Geology And Geophysics
Stalagmite in Carlsbad Caverns

How are Stalagmites Formed

Stalagmite in Carlsbad Caverns
Tim Harry's image for:
"How are Stalagmites Formed"
Caption: Stalagmite in Carlsbad Caverns
Image by: Ansel Adams - National Archives and Records Administration
© Public Domain - work by US Govt official as part of official duties,_%27in_the_Kings_Palace,%27_Carlsbad_Caverns_National_Park,%22_N_-_NARA_-_520033.jpg?uselang=en-gb

Stalagmites, normally in partnership with stalactites, are a common feature of cave systems around the world. These speleothems, or cave formations, can take millions of years to form

Most people will know that stalagmites form on the cave floor; helped by the old saying that stalactites hold tight to the ceiling, whilst stalagmites might eventually reach the ceiling. Formation of a stalagmite though starts with water.

Water, normally in the form of rain water or snow melt, as this water seeps through the bedrock above a cavernous space so it dissolves minerals into a solution. As caves are most commonly found in a limestone environment, the dissolved minerals are normally calcite or aragonite, although dissolved gypsum is possible. The mineral content is the primary differentiation as to the colour of the stalagmite.

When the water reaches the roof of the cave, the water might evaporate; leaving behind the previously dissolved mineral, creating the start of a stalactite, or the water might drop to the ground. When the water evaporates after it has reached the cave floor, then again mineral deposits are left behind. As more water droplets fall in the same place a mineral growth will appear.

Stalagmites can grow in many different shapes; with each type of shape given its own name, hence button stalagmites (round and flat), and broomstick stalagmites (tall and narrow). If the stalagmite reaches the ceiling, or joins a stalactite above it, then it ceases to be called a stalagmite and becomes known as a column.

The rate of stalagmite growth is dependent on many factors including the amount of water seepage, the acidity of the water, the amount of carbon dioxide present, as well as the temperature and humidity of the cave. All this means that stalagmites may grow as slowly as 0.007mm per year, up to a rate of 0.929mm per year.

The oldest stalagmite, one in the Antiparos Cave, Greece, is said to be 45m years old, whilst the tallest yet discovered measures in at 62.2m and is found in the Cueva Martin Infierno in Cuba.

Human presence in the cave will alter the temperature, humidity and carbon dioxide levels within the cavern, and therefore impact upon the growth of the stalagmite. Touching the speleothem might also ultimately destroy it, as the chemicals present in the skin’s oil could chemical transform the growth, and the work of hundreds of thousands of years could disappear.

More about this author: Tim Harry

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