Stalagmites and Stalactites

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Harrison’s Cave, An Underground Adventure in Barbados

Stalagmites and Stalactites 
Stalagmites /  Stalactites

Stalactites and stalagmites are formed by water dripping or flowing from fractures on the ceiling of a cave . They are the most common types of speleothems in caves. In caves, stalagmites grow rather slowly—0.00028–0.037 in/yr (0.007–0.929 mm/yr)—while in artificial tunnels and basements they grow much faster. Soda straw stalactites are the fastest growing (up to 1.57 in/yr, 40 mm/yr), but most fragile stalactites in caves. Soda straw stalactites form along a drop of water and continue growing down from the cave ceiling forming a tubular stalactite, which resembles a drinking straw in appearance. Their internal diameter is exactly equal to the diameter of the water drop. Formation of most stalactites is initiated as soda straws. If water flows on their external surface, they begin to grow in thickness and obtain a conical form. If a stalactite curves along its length, it is called a deflected stalactite. If its curving is known to be caused by air currents, it is called anemolite. Petal-shaped tubular stalactites composed of aragonite are called spathites. When some stalactites touch each other they form a drapery with a curtain-like appearance.

.Buchan Caves, Victoria Australia

When dripping water falls down on the floor of the cave it form stalagmites, which grow up vertically from the cave floor. Any changes in the direction of the growth axis of the stalagmite are suggestive of folding of the floor of the cave during the growth of the stalagmite. If a stalagmite is small, flat and round, it is called button stalagmite. Stalagmites resembling piled-up plates with broken borders are called pile-of-plates stalagmites. Rare varieties of stalagmites are mushroom stalagmites (partly composed of mud and having a mushroom shape), mud stalagmites (formed by mud) and lily pad stalagmites (resembling a lily pad on the surface of a pond). A calcite crust (shelfstone) grows around a stalagmite if it is flooded by a cave pool and forms a candlestick.

Gypsum stalactites inside the Crystal Grotto

When a stalactite touches a stalagmite it forms a column. Usually, stalactites and stalagmites in caves are formed by calcite, less frequently by

aragonite, and rarely by gypsum . Fifty-four other cave minerals are known to form rare stalactites.

HUGE Aragonite Crystals - Flower Cave

Sometimes calcite stalactites or stalagmites are overgrown by aragonite crystals . This is due to precipitation of calcite that raises the ratio of magnesium to calcium in the solution enough that aragonite becomes stable.

Rare dripstone cave in southeastern Turkey’s Hakkari

Rarely, elongated single crystals or twins of calcite are vertically oriented and look like stalactites, but in fact are not stalactites because they are not formed by dripping or flowing water and don't have hollow channels inside. These elongated crystals are formed from water films on their surface.

Stalactite Calcite

In some volcanic lava tube caves exist lava stalactites and stalagmites that are not speleothems because they are not composed of secondary minerals . They are primary forms of the cooling, dripping lava.

Lava stalactites near Hana in Maui in Hawaii, USA

The internal structure of stalactites and stalagmites across their growth axis usually consists of concentric rings around the hollow channel. These rings contain different amounts of clay and other inclusions, and reflect drier and wetter periods. Clay rings reflect hiatuses of the growth of the sample. Stalagmites may be formed for periods ranging from a few hundreds years up to one million years. Stalactites and stalagmites in caves have such great variety of shapes, forms, and color that each of them is unique in appearance. At the same time, their growth rates are so slow that once broken, they cannot recover during a human life span of time. Thus, stalactites and stalagmites are considered natural heritage objects and are protected by law in most countries, and their collection, mining, and selling is prohibited.

Lava stalagmites Viðgelmir cave in Hallmundarhraun

lava field, Iceland

The Formation of Stalactites and Stalagmites

We can trace the words stalactite and stalagmite back to the Greek word "stalassein," which means "to drip." This is fitting because it describes how both are formed in nature. Although they look lifelike and a little creepy, stalactites and stalagmites grow simply because of water running over and through inorganic material.

Limestone caves, where most stalactites and stalagmites are found, are mainly composed of calcite, a common mineral found in sedimentary rocks. Calcite molecules are made of calcium and carbonate ions, and are referred to as CaCO3, or calcium carbonate. When rainwater falls over a cave and trickles through rocks, it picks up carbon dioxide and minerals from limestone. If we add water, carbon dioxide and calcium carbonate together, we get this equation:

H20 + CO2 + CaCO3 = Ca (HCO3)2

Ca (HCO3)2 is known as calcium bicarbonate, and the water carries the substance, basically dissolved calcite, through the cracks of the roof of a cave. Once water comes into contact with the air inside the cave, however, some of the calcium bicarbonate is transformed back into calcium carbonate, and calcite starts to form around the crack. As water continues to drip, the length and thickness of the calcite grows, and eventually a stalactite forms on the ceiling. It can take a very long time for most stalactites to form -- they usually grow anywhere between a quarter-inch and an inch every century.Of course, stalagmites don't just emerge from the ground.

Timpanogos Caves in Utah

 The water dripping from the end of a stalactite falls to the floor of a cave and deposits more calcite into a mound. Soon enough, a stalagmite will form in a conelike shape. This is why you usually find stalactites and stalagmites in pairs, and sometimes they'll even grow together to form one big column. There are many limestone caves around the world famous for their displays of dripstone, including Carlsbad Caverns in New Mexico, Timpanogos Caves in Utah, Mammoth Cave in Kentucky and Jenolan Caves and Buchan Caves in Australi.

Carlsbad Caverns in New Mexico