Fracture cave

Intriguing, mysterious, eerie, call them whatever you like, caves have fascinated man from time immemorial. Caves are found throughout the world and there are many caves even in Sri Lanka. To most of you a cave may be just another geological formation that is similar to a tunnel. But you will be amazed to learn that there are a number of different types of caves in existence around the world and some of them are considered to be unique in their features. So, let us go on a trek into the world of caves to discover some fascinating facts about these natural cavities in the land or sea.

Sea cave

Glacier cave

A cave or cavern as it is also called is generally an underground space or a cavity which is usually in total darkness and large enough for a human to enter. Even small spaces like rock shelters, and grottos are also considered as caves.

There may be millions of caves all over the world but not all of them have been explored and documented. Most of the caves that have been discovered and documented by those who explore caves are the caves in countries where caving has been popular. Some of these countries are Italy, France, the United Kingdom, Australia and the United States of America.

Throughout history, primitive people have made use of caves for shelter, burial, or as religious sites. Since items placed in caves are protected from the climate and scavenging animals, this means caves are an archaeological treasure house for learning about these people. Cave paintings are of particular interest.

Do you know how caves are formed? They are formed by various geologic processes. These may involve a combination of chemical processes, erosion from water, tectonic forces, micro-organisms, pressure, atmospheric influence, and even digging. Most caves are formed in limestone by dissolution. They are formed over thousands of years by water.

What happens is that rain mixes with carbon dioxide in the air and forms a weak solution of carbonic acid. This ‘acid rain’ dissolves limestone and forms caves over time. Some limestone caves like Carlsbad Caverns are formed by rainwater mixing with hydrogen sulfide in the earth.

This creates a weak solution of sulfuric acid which also dissolves limestone.

Limestone cave

Sea cave

Talus cave

In either case, other minerals are dissolved by the acidic water which then drips inside the cave. Over many years this dripping deposits the minerals in the form of stalactites and stalagmites and other beautiful formations.

As we mentioned earlier, there are various types of caves formed as a result of any one of the above mentioned processes. There are solutional caves, primary caves, sea caves or littoral caves, corrasional or erosional caves, glacier caves, fracture caves, talus caves, and anchhaline caves to name a few. From among these caves, the most frequently occurring caves are the ones which are called solutional caves or limetone caves. These caves are formed in soluble rock such as limestone. They can also form in other types of rock which includes dolomite, chalk, salt, marble and gypsum. What appears as cracks initially expand into caves or cave systems over the many years as a result of geological changes.

The largest and most abundant solutional caves are located in limestone and are often adorned with calcium carbonate formations produced through slow precipitation.

According to researchers, portions of a solutional cave that are below the water table or the local level of the groundwater generally get flooded. Lechuguilla Cave in New Mexico and nearby Carlsbad Cavern are now believed to be examples of another type of solutional cave.

Glacier cave

Lava tube

Caves which are formed at the same time as the surrounding rock are sometimes called primary caves. The most common primary caves are Lava tubes formed through volcanic activity. When the lava flows downhill the surface cools and solidifies. Sometimes when the hotter lava continues to flow under that crust, most of the liquid lava beneath the crust flows out, leaving a hollow tub-like formation which is called a cavity.

These type of caves can be found in Hawaii and the Canary Islands, and also many other places. Lava caves, include but are not limited to lava tubes. Other caves formed through volcanic activity include rift caves, lava mold caves, open vertical volcanic conduits, and inflationary caves.

There are many caves which form along coasts around the world and they are called sea caves. Littoral caves are formed by wave action in areas where the sea cliffs are weak. Often these weaknesses are faults, but they may also be dykes or bedding-plane contacts.

Sea caves are generally around five to fifty metres (16 to 160 ft) in length. There are some sea caves that exceed 300 metres (980 ft).

Corrasional or erosional caves are those that form entirely by erosion that takes place due to the rocks and sediments carried by flowing streams.

These can form in any type of rock, including hard rocks such as granite. Generally there must be some zone of weakness to guide the water, such as a fault or joint. A subtype of the erosional cave is the wind or aeolian cave, carved by wind-born sediments.

Many caves formed initially by solutional processes often undergo a subsequent phase of erosional or vadose enlargement where active streams or rivers pass through them.

Then there are glacier caves - those which form in ice and under glaciers as a result of melting ice. They are also influenced by the very slow flow of the ice, which tends to close the caves again. (These are sometimes called ice caves, though this term is properly reserved for caves that contain year-round ice formations).

Fracture caves are formed when layers of more soluble minerals, such as gypsum, dissolve out from between layers of less soluble rock.

These rocks fracture and collapse in blocks of stone. The openings between rocks that have fallen down into a pile, often at the bases of cliffs are called talus caves.

Anchihaline caves occur in many parts of the world, and often contain highly specialised and endemic faunas. They are caves, usually coastal, containing a mixture of freshwater and saline water (sea water).

More on caves next week.

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FAST FACTS

* A large number of explored caves are found in Europe, Asia, North America and Oceania. However, they are not as abundant in Africa, Antarctica and South America .

* China contains half of the world’s limestone (more than 1,000,000 square mi) but it has very few documented caves,

* The science of exploration and study of all aspects of caves and the environment which surrounds the caves is known as Speleology.

* Exploring a cave for recreation or science may be called caving, potholing, or in Canada and the United States, spelunking

* Kazumura Cave near Hilo is a remarkably long and deep lava tube cave. It is 65.6 km long (40.8 mi).

* Great Cave of Niah, in Malaysia, which contains evidence of human habitation dating back 40,000 years.

* The Diepkloof Rock Shelter in South Africa contains evidence of human habitation and use of symbols dating back 60,000 years.

* A lava tube of significant academic value has been found in the Geomunoreum Lava Tube System, a UNESCO World Heritage site in Jeju. The cave, is over 100 m long, 5 m wide and 1.8 m high.

While lava cave products including the lave flow traces on the wall are well preserved, it also features picturesque characteristics of lime caves such as stalactites and stalagmites.

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RECORD HOLDERS

* The cave system with the greatest total length of surveyed passage is Mammoth Cave (Kentucky, USA) at 628 kilometres (390 mi) in length. This record is unlikely to be surpassed in the near future, as the next most extensive known cave is Jewel Cave near Custer, South Dakota, at 242 kilometres (150 mi)

* The longest surveyed underwater cave is Sistema Sac Actun in Yucatin, Mexico at 215 km (134 mi). The record has been exchanged several times with Sistema Ox Bel Ha, currently at 182 kilometres (113 mi).

* The deepest known cave (measured from its highest entrance to its lowest point) is Voronya Cave (Abkhazia), with a depth of 2,191 metres (7,188 ft). This was the first cave to be explored to a depth of more than two kilometres (1.2 mi). The first cave to be descended below one kilometre (0.62 mi) was the famous Gouffre Berger in France.) The Illyuzia-Mezhonnogo-Snezhnaya cave in Abkhazia, (1,753 metres or 5,751 feet) and the Lamprechtsofen Vogelschacht Weg Schacht in Austria (1,632 metres or 5,354 feet) are the current second- and third-deepest caves. The deepest cave record has changed several times in recent years.

* The deepest vertical shaft in a cave is 603 metres (1,978 ft) in Vrtoglavica Cave in Slovenia. The second deepest is Patkov Gu ít at 553 metres (1,814 ft) in the Velebit mountain, Croatia.

* The largest cave room ever discovered is the Sarawak Chamber, in the Gunung Mulu National Park (Miri, Sarawak, Borneo, Malaysia), a sloping, boulder strewn chamber with an area of approximately 700 by 400 metres (2,297 by 1,312 ft) and a height of 80 metres (260 ft). The nearby Clearwater Cave System is believed to be the world’s largest cave by volume, with a calculated volume of 30,347,540 m3.

* The largest passage ever discovered is in the Son Doong Cave in Phong Nha-Ke Bang National Park in Quang Binh Province, Vietnam. Explored by joint Vietnamese-British cave scientists of the British Cave Research Association, it is 4.6 km (2.9 mi) in length, 80 m (260 ft) high and wide over most of its length, but over 140 m (460 ft) high and wide for part of its length.

World’s five longest surveyed caves

* Mammoth Cave, Kentucky, USA

* Jewel Cave, South Dakota, USA

* Optymistychna Cave, Ukraine

* Wind Cave, South Dakota, USA

* Sistema Sac Actun, Mexico.

Facts and pix: Internet