GCSE: Plate tectonics

Convection currents

Internal structure

Millions of years ago there was one large continental land mass called Pangaea. As the plates drifted apart this split into two. The northerly one was called Laurasia and the southern one Gondwanaland. The plates moved through the power of the convection currents operating in the upper mantle. Today the plates have formed a pattern which was very different to the past. For example the white cliffs of Dover were formed in tropical seas, as at one time Dover was in the tropics!

Continental Drift > Alfred Wegner’s theoryEvidence:•Jigsaw Theory – Brazil’s east coast fits into western Africa- this was because at one time they were part of the same supercontinent – Gondwanaland•Fossil evidence – the same fossils have been found in Antarctica and South Africa – because they were once connected•White cliffs of Dover – are made of chalk which was laid down in a tropical sea – so at one time the UK was once in the tropics!•Alternating magnetic bandings in the North Atlantic

Magnetic banding

                                                                                                 

EARTHQUAKES

                                                                              

Plate margins

P10 Q2C/D SummaryAs the strength of an earthquake increases so does the risk of deathThere are exceptions however:LEDC’s are less able to cope with earthquakes - the buildings are often made of poorly constructed materials (eg Turkey)MEDC’s are better able to cope with earthquakes - they have the money to invest in making sure thatthe buildings are strong (eg San Fransisco, USA)Mankind is getting better at predicting and preparingfor earthquakes - which explains why so many peopledied in the Japan quake of 1923 (156,000)

A3 Sheet - EarthquakesCauses•Where 2 plate boundaries collide•Friction, heat and pressure builds up•This is released in sudden jerking movements•The centre of an earthquake = Focus•Above the focus on the ground = Epicentre•Measured on the Richter Scale

A3 Sheet - Earthquakes - Effects•People are made homeless - refugees•Bridges collapse•Looting of buildings after the earrthquake•Millions of £ of damage is caused•Insurance companies struggle to pay the costs of rebuilding•People trapped in buildings and cars•People die•Fires start - eg Kobe Earthquake 1995•Burst gas and water pipes•Electricity wires are damaged - therefore no power

A3 Sheet - Earthquakes - Prediction•Strange animal behaviour - eg dogs, Japanese Cat Fish, cows•Monitoring stations - Richter Scale eg Parkfield, California•Scientists place monitoring equipment in the ground - eg Seismometers•Richter Scale results•Record previous earthquakes - see if there is a pattern

A3 Sheet - Earthquakes - Protection•Stay in open!•Earthquake practice drills - eg Japan•Reinforce the foundation of buildings•Put in rubber shock absorbers under the buildings•Steel rods to strengthen the building•Make a safety kit / survival kit / 1st Aid•Avoid cars and lifts

A3 Sheet - EarthquakesPreventionPutting water into fissures has been tried but to no avail!

A3 Sheet - EarthquakesWhy People live there1. People have no where else to go2. Job opportunities - eg Los Angeles3. Cheap housing4. Feel safe - “it won’t happen to me - not in my lifetime”5. High standard of living there6. Good climate - eg California7. Houses are constructed very safely - eg reinforced foundations

Types of marginsTypes of Margins

1. Constructive Boundaries

Magnetic banding

•(I) Constructive Ocean+Ocean Plate eg Mid Atlantic Ridge

(North American + Eurasian Plate)

Iceland rift

Thingvellir, Iceland

•(II) Continental+Continental Plate Eg East African Rift Valley(African and Indian Plate)

2. Destructive Boundaries

Pacific Ring of Fire

•(I) Ocean+Continental Plates - eg Peru, Andes(eg Nazca and South American Plates)

Andes

•(ii)Ocean + Ocean Plates Eg. Marianus Trench(Pacific and Philippine Plates)

•(iii) Continental+ContinentalEg Himalayas, Nepal

(Indian+Eurasian Plates)

Tibetan plateau

3. Transform Boundaries

Eg. The San Andreas Fault, California, USA

Off-set Highway on the San Andreas Fault

Valleys along the fault line

Gap theory

CASE STUDY

SAN FRANSISCO

SAN FRANSISCO ENCARTA VIDEO

1906 Earthquake

17th October 19897.1 Richter Scale

Causes:

San Andreas Fault - Transform BoundaryBuilding in Marina District - this was poor quality land - unsuitable for houses

Effects

•US$6Bn damage•Fires•62 died•Gas mains broken•Homeless people / Refugees•Motorways / Roads collapsing

Protection

•Reinforced steel •Deep foundations

Why do people live there?

•Warm climate•Good standard of living•Lots of jobs available•People think it wont happen to them

1969-19891969-1989

3 weeks after 19893 weeks after 1989

The seismic gap theoryThe seismic gap theoryThe part of an active fault that has experienced little or no seismic The part of an active fault that has experienced little or no seismic

activity for a long period, indicating the build up of stresses that are activity for a long period, indicating the build up of stresses that are useful in predicting earthquakesuseful in predicting earthquakes

LiquefactionLiquefaction

Japan 1963Japan 1963

Golden Gate Bridge

Port and wharf facilities are often located in areas susceptible to liquefaction, and many have been damaged by liquefaction in past earthquakes.

Most ports and wharves have major retaining structures, or quay walls, to allow large ships to moor adjacent to flat cargo handling areas. When the soil behind and/or beneath such a wall liquefies, the pressure it exerts on the wall can increase greatly - enough to cause the wall to slide and/or tilt toward the water. Liquefaction caused major damage to port facilities in Kobe, Japan in the 1995 Hyogo-ken Nanbu earthquake.

Note the Note the subsidence subsidence in the port in the port in Kobe due in Kobe due to to liquefactionliquefaction

VOLCANOES

Volcanoes - Intro:Are generally found at plate marginsWhere 2 plates collide, the denser, heavier Oceanic Plate “SUBDUCTS”, or sinks below the lighter Continental PlateAs it does so the ocean plate melts due to the build upof friction, heat and pressureThis forms molten rock or MAGMAThis Magma then rises to form a MAGMA CHAMBER -which builds up until it erupts

Volcanoes Video 114Causes:•Where 2 plates collide - (one oceanic and one continental), the denser oceanic plate sinks, or SUBDUCTS, below the lighter continental plate.•As it does so, the friction, heat and pressure builds up to such an extent that the plate melts into molten rock•This molten rock is bouyant (lighter) and rises upwards to form a magma chamber•Over time, the pressure in the magma increases and eventually is released in a volcanic eruption•Eg Mount St Helens, USA - Juan de Fuca and North American Plates 18th May 1980

Volcanoes - Effects continued:•Volcanoes are also found at Constructive Plate Boundaries - eg Mid Atlantic Ridge - where 2 plates are moving apart - magma rises to fill the gap - it cools and solidifies to form islands - eg Iceland•As the magma rises it mixes with gases and travels along lines of weakness under the ground. These gases can cause the volcanoes to be very explosive when they erupt•How explosive an eruption is depends upon how runny or sticky (viscous) the magma is. If magma is thin and runny it escapes easily and flows easily out of a volcano - eg a CALDERA.•If there is a high gas content in the magma the eruption can be explosive = SHIELD VOLCANOES - EG Mount St. Helens, USA

Volcanoes: EFFECTS•People die•homes destroyed•crops destroyed - fertile soils near volcanoes so many farms are near volcanoes•roads destroyed•contamination of water supply•deforestation - I.e. trees uprooted and burnt•animals die - damage to local ecosystem•pyroclastic flows - hot clouds of burning ash and rock•tephra - clouds of ash•lava bombs - eg Mount Etna•ash clouds - can travel hundreds of miles•nuee ardente - powerful cloud of hot gas

Volcanoes - Prediction•Earthquake activity - Richter Scale - eg Mount Pinatubo in Phillippines, 1991•Mountain may bulge as magma moves underneath - eg Mount St. Helens (18th May 1980)•Satellites•Gas measurements at the crater increase•Small pyroclastic flows•Small eruptions of tehphra (ash) - eg Mount Pinatubo 1991•Is the volcano: active, dormant or extinct?

Volcanoes Protection•Good access to escape - roads etc•Emergency shelters - water, food, thick concrete walls•Build huge walls to channel the lava or pyroclastic flows - eg Japan•Annual “Disaster day” evacuation drills - where local people practice what they would do in the event of a volcanic eruption - eg Sakurijima, Japan•Listen to the warnings and evacuate - eg Mount St. Helens•Don’t live near a volcano!

Volcanoes - Prevention•There is little that mankind can do to prevent a volcano

Volcanoes - So why do people live near volcanoes?•The ground is fertile and very good for growing crops - eg Japan•Fishing - eg Heimay, Iceland•They cannot afford to move away - cheaper housing may be there - and so they have no choice•lack of awareness - eg CO2 emissions, Cameroon•densely populated area - eg Japan - so no where else to live - eg Sakurijima Island•Tourism provides money for local people - eg New Zealand, Rotorou or Mount Etna in Europe (Italy), Hawaii •Religion - Bali - volcano represents a local god which they worship up the mountain•Gold mining - Papua New Guinea

Why do people live near volcanoes:Location 1 > BALI:•The volcano is seen as sacred - the Balinese faith says that gods live up the mountain - and they have built a temple on the bottom slopes of the volcano•The rocks near the mountain are useful raw materials for building roads and for carving objects which can be sold•The soil near the volcano is fertile - rice is cultivated here very well - so people are reluctant to leave - as the volcano is seen as providing for their needs•It also adds to the cultural richness of the area

Why do people live near volcanoes:Location 2 > PAPUA NEW GUINEA:

•Large gold reserves and there has been a “gold rush”•There are very rich veins of gold here at Wurou Wurou (30 grams per ton - which is a lot)•Some people have made $25,000 per week gold-mining near the volcano

Why do people live near volcanoes:Location 3 > New Zealand:•Geothermal Industry near the volcanoes - which means that hot “bores” of steam (geysers) come up from the ground and this can be harnessed for energy in power stations - eg Wairaki Power Station, Rotorua•In total 8% of New Zealand’s power comes from such schemes - even hospitals use geothermal schemes•Tourism - people come to bathe in the thermal hot pools•Local people still cook using the thermal pools as the heat source - eg Mauri

Why do people live near volcanoes:Location 4 > Hawaii•Tourism - to see Mount Kilauea - where lava flows gently out of the volcano so can be viewed from a safe distance•Also a good climate for tourists to visit•The indigenous people to Hawaii believed that the volcano was sacred and so feared the gods up the mountain and were scared to leave•More general points:•People feel safe with modern prediction methods - eg satellites•People take the view - that it will not happen to them, not in their lifetime•People have lived there all their lives - so why leave eg Mr Trueman at Mount St. Helens!•The time between volcanoes is long - at least one generation - so people easily forget when the last one was

Hot spotsPlumes of hot mantle rising to the surface

Hot Spots > a small area of the earth’s crust where an unusually high heat flow is associated with

volcanic activity

World Hot Spots

The Trail of Hot Spots

CASE STUDYMOUNT

ST.HELENS

MUDFLOWS

Mount St HelensCauses:•DESTRUCTIVE PLATE BOUNDARY•Magma rises up under the mountain - in Washington State•Small earthquake triggered the landslideEffects:•Trees felled (flattened) 30km away from the mountain•Mudflows•Landslides•Bridges collapsed•Houses demolished - eg Mr Truman!•Hot cloud of ash and gas emitted•Glacier melted on top!•Top 400m of mountain disappeared!•31 people died in total

Effects cont.•animals died•pyroclastic flows•people evacuated - escaped!•State of Emergency Declared in Washington State

•Prediction:•Look to history•Small pre-eruptions•Pig behaviour!•Gas measurements - implies lava is on the move•small earth tremors•mountain bulges

END

ALASKA

Alaska earthquake of 1964Alaska earthquake of 1964

This great earthquake and ensuing tsunami took 125 lives (tsunami 110, earthquake 15), and caused about $311 million in property loss. Earthquake effects were heavy in many towns, including Anchorage, Kodiak, Portage, Seward and Valdez.

Anchorage, about 120 km Northwest of the epicentre, sustained the most severe damage to property. About 30 blocks of dwellings and commercial buildings were damaged or destroyed in the downtown area. The J.C. Penny Company building was damaged beyond repair; the Four Seasons apartment building, a new six-story structure, collapsed; and many other multi-storey buildings were damaged heavily. The schools in Anchorage were almost devastated. The Government Hill Grade School, sitting astride a huge landslide, was almost a total loss. Anchorage High School and Denali Grade School were damaged severely. Duration of the shock was estimated at 3 minutes.

Prince William Sound, Alaska 1964 03:36:14 UTC, Prince William Sound, Alaska 1964 03:36:14 UTC,

9.2 on the richter scale 9.2 on the richter scale

Landslides in Anchorage caused heavy damage. Huge slides occurred in the downtown business section, at Government Hill, and at Turnagain Heights. The largest and most devastating landslide occurred at Turnagain Heights. An area of about 130 acres was devasted by displacements that broke the ground into many deranged blocks that were collapsed and tilted at all angles. This slide destroyed about 75 private houses. Water mains and gas, sewer, telephone, and electrical systems were disrupted throughout the area.

The earthquake was accompanied by vertical displacement over an area of about 520,00 square km. The major area of uplift trended Northeast from southern Kodiak Island to Prince William Sound and trended east-west to the east of the sound. Vertical displacements ranged from about 11.5m of uplift to 2.3m of subsidence relative to sea level. Off the Southwest end of Montague Island, there was absolute vertical displacement of about 13 - 15m.

This shock generated a tsunami that devastated many towns along the Gulf of Alaska, and left serious damage at Alberni and Port Alberni, Canada, along the West Coast of the United States (15 killed), and in Hawaii. The maximum wave height recorded was 67m at Valdez Inlet. It was also recorded on tide gages in Cuba and Puerto Rico.

Close-up of Government Hill elementary school, which was Close-up of Government Hill elementary school, which was destroyed by the Government Hill landslide. Anchorage, Alaska. destroyed by the Government Hill landslide. Anchorage, Alaska.

The waterfront at Seward a few months after the earthquake, The waterfront at Seward a few months after the earthquake, looking north. Note the "scalloped" shoreline left by the looking north. Note the "scalloped" shoreline left by the underwater landslides that severed tracks in the railroad yard underwater landslides that severed tracks in the railroad yard which dangle over the landslide scarp and the windrow-like heaps which dangle over the landslide scarp and the windrow-like heaps of railroad cars and other debris thrown up by the tsunami waves. of railroad cars and other debris thrown up by the tsunami waves. Alaska. Alaska.

The very gently sloping flat The very gently sloping flat rocky surface with the white rocky surface with the white coating which lies between the coating which lies between the cliffs and the water is about a cliffs and the water is about a quarter of a mile wide. It is a quarter of a mile wide. It is a wave cut surface that was wave cut surface that was below sea level before the below sea level before the earthquake. The white coating earthquake. The white coating consists of the remains of consists of the remains of calcareous marine organisms calcareous marine organisms that were killed by desiccation that were killed by desiccation when the wave cut surface was when the wave cut surface was lifted above the high tide during lifted above the high tide during the earthquake. the earthquake.

Uplifted sea floor at Cape Cleare, Uplifted sea floor at Cape Cleare, Montague Island, Prince William Montague Island, Prince William Sound, in the area of greatest Sound, in the area of greatest recorded tectonic uplift on land (33 recorded tectonic uplift on land (33 feet).feet).

Tsunami damage on Kodiak island in AlaskaTsunami damage on Kodiak island in Alaska

One span of the "Million Dollar" truss-bridge of the One span of the "Million Dollar" truss-bridge of the former Copper River and Northwestern Railroad was former Copper River and Northwestern Railroad was dropped into the Copper River by the earthquake, and dropped into the Copper River by the earthquake, and the other truss spans were shifted on their piers. the other truss spans were shifted on their piers.

Close-up of damaged homes at Turnagain Heights landslide, Anchorage.

The Turnagain Heights landslide in Anchorage. Its The Turnagain Heights landslide in Anchorage. Its length was about 1.5 miles; its width was about .25 length was about 1.5 miles; its width was about .25 to .50 miles. to .50 miles.

This landslide reduced to rubble many of the finer This landslide reduced to rubble many of the finer homes of the city. Failure here, and in the "L" Street, homes of the city. Failure here, and in the "L" Street, Fourth Avenue, and Government Hill landslides in Fourth Avenue, and Government Hill landslides in Anchorage occurred on horizontal or near horizontal Anchorage occurred on horizontal or near horizontal slip surfaces in the Bootlegger Cove Clay, a marine slip surfaces in the Bootlegger Cove Clay, a marine silt.silt.

A subsidence trough (or graben) formed at the head of the A subsidence trough (or graben) formed at the head of the "L" Street landslide in Anchorage during the earthquake. The "L" Street landslide in Anchorage during the earthquake. The slide block, which is virtually unbroken ground to the left of slide block, which is virtually unbroken ground to the left of the graben, moved to the left. The subsidence trough sank 7 the graben, moved to the left. The subsidence trough sank 7 to 10 feet in response to 11 feet of horizontal movement of to 10 feet in response to 11 feet of horizontal movement of the slide block. A number of houses seen in this photograph the slide block. A number of houses seen in this photograph were undercut or tilted by subsidence of the graben. Note were undercut or tilted by subsidence of the graben. Note also the collapsed Four Seasons apartment building and the also the collapsed Four Seasons apartment building and the undamaged three story reinforced concrete frame building undamaged three story reinforced concrete frame building beside it, which are on the stable block beyond the graben. beside it, which are on the stable block beyond the graben.

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This truck at Lowell Point, 2 miles from Seward, was bent around a tree by the surge waves generated by the underwater landslides along the Seward waterfront. The truck was about 32 feet above water level at the time of the earthquake.

A detail illustrating the A detail illustrating the violence of the surge violence of the surge waves that struck waves that struck Whittier: man holds Whittier: man holds mounted tire where mounted tire where wave has driven a wave has driven a piece of wood through piece of wood through the tirethe tire

The rails in this approach to a railroad bridge near the head of Turnagain Arm were torn from their ties and buckled laterally by channelward movement of the river banks during the earthquake

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Trees up to 24 inches in diameter and between 88 Trees up to 24 inches in diameter and between 88 and 101 feet above sea level were broken and and 101 feet above sea level were broken and splintered by the surge wave generated by an splintered by the surge wave generated by an underwater landslide in Port Valdez, Prince underwater landslide in Port Valdez, Prince William Sound. William Sound.

KOBE

On Tuesday, January 17, at 5:46 a.m. local time, an earthquake of magnitude 7.2 (Mj)1 struck the region of Kobe and Osaka in south-central Japan. This region is Japan’s second-most populated and industrialized area, after Tokyo, with a total population of about 10 million. The shock occurred at a shallow depth on a fault running from Awaji Island through the city of Kobe, which in itself has a population of about 1.5 million. Strong ground shaking lasted for about 20 seconds and caused severe damage over a large area.

Nearly 5,500 deaths have been confirmed, with the number of injured people reaching about 35,000. Nearly 180,000 buildings were badly damaged or destroyed, and officials estimate that more than 300,000 people were homeless on the night of the earthquake.

The life loss caused by the earthquake was the worst in Japan since the 1923 Great Kanto Earthquake, when about 140,000 people were killed, mostly by the post-earthquake conflagration. The economic loss from the 1995 earthquake may be the largest ever caused by a natural disaster in modern times. The direct damage caused by the shaking is estimated at over ¥13 trillion (about U.S.$147 billion). This does not include indirect economic effects from loss of life, business interruption, and loss of production.

One of the key factors in loss of life and damage to buildings in the Kobe

earthquake was the extend of the fires that resulted.

The risks are particularly high in Japan because of •high population densities; •very narrow streets and alleys, which cannot act as fire breaks; •numerous old wood-frame smaller commercial and residential buildings mixed in the commercial zones of towns; •unanchored or unprotected gas storage tanks or heaters;• and a mix of collapse-prone old buildings in all built-up areas

Nagata ward at Nagata ward at 4.30pm on Jan 4.30pm on Jan 17th.17th.

KFD had minimal staffing on duty at the time of the KFD had minimal staffing on duty at the time of the earthquake, possibly because the previous day had earthquake, possibly because the previous day had been a holiday. Initial actions included recalling off-duty been a holiday. Initial actions included recalling off-duty personnel and responding to fire calls. Approximately personnel and responding to fire calls. Approximately 100 fires broke out within minutes, primarily in densely 100 fires broke out within minutes, primarily in densely built-up, low-rise areas of the central city, which built-up, low-rise areas of the central city, which comprise mixed residential-commercial occupancies, comprise mixed residential-commercial occupancies, predominantly of wood construction. Within 1 to 2 hours, predominantly of wood construction. Within 1 to 2 hours, several large conflagrations had developed. There were several large conflagrations had developed. There were a total of 142 fires reported in Kobe on January 17. Fire a total of 142 fires reported in Kobe on January 17. Fire response was hampered by extreme traffic congestion, response was hampered by extreme traffic congestion, and collapsed houses, buildings, and rubble in the and collapsed houses, buildings, and rubble in the streets. Because of the numerous collapses, many streets. Because of the numerous collapses, many areas were inaccessible to vehicles. areas were inaccessible to vehicles.

Water for fire-fighting purposes was available for 2 to 3 Water for fire-fighting purposes was available for 2 to 3 hours, including the use of underground cisterns. hours, including the use of underground cisterns. Subsequently, water was available only from tanker Subsequently, water was available only from tanker trucks. KFD attempted to supply water with a fireboat trucks. KFD attempted to supply water with a fireboat and relay system, but this was unsuccessful due to the and relay system, but this was unsuccessful due to the relatively small hose used by KFD. An EQE engineer relatively small hose used by KFD. An EQE engineer overflew the area at about 5:00 p.m. on January 17 and overflew the area at about 5:00 p.m. on January 17 and was able to observe all of the larger fires (about eight in was able to observe all of the larger fires (about eight in all) from an altitude of less than 300 meters. No fire all) from an altitude of less than 300 meters. No fire streams were observed, and all fires were burning streams were observed, and all fires were burning freely—several with flames 6 meters or more in height. freely—several with flames 6 meters or more in height. No fire apparatus were observed in the vicinity of the No fire apparatus were observed in the vicinity of the large fires, although fire apparatus could be seen at large fires, although fire apparatus could be seen at other locations (their activities were unclear from the other locations (their activities were unclear from the air). Some residents formed bucket brigades (with air). Some residents formed bucket brigades (with sewer water) to try to control the flames.sewer water) to try to control the flames.

A typical street scene in a residential and light commercial area of Kobe. A house has collapsed, blocking the very narrow street and preventing access to the area by the fire department. Thousands of narrow streets were blocked like this. In other areas, many of the collapses were traditional buildings with ground-floor stores or shops and second-floor residential units.

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IZMIT

Aftershock Maps from Kandilli Observatory and Research Institute

This picture is on the far east end of the rupture. The fault went directly through the school - the chalkboard read something like:

"We're all happy because school is out".

This is where 6 large apartments buildings all were completely flattened. Luckily they were uninhabitated. Residents were

supposed to have moved in during June, but were delayed. The fault is seen in the foreground. Aykut Barka has a photo taken of

this area from a helicopter.