Lava tube

•  Karst topography

  Karst topography is a landscape shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone or dolomite. Due to subterranean drainage, there may be very limited surface water, even to the absence of all rivers and lakes. Many karst regions display distinctive surface features, with sinkholes or dolines being the most common.

  

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•  Calcite

  Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 470°C, and vaterite is even less stable.

  

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•  Rock shelter

  A rock shelter (also known as a rockhouse, crepuscular cave, or abri) is a shallow cave-like opening at the base of a bluff or cliff. 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. Many rock shelters are found under waterfalls. Rock shelters are often important archaeologically.

  

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•  Aragonite

  Aragonite is a carbonate mineral, one of the two common, naturally occurring crystal forms of calcium carbonate, CaCO3 It is formed by biological and physical processes, including precipitation from marine and freshwater environments. Aragonite's crystal lattice differs from that of calcite, resulting in a different crystal shape, an orthorhombic system with acicular crystals. Repeated twinning results in pseudo-hexagonal forms.

  

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•  Sinkhole

  A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or cenote, is a natural depression or hole in the surface topography caused by the removal of soil or bedrock, often both, by water. Sinkholes may vary in size from less than a meter to several hundred meters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. They may be formed gradually or suddenly, and are found worldwide.

  

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•  Grotto

  A grotto (Italian grotta) is any type of natural or artificial cave that is associated with modern, historic or prehistoric use by humans. When it is not an artificial garden feature, a grotto is often a small cave near water and often flooded or liable to flood at high tide. The picturesque Grotta Azzura at Capri and the grotto of the villa of Tiberius in the Bay of Naples are outstanding natural seashore grottoes.

  

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•  List of important publications in geology

  Author: Charles Lyell Publication data: 1830–1833. Online version: Online version at esp.

  

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•  Blowhole (geology)

  In geology, a blowhole is formed as sea caves grow landwards and upwards into vertical shafts and expose themselves towards the surface, which can result in quite spectacular blasts of water from the top of the blowhole if the geometry of the cave and blowhole and state of the weather are appropriate.

  

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•  Cenote

  A cenote is a sinkhole with exposed rocky edges containing groundwater. It is typically found in the Yucatán Peninsula and some nearby Caribbean islands. The term is derived from a word used by the low-land Yucatec Maya to refer to any location where groundwater is accessible.

  

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•  Bashful elephant

  The Bashful elephant is the name given to a small stalagmite in Carlsbad Caverns, New Mexico, that has grown a bulbous top with stalactites hanging off creating "legs. " Its shape gives the impression that it is facing away from the viewer.

  

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•  Viking 2

  The Viking 2 mission was part of the Viking program to Mars, and consisted of an orbiter and a lander essentially identical to that of the Viking 1 mission. The Viking 2 lander operated on the surface for 1,281 Mars days and was turned off on 11 April 1980 when its batteries failed. The orbiter worked until 25 July 1978, returning almost 16,000 images in 706 orbits around Mars.

  

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•  Preben Elkjær Larsen

  Preben Elkjær Larsen (born 11 September 1957), in Denmark simply referred to as Preben Elkjær, is a Danish former professional football player, who played in the striker position. He won the 1978 German Cup with 1. FC Köln and the 1985 Serie A with Italian club Hellas Verona. In 1984, Elkjær finished third and in 1985 second in the European Footballer of the Year awards.

  

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•  Mercatino Conca

  Mercatino Conca is a comune (municipality) in the Province of Pesaro e Urbino in the Italian region Marche, located about 90 km northwest of Ancona and about 35 km west of Pesaro. Mercatino Conca borders the following municipalities: Auditore, Gemmano, Monte Cerignone, Monte Grimano, Sassocorvaro, Sassofeltrio, Tavoleto.

  

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•  Priscilla Sebastian

  

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•  Builder's Labourers Federation

  

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