IB Geography D.3.1 Contrasting Case Studies of Geophysical Hazards Notes

Event Profiles Explain Why Similar Hazards Produce Different Disasters

1. Magnitude measures the physical size or energy released by an event, but it does not by itself predict deaths or damage.
2. Speed of onset affects how much time people have to interpret warnings, evacuate and protect essential services.
3. Duration and frequency shape cumulative disruption because a long eruption, repeated aftershocks or continuing slope movement can exhaust households and institutions.
4. Spatial extent determines whether impacts remain local or spread through transport, trade, tourism and communications networks.
5. Secondary hazards are later processes triggered by the primary event, such as lahars, tsunamis, landslides, fires and dammed rivers.
6. The same event profile can produce different outcomes because exposure, vulnerability and capacity vary between and within communities.

Volcanic Hazards: Eyjafjallajökull Versus Merapi Show How Setting Changes Exposure

Eyjafjallajökull: A Glaciated Rift Volcano Disrupted Distant Networks

1. Geographical context places Eyjafjallajökull on Iceland's south coast beneath an ice cap, with scattered farms and transport routes exposed locally but few large settlements close to the vents.
2. Tectonic setting combines divergence between the North American and Eurasian plates with Iceland's mantle plume, allowing basaltic magma to rise through a spreading plate boundary.
3. The eruption began on 20 March 2010 as a relatively effusive fissure eruption at Fimmvörðuháls, so the first phase produced lava with limited regional disruption.
4. The event changed character on 14 April when activity shifted beneath the ice-covered summit caldera, where magma fragmented as meltwater entered the vent and generated much finer ash.
5. The event profile included an ash plume rising above 8 kilometres, repeated pulses of ash and a summit phase lasting about 39 days.
6. Secondary hazards included jökulhlaups, or sudden glacial outburst floods, which damaged roads, farmland and other infrastructure as meltwater and debris escaped beneath the glacier.
7. Local consequences included the precautionary evacuation of about 700 residents, ash contamination of farmland and short-term disruption to livestock and transport, but no direct mass-casualty disaster.
8. Network consequences were much larger because fine ash entered busy North Atlantic air routes and contributed to about 104,000 cancelled flights across Europe.
9. Preparedness and capacity reduced local loss through seismic and ground-deformation monitoring, flood warnings, road closures and organised evacuation in a sparsely populated, well-connected state.
10. Fine ash from a moderate eruption caused geographically extensive disruption because it entered a highly connected air-transport network.

Merapi: Dome Collapse Exposed Dense Settlements to Pyroclastic Flows

1. Geographical context places Merapi in densely settled Central Java immediately north of Yogyakarta, where fertile volcanic soils support farming and long-established communities occupy valleys radiating from the cone.
2. Tectonic setting is the convergent Sunda margin, where subduction of the Indo-Australian plate generates volatile-rich magma beneath Indonesia.
3. The crisis began on 26 October 2010 after weeks of escalating unrest, and the exclusion zone had to expand as eruptive intensity increased during early November.
4. The primary mechanism was rapid lava-dome growth followed by collapse, which generated pyroclastic density currents made of fast-moving hot gas, ash and rock fragments.
5. The event exceeded recent experience because some flows and surges travelled 15 to 16 kilometres down the Gendol drainage, extending beyond patterns familiar from smaller eruptions.
6. Secondary hazards persisted after the main explosive phase because rainfall remobilised loose volcanic material into lahars that damaged houses, farms and infrastructure.

1. Human consequences included 386 deaths, 131 injuries and the initial evacuation or displacement of more than 300,000 residents.
2. Exposure was high because dense farming settlements and transport routes occupied productive volcanic slopes and the same valleys that channelled pyroclastic flows and lahars.
3. Vulnerability varied within the community because official warnings competed with livelihood needs, attachment to place, previous experience of smaller eruptions and differing trust in scientific and local authorities.
4. Monitoring identified the escalating eruption, but safe outcomes still depended on danger zones expanding quickly enough and residents being able to follow evacuation orders.

Volcanic Hazard Comparison

Earthquake Hazards: Nepal Versus Kaikōura Show Why Similar Magnitudes Cause Different Losses

Gorkha, Nepal: Shallow Thrusting Struck Vulnerable Mountain Settlements

1. Geographical context placed the 25 April 2015 earthquake beneath central Nepal, close to Kathmandu and numerous mountain settlements connected by roads vulnerable to slope failure.
2. Tectonic setting reflects convergence between the Indian and Eurasian plates, which stores strain on the Main Himalayan Thrust as India continues to move beneath Eurasia.
3. The main shock had a moment magnitude of 7.8 and began about 82 kilometres northwest of Kathmandu at shallow depth, so damaging shaking affected a wide populated area.
4. The event sequence continued with thousands of aftershocks, including a magnitude 7.3 event on 12 May that renewed fear, caused further collapse and interrupted recovery.
5. Secondary hazards included tens of thousands of landslides, the destruction of Langtang village, an avalanche at Everest Base Camp and the blockage of roads, valleys and some rivers.
6. Human consequences included about 9,000 deaths, around 23,000 injuries, more than 500,000 destroyed houses and roughly 270,000 additional damaged houses.
7. Building vulnerability was high where unreinforced stone, brick and adobe walls or poorly engineered concrete frames could not resist lateral shaking.
8. Accessibility deepened the disaster because steep terrain, landslides and damaged roads delayed rescue and relief for remote settlements while aftershocks kept slopes unstable.

1. Unequal impacts fell most heavily on households in weak housing, isolated communities and people with limited savings, mobility or access to state assistance.
2. Shallow shaking, vulnerable construction and difficult mountain access converted the Gorkha earthquake into a high-mortality disaster.

Kaikōura, New Zealand: A Complex Rupture Damaged Lifeline Infrastructure

1. Geographical context placed the 14 November 2016 earthquake in a less densely populated part of New Zealand's South Island, where Kaikōura depends heavily on coastal road, rail and tourism links.
2. Tectonic setting lies within the Marlborough fault system near the boundary between the Pacific and Australian plates, where strike-slip and compressional motion interact.
3. The main shock also had a moment magnitude of 7.8, which makes Kaikōura a useful comparison with Nepal because the energy released was similar.
4. The rupture was unusually complex because movement propagated northeast for about 180 kilometres across more than 20 faults and continued for nearly two minutes.
5. Surface deformation reached as much as 12 metres in places, while coastal uplift permanently altered sections of shoreline.
6. Secondary hazards included a local tsunami, more than 10,000 landslides and landslide dams that cut road and rail links and isolated Kaikōura.
7. Human consequences included two deaths, damaged homes and infrastructure, stranded residents and visitors, disrupted tourism and a costly reconstruction of transport corridors.
8. Capacity reduced mortality through stronger building regulation, public hazard education, emergency planning, coordinated communications and rapid national support.
9. Residual vulnerability remained because isolated households, tourists unfamiliar with local hazards and communities dependent on a small number of lifeline routes still faced severe disruption.
10. High capacity shifted much of Kaikōura's loss from building collapse and mortality towards infrastructure isolation, business interruption and reconstruction cost.

Earthquake Hazard Comparison

Mass-Movement Hazards: Vajont Versus Slumgullion Contrast Sudden Catastrophe and Slow Deformation

Vajont: A Rapid Rockslide Generated a Catastrophic Reservoir Wave

1. Geographical context placed the Vajont reservoir in a steep Alpine valley in northeastern Italy, with Longarone and smaller settlements located below the dam.
2. The slope was already known to be unstable because movement and geological concerns had been observed on Monte Toc while the reservoir was being filled and operated.
3. Human modification increased risk because changing reservoir levels altered water pressure within the slope while placing a large volume of water beside the unstable rock mass.
4. The main event occurred on 9 October 1963 when about 270 million cubic metres of rock accelerated into the reservoir at more than 90 kilometres per hour.
5. The decisive secondary hazard was a wave created by the displaced reservoir water, not collapse of the dam itself.
6. The wave overtopped the dam after roughly 50 million cubic metres of water were displaced, sending destructive water and debris into Longarone and nearby settlements.
7. Human consequences included 1,917 deaths and the near-total destruction of communities lying in the wave's path.
8. Governance failure increased vulnerability because warning signs were normalised, uncertainty was not communicated effectively and reservoir operations continued despite evidence of accelerating movement.
9. The reservoir converted a rapid solid rockslide into a larger downstream wave hazard.

Slumgullion: Slow Earthflow Allows Monitoring and Avoidance

1. Geographical context places the Slumgullion Earthflow in the sparsely populated San Juan Mountains of Colorado, where an active flow moves within the deposit of a much older landslide.
2. Physical character differs from Vajont because weathered, relatively loose earth deforms continuously rather than failing as one coherent block.
3. Scale and movement make it a large natural laboratory of about one square kilometre, with much of the active earthflow moving at roughly 10 to 20 millimetres per day.
4. The event profile is slow, persistent and seasonally variable, with faster movement where snowmelt or rainfall increases water pressure and reduces friction within the material.
5. Onset is observable because repeated surveys, GPS and remote sensing can measure displacement before it becomes an immediate threat to people.
6. Human consequences are limited because the active flow crosses a sparsely settled landscape and land use can avoid its most mobile parts.

1. Management focuses on monitoring rather than emergency evacuation, because mapping and movement records can guide land-use and infrastructure decisions.
2. Slow movement still damages land, but it provides time for observation and adaptation that was absent at Vajont.

Mass-Movement Hazard Comparison

Well-Being Impacts Extend Beyond Immediate Deaths and Damage

1. Physical well-being is affected by deaths, injuries, respiratory illness, contaminated water, interrupted medical care and prolonged displacement.
2. Material well-being falls when homes, farmland, livestock, roads, electricity and employment are lost or made inaccessible.
3. Social well-being can decline when evacuation separates households, schools close, community networks weaken and cultural places are damaged.
4. Mental well-being may be affected by bereavement, uncertainty, repeated aftershocks, fear of renewed eruption and the stress of long recovery.
5. Distribution matters because the same event can be a temporary inconvenience for insured households but a permanent livelihood crisis for people without savings or secure land rights.
6. Scale matters because Eyjafjallajökull damaged local farms while disrupting distant passengers and supply chains that were not physically exposed to the eruption.

Vulnerability Varies Within Communities as Well as Between Countries

1. Age and health influence mobility, evacuation speed, respiratory sensitivity and the ability to survive disrupted care.
2. Income and tenure affect building quality, insurance, transport access, savings and whether households can relocate from dangerous land.
3. Livelihood can keep farmers, tourism workers and informal workers close to hazardous slopes, coasts or transport routes even when they understand the risk.
4. Knowledge improves hazard recognition only when warnings are understandable, trusted and connected to realistic actions.
5. Perception is shaped by previous experience, cultural beliefs, warning fatigue and whether past evacuations appeared necessary.
6. Preparedness includes drills, evacuation routes, household supplies, building enforcement, emergency communication and plans for people needing assistance.
7. Governance determines whether monitoring evidence changes land use, whether building rules are enforced and whether authorities communicate uncertainty honestly.
8. Connectivity can provide rescue and supplies, but dependence on one road, bridge, airport or communications network creates critical points of failure.
9. The contrast between Nepal and Kaikōura therefore reflects unequal vulnerability and capacity, not a difference in earthquake magnitude.

Use the Comparisons to Build Causal Explanations

1. Start with the physical contrast by identifying plate setting, magnitude, onset, duration, material, spatial extent and secondary hazards.
2. Then explain exposure by locating people, buildings, livelihoods and infrastructure in relation to the hazardous processes.
3. Next explain vulnerability using specific evidence about construction, inequality, accessibility, perception, knowledge and preparedness.
4. Finish with a judgement about which factor best explains the contrast while recognising that physical and human factors interact.

The Comparison Matrix Separates Hazard from Disaster

1. Eyjafjallajökull versus Merapi demonstrates that plate setting and eruption style matter, but population density, evacuation and network connections control who experiences loss.
2. Nepal versus Kaikōura demonstrates that equal earthquake magnitude can coexist with radically different mortality because vulnerability and capacity differ.
3. Vajont versus Slumgullion demonstrates that speed, material coherence, water interaction and settlement exposure transform mass movement risk.
4. No single indicator such as national income, magnitude or population density is sufficient, so evaluation must trace interacting causes.