Composition of the Earth | Global Statistics | Glossary | Geological Periods

alluvial plain. A plain built up from the deposition of water borne sediment. See flood plain.

anticline. An upward fold in the crust. See syncline.

aquifer. A permeable layer of rock that retains water.

archipelago. A group of islands.

Arctic and Antarctic. The polar regions, the limits of which are 66.5o above and below the equator.

arête. A knife edge ridge formed by glacial erosion.

artesian basin. A source of fresh water formed where an aquifer is trapped between two layers of impervious rock.

atoll. Island surrounded by a coral reef.

bar. A strip of sediment parallel to the coastline.

barchan dune. A crescent shaped dune, moved forwards by the wind.

bight. A large bay.

carbonates. Minerals (such as calcite) that contain carbon.

cataract. A large waterfall.

catchment area. An area of land that feeds a river.

cirque glacier. A glacier formed at the head of a valley.

col. A ridge between two mountains.

continent. A single large land mass.

continental shelf. The offshore seabed down to a depth of about 200m.

coral. A structure built from the skeletons of calcareous marine animals.

dale. A valley open at both ends.

delta. Fan shaped area of land at the mouth of a river, built up from the deposition of alluvium and broken by a number of streams.

desert. An arid area with little vegetation that is not necessarily sandy, the lack of rainfall is the determining factor.

dune. Accumulation of wind borne sand.

earthquake. Earthquakes are the result of movement along faults in the Earth's crust usually when two tectonic plates slide across one another. The source of an earthquake is called the epicentre.

equatorial rain forest. A hot, wet forest with a heavy daily rainfall.

erg. An area of shifting sand dunes.

erosion. The physical removal of the crustal rocks.

escarpment. A long steep rock face on a ridge or edge of a plateau.

estuary. The widening, tidal part of a river.

extrusive (volcanic) rocks. Igneous rocks formed on the surface and usually fine-grained (andesite, basalt, pumice and rhyolite).

fault. A fracture in the crust along which movement occurs.

fault-block mountains. Mountains formed by the vertical movement of rocks along a set of fault lines.

fen. Flat, low-lying, marshy ground.

fjord. A narrow, steep-sided sea inlet.

flood plain. An area of land covered with water during river flooding. Flood plains are the basis of alluvial plains.

fold mountains. Compressed sedimentary rocks that rise in a series of concertina-like folds.

forest. A predominately wooded area of land.

fossils. The mineralised remains of plants and animals embedded in rocks.

gemstones. Minerals that have an aesthetic or rarity value. Gemstone list.
geosyncline. A broad trough in the crust, often filled with sediment.

glacier. A slow moving mass of ice that is replenished at its source.

gorge. A deep steep-sided valley.

grassland. A predominately grassed area of land where there is not enough rainfall to support a forest.

gulf. A large bay.

hanging valley. A tributary that joins the main river through a series of rapids or waterfalls.

igneous rocks. Igneous rocks are formed by the crystallization of minerals within cooling magma. Either intrusive or extrusive.

intrusive (plutonic) rocks.  Igneous rocks formed underground, predominately quartz and usually coarse grained. (gabbro, granite and peridotite).

inverted relief. A landscape in which synclines form high ground and anticlines form valleys.

isthmus. Narrow strip of land linking two larger land masses.

jungle. A tropical monsoon forest.

kame. A mound of material marking the former edge of an ice-sheet or glacier.

karst scenery. An uneven fissured landscape formed by underground drainage and caves.

knick point. A break in the slope of a river marked by rapids or waterfalls.

laccolith. A blister of magma that forces the overlying rocks into a dome.

lava. Magma that reaches the surface.

levee. An alluvial bank built up on either side of a river.

littoral zone. An area between high and low tide.

longshore drift. The build up of river borne sediment along a coastline.

magma. Molten rock, the raw material for all igneous rocks.

marsh. Poorly drained ground, sometimes flooded, often found next to open water.

meander. A loop in a river.

metamorphic rocks. Rocks that have been changed by pressure or heat but not melted.

minerals. Naturally formed inorganic substances with a defined homogenous chemical structure, usually crystalline.

moor. Open ground, usually coarse grass, heather and bracken.

moraine. A mass of boulder clay carried by a glacier.

oceanic ridge. A volcanic mountain chain formed at the boundary between two oceanic tectonic plates.

ore. A mineral from which metals can be extracted.

pampas. South American grasslands.

Pangea. The primeval continental mass. Pangea split during the cretaceous period into Gondwanaland and Laurasia which split further to form the present continental masses.

pediment. The sloping ground leading to a mountain range.

permafrost. A layer of earth that is permanently frozen even though the overlaying layers may thaw.

plain. Low altitude area of land, unbroken by mountain ranges.

plateau. High altitude area of land, unbroken by mountain ranges.

reef. A submerged line of rocks (or coral).

rift valley. A valley formed when the strip of land between two faults subsides.

rocks. Rocks are consolidated or crystalline aggregates of minerals and are classified as sedimentary, igneous or metamorphic.

savannah. Open tropical grassland with few trees.

scar. A rock formation on the side of a mountain.

sediment. A build-up of water or air borne particles.

sedimentary rocks. Sedimentary rocks are formed by the layering of air or water borne mineral grains cemented together (chalk, clay, coal, limestone, mudstone, sandstone and shale).

seif dune. A long, sinuous, ridged sand dune parallel to the prevailing wind.

silicates. Common minerals: quartz, feldspar, mica, amphibole, pyroxene and olivine.

shoal. A group of sandbanks.

sinkhole. A limestone hole into which a stream disappears.

spit. A narrow accumulation of sediment projecting into the sea.

steppe. Grasslands spreading from central Europe to Siberia.

straight. A narrow stretch of water separating two landmasses

swamp. Permanently waterlogged ground, usually overgrown.

syncline. A downward fold in the crustal rocks, See anticline.

taiga. Temperate evergreen forests, particularly those in North America and Asia.

tectonic plate. A section of the Earth's lithosphere. Each tectonic plate is bounded by oceanic ridges, trenches or mountain chains. The 7 major plates and numerous minor plates link together to form the Earth's surface.

temperate zone. The area between the tropics and Arctic circles.

tombolo. A bar or spit linking an island to the mainland.

trench. A submarine valley.

tropical monsoon forest. A forest with a distinct wet and dry season.

tropics. The area between the Tropics of Cancer and Capricorn. The Tropic of Cancer is 23.5o north of the equator and the Tropic of Capricorn is 23.5o south of the equator.

tsunami. A huge wave, the result of an undersea earthquake.

tundra. Treeless zone between the icecaps and taiga.

vaclusian stream. A stream that begins underground.

veld. South African grasslands.

volcano. A break in the crust from which lava emerges. Volcanoes are a major source of continental igneous rocks.

wadi. A deep sided ravine, accentuated by arid, blasting winds.

watergap. A river that cuts through a ridge.

yardang. A steep-sided rock rib, etched by the wind in arid areas.

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