The volcanic island of Ranua lies in the western Pacific Ocean, approximately 600 km from the nearest mainland. The island covers an area of 120 km2 and has...

(a)(i) Using Fig. 1, the type of plate boundary shown is a destructive plate boundary (also called a convergent plate boundary) [1]. At this boundary, two tectonic plates are moving towards each other, as shown by the opposing arrows in the diagram.

(a)(ii) At this destructive plate boundary, the denser oceanic plate is forced beneath the less dense continental plate in a process called subduction [1]. As the oceanic plate descends into the mantle at a steep angle, friction between the two plates causes earthquakes along the subduction zone. These earthquake foci are marked with 'x' symbols in Fig. 1 [1].

(b) Magma is produced at a destructive plate boundary through three stages:

1. As the oceanic plate subducts into the mantle, it is subjected to extremely high temperatures and friction, which cause the rock to melt [1].
2. This melting produces magma, which is less dense than the surrounding solid mantle rock [1].
3. Because it is less dense, the magma rises through cracks and weaknesses in the overlying continental plate. Eventually it reaches the surface, erupting to form a volcano. Fig. 1 shows this process with the dashed 'Magma rising' line [1].

(c) One volcanic hazard other than lava flow [1]:

• Pyroclastic flows - fast-moving currents of hot gas, ash and rock fragments that travel down the volcano's slopes at high speed.

Other valid answers include: volcanic ash fall, lahars (volcanic mudflows), or toxic gas emissions (such as sulphur dioxide).

(d) Comparing the effects of the two earthquakes using Table 1:

1. The earthquake in Ranua caused far more deaths (1,850) compared to Country J (4), despite Ranua having a smaller population [1].
2. Similarly, far more buildings collapsed in Ranua (6,400) than in Country J (28), even though both earthquakes were of similar magnitude (7.2 vs 7.0) [1].

(e) The earthquake caused far more deaths and damage in Ranua despite similar magnitudes because of four key differences:

1. Building construction: Ranua is a low-income island where buildings were not designed to withstand earthquakes. They lacked reinforced steel frames and flexible foundations, so they collapsed easily under seismic shaking [1].
2. Building codes: Country J has strict building codes requiring earthquake-resistant construction. Buildings are designed to flex rather than break during shaking [1].
3. Emergency response: Country J has well-equipped emergency services with trained search-and-rescue teams that respond rapidly. Ranua had limited rescue capacity, meaning trapped victims waited longer for help [1].
4. Earthquake depth: The earthquake beneath Ranua was shallower (15 km) compared to Country J (22 km). Shallower earthquakes release energy closer to the surface, causing more intense ground shaking [1].

(f) The economic cost was higher in Country J despite less severe physical damage because:

1. Higher asset values: Property, infrastructure and businesses in Country J have a much higher monetary value. A single damaged office building in a wealthy country may be worth more than entire neighbourhoods in a developing nation [1].
2. Economic disruption: Disruption to industry, commerce and financial services in a wealthy, integrated economy generates a much larger financial loss than equivalent disruption in a less developed economy [1].

(g) One long-term effect of the earthquake on Ranua's population [1]:

• Long-term displacement: Large numbers of people living in temporary shelters for months or years while reconstruction proceeds slowly due to limited resources.

Other valid answers include: disruption to the economy and increased national debt, loss of essential infrastructure (schools, hospitals), or increased poverty and food insecurity.

(h) An exclusion zone was established around the crater because:

1. The zone prevents people from entering the area closest to the crater where the most dangerous volcanic hazards (lava flows, pyroclastic flows, toxic gases) occur [1].
2. Within this zone, these hazards pose an immediate threat to life. Keeping people at a safe distance is the most effective way to reduce deaths and serious injuries during and after the eruption [1].

(i) The volcanic hazards affecting the three settlements vary with distance from the crater:

1. Vuna (8 km from crater) experienced the most severe effects: 12 cm of ash fall, high risk of both lava flows and pyroclastic flows. All 12,000 residents were evacuated [1].
2. Port Daru (18 km) experienced lighter effects: 3 cm of ash fall and low risk from lava and pyroclastic flows. 5,200 people were evacuated as a precaution [1].
3. Kalo (22 km) was least affected: only 1 cm of ash and no risk from lava or pyroclastic flows, so no evacuation was needed [1].

The data shows that volcanic hazards decrease with distance from the crater.

(j) Two effects of volcanic ash fall on people and agriculture [2 marks each]:

1. Crop destruction: Volcanic ash covering farmland smothers crops and damages plant leaves, reducing or completely destroying harvests. This threatens the food supply for the 8,000 farming families around Mount Tilara [1+1].
2. Water contamination: Ash contaminates freshwater sources and water storage tanks, making drinking water unsafe and requiring expensive treatment or alternative sources [1+1].

Other valid effects include: respiratory problems from inhaling fine ash particles, or roof collapse from the weight of accumulated ash (especially when wet).

(k) Three reasons why people continue to live near Mount Tilara despite the hazards:

1. Fertile volcanic soils: The volcanic soils around Mount Tilara are extremely fertile, providing excellent conditions for growing crops. Over 8,000 families depend on farming these soils [1].
2. Established community ties: People have lived on the island for many generations and have strong family, cultural and social connections to the area [1].
3. Tourism income: Geothermal hot springs near the volcano attract approximately 15,000 tourists per year, providing revenue for local businesses [1].

Other valid reasons include: lack of financial resources to relocate, or the perceived low frequency of eruptions making the risk seem acceptable.

(l) Two benefits of volcanic activity for local people [1 each]:

1. Fertile soils: Volcanic soils are very fertile and support productive farming.
2. Geothermal energy potential: Volcanic heat can be used to generate electricity or for direct heating.

Other valid answers include: volcanic rock quarried for building materials, or volcanic landscapes attracting tourists and creating jobs.

(m) Two methods of monitoring volcanic activity [2 marks each: 1 for naming, 1 for describing]:

1. Seismographs: Instruments placed around the volcano detect and record small earthquakes that often increase in frequency before an eruption. An increase in seismic activity gives scientists days or weeks of advance warning [1+1].
2. Gas monitoring: Equipment measures changes in the amount and composition of gases released from the volcano (especially sulphur dioxide). Rising gas emissions often indicate that magma is moving upward beneath the surface [1+1].

Other valid methods include: tiltmeters and GPS instruments detecting changes in the volcano's shape, or satellite thermal imaging detecting temperature changes.

(n) Three ways the government of Ranua could improve earthquake preparedness:

1. Building codes: Enforce codes requiring new structures to use reinforced materials and seismic-resistant designs, reducing building collapse in future earthquakes [1].
2. Early warning systems: Establish earthquake detection systems that give residents seconds to minutes of warning to take protective action before strong shaking arrives [1].
3. Public education: Educate the public about earthquake safety procedures such as taking cover under sturdy furniture and moving away from unstable buildings [1].

(o) Earthquakes cannot be prevented because:

1. They are caused by the movement of tectonic plates, which is driven by convection currents in the Earth's mantle operating over thousands of kilometres [1].
2. Humans cannot control or stop these powerful geological forces that operate deep beneath the surface (tens to hundreds of kilometres down) [1].
3. The energy that builds up along plate boundaries and fault lines is released suddenly and unpredictably. No technology exists that can prevent this energy release or redirect it [1].