| RADON | A radioactive inert gas (Rn86 half life 3.8 days) formed continuously in the earth's interior by radioactive decay. Densest of all known gases, tends to collect in caves as well as man made cellars etc. Concentration varies greatly between localities. Geology. Ref MM |
| RAFT | A speleothem consisting of a thin layer of crystalline material which forms and floats on the surface of a cave pool. Sinks if water surface is disturbed. May form many layers in a dried out pool. Cave - Depositional Features. Ref HF |
| RAPPEL | Syn. Abseil. Climbing and SRT. Ref JJ |
| RAPPEL RACK | A descender consisting of a frame mounting 5 or 6 brake bars. Climbing and SRT. Ref JJ |
| REBELAY | The placing of an additional belay on a rope so as to avoid a rub point on a pitch. Or merely to split long pitches. Syn. Deviation, Redirection. Climbing and SRT. Ref JJ |
| RECHARGE | The process involving the input or intake of water into the saturated zone in karst aquifers. Relates to the quantity of water added. Hydrology terms. Ref AC |
| REGRESSION | A withdrawal of the sea from the land, due to uplift or a eustatic drop in sea level. See transgression. Geology. Ref KG |
| REGRESSIVE EVOLUTION | Reduced body pigmentation (or no pigment); Loss of wings (in insects, such as carabid beetles); Elongated appendages including antennae; Longer and greater density spines or setae (hairs); Reduced metabolic rate. Fauna. Ref MM |
| REGRESSIVE EVOLUTION | Concept used to describe the adaptive traits or troglomorphies of obligate cavernicoles, particularly those species that only live in the dark zone. eg Reduced eye size; Loss of visual ability or loss of eyes; Fauna. Ref MM |
| RELATIVE HUMIDITY | See Humidity. Speleology term. Ref MM |
| RELICT | See Distributional Relict. Fauna. Ref MM |
| RELICT KARST | Old cave forms produced by earlier geomorphic processes within the present phase or period of karstification and open to modification by present day processes. Such as deposition of speleothems, sediments or skeletal deposits. Karst - Kinds of. Ref RW |
| RESURGENCE | A Spring where a stream, which has a course higher up on the surface, reappears lower down at the surface. Speleology term. Ref JJ |
| RHIZOMORPH | A calcareous structure formed around roots, and preserving the form of the root. Speleology term. Ref KG |
| RHODAMINE | A red organic dye detectable in very dilute solutions. Used in water tracing and dye gauging. Survey & Mapping term. Ref JJ |
| RIFT | A long narrow high and straight cave passage controlled by planes of weakness in the rock. cf Fissure. Speleology term. Ref JJ |
| RIGGING | In climbing, the process of establishing the belays for ropes and or ladders. Climbing and SRT. Ref RW |
| RILL | Small solution groove on surface exposures of limestone. Most common in arid or semiarid areas. Karst - Minor Forms of. Ref WM |
| RILLENKARREN | A type of Karren, runnels about 20mm wide with sharp ridges between them. Usually solutional, formed by air currents with airborne moisture forming closely situated often parallel to sub-parallel vertical grooves on a sloping limestone surface. Karst - Minor Forms of. Ref KG |
| RIMSTONE | A deposit formed by precipitation from water flowing over the rim of a pool. Cave - Depositional Features. Ref JJ |
| RIMSTONE DAM | A ridge or rib of rimstone, often curved convexly downstream. Cave - Depositional Features. Ref JJ |
| RIMSTONE POOL | A pool held up by a rimstone dam. Cave - Depositional Features. Ref JJ |
| RIPARIAN | Pertaining to the banks of a river or stream. And expanded to include the perimeter area around dolines, particularly those which act as swallets. Geology. Ref MM |
| RISING | Another term for a spring. A feature where water returns to the surface from an underground body of water. Speleology term. Ref JJ |
| ROCK | A warning given (shouted) when a rock is seen to be falling, or is about to fall, and which could endanger those below. See also "Below". Climbing and SRT. Ref MM |
| ROCK | Any naturally formed coherent and relatively hard mass of mineral matter. Geology. Ref MM |
| ROCK PENDANT | A smooth surfaced projection from the roof of a cave due to solution. Usually occur in groups. Cave - Erosional & Solutional Features. Ref JJ |
| ROCK SHELTER | A cave, often at a cliff base, with more or less level floor extending only a short distance so that no part is beyond daylight. Cave - Kinds of. Ref JJ |
| ROCKHOLE | A shallow small hole in rock outcrops, often rounded in form and holding water after rain. A feature of the Nullarbor Plain. Karst - Minor Forms of. Ref JJ |
| ROCKMILK | See Moonmilk. Speleology term. Ref MM |
| ROCKPILE | A heap of rocks in a cave, usually formed by local collapse, roughly conical in overall shape. Cave - Parts of. Ref JJ |
| ROOF CRUST | A thin speleothem on a cave precipitated from water films exuding from pores or cracks. Cave - Depositional Features. Ref JJ |
| ROOF SNIFFING | Describes progress in a water filled passage with only sufficient air space for the nose to be above the water. Speleology term. Ref MM |
| ROOM | A wider part of a cave than a passage, but not considered as large as a chamber. Cave - Parts of. Ref JJ |
| ROPE PROTECTOR | A length of fabric or plastic hose etc placed around a rope where it may rub against rock. Climbing and SRT. Ref JJ |
| ROPY LAVA | Another term for pahoehoe, especially the type with curved and twisted ridges. Lava Cave term. Ref KG |
| RUNDKARREN | A type of karren. Generally about 200mm wide with rounded profile. Surface karst solution feature consisting of rounded grooves in eg, limestone, normally formed under soil or under heavy litter or moss layers. cf Rillenkarren. Karst - Minor Forms of. Ref MM |