Acid volcanics |
Light coloured volcanic rocks containing more than 66 per cent silica, free quartz and a minimum of dark coloured minerals. |
Aeolian |
Moved by the wind. |
Alluvial |
Deposited by streams. |
Alluvial fan |
Fan shaped alluvial deposit of sediment where streams disperse after leaving confined valleys. Steepness (gradient) relates to sediment grain size. |
Amphibolite |
Metamorphic rock composed essentially of amphiboles or dark coloured minerals such as hornblende. Usually derived from submarine basalt. |
Anabranch |
Branch of an anastomosing stream that leaves the main channel and rejoins it some distance down stream. |
Anastomosing |
Multi-branched stream system. |
Backplain |
Parts of a river floodplain furthest from the channel. |
Barrier |
See coastal barrier. |
Basalt |
Dark coloured, fine grained volcanic rock composed of olivine, pyroxene and feldspar. No free quartz. |
Basement rock |
General term to describe older rocks beneath a sedimentary basin. |
Bedrock |
Hard rock beneath a superficial cover of soils and sediments. |
Black earth |
Dark coloured pedal clay soils usually found in valleys and often derived from basalt. |
Blockstream |
Periglacial landform composed of a "river" of boulders on low angle slopes. |
Braided river |
River in which the main channel is braided with multiple paths that split and join frequently. Usually a gravel or sand bed stream. |
Caldera |
Large volcanic crater created by explosion or internal collapse of a volcanic cone. |
Cambrian |
Period of geologic time 500-570 million years ago. |
Carboniferous |
Period of geologic time 280-345 million years ago. |
Cauldron subsidence |
See caldera. |
Central volcano |
A single major volcanic vent responsible for a large area of volcanic rocks. |
Chert |
Fine grained siliceous rock usually formed in deep sea environments either as a chemical precipitate, or as accumulated remains of siliceous single celled organisms such as radiolaria. |
Cirque |
Small glaciers and the basins they excavate at the head of valleys. |
Claystone |
Sedimentary rock composed of clay. Also referred to as mudstone. |
Cliff top dunes |
Sand dunes located well above the beach from which the sand was derived. |
Coastal barrier |
Complex landscape of beach, dunes and enclosed lagoon or swamps that form between headlands during rising sea levels. |
Colluvial |
The movement and deposition of sediment and debris on slopes. |
Columnar lava |
Basalt or other volcanic rocks with well developed columns (organ pipes) formed by cooling joints. |
Competence |
The ability of a stream to carry sediment of different size. |
Conglomerate |
Sedimentary rock composed of particles coarser than sand, for example, pebbles. |
Contact metamorphic |
Metamorphic change induced in rock that comes in contact with a heat source such as a granite intrusion. |
Continental shelf |
Shallow seas adjacent to the continent. Most were exposed during times of low sea level in the Pleistocene ice age. |
Contour banding |
Alternating zones of different soil, sediment and vegetation approximately following the contour on gentle slopes in the arid zone. Often stony and stone-free bands. |
Cracking clay |
Alluvial clays with high shrink/swell potential that crack deeply on drying. |
Cretaceous |
Period of geologic time 65-136 million years ago. |
Debris dam |
Floating load debris (logs etc.,) that have accumulated across a river channel and that may divert the stream. |
Dendritic |
Multiple branching pattern like a tree. |
Desert pavement |
Lag gravel surface of gibbers (pebbles and boulders) on the soil surface. |
Devonian |
Period of geologic time 345-395 million years ago. |
Diatomite |
Very light weight sedimentary rock composed of the remains of diatoms. |
Diatreme |
Pipe like vertical volcanic vent filled with broken and cemented country rock created by a single explosion. |
Dip-slope escarpment |
Asymmetric landform where rock bedding controls the cross-sectional shape of ridges. Cliffed on one side with a gentle slope following the dip of bedding planes on the other side. |
Discharge |
Volume of water flowing past a point in a stream over time. |
Dolerite |
Medium grained igneous rock with composition similar to basalt. Usually found in dykes or sills. |
Downs |
Extensive undulating and gently rolling plains. |
Dune |
Sand accumulating and moving in dune forms. |
Dyke |
Vertical sheet of intrusive igneous rock. |
Endemic |
Restricted distribution. |
Ephemeral |
Lasting only a short time. |
Escarpment |
A cliff or the steep slopes of a plateau edge. |
Fault |
Fracture zone in rock along which there has been movement of the crust. |
Feldmark |
Community of prostrate plants growing on a stony pavement in an extreme alpine environment. |
Floodout |
Area of an alluvial fan where the stream disperses across a plain. |
Fold belt |
Region in which all the bedrock has been subject to similar phases of disturbance by folding and faulting. |
Footslope |
Lower part of a hillslope merging with the alluvial plain. |
Gabbro |
Coarse grained igneous rock with composition similar to basalt. |
Gibber |
Stones in a desert pavement. |
Gilgai |
Hummocky micro-relief pattern common in heavy alluvial clays. |
Glacio-marine |
Poorly sorted sandstones and conglomerates formed in an environment where icebergs move glacial debris offshore. |
Gneiss |
High grade, coarse grained metamorphic rock with an overall composition similar to granite. |
Gondwana |
Name given to the super continent formed when Australia, Antarctica, Africa, India and South America were all joined. |
Gorge |
Steep narrow river valley. |
Gradational Soil |
A soil with a gradual increase in texture (ie. becomes more clayey) as the profile deepens. |
Granite |
Light coloured, coarse grained plutonic rock with free quartz. Usually composed of potassium feldspar, quartz and mica. |
Granodiorite |
Coarse grained plutonic rock, similar to granite but with less quartz and more dark minerals. |
Great Artesian Basin |
Extensive area of inland Australia filled with Mesozoic sedimentary rocks and containing an important resource of artesian water. |
Great Dividing Range |
Eastern highlands of Australia that separate coastal streams from those flowing inland and particularly the Murray-Darling Basin. |
Great Escarpment |
Eastern margin of the Great Dividing Range where the most rugged topography is found. |
Groundwater window |
Place where the topography is lower than the groundwater table and a lake or salina forms. |
Guano |
Accumulation of bird (or bat) faeces and the soil it interacts with. |
Gypsum |
A common mineral of evaporates in inland salt playas. Calcium sulphate |
Harsh clay |
Hard, dense clay with high shrink/swell potential and highly dispersible. See also: Mellow clay. |
Horizon |
Layers in a soil formed by surface processes, by convention A and B horizons are equivalent to topsoil and subsoil. |
Hypersaline |
Very saline brines. Salt concentration greater than sea water. |
Igneous |
Rocks formed from melts in the Earth's crust. eg. Granite, gabbro or basalt. |
Inner barrier |
Older coastal barrier system sometimes found on the landward side of the outer (or modern) barrier. |
Intrusives |
Igneous rocks that have intruded other rocks. eg. A granite body or an igneous dyke. |
Island arc |
Complex of volcanic islands, and shallow seas adjacent to an oceanic trench. For example, Indonesia. |
Joints |
Natural fractures in a body of rock that cause it to break into regular blocks on weathering or when quarried. |
Jurassic |
Period of geologic time 136-190 million years ago. |
Karst |
Landforms created by solution of rock in which most of the drainage is by underground channels that may lead to the formation of caves. Normally refers to limestone karst but can occur in other rock types. |
Lava field |
Extensive area of volcanic rock derived from many small volcanic vents rather than a central volcano. |
Leucitite |
Rare basalt dominated by the felspathoid leucite, rather than the more common calcic plagioclase. |
Lignite |
Soft brown coal. |
Limestone |
Any sedimentary rock composed essentially of calcium carbonate. |
Linear dunes |
Sand dunes forming regular lines oriented parallel to dominant winds. |
Lithic sandstone |
Sandstone composed of sand sized rock fragments. |
Loam |
Soil material with approximately equal quantities of sand, silt and clay. |
Lunette |
Crescent shaped beach and dune complex found on the eastern sides of lakes in arid Australia. Usually composed of quartz sand but can also be partly or wholly composed of sand sized clay pellets and occasionally gypsum sand (copi or seed gypsum). |
Meander |
River with a single channel that sweeps back and forth in smooth curves. |
Mellow clay |
A soft stable clay with minimum shrinkage potential. |
Mesa |
Small flat topped hill. See also Tableland. |
Mesozoic |
Era of geologic time 65-225 million years ago. |
Metamorphic |
Any rock formed from a pre-existing rock by application of heat and pressure. For example, quartzite, slate, schist, or gneiss. |
Meta-sediments |
Low grade metamorphic rock derived from sedimentary rocks and retaining some original structure or composition. |
Monocline |
One sided fold in a geological basin. |
Monzonite |
Coarse grained igneous of the granite type. |
Mound spring |
Point of surface flow of artesian water. Mounds normally formed by concentration of soluble minerals. |
Mulga groves |
Contour banded pattern of mulga growth on extensive sandplains. |
Ordovician |
Period of geologic time 430-500 million years ago. |
Overflow lakes |
Lakes fed by floodwaters from a stream. |
Pagoda country |
Sandstone landscapes formed by erosion with tall rock pillars that look like pagodas. |
Palaeodrainage |
Abandoned river patterns evident in the landscape formed under different climatic conditions. |
Palaeozoic |
Era of geologic time 225-570 million years ago. |
Parabolic dunes |
Curved dune patterns oriented parallel to dominant winds. May be a pre-cursor to linear dunes. |
Pedal |
Natural aggregates in soils, often with a geometric shape. eg. blocky or prismatic. |
Pegmatite |
Very coarse grained rocks of granitic composition containing large mineral crystals. |
Peneplain |
A lowland plain formed by erosion to the extent that rock structure and composition no longer influence the landscape. Supposed to be the end phase of an erosion cycle, which is an old concept that is not universally accepted. |
Periglacial |
Environments dominated by ground ice and freeze/thaw processes, as in the tundra. |
Permian |
Period of geologic time 225-280 million years ago. |
Phyllite |
Fine grained metamorphic rock with well developed cleavage, derived from shale. |
Pillow lava |
Volcanic rock with unusual pillow structure caused by lava cooling under water. |
Plateau |
Generally high ground with more or less concordant summits and low relative relief. |
Playa |
Clay plain that is temporarily flooded to form a lake or swamp after exceptional rainfall. |
Pleistocene |
Epoch of geologic time 10,000 to 1.8 million years ago. |
Pliocene |
Epoch of geologic time 1.8 - 5 million years ago. |
Ploughing block |
Large boulder moved through the soil mantle by periglacial processes, or by high snow loads. |
Plugs |
Bodies of igneous rock that have cooled in the throat of a volcano and subsequently been exposed by erosion. Often columnar jointed. |
Podsol |
Soil profile with distinctive horizons of a bleached lower topsoil and cemented iron oxide pans in the subsoil. Formed in quartz sand under special conditions and special vegetation. Common in coastal dunes. |
Porphyry |
Any igneous rocks with a porphyritic texture, that is, coarse crystals in a fine groundmass. Indicates that two phases of cooling were involved. |
Prior streams |
Relic channels and channel traces on an alluvial fan created by streams in a different climate. |
Psuedokarst |
Cave-like land forms and features in non-soluble rocks such as granite boulders. |
Quartz sandstone |
Sandstone composed largely of quartz sand grains. |
Quartzite |
Metamorphosed quartz sandstone. |
Quartzose |
General term for a sedimentary rock composed of quartz grains that is intermediate between a quartz sandstone and a quartzite. |
Quaternary |
Period of geologic time 0-1.8 million years ago. |
Rain shadow |
Area of low average rainfall such as the region behind a mountain range. |
Regolith |
All layers of weathered rock, sediments and soil material covering the surface. |
Residual |
A soil material or landform that remains in place from the past. |
Rhyolite |
Fine grained, light coloured volcanic rock with a high proportion of quartz, equivalent in composition to granite. |
Rock platforms |
Coastal rock benches in the inter-tidal zone. |
Runoff |
Precipitation that flows across the ground surface and enters streams leading to lakes or oceans. |
Run-on sites |
Parts of footslopes or alluvial fans that receive runoff from upper slopes. |
Sandplains |
Extensive sheets of aeolian sand that do not exhibit dune forms. |
Sandstone |
Sedimentary rock composed of sand sized particles. |
Scarp |
See Escarpment |
Schist |
Foliated, high grade metamorphic rock |
Sedimentary |
Rocks composed of sediments. For example, claystone, sandstone, conglomerate. |
Serpentinite |
A green metamorphic rock composed of hydrated magnesium silicates formed by the alteration of olivines and pyroxenes usually in a submarine environment. |
Shale |
Sedimentary rock composed of silt and clay sized particles, weakly cemented. |
Shield volcano |
Very large composite and symmetric volcano. |
Silcrete |
Fine grained orthoquartzite formed by cementation of shale or siltstone with silica. |
Sill |
Horizontal sheet of intrusive igneous rock. |
Silurian |
Period of geologic time 395-430 million years ago. |
Slate |
Fine grained metamorphic rock with perfect cleavage formed by metamorphism of shale. |
Snow patch |
Area of persistent summer snow on a protected aspect. |
Solifluction lobes |
Lobes and bulges of deformed soil and vegetation on hillslopes subject to periglacial activity. |
Structure |
Overall geometry of folds, faults and joint patterns in a rock mass. |
Subsoil |
B horizon usually derived from rock by in situ weathering. |
Swale |
Valley between dunes. |
Tableland |
Large flat top hill, extended mesa or small plateau. Also used to describe a plateau. |
Terminal channels |
River channels that terminate in an inland region without reaching the sea or a lake. |
Terraces |
Level areas of valley floors that are not flooded. Abandoned floodplains. |
Tertiary |
Period of geologic time 1.8-65 million years ago. |
Texture contrast profile |
Soil profile in which the topsoil (A horizon) has a sandier texture than the subsoil (B horizon). Typically a sandy loam over a clay. |
Throughflow |
Water moving through the soil between the A and B horizons. Or, water passing through a swamp in a valley. |
Topsoil |
Surface layer of soil with higher organic content, A horizon. |
Tor |
Large outcrop of bedrock. In granite country tors are typically round boulders. |
Trachyte |
Fine grained igneous rock equivalent in composition to a syenite. Contains a small amount of free quartz. |
Triassic |
Period of geologic time 190-225 million years ago. |
Tuff |
Consolidated volcanic ash. |
Turbidites |
A suite of deep marine sedimentary rocks formed as a result of sediment transport by turbidity currents. |
Ultrabasic rock |
Igneous rocks containing less than 45 per cent silica. Usually coarse grained and contain no free quartz or feldspar. |
Unconformity |
Surface between two rock units of different ages with different attitudes, represents an interval of time. |
Uniform textured soils |
Soils in which the topsoil and subsoil have very nearly the same textures. |
Veins |
Thin body of mineral such as quartz, intruded through a rock, usually following structural weaknesses such as joints. |
Volcanic |
Igneous rocks that have been formed on the Earth's surface as from a volcano. |