Secondary 4 Geography

The theory that the lithosphere is broken into plates which, driven by mantle convection, shape landforms and cause tectonic hazards.

Where two plates meet; crustal activity is most intense, so earthquakes, volcanoes and tectonic landforms concentrate here.

A boundary where plates move apart; rising magma creates new crust, forming mid-ocean ridges and rift valleys.

A boundary where plates collide; oceanic crust subducts, forming trenches, island arcs, fold mountains and volcanoes.

A boundary where plates slide past one another without crust being made or destroyed; friction stores energy released as earthquakes.

A long, deep zone where oceanic crust subducts beneath another plate; the deepest places on Earth.

Mountains formed when rock layers are squeezed and buckled upwards, such as the Himalayas.

A fixed, unusually hot zone in the mantle where magma keeps rising; plates moving over it form volcanic chains such as Hawaii.

The earthquake and volcanic belt around the Pacific rim, holding about 80 per cent of large earthquakes and three quarters of active volcanoes.

The point on the surface directly above the focus; shaking and damage are usually strongest nearest to it.

A series of giant waves caused when submarine earthquakes, eruptions or landslides suddenly displace a large body of water.

An earthquake whose epicentre lies on the seabed; displacement of the seabed shifts the water above — the commonest cause of tsunamis.

The distance between two successive crests; in the deep ocean a tsunami's wavelength can exceed 100 km.

The highest elevation a tsunami reaches as it floods inland — a key measure of tsunami size.

The international centre set up in 1949 to watch the Pacific and issue tsunami warnings to member states.

An instrument recording ground shaking; within minutes of a quake it can locate the epicentre and estimate magnitude.

Moving coastal residents to high ground or inland before the waves arrive — the last line of defence for saving lives.

Disasters triggered by the main event, such as fires, nuclear accidents and epidemics, which prolong its effects.

The degree to which an area suffers from a hazard, given its population, buildings, awareness and capacity to respond.

The degree to which an area suffers badly from hazards because of poverty, building quality, awareness and response capacity.

Residents' knowledge of hazard risks and readiness to respond; low literacy can leave warnings unread.

Long-term action before disasters strike to lessen their impacts, such as earthquake-resistant buildings, planting and protective works.

Immediate action during and after a disaster, such as evacuation, search and rescue, temporary shelter and relief supplies.

A planning tool that restricts or bans building in hazardous zones, reducing exposure of lives and property at source.

Buildings designed with flexible frames and reinforced foundations to absorb shaking, greatly reducing collapse risk.

Energy from underground heat in volcanic areas, used for power or heating; most of Iceland's energy is geothermal.

A decision made by weighing benefits and costs within one's own circumstances and information, which outsiders may not share.

Advance preparation such as drills, stockpiles and education so that people respond correctly when disaster strikes.

The drainage area enclosed by watersheds that gathers water into one river, including source, mainstream, tributaries and mouth.

The wearing away and removal of bed and bank material by hydraulic action, abrasion and solution.

The ways a river carries its load downstream: traction, saltation, suspension and solution.

The dropping of a river's load when the current slows and energy is insufficient.

Erosion as water forces into cracks and compresses air, loosening rock fragments to be carried away.

A deep, narrow valley with a V-shaped cross-section, cut by vertical erosion in the upper course.

A winding channel formed by lateral erosion and deposition downstream; the concave bank erodes while the convex bank deposits.

A broad, flat lowland built of silt laid down by repeated floods, with natural levees along the banks.

A low-lying depositional landform built where a river meets the sea or a lake and its load settles, such as the Yangtze delta.

A wave whose swash is stronger than its backwash, carrying sediment ashore and building the beach.

A steep, frequent wave whose backwash drags sediment seaward, eroding the beach.

Erosion as waves force water and compressed air into cracks, blasting rock apart.

Erosion as hurled sand and stones grind the cliff and platform like sandpaper.

A hollow cut by concentrated attack at a weak line at the cliff foot; as it deepens the rock above is left overhanging.

An arch-shaped opening cut through a headland; when its roof collapses a sea stack remains.

An isolated rock column left in the sea after an arch collapses, later worn away.

A near-level, gently sloping rock surface left at the cliff foot as the cliff retreats, covered at high tide and exposed at low tide.

The zigzag movement of sediment along the shore as waves swash obliquely and backwash straight back.

A sand ridge tying an island to the mainland, such as the tombolo at Kiu Tsui Chau, Sai Kung.

Management that reshapes nature by engineering, such as dams, channelisation, sea walls, groynes and breakwaters.

Management that works with natural processes, such as beach nourishment, afforestation, zoning, warnings and drills.

Straightening, deepening and widening a channel to speed drainage — which can raise flood peaks downstream.

A structure across a river that stores floodwater and can generate power, supply water and aid navigation — at the cost of resettlement and lost land.

A wall built along the shore that reflects and absorbs wave energy to protect the land, though scour can undermine the beach in front.

A low wall built out at right angles to the shore that traps longshore drift and widens the beach — while starving the coast down-drift.

An offshore barrier that blocks wave energy to shelter a harbour or coast; the official guide lists it as a hard strategy.

A soft strategy of adding imported sand to widen a beach and offset erosion, needing regular replenishment.

A planning measure that reserves flood- or erosion-prone land for low-density or non-building uses, cutting losses at source.

Management balancing present needs with environmental protection so that future generations are not harmed.