Management of earthquake and volcanic hazards

Management of Earthquake and Volcanic Hazards

1. Introduction

Earthquakes and volcanoes are the most destructive natural hazards covered in Topic 9 – Hazardous Environments of the Cambridge International AS & A Level Geography (9696) syllabus. Effective management follows the four‑stage cycle:

• Mitigation – reduce the likelihood or severity of impacts
• Preparedness – plan and train for possible events
• Response – immediate actions after an event
• Recovery – long‑term rebuilding and learning

Key syllabus terminology (risk mapping, hard/soft engineering, prediction, etc.) is highlighted throughout.

2. Global Distribution and Tectonic Setting (9.1.1)

2.1 Earthquakes

• Concentrated along convergent (subduction) and transform plate boundaries. The Pacific “Ring of Fire”, the Alpine‑Himalayan belt and the East African Rift are the principal zones.
• Intraplate earthquakes also occur within plates (e.g., New Madrid, USA; 2020 Zagreb, Croatia).
• Distribution is shown on the standard “World seismicity map” used in the syllabus.

2.2 Volcanoes

• Cluster at three tectonic settings:
  • Subduction zones – explosive stratovolcanoes (e.g., Mount Pinatubo)
  • Divergent ridges – fissure eruptions, basaltic shield volcanoes (e.g., Iceland)
  • Intra‑plate hotspots – isolated islands (e.g., Hawaiian Islands)
• More than 75 % of world volcanoes lie in these settings, illustrated on the “Global volcano map”.

3. Earthquake Hazards, Impacts and Quantitative Context (9.1.2‑9.1.3)

3.1 Primary Hazards

• Ground shaking – measured by the Modified Mercalli Intensity (MMI) scale (I–XII).
• Surface rupture – displacement along the fault trace.
• Secondary effects:
  • Liquefaction of saturated soils
  • Landslides on steep slopes
  • Tsunamis generated by offshore thrust events
  • Aftershocks – smaller magnitude events that can continue for weeks or months.

3.2 Factors Controlling Earthquake Severity

• Focus (hypocentre) – depth of the rupture; shallow focus (< 70 km) produces stronger surface shaking.
• Epicentre – point on the surface directly above the focus; proximity to populated areas increases damage.
• Wave types:
  • P‑waves – primary, compressional, travel fastest, cause little damage.
  • S‑waves – secondary, shear, cause most of the shaking.
  • Surface waves (Rayleigh & Love) – travel along the ground, produce the greatest damage.
• Magnitude scales:
  • Richter (M_L) – useful for moderate, local quakes.
  • Moment magnitude (M_w) – preferred for large events; relates to energy released.

3.3 Physical and Human Factors of Vulnerability

• Physical factors – building materials, construction quality, soil type (e.g., susceptibility to liquefaction), topography.
• Human factors – population density, poverty levels, level of preparedness, effectiveness of building codes, land‑use planning.
• Vulnerability is highest where non‑seismic structures are built on soft, water‑logged soils near fault lines.

3.4 Impacts

1. Loss of life and injuries – greatest where structures are weak.
2. Destruction of housing, schools, hospitals and critical infrastructure.
3. Economic loss – often expressed as a percentage of national GDP (e.g., 2010 Haiti earthquake ≈ 120 % of GDP).
4. Social disruption – displacement, loss of livelihoods, long‑term poverty.
5. Environmental damage – soil erosion, water contamination, altered river courses.

3.5 Quantitative Detail (AO2)

• Recurrence interval – average time between earthquakes of a given magnitude on a fault (e.g., ~ 150 yr for M ≥ 7.0 on the San Andreas).
• Seismic hazard maps – display Peak Ground Acceleration (PGA) values; form the basis for risk mapping.

4. Management of Earthquake Hazards (9.2.1‑9.2.4)

4.1 Mitigation (Hard & Soft Engineering)

• Hard engineering:
  • Seismic‑resistant design – ductile steel frames, reinforced concrete, base isolation, energy‑dissipating devices.
  • Retrofitting – strengthening existing schools, hospitals and historic buildings.
• Soft engineering:
  • Land‑use planning – avoid construction on active faults, liquefaction‑prone soils, steep slopes.
  • Risk mapping – combine seismic hazard maps with population and building‑type data to produce earthquake risk maps (example shown in Figure 1).
  • Public education – “Drop, Cover, Hold” drills, school programmes, community awareness campaigns.

4.2 Preparedness & Prediction

• Early‑warning systems – detect P‑waves and issue alerts seconds to minutes before damaging S‑waves arrive (e.g., Japan’s J‑Alert).
• Probabilistic Seismic Hazard Analysis (PSHA) – provides probability of exceeding a given magnitude at a location; underpins national building codes.
• Emergency response plans – clearly defined roles for police, fire, medical services and civil defence.
• Stockpiling – food, water, medical kits, temporary shelters.
• Community training – regular drills, distribution of “earthquake kits”.

4.3 Response

• Rapid damage assessment using satellite imagery, UAVs and field surveys.
• Search & rescue – specialist teams, canine units, heavy‑equipment extraction.
• Provision of emergency shelter, clean water, sanitation and medical care.
• Restoration of critical utilities (electricity, water, telecommunications).

4.4 Recovery

• Build back better – reconstruction to higher seismic standards.
• Financial support – insurance payouts, government grants, international aid.
• Psychosocial services for trauma‑affected populations.
• Long‑term monitoring of aftershocks and periodic updating of hazard and risk maps.

4.5 Case Study – 2023 Turkey‑Syria Earthquake

A Mw 7.8 thrust earthquake on the East Anatolian Fault caused > 50 000 deaths and massive displacement. Key lessons:

• Enforcement of modern seismic building codes is vital; many collapsed buildings pre‑dated the 1999 code.
• International search‑and‑rescue coordination saved lives.
• Reconstruction programmes now incorporate “building back better” principles, including retrofitting of existing structures.

5. Volcanic Hazards, Impacts and Quantitative Context (9.1.2‑9.1.3)

5.1 Primary Hazards

• Lava flows – usually low‑temperature but can destroy infrastructure.
• Pyroclastic density currents (PDCs) – fast, hot mixtures of gas and rock fragments.
• Ash fall – can affect areas hundreds of kilometres down‑wind.
• Volcanic gases – SO₂, CO₂, H₂S; cause acid rain, asphyxiation and climate effects.
• Lahars – volcanic mudflows triggered by rain mixing with loose tephra.
• Secondary effects – tsunamis (e.g., 1883 Krakatoa) and short‑term climate cooling from sulphate aerosols.

5.2 Factors Controlling Volcanic Hazard Severity

• Volcano type (stratovolcano vs. shield) and magma composition (silica‑rich = more explosive).
• Eruption style (explosive vs. effusive) influences the proportion of PDCs, ash, and lava.
• Topography – channels PDCs and lahars; steep slopes accelerate flows.
• Population density and land‑use in hazard zones.

5.3 Physical and Human Vulnerability

• Physical – building roof strength (ash load), drainage capacity (lahar risk), distance from vents.
• Human – awareness of warning signs, evacuation plans, availability of respiratory protection, socioeconomic status.

5.4 Impacts

1. Loss of life – especially from PDCs and lahars.
2. Destruction of housing, infrastructure and agricultural land.
3. Air‑quality problems – respiratory illness from ash inhalation.
4. Disruption to transport and aviation (ash clouds can ground flights).
5. Long‑term economic loss – decline in tourism, loss of fertile soils.
6. Global climate impacts – temporary cooling (e.g., Pinatubo 1991 lowered global temperatures by ~0.5 °C).

5.5 Quantitative Detail (AO2)

• Volcanic Explosivity Index (VEI) – 0 (non‑explosive) to 8 (mega‑eruption). Pinatubo 1991 = VEI 5; Tambora 1815 = VEI 7.
• Recurrence intervals – roughly 500 yr for VEI ≥ 5 eruptions at many subduction‑zone volcanoes.
• Gas emission rates – SO₂ flux measured in tonnes per day; rapid increases often precede eruptions.

6. Management of Volcanic Hazards (9.2.1‑9.2.4)

6.1 Monitoring and Early Warning (Prediction)

• Seismic monitoring – increase in volcano‑tectonic earthquakes indicates magma movement.
• Ground deformation – GPS and InSAR detect uplift/subsidence of the edifice.
• Gas emissions – SO₂ and CO₂ measured by spectrometers; spikes can signal imminent eruption.
• Thermal imaging – satellite or drone infrared detects heating of vents or lava flows.
• Data are integrated into a colour‑coded alert system (Green → Yellow → Orange → Red) used for evacuation decisions.

6.2 Hazard Mapping

Separate maps are produced for each major hazard, allowing risk‑based land‑use planning:

• Lava‑flow zones – based on slope, magma viscosity and historic flow paths.
• PDC corridors – modelled using topography and eruption column height.
• Ash‑fall distribution – calculated from prevailing wind data and plume height.
• Lahar susceptibility – combines drainage basin analysis with tephra thickness maps.

6.3 Land‑Use Planning and Zoning

• Prohibit permanent settlement in high‑risk zones identified on hazard maps.
• Designate evacuation routes, safe zones and temporary shelters outside PDC and lahar corridors.
• Implement building codes that require roofs to withstand ash loads (e.g., 100 kg m⁻²).
• Construct diversion channels or check‑dams to redirect lahars away from communities.

6.4 Community Preparedness

• Public education on eruption precursors, evacuation procedures and health risks of ash.
• Regular “volcano evacuation day” drills and distribution of respiratory protection kits (masks, goggles).
• Local emergency committees that coordinate with national volcano observatories.

6.5 Emergency Response

• Evacuation of at‑risk populations according to alert level.
• Provision of clean water, food and medical care (especially for respiratory problems).
• Rapid removal of ash from roads, roofs and drainage systems to prevent collapse and flooding.
• Damage assessment using satellite imagery, UAV surveys and ground teams.

6.6 Recovery

• Re‑construction of housing using ash‑resistant designs (steep roofs, reinforced frames).
• Soil rehabilitation – add organic matter, lime and phosphorus to restore fertility after ash burial.
• Tourism revitalisation – develop “volcano tourism” with safety infrastructure and interpretive centres.
• Long‑term monitoring of volcanic activity and periodic updating of hazard maps.

6.7 Case Study – 2022 Hunga Tonga‑Hunga Ha’apai Eruption

The submarine eruption produced a VEI 6 plume, a trans‑Pacific tsunami and widespread ash fall. Management actions included:

• Real‑time seismic and hydroacoustic monitoring that triggered a Level 4 (major) alert.
• Evacuation of coastal villages and distribution of clean‑water supplies.
• International aid for ash‑clearance, roof reinforcement and rebuilding of damaged homes.
• Long‑term sea‑level monitoring and reassessment of tsunami risk for the Pacific region.

7. Comparative Table of Management Strategies

Aspect	Earthquake Management	Volcanic Management
Primary Monitoring	Seismic networks (P‑ and S‑waves), strong‑motion accelerometers	Seismicity, ground deformation (GPS/InSAR), gas emissions, thermal imaging
Prediction / Early Warning	Seconds‑to‑minutes alerts (P‑wave detection); Probabilistic Seismic Hazard Analysis	Hours‑to‑days alerts based on eruption precursors; colour‑coded alert levels
Risk / Hazard Mapping	Seismic hazard maps (PGA) + risk maps (population, building type)	Lava‑flow, PDC, ash‑fall and lahar hazard maps linked to topography and wind data
Mitigation (Hard/Soft Engineering)	Seismic‑resistant construction, base isolation, retrofitting, land‑use zoning	Land‑use zoning, ash‑load building codes, lahar diversion channels, evacuation routes
Community Preparedness	“Drop, Cover, Hold” drills, emergency kits, public education campaigns	Evacuation drills, respiratory‑protection kits, education on eruption signs
Response Priorities	Search & rescue, restore water/electricity/communications	Evacuation, ash removal, medical care for inhalation injuries
Recovery Focus	Re‑building to higher seismic standards (“build back better”)	Soil rehabilitation, ash‑resistant housing, tourism redevelopment

8. Suggested Diagrams

9. Summary

Effective management of earthquake and volcanic hazards requires an integrated approach that combines:

• Scientific monitoring and prediction (seismic, deformation, gas, thermal data).
• Comprehensive risk and hazard mapping to guide land‑use planning and building regulations.
• Hard engineering (seismic‑resistant structures, diversion channels) and soft engineering (retrofitting, public education).
• Preparedness actions – early‑warning systems, community drills, stockpiling of supplies.
• Coordinated response – rapid search & rescue, evacuation, provision of essential services.
• Long‑term recovery – “build back better”, environmental rehabilitation, and continual review of hazard information.