Causal chain begins with a physical process, passes through an exposed place and produces loss according to vulnerability and available capacity.
Spatial coincidence is essential because high hazard without exposed people creates little disaster risk, while high vulnerability outside the footprint is not activated by that event.
Temporal change alters the relationship as settlement expands, infrastructure ages, slopes are modified and preparedness improves or declines.
Hazard processes create a potential threat; ground shaking, eruption products or slope failure become dangerous where they meet people, buildings and infrastructure.
Exposure places people and assets in the affected area; settlement growth on unstable slopes or near active faults increases what can be harmed.
Vulnerability determines susceptibility to loss; weak construction, poverty, age, disability and insecure access to services can turn the same event into a more severe disaster.
Capacity limits losses; trusted warnings, enforced building standards, accessible evacuation and effective emergency services help people withstand and recover from disruption.
Risk is therefore relational; a powerful event in a sparsely occupied area may cause fewer losses than a smaller event affecting a dense and vulnerable settlement.
Cascading Hazards Extend the Initial Footprint
Trigger sequence should name the mechanism at each link, such as shaking destabilising a slope and the resulting debris blocking a river.
Pathway shift occurs when the secondary hazard follows valleys, coasts or networks beyond the zone of strongest initial impact.
Compounding demand increases when responders must manage aftershocks, landslides, fire and infrastructure failure at the same time.
Primary processes can trigger secondary hazards; earthquakes may cause landslides and dam rivers, while eruptions can generate ashfall, pyroclastic flows and later lahars.
The 2015 Gorkha earthquake illustrates a cascade; shaking destabilised steep slopes, landslides blocked access and damaged roads then delayed rescue and relief.
The 1963 Vajont disaster shows human and physical coupling; reservoir loading, geological weakness and slope instability combined before a landslide displaced water over the dam.
Merapi demonstrates delayed interaction; ash and loose volcanic debris remained on slopes after the 2010 eruption and could be remobilised by rainfall as lahars.
A cascade changes the geography of risk; impacts may move downslope, downstream or along transport and service networks beyond the original hazard zone.
Key Idea
Follow the Causal Chain: Identify the initiating physical process before tracing each secondary hazard.
Explain how exposure, vulnerability or capacity changes at every link.
Finish with the impact on a named group or place rather than stopping at the physical process.
Networks Transfer Disruption Across Space
Node importance means failure at a bridge, port, airport or substation can cause losses far beyond its small physical footprint.
Network redundancy reduces disruption when alternative routes, suppliers or communication systems can take over after one link fails.
Unequal connectivity creates contrasting outcomes because well-connected places may receive aid quickly while isolated communities wait longer.
Transport networks transmit impacts; the 2016 Kaikōura earthquake severed road and rail links, isolating communities beyond the most intensely shaken locations.
Air travel transmitted volcanic disruption; the 2010 Eyjafjallajökull ash cloud caused widespread flight cancellations even though severe physical damage remained concentrated in Iceland.
Infrastructure networks are interdependent; damage to electricity can interrupt water treatment, communications, health care and business activity.
Supply chains create distant exposure; a closed port, airport or road corridor can delay goods and income in places that did not experience the hazard directly.
Connectivity can also increase capacity; the same networks can carry warnings, rescue teams, finance and supplies into affected areas.
Human Decisions Redistribute Risk
Risk transfer occurs when a wall, diversion, exclusion zone or relocation protects one place but shifts water, debris, cost or exposure elsewhere.
Path dependence keeps earlier planning decisions influential because roads and settlements attract further development even after risk becomes known.
Power shapes whose property is protected, whose movement is restricted and whose knowledge is accepted in risk decisions.
Land-use planning alters exposure; excluding development from mapped fault, tsunami, lava or landslide zones reduces the number of people in the path of a future event.
Engineering changes vulnerability; earthquake-resistant buildings reduce collapse risk, although benefits depend on design quality, enforcement and maintenance.
Reservoirs and excavations can modify physical conditions; changes to slope loading, drainage or support may increase instability when geological limits are ignored.
Warnings depend on trust and access; accurate monitoring cannot reduce loss if messages arrive late, use inaccessible formats or provide no realistic action.
Recovery decisions shape future risk; rebuilding in the same unsafe location restores exposure, whereas relocation or stronger construction may lower it.
Synthesis Connects Process, Place and Power
Process evidence explains what moves, at what speed and along which pathway before social impacts are discussed.
Place evidence identifies the exposed population, built environment and networks that convert the process into a particular pattern of loss.
Power evidence evaluates who can enforce protection, access information and recover, allowing a judgement about why risk remains uneven.
Begin with the process; state how the geophysical event develops and where its direct effects are strongest.
Add the spatial interaction; trace how people, land use, networks and institutions amplify or reduce the physical threat.
Name the distributional outcome; identify who gains protection, who remains exposed and where costs are transferred.
Use comparison to test the explanation; contrasting events show whether hazard magnitude or social conditions better explain the observed losses.
Reach a conditional judgement; the dominant control changes with event profile, settlement pattern, governance and the time available to act.
Construct a causal chain from the Gorkha earthquake to delayed relief.
Compare how transport networks increased disruption and capacity after a geophysical event.
Judge which human decision most strongly changes long-term hazard risk.
Definition
Spatial interaction
Spatial interaction is the way processes, people, places and networks affect one another across space, so an impact in one location can alter risk in another.
