Caves

Caves played an important role in people's development of the Earth's surface. They served as natural shelters against rain and snow, wild animals and blood-thirsty neighbours.  Most ancient primitive man sites in caves with galleries of wall drawings were dated back as far as 15,000- 17,000 years (Altamir in Spain, Lasco in France) and even back as far as 31,000 years (Chove in France).  Many caves have been providing not only a shelter, but also water from under­ground streams and lakes.

 

The major number of caves de­velops in easy-soluble rocks of lime­stone, dolomite, and rarely in gypsum, salt, and similar sedimentary rocks.  Water dissolves rock and takes away its components, depositing them else­where. 

 

The process of rock dissolu­tion, deposition of dissolved material, and development of specific relief fea­tures is called karst process. Karst is termed after Karst Plateau in Slovenia.  Kras is a local Slovenian name.

 

Development of karst relief be­gins with uneven erosion of the Earth's surface with formation of sink holes, e.g., furrows and holes separated by uneroded residual rock of different forms.  More inten­sive erosion takes piece along frac­tures.  At their intersection, there are small funnels (ponors), through which water channels downward and gives rise to underground streams, rivers and lakes.

 

Underground water creates caves with numerous halls connected via corridors and shafts, and then it often gets back to the surface, producing as­cending springs or vauclus­es (after Vaucluse Karst Spring in France). Disappearing lakes located within funnels also relate to karst.  They are being filled with water dur­ing snow melting season and during years with abundant precipitation.  Then, water is disappearing.  This may happen slowly or very fast, when a deep obstacle is broken through, and the funnel remains empty and dry.

 

Stalactites and stalagmites create a specific appearance of karst caves, Stalactites develop, when water con­tains dissolved calcium carbonate and percolates through the cave ceiling.  Water leaks out of rock to the cave hollow and deposits calcite crystals. 

 

With time, they form a stone icicle with narrow end. Water, dropping down from its end on the cave floor, also deposits calcite.  Gra­dually, a candle of stalagmite grows up towards stalactite, hanging from the ceiling (like in the Sorek Cave in Israel,  or in the Italian cave). 

 

Various deviations from a simple scheme of formation result in confluence of stalactites and forma­tion of curtains (like in the caves of South Africa) or umbrel­las on stalagmites (Ponoare Cave in Romania) and fantastic lace pagodas (Guacharo Cave in Vene­zuela, Tropfstein Cave in Austria).

 

Stalactites and sta­lagmites grow very slowly.  For in­stance, it was calculated that the 9m ­high Kleopatra's Needle Stalactite in the Cango Cave System in the South African Republic has being grown during 150.000 years.

 

Karst caves, funnels, cavities, dis­appearing lakes and rivers are not on­ly beautiful tourist sites.  Often, these are mineral deposits. 

 

Significant re­sources of oil and fuel gas in the USA, Canada, Mexico, and other countries relate to karst rocks.  Bauxite is being mined from karst deposits on Jamaica Island; karst hosts zinc ores in the Missouri State, USA; saltpeter is known in the Kentucky State.

 

A water supply of the Cuban capital of Havana is based on karst waters. 

 

Text from: V.I. Feldman, Philatekic Geology - 2000 - revised by Grubessi O. 2008 

 

Last modified: Mercoledì 8 gennaio 2014

 

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