Earthquakes
Earthquakes are sudden, rapid shaking of the ground caused by movement along faults (fractures in rock) or at plate boundaries. They release enormous amounts of energy.
- Tectonic earthquakes: Most common, caused by movement at plate boundaries (convergent, divergent, or transform).
- Magnitude: Measured on the Richter scale, it quantifies earthquake energy (typically range 0-9).
- Intensity: Measures earthquake effects and damage at specific locations (Modified Mercalli scale, I-XII).
- Aftershocks: Smaller earthquakes that follow the main shock as the fault adjusts.
Most earthquakes occur at plate boundaries, particularly in the Pacific Ring of Fire, which encircles the Pacific Ocean.
Volcanoes
Volcanoes are openings in Earth's crust where molten rock (magma/lava), gases, and solid material erupt. They occur primarily at plate boundaries.
- Hazards: Lava flows, pyroclastic flows, lahars (volcanic mudflows), ash fall, toxic gases.
- Eruption types: Shield volcanoes (gentle), composite volcanoes (explosive), cinder cones (small, violent).
- Volcanic explosivity index (VEI): Measures eruption size and explosiveness (0-8 scale).
- Benefits: Volcanic soils are very fertile. Geothermal energy can be harvested.
The Ring of Fire hosts about 75% of the world's active volcanoes, coinciding with earthquake zones at subduction zones.
Tsunamis
Tsunamis are ocean waves caused by sudden disturbances of large water masses, usually triggered by undersea earthquakes, volcanic eruptions, or underwater landslides.
- Generation: Vertical earthquake displacement can displace large water masses, creating tsunami waves.
- Characteristics: Long wavelength, small amplitude at sea, but massive run-up near shore.
- Impacts: Can travel across ocean basins at speeds of 500+ km/h, causing devastating damage to coastal communities.
- Detection: Seismic networks and ocean buoys help detect tsunamis and issue warnings.
The 2004 Indian Ocean tsunami killed over 230,000 people, highlighting the need for early warning systems.
Landslides
Landslides are rapid downslope movements of rock, soil, and debris triggered by steep terrain, weathering, water saturation, or earthquakes.
- Types: Rockfalls, rockslides, mudslides, debris flows, slumps, lateral spreads.
- Triggers: Heavy rainfall, earthquakes, undercutting by erosion, vegetation removal.
- Impacts: Property damage, loss of life, blocking of roads and waterways.
- Mitigation: Slope stabilization, drainage control, vegetation management, zoning restrictions.
Landslides are among the most common natural hazards, occurring worldwide in mountainous and hilly terrain.
Flooding
Flooding occurs when water overflows from rivers, lakes, or oceans onto land, caused by heavy rainfall, snowmelt, storm surge, or dam failure.
- Flash floods: Rapid onset, often in narrow valleys and narrow canyons, with little warning.
- River floods: Develop over days to weeks in major river systems during high water conditions.
- Coastal floods: Storm surge and high tides can cause inundation of coastal areas.
- Mitigation: Dams, levees, flood plains designation, early warning systems.
Flooding is the most costly natural disaster globally, affecting millions of people annually.
Other Natural Hazards
- Droughts: Extended periods of low rainfall causing water shortages and crop failure.
- Coastal erosion: Loss of coastal land due to waves, currents, and rising sea levels.
- Subsidence: Sinking of land caused by groundwater extraction, mining, or compaction.
- Avalanches: Rapid downslope movement of snow and ice in mountainous regions.
- Sinkholes: Sudden collapse of ground due to subsurface erosion or dissolution of soluble rock.