Ice columns appear in many caves or caverns. They are called stalactites and stalagmites. Stalactites are the stony deposits hanging like icicles from roofs of the caves. Stalagmites are similar deposits rising in columns and cones from floors of the caves. Do you know how are they formed?
Most of the caves occur chiefly in lime stone and chalk formations. Limestone is a fairly soft rock mainly made of calcium carbonate that can be dissolved by a weak acid. The acid that dissolves limestone comes from rain water. Falling drops of rain pick up carbon-dioxide from the air. This carbon dioxide changes the rain water into carbonic acid that dissolves the limestone. The seepage of water down the cave walls and through the roof produces constant dripping and evaporation. Stone icicles formed on the cave roof, slowly grow with the addition of successive layers of calcium carbonate. The word ‘stalactite’ has Greek origin and means ‘drop by drop’. This is why these stone icicles are also known as “dripstone”.
At the initial stage, the stalactite remains hollow due to faster, carbonate deposit at the outer ring of the water drops. However it slowly turns to solid when the cavity fills up in the process of evaporating the water particles from the mineral substances.
If the seepage of water is quick the drop might fall on the cave’s floor. It deposits its calcium carbonate there and cones and domes of stone are formed. These are called as stalagmites. They may grow up to join the stalactites above and form single columns. They may even grow as high as to block the entrance of the cave. Each stalactite or stalagmite grows at a different rate, depending on the wetness of the cave, the inside temperature of the cave and the thickness of the limestone bed above it. Some stalactite might grow an inch a year while others would take one hundred years or so to grow that much. When water stops reaching the underground caves, the stalactites stop growing and the cave is considered “dead”.