Geography · Ch 12 — Landforms and their Evolution
Stalactites, Stalagmites and Pillars
Stalactites, Stalagmites and Pillars
The diagram is a pair of black-and-white photographs taken inside a limestone cave, presented side by side to show the two complementary growth forms that develop from dripping water. In the upper part of the frame, the cave ceiling is lined with numerous stalactites — long, icicle-like projections hanging downward. They are not uniform: some are thick and broad where they attach to the ceiling, tapering toward their free lower ends, while others are thinner and more pipe-like. The photograph captures them in clusters, giving the ceiling a jagged, fanged appearance.
Below them, on the cave floor, the corresponding stalagmites rise as mounds of varying height and shape. Some are squat and rounded, others rise into taller columns with smooth, bulging tops, and a few show a small crater-like depression at their summit — the mark left by repeated drops of water striking the same spot. In places, a stalactite and the stalagmite directly beneath it have grown long enough to meet, fusing into a single continuous pillar that spans from floor to ceiling. These fused forms are the "columns and pillars" the section describes, and the photographs show them at different stages: some barely separated, others already joined. …
Caves are not empty chambers. Water that seeps through limestone carries dissolved calcium carbonate, and as that water drips from the cave ceiling, it slowly deposits the mineral back. Over long spans of time, these deposits build into the dramatic rock forms that decorate caves — and the most famous of these are stalactites, stalagmites, and the pillars they eventually create together.
Stalactites hang downward from the ceiling of a cave, looking like icicles of different diameters. They are normally broad at their bases — where they attach to the ceiling — and taper towards their free ends. Because dripping water follows slightly different paths and carries different amounts of dissolved material, stalactites show up in a variety of forms, not just the classic pointed spike.
Stalagmites rise up from the floor of the cave, directly beneath the stalactites. They form because of the dripping water itself: when water falls from the cave surface, or drips through the thin pipe of a stalactite, it strikes the floor immediately below and deposits its dissolved load there. Over time, this builds upward. Stalagmites may take the shape of a column or a disc, and their tops can end in different ways — either with a smooth, rounded bulging end or with a miniature crater-like depression. …
Many depositional forms develop within 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. Stalactites hang as icicles of different diameters from the cave roof, normally broad at their bases and tapering towards the free ends, showing up in a variety of forms. Stalagmites rise up from the floor of the caves, forming due to dripping water from the surface or through the thin pipe of the stalactite immediately above it; they may take the shape of a column, a disc, with either a smooth, rounded bulging end or a min …