Speleology is the science of exploration and study of all aspects of caves and the cave environment.
A cave is a hollow place in the ground, specifically a natural underground space large enough for a human to enter. Caves form naturally by the weathering of rock and often extend deep underground. The word cave can also refer to much smaller openings such as sea caves, rock shelters, and grottos.
Sea Caves
A sea cave, also known as a littoral cave, is a type of cave formed primarily by the wave action of the sea. The primary process involved is erosion. Sea caves are found throughout the world, actively forming along present coastlines and as relict sea caves on former coastlines. Littoral caves may be found in a wide variety of host rocks, ranging from sedimentary to metamorphic to igneous, but caves in the latter tend to be larger due to the greater strength of the host rock. The driving force in littoral cave development is wave action. Erosion is ongoing anywhere that waves batter rocky coasts, but where sea cliffs contain zones of weakness, rock is removed at a greater rate along these zones. As the sea reaches into the fissures thus formed, they begin to widen and deepen due to the tremendous force exerted within a confined space, not only by direct action of the surf and any rock particles that it bears, but also by compression of air within. True littoral caves should not be confused with inland caves that have been intersected and revealed when a sea cliff line is eroded back, or with dissolutional voids formed in the littoral zone on tropical islands.
Rock Shelters
A rock shelter — also rockhouse, crepuscular cave, bluff shelter, or abri — is a shallow cave-like opening at the base of a bluff or cliff. In contrast to solutional cave (karst) caves, which are often many miles long, rock shelters are almost always modest in size and extent. Rock shelters form because a rock stratum such as sandstone that is resistant to erosion and weathering has formed a cliff or bluff, but a softer stratum, more subject to erosion and weathering, lies just below the resistant stratum, and thus undercuts the cliff.
In arid areas, wind erosion (eolian erosion) can be an important factor in rockhouse formation. In most humid areas, the most important factor in rockhouse formation is frost spalling, where the softer, more porous rock underneath is pushed off, tiny pieces at a time, by frost expansion from water frozen in the pores. Erosion from moving water is seldom a significant factor.
Grotto
A grotto (Italian grotta and French grotte) is a natural or artificial cave used by humans in both modern times and antiquity, and historically or prehistorically. Naturally occurring grottoes are often small caves near water that are usually flooded or liable to flood at high tide. Sometimes, artificial grottoes are used as garden features.
Whether in tidal water or high up in hills, grottoes are generally made up of limestone geology, where the acidity of standing water has dissolved the carbonates in the rock matrix as it passes through what were originally small fissures.
Caverns
A cavern is a specific type of cave, naturally formed in soluble rock with the ability to grow speleothems. Speleothms are secondary mineral deposits formed in a cave. Speleothems typically form in limestone or dolostone solutional caves. Speleothems take various forms, depending on whether the water drips, seeps, condenses, flows, or ponds. Many speleothems are named for their resemblance to man-made or natural objects. Types of speleothems include: Stalactites, Soda straws, Helictites, and Stalagmites.
Limestone
Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).
About 10% of sedimentary rocks are limestones. The solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock.
Limestone has numerous uses: as a building material, an essential component of concrete (Portland cement), as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. These organisms secrete shells made of aragonite or calcite, and leave these shells behind when they die. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and extraclasts.
Limestone often contains variable amounts of silica in the form of chert (chalcedony, flint, jasper, etc.) or siliceous skeletal fragment (sponge spicules, diatoms, radiolarians), and varying amounts of clay, silt and sand (terrestrial detritus) carried in by rivers.
Some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular (oolite) appearance.
Sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) mineral particles or rock fragments.
Most sandstone is composed of quartz or feldspar because they are the most resistant minerals to weathering processes at the Earth's surface, as seen in Bowen's reaction series. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, brown, yellow, red, grey, pink, white, and black. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone have been strongly identified with certain regions.
Rock formations that are primarily composed of sandstone usually allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are better able to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity.
Quartz-bearing sandstone can be converted into quartzite through metamorphism, usually related to tectonic compression within orogenic belts.
Basalt
Basalt is an aphanitic (fine-grained) igneous rock with generally 45-53% silica (SiO2)[2] and less than 10% feldspathoid by volume, and where at least 65% of the rock is feldspar in the form of plagioclase. This is as per definition of the International Union of Geological Sciences (IUGS) classification scheme. It is the most common volcanic rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands, including Iceland, the Faroe Islands, Réunion and the islands of Hawaii. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains. The average density is 3.0 g/cm3.
Basalt is defined by its mineral content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic (iron-rich) minerals into hematite and other iron oxides and hydroxides. Although usually characterized as "dark", basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured, superficially resembling andesite to untrained eyes. Basalt has a fine-grained mineral texture due to the molten rock cooling too quickly for large mineral crystals to grow; it is often porphyritic, containing larger crystals (phenocrysts) formed prior to the extrusion that brought the magma to the surface, embedded in a finer-grained matrix. These phenocrysts usually are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt.
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1. What type of cave is this a sea cave, Rock Shelter, Grotto or a cavern and explain your answer.
2. Take a look inside the cave and observe the colour, texture and formation. Based on these observations, what type of rock is this cave, limestone, sandstone or basalt? Explain your answer
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Information from
Sjöberg, Rabbe (1988). "Coastal Caves Indicating Preglacial Morphology in Norway". Cave Science, The Transactions of the British Cave Research Association.
National Caves Association.