

Volcano Hazards

Volcanic eruptions, especially explosive eruptions, eject

fragments of volcanic rocks and lava collectively

called tephra.

Pyroclastic flows are fast-moving gas and fragments

of rock having temperatures of 500oC that can rush

down the flanks of a volcano at speeds reaching 100

km/hr, carbonizing all in their path.

Volcano Hazards

Acid Rain: Volcanic eruptions are accompanied by the

release of noxious and sometimes lethal gases.

Steam makes up the majority of gas that is released by a

volcano followed by carbon dioxide, sulphur dioxide, and

hydrogen chloride.

When lava spills into the ocean, the intense heating of salt

water produces a noxious steam cloud of hydrochloric acid.

Sulphur dioxide combines with water in the atmosphere to

produce acid rain.

Naturally produced acid deposition around the top of

Mauna Loa has devastated the local vegetation.

Volcano Hazards

Lahars - A mixture of ash with rain or glacier melt

water which forms a deadly river of mud

Lava Flow - A river of molten rock 1000oC that

can travel at 40mph

Ash Fall - Millions of tons of ash can bury buildings,

roads etc.

Volcanic bombs - Rocks and lava the size of houses

and cars can be hurled into the sky

Volcano Hazards

Tephra

Pyroclastic flows

Lahars

Lava Flow

Ash Fall

Volcanic bombs

Montserrat

Prior to July 1995, the island of Montserrat, located

in the Northern Leeward Islands, had achieved

significant growth in its economic, social and health

sectors.

This level of growth heightened the quality of life

and health status of the indigenous population and

visitors alike.

Soufriere Hills Volcano

Soufrire Hills volcano is a complex stratovolcano that forms the northern half of the small Island of Montserrat in the British Lesser Antilles.

After 350 years of being dormant, it came back into life in 1995 and started to build a new lava dome.

The eruption alternated between less or more intense phases including rapid dome growth with associated powerful explosions and large pyroclastic flows from dome collapse.

The eruption, in particular the effects of pyroclastic flows and lahars caused by heavy rains have destroyed a large part of the island, including the capital Plymouth, and the population has been relocated to the northern part of the island and has been fighting, with the help of the UK government, to maintain life on the island.

Soufriere Hills Volcano

The volcanic eruption began on 18 July 1995 and has

devastated Montserrat.

By 26 December 1997, the most extreme explosive

event took place, resulting in approximately 90% of the

resident population of over 10,000 having to relocate at

least once and over two-thirds had to leave the island.

Virtually all the important infrastructure of the island was

destroyed or put out of use for the short to medium term.

The private sector collapsed and the economy became

largely dependent on British aid.

Before & After

Aftermath

Check website for PDF files

Question

How do natural hazards, such as earthquakes and

volcanoes affect people in the Caribbean

economically and socially? Give examples, using

events in the Caribbean countries.

THE END

Documents

Impact of Geographical Phenomena- Form 6