Natural Hazards and Earth Structure

Natural Hazards

• Natural hazards occur when natural forces (e.g., tectonic activity, weather) cause harm to humans.
• Examples include: tsunamis, droughts, supervolcano eruptions, avalanches, blizzards, forest fires, sinkholes, mudslides, flash floods, tropical storms, volcanoes, and earthquakes.

Factors Affecting Hazard Risk

• Wealth: A country's wealth impacts its ability to prepare for and cope with hazards.
• Population Density: High population density areas are more vulnerable to hazard impacts.

Earth Structure and Plate Tectonics

• Earth's crust is divided into tectonic plates, which are constantly moving.
• Plate boundaries (margins) are locations where earthquakes, volcanoes, mountains, and ocean trenches form.
• About 8 major plates and many smaller ones exist.
• Plate movement is largely driven by convection currents in the Earth's mantle.

Types of Plate Margins

• Destructive Margin: An oceanic plate subducts beneath a continental plate, causing earthquakes, volcanoes, and forming trenches and fold mountains. (e.g., Nazca and South American plates)
• Conservative Margin: Two plates slide past each other, resulting in powerful earthquakes. (e.g., San Andreas Fault)
• Constructive Margin: Two plates move apart, creating a gap filled by magma, leading to volcanic eruptions and gentle earthquakes. (e.g., mid-Atlantic ridge)

Earthquake Locations

• Earthquakes are commonly found in bands aligning with plate margins (e.g., Pacific Ring of Fire, mid-Atlantic).
• Some earthquakes occur away from plate boundaries, potentially due to human activities (e.g., fracking).

Volcano Locations

• Volcanoes are often located along plate margins.
• A significant belt encircles the Pacific Ocean (Pacific Ring of Fire), and another exists along the mid-Atlantic ridge.

Case Study: 2016 New Zealand Earthquake (Kaikoura)

• Magnitude: 7.8
• Primary Effects: 2 fatalities, injuries, damaged/destroyed homes, economic losses, and infrastructure damage.
• Secondary Effects: Landslides, flooding, tsunami.
• Immediate Responses: Tsunami warning, emergency housing, power and water restoration. International aid.
• Long-Term Responses: Funding for reconstruction, road and rail repair, community support initiatives, and earthquake-resistant infrastructure development.

Case Study: 2015 Nepal Earthquake

• Magnitude: 7.8
• Primary Effects: Thousands of deaths and injuries, numerous damaged/destroyed buildings widespread homelessness, significant economic loss, and water/sanitation issues.
• Immediate Responses: International aid, rescue efforts, emergency support by NGOs and aid organisations.
• Long-Term Responses: Relief efforts for recovering from destroyed building, World Bank financed reconstruction projects to build earthquake resistant housing, and improve infrastructure.

Reasons for Living Near Hazards

• Limited alternatives/affordability: Moving away might not be an option
• Familiarity: The people and places are well known.
• Effective monitoring/governance: Risk is minimized through preparedness and responses.
• Economic activity: Opportunities for tourism and agriculture.
• Fertile soil: Volcanic activity results in high-quality soil for crops.