Plate tectonics and three boundary types
Plate tectonics: the rigid lithosphere is broken into slow-moving tectonic plates, driven by mantle convection. Three boundary types. Constructive: plates move apart, magma rises to form new crust. Destructive: plates converge, the denser plate subducts at a trench, causing earthquakes and usually a volcano. Conservative: plates slide past, causing earthquakes by friction but no crust and no volcanoes. Name the boundary and its movement.
Hazards cluster in belts on plate boundaries
Earthquakes and volcanoes are spread unevenly, in narrow belts following plate boundaries. The clearest is the Pacific Ring of Fire, a horseshoe around the Pacific rim, holding most active volcanoes and many large earthquakes. Others follow the mid-ocean ridges and the East African Rift. Volcanoes occur mainly at constructive and destructive boundaries (both make magma); earthquakes at all three. Continental interiors have almost none.
2015 Gorkha earthquake, Nepal (M7.8)
The 2015 Gorkha earthquake, Nepal (magnitude 7.8), is a strong 7-mark case study. It struck the destructive boundary where the Indian Plate pushes beneath the Eurasian Plate; epicentre near Barpak, ~80 km from Kathmandu. People: around 9,000 killed, ~600,000 homes destroyed; Durbar Square and Dharahara Tower fell. Environment: a large Everest avalanche and valley-blocking landslides. Response: aid and NGOs helped rebuilding; Nepal brought in stricter building codes.
Drawn from real examiner reports.
Wrong boundary type / reversed subduction
The key definition trap. Examiners find candidates naming the wrong boundary type -- divergent or conservative -- even when the diagram shows subduction (destructive). A related error reverses the subduction direction: the denser plate (usually oceanic) is always forced beneath the less dense continental. Check the arrows before naming a boundary.
Digest (## 2.1): plate-boundary type errors recur constantly -- divergent/conservative margins described despite clear destructive-margin diagram evidence, or the denser (subducting) plate direction reversed (s23 P11 Q3b(ii); w22 P11 Q4a(ii)).
Focus ≠ epicentre
Focus and epicentre are examined together and mixed up. The focus is the point inside the crust where the energy is released (often deep). The epicentre is the point on the surface directly above it. Examiners flag candidates transposing them, or giving an answer fitting either -- the terms must stay distinct. Check: the E-picentre is on the surfacE.
Digest (## 2.1): focus and epicentre are commonly transposed or answered identically to guarantee at least one mark (s23 P11 Q3b(i); s22 P23 Q4a).
Problems near a volcano ≠ its benefits
Volcanic areas have real benefits, and the topic asks WHY people live in hazardous areas -- but when a question asks only for problems, candidates drift into benefits for no credit. "Problems/hazards" wants dangers (lava flows, pyroclastic flows, ash fall, gases, lahars); "benefits" wants soil, tourism and jobs. Answering the wrong half loses marks.
Digest (## 2.1): "problems" answers sometimes drift into benefits of volcano proximity (fertile soil, tourism) despite the question asking only for problems (s23 P11 Q3c).
Death toll ≠ magnitude alone
Asked why an earthquake killed so many, candidates give unqualified "poor infrastructure" or blame magnitude alone. The toll depends on named factors: building design (earthquake-resistant or not), emergency-service funding, population density, and a country's wealth -- an MEDC usually suffers fewer deaths than an LEDC. Name a factor and link it to the deaths.
Digest (## 2.1): death-toll reasons are often unqualified "infrastructure"/"building quality" (s23 P11 Q3a(iv)).
Conservative boundaries have no volcanoes
A common error is placing a volcano at a conservative boundary. Earthquakes occur at all three types. Volcanoes need magma at the surface, which happens only where plates move apart (constructive) or subducted crust melts (destructive). A conservative boundary just slides plates past -- no magma -- so earthquakes but no volcanoes.
Magma ≠ lava
The two terms are often used interchangeably, but they differ by location. Magma is molten rock while still below the surface -- in the chamber or vent. Lava is the same rock once it has erupted onto the surface. Using "lava" for underground rock, or "magma" for what flows down the sides, loses the precision mark on volcanic structure and eruptions.
Earthquakes cannot be reliably predicted
An examiner-flagged wrong belief: that earthquakes, like volcanoes, can be reliably predicted for full evacuation. Volcanoes are fairly predictable -- seismometers, tiltmeters and gas sensors give warning. Earthquakes cannot: scientists find high-risk zones but not the day, place or size of the next. Protection relies on resistant design, drills and early-warning.
Digest (## 2.1): a specific misconception is that earthquakes (unlike volcanoes) can be reliably predicted, allowing full evacuation (s23 P11 Q3a(iv)).
Level 3 on the 7-mark hazard case study
For the named-event 7-marker: name a real event with date and place (Gorkha, Nepal, 2015) -- "an earthquake in Asia" stays Level 1. Give figures (deaths, homes, a landmark). Cover BOTH people AND environment; omitting either caps the mark. Link cause to effect, don't just list.
Name the specific hazard, not "damage"
Vague terms like "a lot of damage" earn little credit -- name the specific hazard. Earthquakes: ground shaking, building collapse, liquefaction, landslides, tsunamis. Volcanoes: lava flows, pyroclastic flows, ash fall, gases, lahars. Use the exact term, not a general word.
Compare = comparative language, not two lists
Asked to compare (e.g. MEDC vs LEDC impacts), use comparative language (whereas, more/less than) with figures side by side. Two separate descriptions is not a compare answer; write "the MEDC lost fewer lives (20) than the LEDC (2,000)".
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