HAZARDOUS ENVIRONMENTS - the whole chapter 🌪️🌋

Hazardous Environment

• Hazard: An event that has the potential to cause harm to lives and property.

  • Example: An earthquake in unpopulated areas is a physical event; however, it becomes a hazard if the area is built up.

• Disaster: A hazard that causes so much injury and damage that help is needed to recover.

• Risk: The level of exposure of people to a hazardous event.

• Vulnerability: Degree to which conditions make people more likely to experience an unexpected hazardous event that they cannot cope or recover from.

• Resilience: How well people recover from a hazard.

Hazards From Tectonic Processes

Volcanoes and Earthquake Distribution

• When describing distribution, use the T(CLUES)EAM method:

  • Trends: Loose/strong correlations, positive/negative correlation.

  • Clustered, Linear, Uneven, Even, Scattered.

  • Evidence: Include specific place names for support.

  • Anomalies: Identify features that contradict the trend.

  • Manipulate: Perform simple calculations if data is provided.

• Earthquakes:

  • Exhibit clear linear chains along plate boundaries (e.g., Mid-Atlantic Ridge).

  • Broad chains found along subduction zones (e.g., Nazca/South American plate).

  • Some earthquake events occur not on boundaries due to human activities or hotspots like the Hawaiian Hot Spot.

• Volcanoes:

  • Form strong bands of linear structures along boundaries.

  • Approximately ¾ of Earth’s volcanoes are located around the Pacific Ring of Fire.

  • Clustered volcanoes are often found over hotspots (e.g., Hawaii).

  • Most intense activity occurs along subduction zones.

Hazards on Boundaries

• Different types of tectonic boundaries produce various hazards:

Conservative Boundaries

• Cause intense earthquakes due to severe friction along the boundary (e.g., San-Andreas fault line).

• No volcanic eruptions are associated.

Collision Boundaries

• Lead to earthquakes due to the collision and friction at the boundary.

• No volcanic activity is observed.

Destructive Boundaries

• Produce shallow to deep earthquakes, inclined along the Benioff zone where slab pull occurs.

• Result in explosive, ashy, and viscous volcanic eruptions due to increased melting creating silica-rich magma.

Constructive Boundaries

• Result in moderate earthquakes caused by the movement of weak oceanic crust, influenced by volcanic intrusions or transform faults from differing spreading speeds along the boundary (e.g., Mid-Atlantic Ridge).

• Fluid basaltic lava forms new oceanic crust.

Hotspot Theory

• The uneven heat in Earth’s core causes radioactive decay leading to:

  • Intense heat transfer from the core through the mantle.

  • Movement in the upper mantle caused by convectional processes.

  • Thermal plumes causing magma build-up beneath tectonic plates, leading to volcanic activity.

• Pressure forces magma through cracks onto the seafloor.

• As plates move over a stationary plume, it creates a chain of islands.

  • Inactive volcanoes subsequently erode into inactive seamounts.

Earthquake Processes

• Tectonic Plates Movement:

  • Plates move as a result of convectional currents in the mantle.

  • Movement is not smooth due to intense friction; they 'lock up' building tension.

  • When tension exceeds the frictional force, plates slip, leading to an earthquake, accompanied by foreshocks and aftershocks.

• Epicentre: The point on the Earth’s surface directly above the focus of the earthquake.

• Focus: The subsurface point where energy is released, and plates slip past each other, generating seismic waves.

Seismic Waves

• Resultant waves produced from an earthquake are classified into:

  • Body Waves: Passed through the Earth’s structure, these include:

  • Primary Waves (P-waves): Compress rock and create high-density bands that move in the direction of the wave. These waves travel alongside the direction of energy propagation.

  • Secondary Waves (S-waves): Compress rock sideways, causing adjacent layers to move opposite the direction of energy propagation. These travel slower than P-waves and can only pass through solids.

  • Surface Waves: Result from body waves reaching the surface, generating:

  • Raleigh Waves: Exhibit motion similar to water waves, with ground particles rolling as they move.

  • Love Waves: Faster than Raleigh waves, moving sideways and perpendicular to the wave's energy path.

• Surface waves cause most damage during earthquake events, derived from body waves.

Seismic Scales

• (Modified) Mercalli Scale: Measures qualitative damage experienced during an earthquake. Low Richter scale readings can correspond to high Mercalli results in areas with poorly constructed infrastructure.

• Richter Scale: Quantitative measurement of earthquake amplitude, determined with a seismometer.

  • Scale ranges from 0 to 10, measured to one decimal point.

  • Mapped onto a logarithmic scale, where a 1-unit increase reflects a tenfold increase in quake strength and a thirty-twofold increase in energy release.

Frequency of Earthquakes

• Approximately one million earthquakes of Richter scale 2 occur annually globally, yet only three reach Richter scale 8.

• Factors affecting damage include:

  • Strength, depth of focus, and number of shocks.

  • Population density and time of day.

  • Types of buildings, soil, and sediment influence damage severity.

  • Distance from the epicenter and economic development also play roles.

  • Secondary hazards can additionally exacerbate effects.

Human Interference and Earthquake Hazards

• Activities augmenting seismic hazard include:

  • Disposal of liquid waste.

  • Underground nuclear testing.

  • Fracking, mining, explosions, and tunnelling.

  • Increased crustal loading.

Earthquake Hazards

Primary Hazards

• Ground Shaking:

  • Seismic waves cause ground shaking, leading to infrastructure collapse.

• Surface Faulting:

  • Displacement of the ground leading to failures of underground pipes and wires.

Secondary Hazards

• Result from primary hazards, include:

  • Landslides and Avalanches:

  • Entire mass quickly descends a slope while retaining structural integrity.

  • Avalanches specifically refer to snow movement.

  • Triggered by a sudden increase in shear stress from seismic shocks.

  • Requires the presence of a pre-existing line of weakness or slip plane for disruption.

  • Effects of landslides include:

  • Destruction of infrastructure, e.g., sewage and water pipes, electrical cables, isolating populations.

  • Road blockages obstructing emergency access and aid delivery.

  • Flooding if mass detaches into a water body, potentially displacing water or failing dam walls.

• Management of Landslide Hazards:

  • Measures include snow compaction, land use planning, pinning, netting, grading, and afforestation.

• Soil Liquefaction: Occurs when ground shaking causes unconsolidated material to act as a liquid.

  • Most prone when soil is saturated or near a water body.

  • Effects include:

  • Gas and water pipe buckling: Due to instability of soil causing pipes to fail, cutting off services to residents.

  • Ground spreading: Soil behaves like a liquid during shaking, creating surface expansion.

  • Sinking buildings: Structures become unsupported as their foundation compresses.

• Management of Soil Liquefaction Hazards:

  • Improve foundations and drainage; avoid construction on saturated soils; use flexible piping with automatic shut-off valves.

Tsunamis.

• Formation:

  • Series of long waves (up to 200 km wavelength) caused by large oceanic disturbances (not tidal).

  • Result from sudden water displacement due to seismic events or seabed movements.

  • Build-up of pressure along an earthquake boundary sets off a 'stick and slip' mechanism between tectonic plates, eventually leading to a catastrophic slippage.

  • Energy released transfers to water, creating significant waves.

• Effects:

  • Wave shoaling occurs as they approach the shore, compressing energy into a smaller water volume, resulting in height increases and speed decreases (roughly 800 km/h to 50 km/h).

  • Coastal retreat occurs as wave peaks approach.

  • Coastal flooding can result in substantial inland devastation over the course of several kilometers.

  • Management involves establishing coastal abatement and tsunami warning systems.

Volcanic Hazards

Prediction, Preparation, and Monitoring

Earthquakes

• Prediction remains challenging; however, tools such as strain analysis and the seismic gap theory can help.

• Preparedness involves designing resilient buildings and evacuation processes, with public knowledge of safe zones key in reducing casualties.

• Monitoring Techniques: Use of gas emission sensors, ground tilt meters, and strain gauges.

Volcanic Hazards

• Prediction often attainable through observing brewing activities and monitoring gas emissions or seismic activity.

• Preparedness strategies may involve evacuations and construction of lava dams.

Tsunamis

• Requires systems like the International Tsunami Warning System for timely alerts.

• Preparation includes flood walls and coastal evacuations, hinged on effective communication and monitoring systems.

Risk Perceptions of Natural Hazards

• Influenced by individual experience, affluence, and personality. Responses can vary from acceptance of risks to proactive measures such as evacuation or modification of infrastructures to enhance safety.

Conclusion

• Understanding diverse hazards and effective management strategies is critical in minimizing risk and enhancing resilience in hazardous environments. Sustainable approaches must address immediate and long-term community needs, ensuring recovery is comprehensive and empowering.