Tectonic Hazards and Plate Tectonics

• These are essential study notes for Edexcel Geography A-level, focusing on the topic of tectonics.

The Global Distribution of Hazards

• A hazard presents a potential threat to property and human life.
• Natural hazards are either hydro-meteorological (climatic processes) or geophysical (land processes).
• Geophysical hazards typically occur near plate boundaries, where plate movement at varying speeds causes collisions, volcanic activity, and earthquakes.
• Earthquakes can also occur mid-plate (intra-plate) where pre-existing weaknesses are reactivated, forming seismic waves within weakened crust.
• Volcanic hotspots, like the Ring of Fire, are located within plate centers, characterized by high temperatures from upwelling molten material.
• Hotspots, like Hawaii, experience magma rising as a plume (hot rock).

Plate Tectonics and Theories

• The Earth's structure can be divided into the crust, mantle, outer core, and inner core.
• The crust is divided into oceanic (thin and dense) and continental (thick) plates.
• Radioactive reactions occurs inside the core, producing convection currents in the mantle, causing tectonic plates to move.
• Mid-ocean ridges see push and slab pull where oceanic plates are pushed through subduction.
• Oceanic plates are heavier than continental ones, and the Pacific Plate is an example. The Plate Tectonic Theory states the shapes fit together and similar fossils can be found.
• Wadati-Benioff foci help determine plate subduction as waves show the location in the upper mantle.
• At the sea floor, two oceanic plates move away from each other, with magma rising to form new crust ridges, resulting in widening.
• Studying the magnetic patterns of cooled magma shows the earth's magnetic field switching helps determine the age of oceanic crust, proving the earth did once fit together.

Plate Boundaries

• Plate boundaries can be constructive, conservative, or destructive.
• At continental and oceanic destructive plate boundaries, the denser oceanic plate subducts below the continental plate, leaving a deep ocean trench.
• Built-up pressure from the melting plate causes explosive volcanoes to burst through the continental plate.
• At oceanic and oceanic destructive plate boundaries, a heavier plate subducts leaving an ocean trench. As pressure builds up, underwater volcanoes burst through the oceanic plate. These resulting in new land called island arcs.
• At continental and continental destructive plate boundaries, plates are less dense than oceanic plates, building pressure and slightly subducting ancient crust. Piles of crust on top of the lithosphere create fold mountains from piles of the continental crust.

Constructive Plate Boundaries

• At oceanic and oceanic constructive plate boundaries, magma rises between separating gap and forms volcanoes. The resulting new is known as sea floor spreading as the floor spreads with lava.
• At continental to continental constructuve plate boundaries, separation causes a rift valley. Volcanoes form when magma rises which will eventually fill with water to separate the land from the main land.
• Ridge push and slab pull are forces influencing how convergent boundaries occur. Slopes from plates moving act due to gravity as the plataes are pushed away, and subducting plates pull the plate further down.

Conservative Plate Boundary

• Parallel plates move in different directions or at different speeds. However, no plates are destroyed thus landforms are not created.

Geophysical Primary Hazards - Earthquakes

• Earthquakes can occur at destructive and conservative boundaries.
• At constructive: plates move at diff. speeds creating fault lines, resulting in seismic waves to create earthquakes.
• At destructive: as plates jerk past one another, large seismic waves create a powerful earthquake.
• At conservative: plates lock and sudden seismic waves occur.
• Seismic Waves: Seismic waves: Primary waves happen immediately, secondary waves take seconds, Love Waves go horiztonally, and Rayleigh Waves cause rolling of the crust.
• These waves also causes crustal fracturing and landslides and avalanches.

Geophysical Primary Hazards - Tsunamis

• A tsunami is produced by sub-marine earthquakes, causing displacement of the water. Result is coastal erosion. Under the ocean, the plates cause uplifting, disrupting the sea bed.

Geophysical Primary Hazards - Volcanic

• Volcanoes are found at hotspots and plate boundaries which magma ejects gases adn dust.
• At constructive margins, the plates rise as volcanoes as magma is less dense.
• At destructive margins, subduction causes explosive volcanoes.
• Volcano shapes determine ability which also causes lahars and jokulhaulps. Pyroclastic flows carry over distances.

Hazards, Disasters and Vulnerability

• In 2000, 700 million were affected by 170 reported disasters
• A disaster is a hazard affecting human life and Degg's Disaster Model suggests it only occurs when a hazardous meet vulnerable.
• Vulnerability is the susceptibility to a hazard while resilience is recovery. They determine risk using the equation "Hazard x Vulnerability / Capacity to Cope" which demonstrates why similar hazards cause disasters of different degrees.
• A similar earthquake in Turkey caused only 1800 deaths, but one in Kashmir caused 75,000, because Kashmir is more remote and mountainous.
• Richer countries face high financial losses, while poorer countries wellbeing and infrastructure.
• Emerging countries risk slowing of growth.
• PAR (Pressure & Release) Models tackle disaster by addressing 5 areas: economic, environmental, social, knowledge and physical.

Measuring Tectonic Hazards

• Tectonic disasters can be measured using logarithmic scales such as the Richter Scale and the Moment Magnitude Scale. The Mercalli Scale measures what damage is produced.
• They measure the Volcanic Explosivity Index (VEI) by amount of energy released. Characteristics can be used to compare hazards using a Hazard Scale.
• Disasters also vary in its destructive capacity which includes the impact on those who are less developed and therefore face more severe consequences.

Development and Governance of a Disaster

• People become vulnerable because of inequality. Urbanization and population also cause an overlap, so vulnerability and exploitation create a loss of resilience for one group of people in area.
• Urban goverments are challenged in establishing plannign measures. Japan is one such government has focused on educating the community in preparation measures, and so mitigating the risks.

Management and Mitigation of Tectonic Hazards

• Death rates have decreased globally because of econmic losses, preparedness and international aid. It can be hard to produce earthquakes for accurate.
• Disasters vary on the degree to which spread causing disasters globally such as financial impacts on travel companies and tourists. It is more common now that famines are causing fatalities slowly.
• The Phillippines experiences a mix of hazards as storm belts intersect.

Prediction of Tectonic Hazards

• Park's Model shows graphical representation of the hazard steps, but depends on length of income.
• 3 stages:
  • relief (getting medical help - hrs to days)
  • rehabilitation (days to weeks to help with shelters)
  • reconstruction (back to normal but now can mitigate risk for further)

Disaster risk and what is its purpose?

• The Hazard Management Cycle shows the stages of responding where events re-occur, by beginning a new cycle with prepardeness events and eventually mitigation against the impact again. The cycle ensures that those that are affected can be defended using engineering or insurance to protect the vulnerable.
• Governments attempt to reduce the loss by modifying resilience with Land-Use Zoning which ensures safety, but may also lead to hazard-resistant buildings featuring designs that protect the construction.
• HI-Tech Monitoring helps understand risk areas and whether it means risk.
• The community can also be educated while the capacity of the community is being approved, such as the correct alarm system.
• Key players should be insurers, which have both short and long term effects, but may lead to dependency on insurance for the losses.

Explore the factors increasing tectonic hazard risks. Understand plate movement causes, subduction zones, and intra-plate earthquakes. Learn about magma plumes, continental drift evidence, slab pull, crust density, hydro-meteorological hazards, and hazard prediction.