6.5.1. Caves

In areas where there are alternating beds of rocks (shales, sandstones, quartzites) with limestones or dolomites in between or in areas where limestones are dense, massive and occurring as thick beds, cave formation is prominent. Water percolates down either through the materials or through cracks and joints and moves horizontally along bedding planes. It is along these bedding planes that the limestone dissolves and long and narrow to wide gaps called caves result. There can be a maze of caves at different elevations depending upon the limestone beds and intervening rocks. Caves normally have an opening through which cave streams are discharged. Caves having openings at both the ends are called tunnels.

Caves are natural underground spaces formed primarily in limestone. The process begins when rainwater, which absorbs carbon dioxide from the atmosphere, becomes slightly acidic as it hits the ground. This acidic water then seeps through soil and cracks in the rocks. When it reaches limestone, it dissolves the rock, creating cavities over time. These cavities can expand to form caves. The orientation and elevation of these caves depend largely on the geological layers present, as some layers can direct the flow of water. Caves often feature openings, allowing streams to flow in and out, and some may even form tunnels if a passage extends through the rock.

Imagine a sponge soaking up a puddle of water. Just as the sponge absorbs the water and can eventually change shape, limestone will dissolve like the sponge, creating an underground cavity over time. A real-life example of this is Carlsbad Caverns in New Mexico, where countless caves were formed by this process.

Many depositional forms develop within the limestone caves. The chief chemical in limestone is calcium carbonate which is easily soluble in carbonated water (carbon dioxide absorbed rainwater). This calcium carbonate is deposited when the water carrying it in solution evaporates or loses its carbon dioxide as it trickles over rough rock surfaces.

Inside caves, as water drips or flows, it can leave behind minerals it carries. Calcium carbonate, the main component of limestone, is dissolved and then precipitated out as the water loses carbon dioxide or evaporates, leading to the formation of various structures. The most common deposits are stalactites that hang from the ceiling and stalagmites that grow from the floor. If they grow together, they form columns or pillars.

Think about how sugar dissolves in tea. If you leave the tea out for a while, the water will evaporate, and you might see sugar crystals forming at the bottom. Similarly, in caves, as water evaporates, it leaves behind minerals that create beautiful and unique formations.

Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms. Stalagmites rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the surface or through the thin pipe, of the stalactite, immediately below it. The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.

Stalactites and stalagmites are key features found in limestone caves. Stalactites are formed by mineral-rich water dripping from the cave ceiling and leaving behind deposits as it falls. The water evaporates leaving calcium carbonate behind, causing the stalactite to grow downward. Conversely, stalagmites develop on the cave floor from the same dripping water, building upward. Over time, if conditions permit, the two can merge to form a pillar. This process takes thousands of years, leading to the fascinating formations we see today.

Visualize a frozen icicle hanging from a rooftop during winter. Just like it grows from water dripping and freezing, stalactites grow from minerals in water dripping from the cave ceiling. If you've ever seen a huge stalagmite in a cave, think of it as a rock version of a tree trunk growing up from the cave floor!

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