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• These are study notes for the Edexcel Geography A-level topic: "Tectonics"

Global Distribution of Hazards

• A hazard poses a potential threat to human life and property.
• Natural hazards are either hydro-meteorological (climatic processes) or geophysical (land processes)
• Geophysical hazards typically occur near plate boundaries.
• Plates moving at different speeds and directions can cause collisions, earthquakes, and volcanic activity.
• Earthquakes can also occur near the middle of plates (intra-plate), where pre-existing weaknesses become reactivated.
• Volcanic hotspots, such as the Ring of Fire, are situated amongst the centre of plates due to high temperature from the core upwelling.
• At hotspots, magma rises as plume (hot rock).

Plate Tectonics and Theories

• The Earth is structured into four sections: crust, mantle, outer core, and inner core.
• The crust is divided into oceanic (thin and dense) and continental (thick) plates.
• Radioactive reactions in the core produce convection currents in the mantle, causing tectonic plates to move. This can cause push and slab pull
• Subduction occurs at mid-ocean ridges, where oceanic plates are pushed.
• The Pacific Plate is an example of one with lots of subduction around its edges as oceanic plates are heavier than continental.
• Plate Tectonic Theory is believed to be correct due to Wegner's Continental Drift Theory, the shapes of South America and Africa seem to fit together so were once part of a supercontintent.
• Seismic waves travel through the Earth, showing subduction using depth of waves at the Wadati-Benioff foci.
• Sea Floor Spreading occurs when two oceanic plates move apart, allowing magma to rise and form new crust ridges within the ocean, widening it.
• Studying magnetic patterns of cooled magma (palaeomagnetism) reveals the age of the oceanic crust and proves the earth once fit together.

Plate Boundaries: Destructive

Continental and oceanic:

• Denser oceanic plate subducts below the continental plate, leaving a deep ocean trench.
• Pressure from the melting plate causes explosive volcanoes bursting through the continental plate.

Oceanic and oceanic

• The heavier oceanic plate subducts, leaving an ocean trench.
• Built up pressure causes underwater volcanoes bursting through oceanic plate, and lava cools tocreates island arcs.

Continental and continental

• Plates aren't as dense as oceanic, so lots of pressure builds
• Ancient oceanic crust is subducted slightly, but there is not a lot of subduction of continental crust
• Pile up of continental crust on top of lithosphere due to pressure forms fold mountains.

Plate Boundaries Constructive

Oceanic and oceanic

• Magma rises between separating plates, forming new land when it cools.
• Less explosive underwater volcanoes form as magma rises, creating new land on the ocean floor through sea floor spreading.

Continental to continental

• Land in the middle of separating plates is forced apart, causing a rift valley.
• Volcanoes form where the magma rises, eventually filling the gap with water and separating completely from the main island.

Ridge Push and Slab Pull

• Ridge push happens as gravity acts on the slope created when plates move apart, pushing them further away, widening the gap (gravitational sliding).
• Slab pull: a subducting plate sinking into the mantle pulls the rest of the plate (slab) with it, causing further subduction.

Conservative Plate Boundary

• Parallel plates move in different directions or speeds.
• No landforms are created as no plates are destroyed.

Geophysical Primary Hazards: Earthquakes

• The most powerful earthquakes occur at destructive and conservative boundaries.
• At constructive boundaries, uneven plate movement releases energy as seismic waves, producing earthquakes.
• At destructive boundaries, stuck plates jerk past each other, releasing large seismic waves and causing a powerful earthquake.
• At conservative boundaries, locked plates release pressure as sudden seismic waves.
• Types of seisimic waves include: Primary waves, secondary waves, love waves and rayleigh waves (rolling Earth's crust. .
• Seismic waves result in crustal fracturing (faults) and secondary hazards (landslides, avalanches, liquefaction).

Tsunamis

• Tsunamis are produced by sub-marine earthquakes at subduction zones.
• Tsunamis are secondary to earthquakes, and present additional coastal erosion damage.
• Movement of plates causes an uplift of ocean water, disrupting the sea bed.

Volcanic Hazards

• Active volcanoes are found at constructive and destructive plate boundaries, and at hotspots. Volcanoes eject magma, gases, ash and dust.
• At constructive margins, magma is less dense than the plate, forming a volcano such as those within the Rift Valleys.
• At destructive margins, subduction causes explosive volcanoes such as Mt. St. Helens.
• The shape of a volcano determines its destructive ability.
• Volcanic hazards include lava flows and phreatic eruptions.
• Greatest threats are pyroclastic flows and secondary hazards such as lahars and jokulhaups.

Hazards, Disasters and Vulnerability

• In 2000, 700 million were affected by 170 reported disasters.
• A disaster occurs when a hazard affects human wellbeing (Degg's Disaster Model).
• Vulnerability is susceptibility to damage; resilience is the ability to recover.
• Risk is the likelihood of humans being affected by a hazard, and it is determined by: Risk= Hazard x Vulnerability / Capacity To Cope
• The disaster risk shows why similar hazards cause disasters of different degrees due to differing community accesibility. Poorer countries are also more vulnerable to secondary hazards
• Emerging world disasters can slow growth and potentially destroy economic systems.
• The Pressure and Release model (PAR) proposes what should be tackled if the risk of a disaster is to be reduced
• Influenced by Economic, Environmental, Social, Knowledge and Physical vulnerabilities.

Measuring and Comparing Tectonic Hazards

• Tectonic disasters can be measured: Earthquake magnitude uses the Richter Scale and the Moment Magnitude Scale.
• Earthquake intensity can be measured using the Mercalli Scale, according to damage produced.
• Volcanic eruptions use the Volcanic Explosivity Index (VEI), calculated using the amount of energy released and the type of eruption.
• Hazards can be compared using a hazard profile to measure magnitude, speed of onset, duration, frequency and spatial probability.
• Each disaster varies in its destructive capacity - being social, economic and environmental whilst direct/indirect, primary/secondary and long-term/short-term.
• Less developed countries face more severe impacts.

Development and Governance of a Disaster

• Vulnerability to disaster risks increases due to inequality due to lack of accesibility.
• Pressures - Increasing urbanisation, population growth, world poverty, and the exploitation of resources causes more people to be vulnerable.
• The World Risk Report in 2014 noted governments must face the challenge of establishing planning measures.
• The 'Disaster Preparedness Day' prepares communities for evacuation and educates them in mitigating social or economic loss.

Management and Mitigation of Tectonic Hazards

• Adequate infrastructure, housing, food supplies, and healthcare in more economically developed lowers the impact of a disaster.
• Corruption government, poor warning systems and weak community strength will exacerbate a hazard into a disaster.
• Trends show that deaths have decreased whilst economic losses have risen.
• There is increase use of international aid alongside preparedness.
• The number of tectonic disasters have fluctuated and are hard to predict.
• Earthquake and Hurricanes are examples of regional disasters (2010 Eyafjallajokull eruption in Iceland for example).

Hazard Hotspot Example- Philippines

• There is a complex mix of geophysical and hydro-meteorological hazards as the plate boundaries intersect in Philippine't major storm belt
• Philippines faces explosive volcanic threats, landslides, earthquakes, typhoons, tsunamis, drought and flooding.

Prediction of Tectonic Hazards: Park's Model

• Is a graph highlighting the steps carried out in hazard recovery with a rough indication of time frame which:
• Compares hazardous events
• The steep curve shows how quickly an area deteriorates and recovers.
• The depth shows the scale of the disaster.
• Stage 1, Relief (Immediate local response, Medical aid with appeal for foreign aid)
• Stage 2, Rehabilitation ( Services are restored, Shelters and hospitals arise, Food and water)
• Stage 3, Restoring, Infrastructure is rebuilt, Mitigation efforts for future events

Mitigation

• The Hazard Management Cycle outlines the stages of responding to events

Mitigation and Adaptation Techniques to Modify the Event

• Land-Use Zoning: Policies on where it is the safest to build, reducing the population living buildings
• Hazard-Resistant Buildings: Invest/produce long-term construction projects with safety designs with aseismic skyscrapers
• Engineering Defences: Modify tsunamis by creating stronger sea walls
• Diversion of Lava Flows: Divert lava by spraying seawater to cool and solidify the flow
• Strategies to modify vulnerability and resilience: Includes:
• Hi-Tech Monitoring such as New Zealand who uses light detection
• Education such as teaching hazards
• Community Preparedness to drill alarms

Actions To Improve Community Coping

• They can improve their capacity if they use good warming systems - though preparedness will determine recovery timescales
• To modify loss, emergency aid must continue to be delivered as well insurance
• Major key players come from NGO's and Insurers