Stalactite
A stalactite (
The corresponding formation on the floor of the cave is known as a stalagmite. Mnemonics have been developed for which word refers to which type of formation; one is that stalactite has a C for "ceiling", and stalagmite has a G for "ground".[5] Another example is that stalactites "hang on Tight" and stalagmites "Might grow up" – with emphasis on the "T" and "M" linked to similar sounding words.
Formation and type
Limestone stalactites
The most common stalactites are
- CaCO3(s) + H2O(l) + CO2(aq) → Ca(HCO3)2(aq)
This solution travels through the rock until it reaches an edge and if this is on the roof of a
- Ca(HCO3)2(aq) → CaCO3(s) + H2O(l) + CO2(aq)
An average growth rate is 0.13 mm (0.0051 inches) a year. The quickest growing stalactites are those formed by a constant supply of slow dripping water rich in calcium carbonate (CaCO3) and carbon dioxide (CO2), which can grow at 3 mm (0.12 inches) per year.[8][9] The drip rate must be slow enough to allow the CO2 to degas from the solution into the cave atmosphere, resulting in deposition of CaCO3 on the stalactite. Too fast a drip rate and the solution, still carrying most of the CaCO3, falls to the cave floor where degassing occurs and CaCO3 is deposited as a stalagmite.
All limestone stalactites begin with a single mineral-laden drop of water. When the drop falls, it deposits the thinnest ring of calcite. Each subsequent drop that forms and falls deposits another calcite ring. Eventually, these rings form a very narrow (≈4 to 5 mm diameter), hollow tube commonly known as a "soda straw" stalactite. Soda straws can grow quite long, but are very fragile. If they become plugged by debris, water begins flowing over the outside, depositing more calcite and creating the more familiar cone-shaped stalactite.
Stalactite formation generally begins over a large area, with multiple paths for the mineral rich water to flow. As minerals are dissolved in one channel slightly more than other competing channels, the dominant channel begins to draw more and more of the available water, which speeds its growth, ultimately resulting in all other channels being choked off. This is one reason why formations tend to have minimum distances from one another. The larger the formation, the greater the interformation distance.
Pillars
The same water drops that fall from the tip of a stalactite deposit more calcite on the floor below, eventually resulting in a rounded or cone-shaped stalagmite. Unlike stalactites, stalagmites never start out as hollow "soda straws". Given enough time, these formations can meet and fuse to create a speleothem of calcium carbonate known as a pillar, column, or stalagnate.[10]
Lava stalactites
Another type of stalactite is formed in
The generic term lavacicle has been applied to lava stalactites and stalagmites indiscriminately and evolved from the word icicle.[2]
Like limestone stalactites, they can leave lava drips onto the floor that turn into lava stalagmites and may eventually fuse with the corresponding stalactite to form a column.
Shark tooth stalactites
The shark tooth stalactite is broad and tapering in appearance. It may begin as a small driblet of lava from a semi-solid ceiling, but then grows by accreting layers as successive flows of lava rise and fall in the lava tube, coating and recoating the stalactite with more material. They can vary from a few millimeters to over a meter in length.[12]
Splash stalactites
As lava flows through a tube, material will be splashed up on the ceiling and ooze back down, hardening into a stalactite. This type of formation results in an irregularly-shaped stalactite, looking somewhat like stretched taffy[clarification needed]. Often they may be of a different color than the original lava that formed the cave.[12]
Tubular lava stalactites
When the roof of a lava tube is cooling, a skin forms that traps semi-molten material inside. Trapped gases expansion forces lava to extrude out through small openings that result in hollow, tubular stalactites analogous to the soda straws formed as depositional
Ice stalactites
A common stalactite found
Ice stalactites can also form under sea ice when saline water is introduced to ocean water. These specific stalactites are referred to as brinicles.
Ice stalactites may also form corresponding stalagmites below them and given time may grow together to form an ice column.
Concrete stalactites
Stalactites can also form on
The way stalactites form on concrete is due to different chemistry than those that form naturally in limestone caves and is due of the presence of calcium oxide in cement. Concrete is made from aggregate, sand and cement. When water is added to the mix, the calcium oxide in the cement reacts with water to form calcium hydroxide (Ca(OH)2). The chemical formula for this is:[7]
- CaO
(s) + H
2O
(l) → Ca(OH)
2
(aq)
- CaO
Over time, any rainwater that penetrates cracks in set (hard) concrete will carry any free
- Ca(OH)
2
(aq) + CO
2
(g) → CaCO
3
(s) + H
2O
(l)
- Ca(OH)
When this solution drops down it leaves behind particles of calcium carbonate and over time these form into a stalactite. They are normally a few centimeters long and with a diameter of approximately 4 to 5 mm (0.16 to 0.20 inches).[7] The growth rate of stalactites is significantly influenced by supply continuity of Ca2+
saturated solution and the drip rate. A straw shaped stalactite which has formed under a concrete structure can grow as much as 2 mm per day in length, when the drip rate is approximately 11 minutes between drops.[15] Changes in leachate solution pH can facilitate additional chemical reactions, which may also influence calthemite stalactite growth rates.[15]
Records
The White Chamber in the
Etymology
Stalactites are first mentioned (though not by name) by the Roman natural historian Pliny in a text which also mentions stalagmites and columns and refers to their formation by the dripping of water. The term "stalactite" was coined in the 17th century by the Danish Physician Ole Worm,[17] who coined the word from the Greek word σταλακτός (stalaktos, "dripping") and the Greek suffix -ίτης (-ites, connected with or belonging to).[18]
Photo gallery
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Mineralized water drop forming at bottom of stalactites
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Stalactites of the type called "soda straws" from theVercors, France
-
Tubular lava stalactites
-
A tubular lava helictite
See also
- Stalagmite
- Lavacicle
- Rusticle
- Karst
- Icicle
- Bottlebrush - Stalactite coated with pool spar.
- Brinicle
References
- ^ "stalactite". Oxford Dictionary. Archived from the original on August 1, 2021. Retrieved 2021-08-01 – via Lexico.com.
- ^ a b c d Larson, Charles (1993). An Illustrated Glossary of Lava Tube Features, Bulletin 87, Western Speleological Survey. p. 56.
- ^ Hicks, Forrest L. (1950). "Formation and mineralogy of stalactites and stalagmites" (PDF). 12: 63–72. Retrieved 2013-07-08.
{{cite journal}}
: Cite journal requires|journal=
(help) - Nova (American TV series). Retrieved 2013-07-01.
- ^ "Archived copy" (PDF). Archived from the original (PDF) on 2017-02-11. Retrieved 2019-05-03.
{{cite web}}
: CS1 maint: archived copy as title (link) - ^ C. Michael Hogan. 2010. Calcium. eds. A.Jorgensen, C. Cleveland. Encyclopedia of Earth. National Council for Science and the Environment.
- ^ ISBN 0-415-32116-6
- ISBN 978-0-87614-447-3
- ^ a b Hill, C A, and Forti, P, (1986, 1997). Cave Minerals of the World, 1st & 2nd editions. [Huntsville, Alabama: National Speleological Society Inc.]
- ^ "Pillars". showcaves.com.
- ^ Baird, A.K. (1982). "Basaltic "stalactite" mineralogy and chemistry, Kilauea". 4 (4). Geological Society of America Bulletin, abstracts with programs: 146–147.
{{cite journal}}
: Cite journal requires|journal=
(help) - ^ a b c Bunnell, Dave (2008). Caves of Fire: Inside America's Lava Tubes. p. 124.
- ^ Keiffer, Susan (2010). "Ice stalactite dynamics". Retrieved 2013-07-08.
- ^ Lacelle, Denis (2009). "Formation of seasonal ice bodies and associated cryogenic carbonates in Cavene De L'Ours, Que' Bec, Canada: Kinetic isotope effects and pseudo-biogenic crystal structures" (PDF). Journal of Cave and Karst Studies. pp. 48–62. Retrieved 2013-07-08.
- ^ a b c Smith, G K. (2016). "Calcite straw stalactites growing from concrete structures". Cave and Karst Science 43(1), pp4-10.
- ^ "Caves With The Longest Stalactite". Retrieved 2008-06-11.
- ^ Olao Worm, Museum Wormianum. ... (Amsterdam ("Amstelodami"), (the Netherlands): Louis & Daniel Elzevier, 1655), pages 50-52.
- ^ See: Online Etymology Dictionary
- Dripstone in time-lapse ("Tropfsteine im Zeitraffer") - Schmidkonz, B.; Wittke, G.; Chemie Unserer Zeit, 2006, 40, 246.
External links
- "Speleothems (Cave Formations) – Wind Cave National Park (U.S. National Park Service)". www.nps.gov. Retrieved 5 January 2020.
- The Virtual Cave's page on stalactites
- Stalactites by Enrique Zeleny, Wolfram Demonstrations Project.