OCR A-Level Geography - Hazardous earth Flashcards

Question

Why are volcanoes at divergent boundaries effusive? (smooth, gentle flows of lava - when lava has low viscosity)

Answer 1

Basic lava is runny (has low viscosity)

Answer 2

Runny basaltic rock creates pillow lava formations (round igneous rocks) - eruption of magma occurs mostly underwater. Magma erupting directly onto sea bed is rapidly cooled which forms pillow lava. Lava plateaux, e.g. Giant's causeway. Mid-ocean ridge formed by new crust (long chain of underwater mountains). Low, flat shield volcanoes formed by runny lava. Rift valley

Answer 3

Very long chains of mountains on the sea floor. Altogether have a combined length of 60,000km. At intervals, ridges are broken by transform faults. Vary in shape depending on rate of spreading (determined by amount and rate of magma rising).

Answer 4

Transform faults Small, shallow-focus earthquakes occur along their lengths as they slip.

Answer 5

Large-scale faults in the crust at right angles to a mid-ocean ridge, which range from tens to hundreds of km.

Answer 6

Lave flows far which forms low, gently sloping volcanoes. Runny basic lava erupts gently. Less viscous lava flows far (flows easily). Creates wide, gently sloping volcanoes.

Answer 7

(Underwater) Rising magma creates dome/bulge. Plates continue to spread. Brittle rocks fracture and fault. Dome subsides (sinks) forming a steep-sided valley. E.g. African rift valley (African plate splitting apart).

Answer 8

Continental crust must be thin for rifting to occur. E.g. Red Sea northwards to Turkey. Crust has been stretched, causing faulting and forming a sunken valley known as a graben. As rift widened, magma erupted to surface. Eventually rift valley sank below sea level, forming the present-day Red Sea.

Answer 9

Oceanic-continental Oceanic-oceanic Continental-continental (collision) Plates have different densities. Continental: 2.6-2.7kg m^3 Oceanic: 3.0kg m^3

Answer 10

Nazca plate -> South American plate

Answer 11

Convection currents cause plates to converge. The denser oceanic plate subsides beneath the less dense continental. Slab pull accelerates movement of oceanic plate.

Answer 12

1. Plates push together by convection currents. 2. The more dense oceanic crust subducts beneath the less dense continental crust. 3. Friction from plates rubbing together heats plates. Water from the ocean helps crust melt forming viscous acidic magma. Pressure builds up causing deep and shallow earthquakes. 4. Magma forces through continental crust (viscous lava has explosive eruptions). 5. Slab pull pulls subducting plate faster. Volcanoes and fold mountains are formed near the edge of continental crust.

Answer 13

Subduction brings volatiles (water + CO2) which cause melting of rock.

Answer 14

Type: Rhyolitic (more acidic) /Andesitic (less acidic) Acidic/basic: Acidic Silica content: High (high silica = high viscosity) Temperature: Lower Viscosity: High (thick) Frequency: Infrequent (struggles to break through crust) Duration: Short VIOLENT

Answer 15

Acidic lava has a high silica content which makes it viscous (thick). Therefore it does not flow easily so builds up steep composite volcanoes (layers of rock and tephra).

Answer 16

Pressure builds up over long periods of time due to high viscosity and slow flowing magma.

Answer 17

Description: Cone-like Steep-sided Have a crater at the top Composite (made up of layers) Have secondary vents Layers of ash and acid lava built up over successive eruptions. Lava intrudes into layers, forming sills (horizontal intrusion of magma) and dykes (vertical intrusions of magma). Vents of volcano can be sealed by solidified magma/lava (plug). This causes pressure to build up, resulting in explosive eruptions. Magma erupts violently as air bubbles finally burst. Throws droplets of lava as tephra and lava bombs. E.g. Mount Etna, Italy

Answer 18

Description: Basin Explosive eruptions empty the magma chamber beneath the volcano. The lack of support beneath causes the volcano to collapse on itself, forming a caldera crater. Collapsing of volcano's sides can cause tsunamis. E.g. Krakatoa, India

Answer 19

Two plates being pushed into one another which builds up immense amount of pressure. Faulting and fracturing takes place in the benioff zone. Causes pressure and energy to be released which creates earthquakes.

Answer 20

The boundary between the subjecting ocean plate and over-riding continental plate. Seismic energy is released here as rocks fault and fracture.

Answer 21

Slightly denser plate will be subjected.

Answer 22

Ocean trench where the denser plate subducts. E.g. Mariana trench up to 10,994m deep. Island arcs. As descending plates melt, magma is produce and rises to surface. Eruptions form chains of volcanoes. E.g. Mariana islands up to 820m above sea level.

Answer 23

1. Convection currents push crust together. 2. Denser oceanic crust subducts under less dense oceanic crust. 3. Forming an ocean trench at the area of subduction. 4. Volatiles help descending crust to melt and forms magma which rises and erupts forming island arcs. 5. Composite volcanoes are formed from viscous acidic lava.

Answer 24

Creates deep ocean trenches and tall mountain ranges (island arcs).

Answer 25

Explosive eruptions form: Strato (composite) volcanoes made up of layers of tephra and acidic lava which contain complex internal systems which create dykes and sills underground. Caldera craters which appear as a large crater, group of small islands or as a large lake.

Answer 26

Fault lines and cracks can occur in crust as energy from earthquakes

Answer 27

Himalayas (Indo-Australian plate <-> Eurasian plate)

Answer 28

Because they collide. They move together but aren't dense enough to subduct.

Answer 29

2 continental plates converge. Little, if any subduction occurs due to similar densities. Accumulated sediments are compressed into rock which buckle and fold forming mountain ranges.

Answer 30

Convection currents push plates together. However they move slower because there is no slab pull or ridge push to accelerate movement.

Answer 31

Friction builds up at the collision zone. Rocks crack and fault and when pressure reaches the threshold energy is released as an earthquake. Earthquakes are usually have a shallow focus and are of moderate strength. E.g. Nepal, 2015 (7.0MW)

Answer 32

Fold mountain chains are formed - total 2.5 million km. Loss of ocean floor due to tectonic uplift. Cracks and faulting in rocks. Synclines and anti-synclines (bending of rock).

Answer 33

San Andreas Fault California

Answer 34

Crust is neither created or destroyed, just conserved (slide past each other).

Answer 35

Plates move past each other. Pacific plate (LA) moves north west by 5-9cm /year. North American plate (San Fran) moves north west by 2-3cm /year. Slab pull as crust subduct at different boundaries. Difference in rate means North American plate moves south-east in relative terms.

Answer 36

No subduction or spreading occurs. Rock doesn't melt. Therefore no formation and pressure build up of magma.

Answer 37

- Plates do not move steadily (they move intermittently). - Plates rub against each other creating frictional resistance and they sometimes get stuck. - Pressure gradually builds up until it reaches the threshold. - Rocks fracture and energy is released as shallow-focus earthquakes. Plates move in a 'jolt'.

Answer 38

Shallow-focus Major Lateral movements (P and love waves)

Answer 39

- Do not create large landforms. - Can create major faults across landscapes (San Andreas Fault). - Landforms across the faults can also be displaced. e.g. River channels deflected by movement of faults.

Answer 40

Hawaiian islands Middle of pacific plate

Answer 41

A particularly hot section of mantle. This can melt through the crust causing volcanic activity. Hot spots usually occur away from plate boundaries. Some are found at plate boundaries, e.g.Iceland.

Answer 42

1. Plume of particularly hot mantle. 2. Melts through crust forming volcano and island. 3. Movement of plate transports volcano away from hot spot. 4. Volcano becomes extinct. New volcano formed at hot spot. Oldest (smaller) island: Kauai (formed 3.8 million years ago) Newest (bigger) island: Hawaii (big island) Crust moves away from hot spot so it cools and becomes denser making it subside (sink). Islands have been eroded by waves, weathering and mass movement making the older islands much smaller.

Answer 43

Shield, gently sloping, wide volcanoes. Because basaltic lava is less viscous meaning it flows easily and flows further. Effusive eruptions build huge volcanoes.

Answer 44

They are caused by a build-up of pressure and movement of ground due to volcanic activity. Small earthquakes Frequent Caused by movement of magma Most where hot spot it (Hawaii).

Answer 45

Hot spot volcano chain - Magma activity at hot spot - Basic lava - Effusive - Shield volcano - Formed in a sequence - Big age difference Island arcs - Magma activity (subduction and volatiles) - Acidic lava - Explosive - Strato volcano (composite) - Closer together in age, less variation as they are formed together.

Answer 46

Yellowstone, Wyoming North American plate

Answer 47

A volcano that erupts more than 1000km^3 of material in a single eruption. Are usually found as giant calderas. They occur when rising magma cannot break through crust. Pressure increases as more magma rises until magma violently forces its way through as a huge eruption.

Answer 48

Basic (Basaltic) Lava is free-flowing and can run for considerable distances. Hawaii (July 2015) lava flow extended for 20km without stopping. Acidic Thick, pasty lava doesn't flow easily. Everything in the path of lava is burned/buried destroying infrastructure/properties/crops. Rarely cases injuries/fatalities because people can escape the flow.

Answer 49

Combination of hot gases (500degC+), ash and rock fragments travelling at high speeds (100km/hr). Follow contours of ground and destroy everything in path. Inhalation of hot, poisonous gas can result in almost instant death.

Answer 50

Any material ejected from volcano into air. Fine ash/volcanic bombs. Buries farmland, destroying crops, disrupts transport on ground and in air. Iceland's volcanic eruption (2010) led to cancellation of 100,000 flights. Builds can collapse due to weight of accumulated ash. People with respiratory diseases have difficulty breathing.

Answer 51

Deadly threat to humans. SO2 combines with atmospheric water, produced acid rain. Enhances weathering can damage crops and pollute surface water and soils.

Answer 52

Type of mud flow (consistency of wet concrete). Travel up to 50km/hr. Destroy/bury everything in it's path. Eruption in Columbia (1984) killed 23,000 due to lahars.

Answer 53

Volcanic eruptions beneath ice field/glacier results in rapid melting. Iceland's volcano lies beneath ice and snow. Eruptions cause vast quantities of water to accumulate until it finds an exit. Results in torrents of water, can cause devastating floods.

Answer 54

Eruptions of island volcanoes cause displacement of ocean water creating tsunami waves that travel up to 600km/hr. Tsunamis created by eruption of Krakatoa in 1883 believed to have drowned 36,000 people.

Answer 55

A measurement used to rank and compare different volcanic eruptions using: - volume of erupted material. - height the ejected material reaches. - duration in hours. - qualitative measures ('gentle', 'mega-colossal').

Answer 56

The release of stress that has built up within the Earth's crust caused by tension, compression or the shearing of rocks. Release of energy causes seismic waves to be released from the focus.

Answer 57

Focus point at which waves originate from (point where stress is released). Epicentre directly above the focus (where most severe impacts will be). Seismic waves energy released travels as waves. Fault line where movement in plates occur.

Answer 58

Mid-ocean ridge (divergent boundary)/rift valleys (constructive boundary) Ocean trenches (convergent boundary)/island areas (destructive) Collision zones (convergent) Conservative margins (conservative) Away from plate margins

Answer 59

0-70km deep Occur in cold, brittle rock resulting from fracturing of rocks due to stress within the crust Very common Releasing low levels of energy High-energy, shallow quakes are capable of causing severe damage

Answer 60

70-700km deep Increasing depth = extreme temps/pressures

Answer 61

Primary (P) waves Fast-travelling Low-frequency Compressional waves Vibrate in the direction they're travelling Travel through Earth's interior (through solids and liquids) Secondary (S) waves Half the speed of P waves High-frequency Vibrate at right angles to the direction they're travelling Cannot pass through liquids (so cannot travel through outer core) Surface (L) waves Slowest waves Low-frequency Rolling movements that move the surface vertically Travel through outer crust only

Answer 62

Richter scale Measure of energy released on a logarithmic scale (each whole number represents a 10-fold increase in amplitude). Largest record quakes are magnitude of around 9. Doesn't measure damage (partly determined by magnitude but also by population density and level of preparedness). Modified Mercalli Scale (MMS) Qualitative measure of damage experienced related to ground movement (impacts felt and seen by people). Attempts to measure both intensity and impact. Based on observation and description. Moment magnitude scale (Mw) Measures energy released more accurately than Richter. Measures amount of movement of the ground - a direct function of energy. Accurate for large earthquakes but not useful for smaller ones.

Answer 63

Positive correlation Stronger earthquakes = more energy = more damage

Answer 64

Measures direct energy that causes ground movement so can be used to predict damage.

Answer 65

Associated with formation of mountain ranges (e.g. Himilayas) at collision boundaries. Collision of India and Eurasian plates led to complex pattern of folding and faulting of rocks creating the world's highest fold mountains: 96/109 of world's peaks >7000m located here. Rift valleys along mid-ocean ridges (e.g. East Africa - evidence of earthquakes on morphology of Earth's surface) Fault scarps and escarpments of rift valleys mark locations of faults caused by tension and compression within crust. Rift valleys are weathered and eroded so over time fault scarps are worn away and blend into landscape, can even disappear under accumulated sediments.

Answer 66

Every year, around 100 earthquakes with potential to impact significantly. 2000-2015: estimated 800,000-900,000 killed by earthquakes.

Answer 67

Vertical and horizontal movement of ground. Severity depends on: - Earthquake magnitude - Distance from epicentre - Local geology Close to epicentre of high-mag quakes with unconsolidated surface layers with high water content will experience extreme shaking. Swaying of buildings impacts their stability Displacement of rocks along fault lines can: - Rip apart pipelines and sewers - Sever rigid structures (railway tracks and roads) - Cause building collapse - Disrupt drainage systems (diverting streams and rivers, affecting movement of aquifers) - can have serious implications for public water supply and irrigation for agriculture.

Answer 68

Vibrations of quake cause surface materials with high water contents (fine-grained sands, alluvium, landfill) to behave like liquids. Materials loose strength; slopes (river banks) collapse and structures tilt and sink as foundations give way.

Answer 69

Shaking loosens lopes on mountains causing slope failure. E.g. Himilayas - unstable/vulnerable (increased by deforestation and monsoon rains) even small tremors can cause landslides. Nepalese quake (2015) triggered multiple landslides and avalanches caused by ground shaking. - Block transport routes where accessibility is already difficult. - Block rivers - natural dams create temporary lakes which lead to flooding when dam fails.

Answer 70

Underwater earthquakes Cause sea bed uplift - displaces water above, producing powerful waves at surface which spread outwards from epicentre. Wave height increases as they approach shoreline and shallower water. Local height of wave affected by shape of sea bed and coastline. Underwater landslides When large volume of rock displaced underwater it slumps down, displacing water, creating a wave which radiates outwards.

Answer 71

MT ETNA, ITALY (AC) MT MERAPI, INDONESIA (EDC)

Answer 72

Active: erupted within the last 10,000 years. E.g. Kilauea (Hawaii) erupting continuously since 1983. Dormant: has not erupted in last 10,000 years, expected to erupt some time in future. E.g. Yellowstone erupted 70,000 years ago. There are ongoing earthquakes, geothermal features such as geysers and ground inflation). Extinct: not expected to erupt ever again. E.g. Kohala (Hawaii) erupted 120,000 years ago.

Answer 73

JAPAN, 2011 (AC)

Answer 74

Location: - Tohoku, Honshu Island, Japan, East Asia - 70km offshore - North part of main island Tectonic context: - Convergent (destructive) oceanic-continental plate boundary - Pacific (oceanic) subducts beneath Eurasian (continental) - 9.0Mw (BIG) - Shallow focus earthquake (30km deep) - 11th March, 2011 - Numerous aftershocks (7.0-8.0Mw)

Answer 75

Perception of risk - Investment in education/engineering builds feeling of security. - Experiences 400 earthquakes each day (most can't be felt) - minor earthquakes help Japanese feel accustomed to these hazards. Earthquakes and their effects are part of Japanese culture and folklore. Small geo-thermal power plants since the 1960's. - There has been an attempt to increase the scale of operations especially in the wake of the Fukushima nuclear meltdown. Intensive agricultural industry made possible by extremely fertile volcanic soils. Volcanic activity has become a major tourist attraction in Japan.

Answer 76

Largest ever earthquake to hit Japan (9.0Mw). Shaking lasted 3-7 minutes. Many aftershocks. 7.0-8.0Mw Tsunami waves created. Reaching up to 40.5m tall (far higher than sea defences). Travelled 10km inland (reaching the city of Sendai). Waves reached Antarctica and USA. Earthquake nocked out power supply to Fukushima Nuclear Power Plant. Tsunami flooded back-up generators and triggered nuclear meltdown in three reactors. 400km stretch of coastline dropped 0.6m vertically. Honshu island moves 2.4m east.

Answer 77

Cost of the event estimated at nearly $181 billion. 45,700 buildings destroyed; 143,300 damaged. 15 ports damaged, 4 destroyed. 4.4. mullion households and thousands of businesses in northeast Japan were left without electricity. Japanese stock market fell - major companies affected (Sony, Toyota, Panasonic) as power cuts halted production and port damage prevented export of goods. Fishing industry affected as radioactive wast contaminates Pacific Ocean. Farmland flooded by tsunami contained by salt - land made infertile. Fukushima nuclear power plant had to be decommissioned after meltdown.

Answer 78

16,000 people were killed and 6,000 injured. Bodies disposed of in mass graves to reduce the chance of disease. Children separated from families (Save the Children reported 100,000 children affected). 2000 young people were either orphaned or lost 1 parent. Extent of damage meant reconstruction of house, schools and health centres took 5 years. 5,800 people evacuated and permanently relocated from their family home after being evacuated from 30km fallout zone following Fukushima event. Internal migration of people from Tokyo to Osaka in the months following the Fukushima event.

Answer 79

Government increased national debt to help recovery efforts; spent billions of yen to stabilise economy. A large movement against nuclear power has developed and spread globally. The government is yet to decide on the future of nuclear power. International travel advice against visiting Japan (USA, France, Australia). Foreign residents (e.g. international students) left the country.

Answer 80

(H) Frequent hazards would increase risk because... - People do not have time to recover from previous hazard (they're still vulnerable). - Regular disruption would limit economic/social development. - Reduce investment in an area. Stronger hazards would increase risk because... - More energy causing more damage (more likely to be devastating). - Less likely to mitigate successfully against unusually high magnitude hazards. (V) Vulnerability = whether people have to ability to withstand hazards. More vulnerable people are at greater risk from hazards because small changes can have significant socio-economic impacts. E.g. Subsistence farmers losing an area of crops are severely affected. Large landowner with same proportion of land affected would be less severely affected. (C) More resilient populations are at less risk because... - Reduces damage done my hazard. - Able to afford better mitigation strategies.

OCR A-Level Geography - Hazardous earth Flashcards

(106 cards)