What are the features of a limestone cave?

Answer 1

The majority of caves are formed in limestone by water dissolving the rock along its joints, bedding-planes and other discontinuities to form a network of tiny conduits. Defined paths for the water develop through these, and enlarge into enterable cave passages. Eventually the passages lose their formative streams, either by the water cutting down to a lower level within the hill holding the cave, or by surface landscape changes removing the water supply altogether.

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This gives sets of distinct features:

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Passage morphology: the passage may be horizontal (or sloping with the rock's "dip"), or a vertical shaft. Some cave entrances are of the latter form, with the stream dropping down it. If the passage was formed entirely full of water (called its "phreatic" stage") then lost its stream relatively rapidly, its cross-section is circular or oval. If the water can cut down into the floor, with an air space above it (the "vadose" stage) the passage becomes a canyon, with the original phreatic stage in the roof.

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The water may cut intricate shapes into the walls, such as "scallops" - spoon-shaped hollows which indicate the flow direction and relative speed - and "pendants" - down-pointing spikes of bed-rock, not to be confused with stalactites.

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The passages may, and indeed usually, follow the joint pattern of the rock, often giving a distinctly rectilinear layout, but in complex caves this is often shown better by the cave "survey" (map) than by the underground scenery itself, because when you are in the cave you can only see a small portion of it at once and the natural irregularities disguise the geometry.

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The passages may be constricted crawls, of pleasant walking size, or may have been enlarged into vast chambers, some so large you cannot see across them, or see the roof, with normal caving lamps. The floors may be clean-washed by the water, be covered with sediment or cluttered with fallen boulders, perhaps to the extent of being completely choked.

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Then there are the cave's "decorations". The features best-known to show-cave visitors - most of whom I think, sadly, don't really see the cave as a whole (!) in its geological setting - are of course Speleothems: calcite precipitations. These take many forms, with Stalactites (growing down from the roof) and Stalagmites (growing up from the floor) being the best-known. An easy mnemonic: C for ceiling, cling tight; g for ground, mite reach the roof. Or the stalactite above, to form a Column! Sometimes stalactites develop from calcium-carbonate rich water trickling down a sloping roof rather than dripping from a discreet point, then instead of a straw- or carrot- shaped stalactite the result may be a Curtain, often of great beauty. There may be other speleothems to admire too - "cave pearls" formed by calcite coating sand grains, helictites which are oddly-shaped formations so far defying adequate explanation, and gour pools (or, in the US I think, rimstone pools). The last are terraces of pools formed by calcite dams growing in water trickling down a sloping floor.

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The water can be part of the scenery - calm pools or gently-flowing rivers, tumbling cascades, great waterfalls or "sumps" (water-filled passages) of which most can be negotiated only by properly equipped and trained cave-divers.

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That's only a brief summary! You asked about the features of the cave. I haven't touched on cave wildlife, Archaeology etc. I hope it helps!

Answer 2

sinkholes, caves, and aquifers