Cave Features

Taken from http://www.bermudatourism.com/nat_fea.html
cause I hope to learn more about cave features :)

What happens when water meets limestone? What role does calcium carbonate play in what you see when you visit our caves? The answer to both questions: a lot! What most fascinates visitors to our caves are the amazing mineral deposits which occur in this naturally wet limestone environment. All of our cave formations have formed due to water seeping, flowing, retreating, and dripping. Of course, “Going with the flow” has always been natural in Bermuda. Even 80 feet underground!

These beautiful mineral deposits are called speleothems and listed below are some of the more remarkable features to be found in Bermudian caves:

Stalactites
In order to understand and appreciate stalactites, one must realize that it is from sliver-thin soda straws that these giants grow. Look at the ceilings of our caves. Notice how damp they are and how thin “icicles” hang from above. These “icicles” are actually soda straws or adolescent stalactites. These hollow tubes contain water and calcite crystals. As the water slowly drips through the straw, a bit of calcium carbonate is precipitated from the water and added to the end of the soda straw. This is what makes these soda straws grow downward.

And, of course, due to the damp nature of cave ceilings, most soda straws also conduct water on their external surfaces as well. In so doing, the same miraculous growth process occurs: Water flows down, heeding the call of gravity, and a little calcium carbonate is left behind. This adds to the width of the soda straws. Over time, the external growth of the soda straw blocks its hollow core, the internal flow ceases and the soda straw becomes a stalactite, which will be added to externally over the centuries.

NOTE: An important thing to know about stalactites is how to differentiate them from their similar sounding, but very opposite appearing neighbors, the stalagmites. One easy way is to remember the “c” in stalactite. That’s “c” for “ceiling.” Another way is to make the association that stalactites hang “tite” to the ceiling.

Stalagmites
Stalagmites are perhaps one of the most closely observed cave formations because they are generally at ground level. When you are in a cave, close your eyes and listen. More than likely you will hear the sound of water dripping from the ceiling. What you are actually listening to may be the birth or growth of a stalagmite! These mounds are always reaching upward. And it is because of the wet nature of cave ceilings that stalagmites are formed in the first place. The water dripping from above contains calcium carbonate and as this water drips, it evaporates and leaves calcium deposited on the ground. The minerals begin to form a mound on the cave floor or ledges and eventually, if the conditions are just right, a stalagmite grows as—drop by drop and layer by layer—minerals are deposited continuously in the same spot.

Because stalagmites do not have to fight gravity the way stalactites do, they can grow much larger and heavier. Stalagmites have a great variety of possible shapes—from delicate and complex towers to wide disks to spindly “broomsticks.” There is one thing that most stalagmites have in common, though. They generally have blunted or rounded ends. This knowledge can come in handy if you ever see cave photos—especially the ones that feature lakes—and you can’t quite tell which way is up. Stalactites conversely, generally have very pointy tips.

NOTE: Perhaps you have already read the section about Stalactites. If so, here is the second part of the equation which will help you remember the difference between stalactites and stalagmites: the “g” in stalagmite is useful for remembering “ground.” Stalagmites form on the ground. Of course, the other way to remember the difference is to associate the “mite” in stalagmite to “it just mite make it up to the ceiling” or that stalagmites hold “mite” to the ground.

Flowstone
Perhaps the most common of all cave deposits, flowstone is formed in thin layers over existing features on the cave floor, ledges, or wall bedrock. Picture a cake to which someone keeps applying very thin layers of icing. The first several layers of icing will not usually hide the pronounced shape of the cake. However, icing layers six, seven, eight (and so on…) will successively obscure the cake’s shape and as the icing gets thicker, what once appeared to be a cake will become a thick, rounded mound. The icing has basically taken on “a life of its own” beyond the initial shape of the cake. This is very simply the way flowstone is formed. Water flows down walls and ledges and deposits calcite in layers. As a result of these rounding layers, flowstone may take the appearance of waterfalls. Or draperies, or even bacon.

Rimstone
Because caves are basically born of water, it should come as no surprise to find pools in many caves. But what a delightful sight these underground pools and streams are. Usually filled with extremely still, clear water, cave pools offer us a view of fairyland by perfectly mirroring the ceilings and other features of the cave. It is at the edges of these underground pools, that one finds the amazing cave feature called rimstone. Rimstone is usually made of calcite and forms dams around underground pools and streams. Sometimes these dams even have a stair step appearance. Rimstone dams form where there is a downward flow leading to the edge of a pool. And, very often rimstone is an extension of flowstone.

Soda Straws
Think of soda straws as stalactites in their infancy. They are made of calcite and are remarkably delicate and beautiful—often appearing as translucent thin glass rods. Soda straws are very appropriately named as they are simply long, hollow tubes. These remarkable speleothems are only as wide as the diameter of the single water drops which pass through them. Soda straws basically do the job of transporting water drops down from the ceiling of the cave towards the floor of the cave one drop at a time; at this, they excel. When the transported drops of water finally reach the open end of the soda straw, they may hang suspended in the air before falling. It is while clinging to the growing tip of the straw that the water drop loses carbon dioxide to the air in the cave. But, in losing carbon dioxide, the water drop precipitates calcium carbonate. This mineral is added to the end of the straw, lengthening it. Sometimes soda straws reach remarkable lengths before maturing into stalactites.

Cave Pearls
Most everyone knows that pearls are formed by successively layering minerals over a single grain of sand. And cave pearls are no different. They often begin with a grain of sand too, although they can also form on a piece of bone, fragments of soda straws or other foreign matter. Usually found in pools, cave pearls can be many different shapes and sizes, but the most well-known is the polished, spherical variety, which closely resembles the pearls found in oysters. As usual for most cave features, cave pearls form when water dripping into the pool loses carbon dioxide and precipitates calcite. Sometimes groups of totally unattached pearls are encountered lying within small cups in the cave. Experts believe that these pearls do not become attached because water dripping from above causes a constant subtle movement of the pearls.