Borra Caves
History
In 1807, William King George of the Geological Survey of India discovered the caves.[5]
Legend
On the discovery of the caves, there are several legends, which the tribals (Jatapu, Porja, Kondadora, Nookadora, valmiki etc.[4]) who inhabit the villages around the caves narrate. The popular legend is that a cow, grazing on the top of the caves, dropped 60 m (196.9 ft), through a hole in the roof. The cowherd while searching for the cow came across the caves. He found a stone inside the cave that resembled a Lingam, which he interpreted as the Lord Shiva who protected the cow. The village folk who heard the story believed it and since then they have built a small temple for Lord Shiva outside the cave. People flock to the temple for worship and the cave to get a glimpse of the Lingam.[5]
Another lyrical legend is that the Shiva Lingam representing the Hindu God Lord Shiva, is found deep in the caves and above which is a stone formation of a cow (Sanskrit: Kamadhenu). It is surmised that the udder of this cow is the source of the Gosthani (Sanskrit: Cow’s udder) River which originates from here, flows through Orissa before debouching into the Bay of Bengal.[5]
Geography and climate
The caves are located in the Araku Valley of the Ananthagiri hill range and is drained by the Gosthani River. At the entry, the cave measures up to 100 m (328.1 ft) horizontally and 75 m (246.1 ft) vertically. Stalagmite and Stalactite formations are found in the caves.[6] The average annual temperature of Araku hills, where the caves are situated, is about 25 °C (77.0 °F). The average annual rainfall reported is 950 mm (3.1 ft) (mostly occurring during the northeast monsoon).[7] The Gosthani river provides water supply to the Visakhapatnam city.[4]
[edit] Geology
The Regional Geology in the Eastern Ghats mobile belt, where the caves are located, is represented by the Khondalite suite of rocks (garnetiferrous sillimanite gneisses, quartzo-feldsphatic garnet gneisses) of Archaen age. Quaternary deposits consist of red bed sediments, laterites, pediment fans, colluvium, alluvium and coastal sands. Particularly, the Borra caves are stated to be one of the largest caves in the Indian subcontinent.[1] The caves, in the reserved forest area consisting of 14 villages inhabited by tribals, basically host a variety of speleothems ranging from very small to big and irregularly shaped stalactites and stalagmites. The carbonate rocks are pure white, and coarsely crystalline and the deformed and banded marbles cover a triangular area of 2 km2 (0.8 sq mi); surrounded by Diopside–scapolite–feldspar calc-granulites. The pyroxenite outcrops are dark and massive and include discontinuous calc-silicate bands, some of brown mica and others with calcite.[7] The Gosthani River, which originates from these caves and flows between the solidified stalactites and stalagmites in the Karstic lime stones formation, is the cause for the development of the odd shapes of structures. Water percolating from the roof of the caves dissolve limestone and trickle drop by drop to form stalactite at the roof of the cave and then dripping down to the ground form stalagmite. (see picture). Stalactites are calcium carbonate deposits that hang from the top of the cave. Stalagmites are deposits that form at the bottom of the cave and grow upward. These deposits have developed into interesting forms and structures inside the caves such as Shiva –Parvati, Mother–Child, Rishi’s beard, Human brain, mushrooms, crocodile, temple, church, etc. These shapes have captured the imagination of tourists, while some have been given religious interpretations.[7][8] The Caves are deep and totally aphotic. There is a twilight zone in the caves with limited light penetration. The Stalactites seen in the caves are about 0.1 m (0.3 ft) to 3.5 m (11.5 ft) in length while the Stalagmites are 1.2 m (3.9 ft) long and columns are 6 m (19.7 ft) in height and 0.75 m (2.5 ft) in width. The height of the cave is 12 m (39.4 ft) and the length is about 200 m (656.2 ft). The average temperature of the inner cave wall is reported to be about 16 °C (60.8 °F). Sulphur springs discharge into the cave passages causing corrosion of limestone. The spring waters display floating Mucus-like biofilms. These are thick orange microbial mats (2.5 cm (1.0 in)–3 cm (1.2 in) thick) with patches of yellow biofilms extending 3 m (9.8 ft) from the aphotic deep cave orifice.[7] While the caves are basically limestone formations, the area surrounding these are of mica formations which are prospected for precious stones like rubies.[6] The geological features of these caves are stated to be found only in Borra in India. Archeological artifacts (Paleolithic implements) have been found in the caves.[9] The excavations carried out in the caves by the Archeologists of the Andhra University, have unearthed stone tools of middle Paleolithic culture dating back to 30,000 to 50,000 years, which confirm human habitation.[4]
Genesis
Speleothem carbonates (considered as inorganic precipitates) found in the caves have been subject to scientific studies. In fluviatile, spring, cave and soil environments Microbial carbonates are important. In the biofilms and/or microbial mats, which are formed in the caves, the principal organisms associated are bacteria, particularly cyanobacteria, small algae and fungi. Petrographic analysis of a thin section has uncovered the presence of lithified structures and micrite, present as laminated to clotted with chocolate-brown blebs. These are identical to microbialites observed in modern and ancient stromatolitic carbonates. Laboratory observations with Scanning Electron Microscope (SEM) have also confirmed the presence of calcified bacteria, micro-rods, and needle calcite. Organic mats (yellow-orange in colour) comprise of mineralized filamentous bacteria, bacterial stalks, cells and sheaths. Thus, these studies have indicated that biological (microorganisms) have actively influenced in the genesis of speleothem carbonates of the Borra Caves.[7]
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