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Geological Notes

How Caves are Formed

With thanks to Australian Geographic and Armstrong Osborne

Types of Cave Forms

Words to come ...

Glossary of Caving Terms

ACCIDENTAL CAVERNICOLE. n. An animal living in a cave which has arrived accidentally (eg fallen or washed in).

AEOLIAN CALCARENITE. n. Calcareous fine sand size particles which have become air-borne due to wind and are deposited as dunes, later to undergo consolidation and diagenesis to form dune limestone. Also see calcarenite and Syngenetic Karst.

AEOLIAN. (1) adj. Pertaining to or caused by the wind; wind-borne. (2) n. Landforms generated by the wind, or sediments transported by the wind. Derived from Æolus, the Latin God of the wind.

ALLUVIUM (hence ALLUVIAL). n. Deposits arising from the work of rivers.

ANABRANCH. n. A branch of a stream which leaves the main flow and then re-enters further downstream.

ANASTOMOSES (hence ANASTOMOSING). n. A form of SPELEOGEN consisting of a network of small tubes; often confined to a BEDDING PLANE.

ANGELS HAIR. n. An American term. A SPELEOTHEM consisting of very fine crystals resembling fine hair or whiskers; usually of GYPSUM.

ANTHODITE. n. Radiating clusters of crystal needles, usually of ARAGONITE but sometimes as PSEUDOMORPHS after CALCITE or as CALCITE.

ANTICLINE (hence ANTICLINAL). n. Sedimentary rock beds deformed into an upwards fold. (q.v. SYNCLINE).

ARAGONITE. n. A calcium carbonate mineral producing characteristic crystal forms different to that of the more common CALCITE (q.v.). It is denser than calcite and the structure is orthorhombic.

ARMCHAIR CAVER. n. Colloquial term for an experienced caver who is now incapable of caving or a person still able to, but has lost the urge to actually go caving. On the other hand they may spend much of their time writing or reading caving books and hours may be spent reminiscing over photographs from past trips.

AVEN. n. A shaft which rises from a passage, sometimes leading to a passage above, but not open to the surface.

BEDDING PLANES. n. Planes of weakness between beds of sedimentary rock.

BEDROCK. n. The solid mass of parent rock originally laid down - from which a cave or feature has been eroded by mechanical or chemical action. This term includes bedrock which has been transformed in crystalline structure due to heat (eg. marble) but does not include redeposited minerals (eg. speleothems).

BIOGENIC. adv. Of biological origin.

BIOTA. n. Plants and animals.

BLIND VALLEY. n. A surface karst feature where a valley terminates in a wall (and thus there is a closed contour); flood waters never flow over the wall (q.v. SEMI-BLIND VALLEY). It may or may not have a stream flowing in it.

BREAKDOWN. (1) v. A fall of bedrock from cave roof or wall under its own weight. (2) n. A pile of broken bedrock.

BREATHING, (relating to cave) v. Movement of air in and out of a cave due to changes in atmospheric pressure and/or temperature changes on the surface.

CALCITE RAFT. n. A thin layer of calcite deposited on the surface of a still pool.

CALCITE. n. The most common polymorph of calcium carbonate (CaCO3) mineral with a number of different forms in the rhombohedral system. The most common constituent of stalactites, stalagmites, flowstone etc. Limestone, marble and chalk consist largely of calcite.

CANYON. n. A tall, narrow rift produced by water eroding the rock.

CAVE CORAL. n. A class of SPELEOTHEM (q.v.) characterised by irregular clusters of calcite or aragonite; often of rounded or coralline form but produced by chemical and not biological processes.

CAVE SYSTEM. n. The whole known extent of interconnected caves and cavities underground, including those too small to enter, which have been proven to be atmospherically or hydrologically connected.

CAVE. n. A natural cavity in rock. Cavers use the term for holes large enough to be entered by a person. Strictly, it may be far smaller.

CAVER. n. A person who goes caving. (American, 'spelunker'). (British, 'Potholer') Syn. speleologist.

CAVERNICOLE. n. An animal which normally lives in caves for the whole or part of its life cycle.

CLAST. n. A fragment of rock which may range in size from microscopic to metres across (hence CLASTIC).

COBBLE. n. A CLAST (q.v.) between 64 and 256mm in size.

COLLAPSE. n. Rapid catastrophic breakdown of the rock mass produced by removal of HYDROSTATIC (q.v.) and/or mechanical support.

COLLUVIUM (hence COLLUVIAL). n. Detritus moved downslope by gravity alone.

CRYSTAL WEDGING. n. The destruction of rock produced by the expansion of crystals as they form.

DIP (hence DIPPING). n. The angle at which the beds within the rock mass are inclined (q.v. STRIKE).

DOLINE. n. A closed depression draining underground of simple but variable form produced by solution, SUBSIDENCE or COLLAPSE.

DOLOMITE. (1) n. A double carbonate mineral consisting of calcium and magnesium. CaMg(CO3)2. (2) n. A rock consisting largely of dolomite. cf. magnesite.

DOME. n. A large hemispherical hollow in the roof of a cave formed by breakdown, often in mechanically weak rocks where bedding and/or joints play little, or no part in dominating the form.

DUCK-UNDER. (1) n. A constriction in a passage where water is at or close to the cave roof for a short distance, which requires a caver to become (more or less) fully submersed for a brief period before continuing. (2) v. The act of going through a duck-under. Also see trap.

EDAPHOBITE. n. An animal dwelling in the soil.

EFFLUX. n. Point of outward drainage of water from a cave system or karst area. May or may not be large enough to allow passage of a caver. cf. outflow cave and resurgence.

FAULT. n. A fracture in a continuous body of rock where one side has displaced relative to the other. Movement has occurred along the fault plane.

FLOWSTONE. n. A deposit of calcite formed by a thin film or trickle of calcium bearing water, flowing over walls or floors. cf. travertine and speleothem.

GASTROPOD. n. One of a large class of aquatic and terrestrial molluscs including the snails, slugs, limpets and whelks etc., usually having a single-piece spirally-coiled shell (univalve) and a flattened muscular creeping organ which acts as a foot on which they move about. Sometimes spelt gasteropod.

GEOMORPHOLOGY. n. The scientific study of landforms and landscapes. The term usually applies to the origins and dynamic morphology (changing structure and form) of the land surfaces of the earth, but it can also include the morphology of the seafloor. The science has developed in two distinctive ways that must be integrated in order for the whole picture of landscapes to emerge.

GOUR. n. Synonymous with rimstone dam. Derived from the French, the term 'gour' is now widely used in Europe. It should not be confused with the same word used for surface erosion features in deserts. cf. microgour.

GUANO. n. A large accumulation of bat excrement which may also consist partly of decomposing animal skeletal material and small fragments of rock particles. To a lesser extent in caves it may consist of bird droppings.

HELICTITE. n. A speleothem which often resembles the form of a twisted or worm-like shape and having appeared to defy gravity during its growth process.

HISTOPLASMOSIS. n. A fungal disease which initially affects human lungs and may spread to other organs if untreated. The fungus - Histoplasma capulatum - is an organism which grows in soil having a high nitrogen content, generally associated with guano of birds and bats. Spores are breathed in with airborne dust stirred up by the movement of cavers. The disease usually appears as a mild cold before complete recovery. Occasionally severe infections occur and if left untreated can lead to death. Other names for this disease include: "Histo", "cave disease", "cave fever", "Darling's disease", "Ohio Valley disease", "Tingo Maria fever", "reticuloendotheliosis" and "reticuloendothelial cytomycosis".

INVERTEBRATE. n. An animal without a backbone or spinal column.

JOINT. n. A natural division or gently curving crack, which bisects a bedding-plane. Separating two parts of a once continuous rock without relative movement along the bedding-plane.

KARREN. n. The minor forms of karst due to solution of rock on the surface or underground. eg. rillenkarren, rundkarren and spitzkarren.

KARST FEATURE. n. Any feature formed by natural waters dissolving rock above or below ground. eg cave and karren.

KARST. n. An area of terrain containing features which are formed by natural waters dissolving rock. In most cases these areas contain caves. Derived from the geographical name of a part of Slovenia. See solution.

LAVA CAVE. n. A cave formed in lava, usually as a result of a flow of liquid lava through a solidification mass, or by roofing over of an open channel. Small lava caves may form as gas blisters.

LAVA. (1) n. Molten rock that issues from an active volcano or through a fissure in the earth's crust. (2) n. Rock formed by the solidification of this substance. Lava surface types include 'pahoehoe' and 'aa'.

LIMESTONE. n. A sedimentary rock composed mainly of calcium carbonate (CaCO3). (Containing more than 50% CaCO3). It usually originates from the accumulation of calcareous remains of marine life.

MARBLE. n. Limestone which has been recrystallised after being subjected to high temperatures as may occur in nature from surrounding volcanic action. The resulting marble is much harder than limestone and is able to be polished, making it much sought after for sculptures and architecture. Also see metamorphism.

MOONMILK. n. A term used to describe finely crystalline substances of varying compositions. Texture, not composition is implied by the term "moonmilk". Most commonly composed of calcite which forms a soft white powder when dry and feels like cream cheese or cotton candy when moist.

OOLITE. n. A morphological term meaning a small spherical or subspherical, accretionary body consisting of two or more concentric rings. The overall size being smaller than 2mm in diameter. Anything larger is called a Pisolite. The body can be made of any material and not necessarily calcite. A rock may be said to possess an oolitic texture if it consists largely of oolites. (Pettijohn, F.J., 1975). In general the term oolite should not be used to describe a cave pearl.

PAHOEHOE. n. A type of lava in which the surface was relatively fluid just prior to complete solidifying and so formed smooth or porridge-like surfaces. Variants include wrinkled or 'ropey' surfaces, like thick flowing tar or pitch, and surfaces with small rounded knobs. Surface texture grades from 'pahoehoe' to 'aa' lava.

PERCOLATION WATER. n. Water which is moving downward through pores, cracks and tight fissures in the vadose zone. Syn. seepage water.

PHREATIC DEVELOPMENT. n. Enlargement of existing joints and bedding planes by movement of water under pressure (ie with no free airspace).

PHREATIC ZONE. n. The level in the strata which is below the watertable and all cavities in the rock are filled with water.

POROSITY. n. (1) The property of rock or soil with small voids which may or may not be permeable. (2) porosity due to fractures and joints in rock. (3) porosity of a karst system due to conduits. cf. permeability and percolation water.

QUATERNARY. adv. Of or pertaining to the youngest geological period covering approximately 1.8 million years to the present. - n. The quaternary period.

RESURGENCE. n. The point at which a stream resurfaces like a large spring. This occurs when water of a surface stream disappears into a stream sink, whereupon it flows underground for some distance. The resurfacing point of this stream is the resurgence. The underground water stream may also originate from a combination of many small surface streams and seepage in a cave system, before resurfacing at the resurgence. cf. spring.

RILLENKARREN. n. Well developed solution flutes. Small linear hollows separated by narrow, sharp ribs, which run down the steepest line of slope on steeply inclined to vertical faces. Usually formed on the surface of karst bedrock exposed to the atmosphere. cf. rundkarren, spitzkarren. Syn. solution flute.

RIMSTONE. n. A deposit precipitated from water flowing over the rim of a pool. cf. speleothem.

ROOF-SNIFFING. (1) v. Colloquial term for the act of edging oneself along a small water-filled passage, on your back with only sufficient airspace for eyes and nose. Also roof-sniff. (2) n. A place where a caver must roof-sniff.

SEDIMENTARY ROCK. n. Rock formed from accumulation of sediment, which may consist of rock fragments of various sizes, remains or products of animal or plants, production of chemical action or of evaporation, or mixture of these. Stratification is the single most characteristic feature of sedimentary rocks.

SEMI-BLIND VALLEY. n. A surface karst feature where a valley terminates in a wall (and thus there is a closed contour); flood waters episodically flow over the wall (q.v. BLIND VALLEY).

SILICEOUS (hence SILICIC). adv. Rock or clasts made up of silica (eg sandstone).

SPAR CRYSTALS. n. Crystals of pure CALCITE of perfect form.

SPELEAN. adj. Pertaining to or inhabiting caves. From the L spēlaeum. from GK, spἑlaion

SPELEOGEN. n. A cave feature formed erosionally or by weathering in cave enlargement such as SCALLOPS, CANYONS or SPONGEWORK.

SPELEOLOGY. n. The exploration, mapping, photography, description and scientific study of caves, subterranean environments and phenomena relating to karst terrains. Includes: hydrology, geology, mineralogy, palaeontology etc. The term is often extended to include ground-trogging. adj. speleological.

SPELEOTHEM. n. An object found within a cave. The usage is usually restricted to cave formations (decorations) such as STALACTITES, CAVE CORAL etc, rather than clasts.

SPONGEWORK. n. Characteristic maze-like assemblages of rounded tubes produced by solution beneath the water table in the PHREATIC zone.

SPRING. n. Water rising from a rock (Syn. RISING; q.v. RESURGENCE).

STALACTITE. n. A cylindrical or conical SPELEOTHEM produced by the deposition of a mineral commonly calcite, on the roof of a cave.

STALAGMITE. n. A cylindrical or conical SPELEOTHEM produced by the deposition of a mineral commonly calcite, formed by water dripping onto the floor of a cave.

STEEPHEAD. n. A valley with a steep wall at its upper end commonly with water rising from its foot.

STILLSTAND. n. A halt in the incision of streams in caves.

STRAW. n. A thin, cylindrical and hollow STALACTITE.

STRIKE. n. The orientation, relative to north, of beds of rock. The strike is at right angles to the DIP.

STROMATOLITE. n. A mound-like structure of calcareous sediments, formed by fine layers of inorganic debris (eg sand grains) deposited on successive gum-like mats produced by Cyanobacteria (formally known as Blue-Green Algae). Stromatolite fossils date back to the Archaean and Proterozoic eras, and their presence suggest the process of photosynthesis began at an early age in the development of life on earth. Excellent examples can be found in the limestone deposits of Brachina Gorge - Flinders Ranges, South Australia. Also see stromatolitic stalagmite.

SUBSIDENCE. n. The slow movement of soil or other sedimentary material into caves producing deformation of the surface sometimes producing DOLINES (q.v. COLLAPSE).

SURFICIAL. adj. Of the earth's surface. Surficial materials are usually unconsolidated and deposited over the underlying bedrock.

SYNCLINE (hence SYNCLINAL). n. Sedimentary rock beds deformed into a downwards fold (q.v. ANTICLINE).

THIXOTROPIC. adj. A term applied to certain types of solid/liquid systems (eg wet cave muds) which are effectively solid when stationary but which become mobile liquids when disturbed.

TROGLOBITE (hence TROGLOBITIC). n. A CAVERNICOLE unable to live outside the cave environment; usually displaying adaptations to the cave.

TROGLOPHILE. n. A CAVERNICOLE which frequently completes its life cycle in caves but is not confined to this habitat.

TROGLOXENE. n. A CAVERNICOLE which spends only part of its life cycle in caves.

TUFA. n. A porous, light yellow crystalline limestone often with a sponge-like appearance, deposited in solution from spring or surface water. Calcium carbonate which is deposited over twigs, dead leaves, moss and earth, builds up mounds or terraces in the above ground streams. Over time the vegetation decays, leaving the calcium carbonate with a spongy appearance.

VADOSE DEVELOPMENT. n. The down-cutting action of a cave stream having a free airspace. Cave development due to water (vadose water) which descends freely and is not under hydrostatic pressure. The fast moving water carries rocks and grit which also cause mechanical erosion of the bedrock. A tell-tail sign of vadose development is scallop markings in the bedrock, caused by running water.

VADOSE. adj. Refers to the area above the water table (q.v. PHREATIC).

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