Types of Plate movements - Weeblygeographysanbenedittu.weebly.com/uploads/9/7/0/1/... · Composite cone Volcanoes • Also called stratovolacano • consist of alternating layers

Types of Plate movements

Plate Boundaries

• Continental plates are

older, lighter, cannot

sink and is permanent.

• Oceanic crust is older,

lighter, cannot sink and

is constantly being

destroyed and replaced.

Constructive plate margins

• At constructive margins, such as the Mid Atlantic Ridge, two plates move away from each other.

• Molten rock, or magma, immediately rises to fill any possible gap, and forms new oceanic crust.

Constructive plate boundaries

• In November 1963 an

Icelandic fishing boat

reported an explosion

under the sea. Further

explosions created the

island of Surtsey. By

1967 the island was

2.8km2. within months

plants and insects had

begun colonisation.

Constructive margins

• Iceland is the area

where there has been

the most land added

these last 500 years.

Destructive plate margins

• Destructive plate

margins are where

plates consisting of

oceanic crust move

towards plates of

continental crust.

Destructive plate Margins

• To the west of South

America, the Nazca

plate is moving towards

the South American

plate.

• Where they meet, the

Nazca plate is forced

downward to create a

subduction zone and its

associated deep-sea

trench.

Destructive plate margins• The increase in

pressure, as the plate is

forced downwards, can

trigger sever

earthquakes.

• As the oceanic crust

continues to descend, it

melts, partly due to

heat resulting from

friction and partly as an

increase in temperature

as it re-enters the

mantle.

• This forms volcanoes.

• It also forms volcanic

island arcs.

Destructive plate boundaries

Conservative plate boundaries

• Also known as

transform faults.

• Two plates sliding past

each other.

• No land is created, but

no land is destroyed.

• There are no volcanoes.

• Earthquakes are strong

and frequent.

Conservative plate boundaries

• Most famous

conservative plate

boundary is found on

the San Andreas Fault.

• Here the Juan de Fuca

plate is moving past the

North American Plate.

• A number of large cities

are found on the area.

Earthquakes –

1897 – 7.9 on Richter scale

1906 – 7.8

1989 – 6.9

2004 - 6

Conservative Plate Boundary

Global continents and super

continents

• The continents were once joined as a single global

continent called Pangea. Where did the present day

continents fit?

Pangaea

• Pangaea existed

between 300 million

and 200 million years

ago.

• The single, world ocean

around it was known as

Panthalassa.

• The idea of a super

continent was

pustulated first by

Alfred Wegner in 1917.

Pangaea• Evidence –

• Similar rock types

across different

continents.

• Fossils of same

species across

different continents.

• Similar mineral

deposits.

• Mountain ranges –

Applachian and

Caledonian

Mountains

Pangaea

• Pangaea started to

break up by 175million

years ago.

• It formed two super

continents – Laurasia

and Gondwanaland

Laurasia and Gondwanaland

• Laurasia, the Northern

continent, contained

the continental plates

of North America,

Greenland and Eurasia.

• Gondwanaland, the

Southern continent,

included the following

continental plates –

India, Africa, South

America, Australia,

Antarctica.

Other supercontinents

• Gondwana (~510–~180 million years ago)

• Laurasia (~510–~200 million years ago)

• Pangaea (~300–~200 million years ago)

• Euramerica (~300 million years ago)

• Oldredia (~418–~380 million years ago)

• Pannotia, also called Vendian (~600–~540 million years ago)

• Rodinia (~1.1 Ga–~750 million years ago)

• Columbia, also called Nuna (~1.8–1.5 Ga ago)

• Nena (~1.8 Ga)

• Kenorland (~2.7 Ga ago). Neoarchean sanukitoid cratons and new continental crust formed Kenorland.

Protracted tectonic magna plume rifting occurred 2.48 to 2.45 Ga and this contributed to the Paleoproterozoic

glacial events in 2.45 to 2.22 Ga. Final breakup occurred ~2.1 Ga.

• Ur (~3 Ga ago). Classified as the earliest known landmass. Ur, however, was probably the largest, perhaps even

the only continent three billion years ago. While probably not a supercontinent, one can argue that Ur was a

supercontinent for its time, even if it was smaller than Australia is today. Still, an older rock formation now

located in Greenland dates back from Hadean times.

• Vaalbara (~3.6 Ga ago). Evidence is the Yilgarn Craton, Western Australia and the worldwide Archean

greenstone belts that were subsequently spread out across Gondwana and Laurasia

Earthquakes• Earthquakes are the

sudden release of

energy.

• Over 150,000

Earthquakes happen

every years, which are felt

by people.

Earthquake mechanics

• 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.

• The magnitude of the

shock wave released

into the surrounding

rocks is controlled by

the quantity of stress

built up because of

friction, the distance

the rock moved when

the slippage occurred,

and ability of the rock

to transmit the energy

of the seismic waves.

Earthquake mechanics

Focus

• Focus – The focus is the

exact point in the crust

where the earthquake’s

energy is released. As

such, foci (plural)are

associated with faults

and plate boundaries. It

can be very deep in the

crust or it can be very

shallow.

Earthquake Depth

Epicentre

• The epicentre is the

area on the Earth’s

surface, directly

above the focus.

• As such, it is also

the area where the

earthquake is felt

strongest.

• Areas further away

from the epicentre

suffer less damage.

Seismic waves

• Whenever an

earthquake happens,

the energy produced

travels through the

rocks in the form of

seismic waves.

• There are four main

types of seismic waves

• P-Waves

• S-Waves

• Love Waves

• Rayleigh Waves.

Seismic Waves are measured

by means of the Seismograph

P-Waves and S-Waves • P-Waves are the fastest

type of waves, travelling

at between 1.5km and

8km per second.

• They shake the land as

if it is being

compressed.

• S-Waves move at 60%

to 70% of the speed of

the P-Waves.

• They shake the land

perpendicularly.

• The speed of seismic

waves depends a lot on

the type of rock they

are travelling through.

Seismograph

• Seismographs measure

changes in the displacement

of the land as the seismic

waves are passing through it.

• Seismographs can described

as large weights suspended

over paper, which moves

whenever there is shaking.

Malta Seismograph

• http://seismic.research.

um.edu.mt/about.php#

uss• http://se

ismic.res

earch.u

m.edu.m

t/station

s.php

Richter scale • The Richter scale is a standard scale used to

compare earthquakes. It is a logarithmic scale,

meaning that the numbers on the scale measure

factors of 10. So, for example, an earthquake that

measures 4.0 on the Richter scale is 10 times

larger than one that measures 3.0. On the Richter

scale, anything below 2.0 is undetectable to a

normal person and is called a microquake.

Microquakes occur constantly. Moderate

earthquakes measure less than 6.0 or so on the

Richter scale. Earthquakes measuring more than

6.0 can cause significant damage. The biggest

quake in the world since 1900 scored a 9.5 on the Richter scale. It rocked Chile on May 22, 1960.

Richter Scale

Richter Scale

Mercalli Scale

Volcanic activity

• There are over 500

active volcanoes around

the world.

• Some eruptions are

slight, others are very

damaging.

• Volcanic activity can be

divided into two types

• - Intrusive

• - Extrusive

Volcanoes

• Volcanoes can be

• Active – Are actively

undergoing eruptions, or

showing signs of activity

right now.

• Dormant – are known to

have erupted in the past but

have no erupted recently.

• Extinct – do not show signs

of activity, might show

signs of sever erosion.

Volacaneos

• There are many

different types of

volcanoes.

• Major ones include

• Composite cone,

• Acid

• Basic Lava

Volcanoes

• Constructive plate margins - tend to give rise to

eruptions associated with basaltic magma - forming

features such as shield volcanoes and fissure

eruptions which often form lava plateaux.

• Destructive plate margins - tend to give rise to

eruptions associated with more explosive magma -

giving rise to features such as acid domes, cinder

cones, composite cones and calderas.

Volcanoes

• REMEMBER - there is no volcanic activity associated

with either collision or conservative plate margins -

this is because there is no magma source as

• (i) they are not above the rising limb of a convection

current so there is no rising magma

• (ii) there is no existing crust being destroyed by

subduction to create a magma source

Acid Volcanoes

• Acid/ Lava Dome• dome shaped accumulations of

volcanic rock

• these features have steep, convex

sides;

• narrow base and high cones

• may have secondary cones;

• Steep convex sides due to

dense lava, which soon

cools and solidifies

• Domes often plug vents,

thus forming secondary

vents.

• Eruptions are often

explosive. Lassen Peak volcanic dome

Composite cone Volcanoes• Also called stratovolacano

• consist of alternating layers

of acidic lava and ash;

• often has parasitic or

secondary cone (several are

common due to earlier

eruptions); • Where the passage of magma

becomes blocked and

pressure builds, magma may

flow from fissures on the

volcanoes flank, forming

parasitic or secondary cones.

• Eruptions are violent, with

pyroclasts.Mt St Helens

Shield Volcanoe• gentle sloping cones

• wide base and not

particularly high

• consists of layers of basaltic

lava

Formation of:

• built up due to succesive

flows of basaltic lava

• due to the low viscosity and

high temperatures, the lava

flows over wide distances

away from the vent;

• the lava gradually cools as

thin, gently dipping sheets

of volcanic rock

Mauna Loa, Hawaii

Other volcano types

• Cinder cone

• Caldera

Volcanic Hotspots

• Most earthquakes and

volcanoes take place

near plate boundaries.

• However, in the middle

of plates, one may also

find volcanoes.

• They are sited on what

is know as volcanic

hotspots.

Volcanic hotspots• In hot spots, the crust

moves, but the plume

of magma remains in

the same place.

• In this way, new

volcanoes are created.

• These volcanoes form a

volcanic island chain,

according to the

direction of the

movement of the

plates.

Mt St Helens

Mt St. Helens

Hazards of volcanoes

• Volcanic gases

• SO2 is a colorless gas

with a pungent odor

that irritates skin and

the tissues and mucous

membranes of the eyes,

nose, and throat.

Sulphur dioxide chiefly

affects upper

respiratory tract and

bronchi.

• Helps to cool the lower

athmosphere, but also

destroys the ozone

layer.

Hazards of volcanoes• Hyrdogen sulphide

(H2s) - is a colorless,

flammable gas with a strong

offensive odor. It is sometimes

referred to as sewer gas. At low

concentrations it can irritate the

eyes and acts as a depressant; at

high concentrations it can cause

irritation of the upper respiratory

tract and, during long exposure,

pulmonary edema (bleeding in

lungs). A 30-minute exposure to

500 ppm results in headache,

dizziness, excitement, staggering

gait, and diarrhea, followed

sometimes by bronchitis or

bronchopneumonia

• Carbon Dioxide (CO2) –

Volcanoes release 130 million

tons of CO2 a year. It can only

be dangerous where it is so

concentrated that it replaces

oxygen – at 30%

concentration, usually in some

depressions in the ground

Volcanic Hazard

• Ash cloud – ashes from a volcano

are rocks pulverised to 2mm or

less in diameter. Forms when the

magma explodes upon meeting

the athmosphere.

• Problems –

• Damage to infrastructure - water,

electricity, waste water

treatment, aircraft and airports,

telecomunications

• Animal and human health –

breathing difficulties, eye and

skin irritations, nose and throat

symptoms

• Environment and Agriculture –

destruction of crops and trees

and of pastures

Volcanic Hazards• Lava - it destroys

everything on the

ground but lava flows

are slow enough to

allow many people to

escape. (up to

30km/hr on steep

slopes).

Volcanic hazards• Lahars – a mudflow

composed by

pyroclastic material and

large amounts of

rainwater. They are

extremely destructive

and can cover tens of

meters per second.

Nevado del Ruiz and

Pinatumbo eruptions

cause lahars which

killed thousands of

people.

Volcanic Hazards