GCSE Geography (UK)
UK GCSE Geography (Years 10-11, ages 14-16) aligned with AQA/Edexcel/OCR core content: natural hazards (tectonics, weather, climate change), ecosystems and biomes, UK physical landscapes (coasts, rivers, glaciation), urban issues and challenges, the changing economic world, resource management, and geographical skills.
Ämne: Geografi · Nivå: Högstadium (13–15) · 412 kort
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- The Earth's structure has four layers: the inner core, outer core, mantle and crust. The crust is the thin, rigid outer layer.
- A natural hazard is a natural process or event that has the potential to cause loss of life, injury or property damage — e.g. earthquakes, volcanoes, floods, tropical storms.
- A natural hazard becomes a natural disaster when it actually causes serious loss of life and/or damage to property and infrastructure.
- Factors affecting hazard risk include urbanisation (more people in cities), poverty (forces people into risky areas), farming (fertile floodplains/volcanic soils), and climate change (more extreme weather).
- The lithosphere (crust plus the rigid upper mantle) is broken into tectonic plates that float and move on the semi-molten asthenosphere beneath.
- There are two types of crust: continental crust (thick, less dense, old) and oceanic crust (thinner, denser, younger and can be destroyed).
- Convection currents in the mantle, driven by heat from the core, are a key cause of plate movement, dragging the plates above them.
- Ridge push and slab pull also drive plates: at ridges new crust pushes plates apart, and at subduction zones sinking dense crust pulls the rest of the plate along.
- At a constructive (divergent) plate margin, two plates move apart. Magma rises to fill the gap, forming new crust, gentle volcanoes and minor earthquakes. Example: Mid-Atlantic Ridge.
- At a destructive (convergent) plate margin, oceanic crust is forced (subducted) beneath continental crust. This causes violent earthquakes and explosive volcanoes. Example: Nazca plate under South America (the Andes).
- Where two continental plates collide (a collision margin), neither subducts easily, so crust crumples upward to form fold mountains. Example: the Himalayas (Indian plate meeting Eurasian plate).
- At a conservative (transform) plate margin, two plates slide past each other. No crust is created or destroyed, but friction causes powerful earthquakes. Example: the San Andreas Fault, California.
- Earthquakes happen when stress builds up along a plate margin until rocks suddenly fracture or slip, releasing energy as seismic waves.
- The focus is the point underground where an earthquake starts. The epicentre is the point on the surface directly above the focus, where shaking is usually strongest.
- Earthquake magnitude (energy released) is measured on the Richter scale or moment magnitude scale; it is logarithmic, so each step up represents roughly 30 times more energy.
- The Mercalli scale measures the intensity of an earthquake's effects (observed damage and shaking) on a scale of I to XII, rather than the energy released.
- Primary effects of an earthquake happen immediately as a direct result of the shaking — e.g. buildings collapse, roads crack, people are killed or injured.
- Secondary effects of an earthquake happen later as knock-on consequences — e.g. fires from broken gas pipes, disease from contaminated water, tsunamis, and economic decline.
- Immediate responses to a tectonic disaster happen in the first hours and days — e.g. search and rescue, treating the injured, providing food, water and temporary shelter.
- Long-term responses to a tectonic disaster happen over months and years — e.g. rebuilding homes, repairing infrastructure, improving building codes, and boosting the economy.
- Case study (higher-income): the Chile earthquake of 2010 was magnitude 8.8, on a destructive margin where the Nazca plate subducts beneath the South American plate. Around 500 people died.
- Chile 2010 (HIC) responses: Chile is wealthy, so emergency services responded quickly, temporary repairs to the main highway took only 24 hours, and a strong economy funded rebuilding.
- Case study (lower-income): the Nepal earthquake of 2015 was magnitude 7.8, caused by the Indian plate colliding with the Eurasian plate. Around 9,000 people died and 9 million were affected.
- Nepal 2015 (LIC) effects and responses: poor-quality buildings collapsed, landslides and avalanches blocked remote mountain villages, and Nepal relied heavily on international aid and charities to respond.
- People continue to live in tectonically active areas because of fertile volcanic soil, geothermal energy, mining of minerals, tourism, and simply because it is home and family ties keep them there.
- Monitoring reduces tectonic risk: scientists use seismometers, gas sensors, tiltmeters and satellite (GPS) data to watch volcanoes and faults for warning signs of activity.
- Prediction reduces tectonic risk: volcanic eruptions can often be predicted from monitoring data, but earthquakes still cannot be reliably predicted — only the general at-risk areas are known.
- Protection reduces tectonic risk: earthquake-resistant buildings use deep foundations, cross-bracing, rubber shock absorbers and an automatic shut-off for gas to survive shaking.
- Planning reduces tectonic risk: authorities map high-risk zones to control land use, run earthquake drills, educate the public, and keep emergency supplies and services ready.
- Most volcanoes and earthquakes occur along plate margins, especially around the Pacific Ocean's 'Ring of Fire', a zone of intense tectonic activity.
- A hotspot is a place where a plume of magma rises through the middle of a plate, far from any margin, creating volcanoes — e.g. the Hawaiian Islands.
- Shield volcanoes form at constructive margins and hotspots from runny (low-silica) basaltic lava. They have gentle slopes and erupt frequently but non-violently.
- Composite (strato-) volcanoes form at destructive margins from thick, sticky (high-silica) andesitic lava. They have steep sides and erupt violently with ash and pyroclastic flows.
- Global atmospheric circulation moves heat from the equator towards the poles through a system of cells (Hadley, Ferrel and Polar cells) and creates the world's pressure belts and winds.
- At the equator, intense heating causes air to rise, creating low pressure, clouds and heavy rainfall — this is why tropical rainforests are found there.
- At around 30° north and south, air sinks, creating high pressure, clear skies and dry conditions — this is why most of the world's hot deserts (e.g. the Sahara) are found at these latitudes.
- Tropical storms are called hurricanes in the Atlantic and east Pacific, typhoons in the west Pacific, and cyclones in the Indian Ocean — they are the same kind of storm.
- Tropical storms form over warm tropical oceans (at least 27°C and 50+ m deep), between roughly 5° and 30° latitude where the Coriolis effect can make them spin.
- Tropical storms form when warm moist air rises rapidly, creating intense low pressure. As the air rises it cools, condenses and releases huge amounts of latent heat, which powers the storm.
- The eye of a tropical storm is the calm, clear centre with sinking air, very low pressure and light winds. Around it, the eyewall has the most intense winds and heaviest rain.
- Tropical storm intensity is measured on the Saffir-Simpson scale, from category 1 (weakest) to category 5 (most powerful, winds over 250 km/h).
- A storm surge is a rise in sea level caused by a tropical storm's low pressure and strong winds pushing water onshore. It is often the deadliest effect, causing severe coastal flooding.
- Case study: Typhoon Haiyan struck the Philippines in November 2013. It was a category 5 storm with winds around 275 km/h and a storm surge up to 5 m, killing over 6,000 people.
- Typhoon Haiyan primary effects: around 90% of the city of Tacloban was destroyed, over 6,000 people died (mostly by drowning in the storm surge), and 600,000 people were displaced.
- Typhoon Haiyan secondary effects: flooding triggered landslides and blocked roads, there were outbreaks of disease, shortages of food and clean water, and looting due to a lack of supplies.
- Tropical storms can be managed by monitoring with satellites and aircraft, predicting their path, protecting with sea walls and storm-proof buildings, and planning evacuation routes and shelters.
- Climate change may be making tropical storms more intense and frequent: warmer oceans give storms more energy, and rising sea levels make storm surges more damaging.
- The UK experiences extreme weather including heavy rain and flooding, droughts and heatwaves, strong winds and storms, heavy snow, and occasional thunderstorms with hail.
- Case study: the Somerset Levels floods of winter 2013-14 were caused by prolonged heavy rainfall, high tides and rivers that had not been dredged. Over 600 homes were flooded and farmland was underwater for weeks.
- Somerset Levels management: after the 2013-14 floods, rivers were dredged, road levels were raised, river banks were strengthened, and a long-term flood action plan was introduced.