MEV 012: Unit 14 - Geological Hazards

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 UNIT 14: GEOLOGICAL HAZARDS

14.0 Introduction

Geological hazards are natural threats originating from processes within the Earth's crust and mantle. These hazards have the potential to cause significant destruction, loss of life, and long-term socio-economic disruption. Some of the most devastating natural events in history, such as the 2004 Indian Ocean tsunami or the eruption of Mount Vesuvius, are linked to geological activity. Understanding geological hazards is crucial for effective risk assessment, disaster preparedness, and mitigation strategies.

14.1 Objectives

By the end of this unit, you will be able to:

  • Define geological hazards and distinguish between their types
  • Understand the causes behind major geological hazards
  • Identify regions most prone to geological hazards
  • Evaluate the impact of geological hazards on life and environment
  • Examine real-life case studies of earthquakes, volcanoes, and mass movements
  • Suggest measures for mitigation and disaster preparedness

14.2 Types and Causes of Geological Hazards

Geological hazards arise primarily due to tectonic activity, gravitational forces, and Earth's internal heat. The major types include:

14.2.1 Earthquakes

  • Definition: Sudden shaking of the ground caused by movement along fault lines due to tectonic stress.
  • Causes:
    • Plate tectonics and fault slippage
    • Volcanic activity
    • Human-induced causes (e.g., mining, reservoir-induced seismicity)

14.2.2 Volcanoes

  • Definition: Eruptions that release magma, gases, and ash from the Earth's mantle through crustal weaknesses.
  • Causes:
    • Subduction zones (e.g., Pacific Ring of Fire)
    • Rift zones (e.g., East African Rift)
    • Hotspots (e.g., Hawaiian Islands)

14.2.3 Mass-Movement (Landslides, Rockfalls, Mudflows)

  • Definition: Downward movement of rock, soil, or debris due to gravity.
  • Causes:
    • Weathering and slope instability
    • Earthquakes and heavy rainfall
    • Deforestation and construction activities

14.3 Geographical Distribution

Geological hazards are not randomly distributed but are concentrated along tectonic boundaries:

  • Earthquakes:
    • Circum-Pacific Belt (Japan, Chile, Indonesia)
    • Himalayan Belt (India, Nepal, Pakistan)
    • San Andreas Fault (California)
  • Volcanoes:
    • Ring of Fire (Indonesia, Philippines, Japan, Alaska)
    • Iceland (Mid-Atlantic Ridge)
    • East African Rift Valley
  • Mass-movements:
    • Himalayan and Western Ghats in India
    • Andes in South America
    • Appalachian Mountains (USA)

14.4 Impact on Life, Property and Environment

Geological hazards have wide-ranging impacts that can be catastrophic and long-lasting.

14.4.1 Impacts due to Earthquakes

  • Collapse of buildings and infrastructure
  • Deaths and injuries
  • Fires, tsunamis, and liquefaction
  • Long-term displacement and economic disruption

Example: The 2015 Nepal earthquake killed over 9,000 people and caused severe cultural heritage loss.

14.4.2 Impacts due to Volcanoes

  • Pyroclastic flows and lava destroying towns
  • Ashfall affecting air travel and agriculture
  • Emission of toxic gases (SO₂, CO₂)
  • Climate alteration due to aerosols

Example: The 1991 Mt. Pinatubo eruption cooled global temperatures by 0.5°C for two years.

14.4.3 Impacts due to Mass-Movement

  • Damage to roads, bridges, homes
  • River blockages and formation of landslide dams
  • Soil erosion and sedimentation
  • Loss of life in sudden landslides or rockfalls

Example: The Kedarnath tragedy (2013) in India involved massive debris flows triggered by intense rainfall.

14.5 Case Studies

14.5.1 Case Studies on Earthquakes

Bhuj Earthquake (India, 2001)

  • Magnitude: 7.7
  • Death toll: 20,000+
  • Damaged infrastructure across Gujarat
  • Triggered reforms in building codes and disaster response

Tohoku Earthquake & Tsunami (Japan, 2011)

  • Magnitude: 9.0
  • Caused nuclear meltdown at Fukushima
  • Estimated damage: $360 billion
  • Led to global debates on nuclear safety

14.5.2 Case Studies on Volcanic Activity

Mount Vesuvius (Italy, AD 79)

  • Destroyed Pompeii and Herculaneum
  • Thousands died from pyroclastic flows
  • Preserved Roman cities under ash

Eyjafjallajökull Eruption (Iceland, 2010)

  • Disrupted European airspace for weeks
  • No casualties but huge economic loss in aviation

14.5.3 Case Studies on Mass-Movement

Malpa Landslide (Uttarakhand, 1998)

  • Caused by heavy rains and unstable slopes
  • 221 people died, including pilgrims
  • Highlighted poor disaster preparedness in hilly terrains

Oso Landslide (Washington, USA, 2014)

  • Killed 43 people
  • Caused by prolonged rainfall and unstable glacial sediments

14.6 Let Us Sum Up

Geological hazards such as earthquakes, volcanoes, and mass movements arise due to Earth’s dynamic processes. While these events are natural, human settlement patterns and poor planning often turn them into disasters. Understanding their causes, geographical distribution, and impacts is essential for reducing their consequences. Case studies further help in appreciating the scale of devastation and the importance of preparedness, early warning systems, and resilient infrastructure.

14.7 Keywords

·         Geological Hazard-Natural hazard arising from Earth's internal processes

·         Earthquake-Sudden ground shaking due to tectonic stress release

·         Volcano-Eruption of magma, ash, and gases from Earth’s crust

·         Mass Movement-Downslope movement of rock/soil due to gravity

·         Pyroclastic Flow-Fast-moving current of hot gas and volcanic matter

·         Liquefaction-Saturated soil temporarily loses strength during seismic shaking

·         Hotspot-Volcanic activity occurring away from tectonic boundaries

·         Landslide Dam-River blockage caused by landslide debris

·         Plate Tectonics-Movement of Earth's lithospheric plates causing geological activity

·         Seismic Zone-Region prone to frequent earthquakes due to tectonic activity

 

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