Caves 101

1. “Cave” refers to a natural underground space large enough for a person to enter, and caverns their cave chambers. “Grotto” refers specifically to an inhabitable one, near water.

Cave Formation & Ecological Succession

1. Caves develop largely via gradual erosion by water, and bedrock collapses, such as from chemical, tectonic, or volcanic action. Gradual processes can create passages, obstructions, or crystalline structures.

2. Caves typically reach much more stable equilibrium than other habitats, due to isolation from most disturbances and temperature swings, as well as the high rate of primary producers, including those subsisting off of chemical and mineral interactions instead of sunlight.

3. Nevertheless, cave moisture sustains a foundation of mosses, ferns, liverworts, and fungi, as well as migratory and colonizing fauna. Succession can center around different states arising based on the accumulation of nitrogen via guano, by water flooding, and by air chemical composition changes.

Cave Ecologies

1. Caves have distinct sections: the Entrance Zone interacts with surface soils through cracks and rock seems, groundwater seepage, and root protrusions, which extends toward the Twilight Zone, a threshold portion near cave mouths which reaches the last penetration of sunlight. The progression goes from cool, shaded, and lit, to cool, damp, and dim, then dark.

2. Beyond this exists the Dark Zone, which can still have regular contact with the surface via wind and underground streams or animal migration, or be almost entirely isolated. The farthest reaches become the Underdark Zone, with unique ecologies where primary energy comes from chemicals harvested by bacteria from minerals, rather than from sunlight.

3. Unique cave species adaptations include features like loss of pigment or eyes, elongation of limbs, and certain enhanced senses.

Cave Form Categories

1. Caves can come in simple forms, such as small and shallow rock shelters wider than deep, produced by bedrock erosion in insoluble rock, or as openings among random heaps of large fallen boulders (talus caves) at the base of cliffs.

2. In coastal mixtures of freshwater and saline, underwater (anchialine) caves can form. Wave action can also create sea caves along active or remnant coasts.

3. Water and wind erosion can create corrasional caves, where streamflow carries rock and sediment along a fault or joint. These can expand small openings from solutional processes, processes which can form solutional caves where in soluble rocks, natural groundwater acids seep through and dissolve open cracks. And where soluble minerals dissolve away, fractures and collapses of stone blocks can create fracture caves.

4. Primary caves form from the same surrounding rock type, including lava, blister, tufa, and reef cave types. Similarly, glacial caves arise as hollows within glaciers.

Cave Passage Patterns I

1. Cave passages have varying functional patterns. Along one bed or structure, braided anastomotic passages can form. Other convergences, branchwork passages, meet downstream as tributaries.

2. Pit cave passages function as vertical shafts. The more complex angular network passages appear as sequences of straight and narrow lines persisting in widespread loops.

3. The most complex and three-dimensional passages manifest through chemical action as randomized rooms formed as rising water chemically erodes rock (ramiform caves), or in a sponge-like pattern arising from solution cavities.

Cave Passage Patterns II

1. Cave passages work differently near underground water, where features like submerged passages (sumps) exist. As water swirls under extreme pressures, it can create vertical tubes in cave ceilings (avens). This water can also dissolve rock to create wide and low spaces with smooth ceilings and floors (soluble beds).

2. Cave drain complexes form from free-flowing water, creating channels like narrow keyhole passages and drain shafts, sometimes collapsing ceilings to create vault-like breakout chambers.

3. Transitional floodwater zones in caves have times of higher water and lower water; these sequences can create intertidal passages.

4. Seismic activity, pressure, and slow erosion can create passages with large stretches of hanging walls of split rock (fault-formed passages), or the straight, narrow, and deep fissure or rift passages, where rock splits or cracks widen along a joint.

Dripstone Speleothems

1. Gradual mineral development into deposits can form whitish or translucent speleothem structures. Dripstone forms include descending stalactites, ascending stalagmites, and stalagnate columns, which form when stalactites and stalagmites meet to form pillars, or stalactites reach the cave floor.

2. Stalactites appear as conical pendants growing down from cave ceilings. These can sometimes manifest in a manner resembling chandeliers, various spirals and ribbons and curls (helictites), or elongated cylinders (soda straws).

3. Stalagmites appear as the upward protrusion counterparts to stalactites, often blunt mounds. These can sometimes manifest as tall and spindly broomstick shapes, forms resembling fried eggs, or even totem pole shapes.

Flowstone Speleothems

1. Cave floors and walls can feature sheet-like structures called flowstones. These can manifest as wavy sheets of hanging rods resembling curtains (draperies), as mineral barriers occuring at stream ripples (rimstone dams), or even as stone waterfall formations.

Crystal Speleothems

1. Caves can also feature crystalline structures. This can appear as flower-like clusters (anthrodites), as loose grains of crystal (cryogenic calcite), as large crystals near seasonal pools (dogtooth spar), as needle-like growths (frostwork), or as a white, creamy substance (moonmilk).

Speleogens & Exotics

1. As cave bedrock erodes, colorful structures called speleogens can form. This can manifest as intricate mazes full of holes (boneyard), as preferentially-eroded calcite veins (boxwork), as soft rock pillars, or as small, asymmetrical, scoop-like depressions (scallops).

2. More rare variations include thin accumulations of calcite on cave pool surfaces (calcite rafts), and small cave pearl spheres arising as water drops high above. And also, small, knobby clusters (cave popcorn), submerged bell-shapes (hells bells), or even sulfur-oxidizing bacteria colonies resembling rusty snot (snottites).

Pits & Shafts

1. Caves can have many depressions, hollows, and shafts, particularly from water interactions. Along sea cliffs or coastal terraces, these can manifest as blowholes spraying jets of water from rock crevices. Along glaciers or ice sheets, surface water can flow into circular and vertical well-like shafts (moulin).

2. Bedrock collapses can also give rise to various forms: pits of exposed groundwater (cenote), deep sinkholes above a void (foiba), or depressions or holes in the ground (sinkholes).

3. Simple instances include the unroofed portions of caverns revealing subterranean rivers (karst fenster), or shallow depressions eroded into flat or gently sloping rock (panholes). More sophisticated networks of pits and shafts include the deep vertical shafts in karst terrain (abime), and features ranging from amorphous shallow pits to irregular labyrinthine hollows (scowle).

Special Cave Features

1. Caves can have special obstacles. This includes collections of large rocks or rubble obstructing cave passages (boulder chokes), partial or total collapses of cave structures creating blockages (cave ins).

2. By contrast, caves can also let in the outside, whether holes in a cave roof letting in sunlight and air (sunholes), subterranean tunnels acting as passageways, or subterranean waterfalls along vertical drop-offs.