12 February, 2011

When Water Tears the Stone

           Caves are natural openings in the Earth large enough for a person to get in. According to some the term 'Cave' can be applied only to a place some part of which remains in total darkness but in popular usage this name is given to any cavity in the earth either made by flowing water, eruption of volcanoes or even the melting of a glacier from inside. Most of the caves on earth have been made when rainwater or streams have worn away rock – usually a softer rock such as limestone. This process of wearing-away is called ‘erosion’ and the caves formed in this process are called solutional caves. Usually acidic water causes them to form.
            Even if water is not acidic, over millions of years, it weas away the soft rock, making a small tunnel-like opening inside. As more and more rock wears away, the opening grows even wider and deeper until in time, many of these openings become huge caves, or caverns.
            Mammoth Cave-Flint Ridge in Kentucky, U.S. is one of the longest in the world. It is a linked system of caves and caverns about 555 kilometers long.  In France the Jean Bernard Cave is considered the largest cave on our blue marble: planet earth. Though it is much shorter (17.9 kilometres long), than Mammoth Cave-Flint, it is considered as the deepest cave in the world. It reaches down more than 1,535 meters (meaning an enormously deep natural formation).
            Some caves have beautiful craggy formations called ‘stalactites’ that hang from the cave’s roof like beautiful ornametal decoration pieces. These are made by water seeping into the cave. Each drop leaves a very tiny bit of dissolved rock on the ceiling of the cave. After thousands and thousands of years, an icicle-shaped stalactite forms.
            When water drips to the cave’s floor, it deposits small particles of solids. These slowly build up into a stalagmite, which looks like an upside-down icicle.
            There are other kinds of caves that are made in different ways. When lava flows out of a volcano, it sometimes leaves gaps, making volcanic caves. When ice melts inside a glacier, glacier caves result. And ocean waves pounding on the shore year after year can wear away a cave in the face of a cliff.

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