My Science School

No, stalactites and stalagmites can occur singly. However, it is true that stalagmites are usually formed on the ground from the same drip source that creates a stalactite on the ceiling of the cave. The simplest stalactite takes the form of a thin straw. As more and more of the mineral calcite is deposited, the downward growth takes the form of a cone. The calcite drip that reaches the ground forms a stalagmite, a bit like a spike with a rounded tip. It is possible that, over time, the stalagmite and stalactite may meet to form a column that extends from floor to ceiling.

Stalagmites have thicker proportions and grow up on the bottom of a cavern from the same drip-water source, the mineral from which is deposited after the water droplet falls across the open space in the rock. Not every stalactite has a complementary stalagmite, and many of the latter may have no stalactite above them. Where the paired relation exists, however, continual elongation of one or both may eventually result in a junction and the formation of a column.

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Poll-an-lonain, a limestone cave in Doolin, Ireland, has the longest known free-hanging stalactite in Europe. It is 7.3 m in length and is known as the Great Stalactite. The cave was discovered in 1952 and it is assumed that the Great Stalactite was formed over thousands and thousands of years. The Doolin Cave opened to the public in 2006.

Doolin Caves (or Poll-an-Ionain) is a limestone cave near Doolin in County Clare, Ireland, on the western edge of The Burren. The cave is accessible as a show cave and is marketed as Doolin Cave.

The cave was discovered in 1952 by J. M. Dickenson and Brian Varley of Craven Pothole Club, an English caving club based in the Yorkshire Dales. Doolin Cave is member of the Burren Eco-tourism network and holds a gold award from Eco-tourism Ireland for standards of excellence in sustainable tourism.

Doolin Cave is home to the Great Stalactite. At 7.3 metres (23feet) it is the longest free-hanging stalactite in the Northern Hemisphere. The Great Stalactite, suspended from the ceiling like a chandelier, is truly astounding. Visitors can hardly believe that it was formed from a single drop of water over thousands of years.

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The 8.2-m-long limestone stalactite thought to be the longest in the world is in Jeita Grotto, a limestone cave complex, 18 km north of Beirut, the capital of Lebanon. It was discovered in 1836.

Jeita grotto, a monumental underground karstic wonderland and also the water source for over a million citizens of Beirut, is about 18 kilometers north of the Lebanese capital. It is an extraordinary site which could be one of the wonders of the world but remains an intimate experience. It is a system of two separate, but interconnected, karstic limestone caves spanning an overall length of nearly 9 kilometres, making it the longest cave system in the Middle East. The Lower Cave is home to an underground river some 6.2 kilometers long, while the Upper Cave features innumerable dazzling rock formations including one of the largest hanging stalactites in the world, measuring 8.2 metres (27 feet).

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Yes, stalactites, also called ‘hanging speleothems’, have been found underwater, for example the Hells Bells in Mexico. They are hollow structures that expand conically downwards. In addition to the carbonate that builds stalactites and stalagmites, bacteria and algae help in the formation of these underwater stalactites.

Hanging speleothems, also called stalactites, develop through physicochemical processes in which calcium carbonate-rich water dries up. Normally, they rejuvenate and form a tip at the lower end from which drops of water fall to the cave floor. The formations in the El Zapote cave, which are up to two metres long, expand conically downward and are hollow, with round, elliptical or horseshoe-shaped cross-sections. Not only are they unique in shape and size, but also their mode of growth, according to Prof. Stinnesbeck. They grow in a lightless environment near the base of a 30 m freshwater unit immediately above a zone of oxygen-depleted and sulfide-rich toxic saltwater.

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Limestone stalactites and stalagmites are formed extremely slowly: possibly only about 10 cm over a thousand years. Scientific studies have shown some to be very old, forming for as long as 190,000 years!

Stalactites form when water containing dissolved calcium bicarbonate from the limestone rock drips from the ceiling of a cave. As the water comes into contact with the air, some of the calcium bicarbonate precipitates back into limestone to form a tiny ring, which gradually elongates to form a stalactite.

Stalagmites grow upwards from the drips that fall to the floor. They spread outwards more, so they have a wider, flatter shape than stalactites, but they gain mass at roughly the same rate. Limestone stalactites form extremely slowly – usually less than 10cm every thousand years – and radiometric dating has shown that some are over 190,000 years old.

Stalactites can also form by a different chemical process when water drips through concrete, and this is much faster. Stalactites under concrete bridges can grow as fast as a centimetre per year.

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Speleology, scientific discipline that is concerned with all aspects of caves and cave systems. Exploration and description of caves and their features are the principal focus of speleology, but much work on the chemical solution of limestone, rates of formation of stalagmites and stalactites, the influence of groundwater and hydrologic conditions generally, and on modes of cave development has been accomplished within this discipline. Speleology requires, essentially, the application of geological and hydrological knowledge to problems associated with underground cavern systems. Amateur exploration of caves, as a hobby, is called spelunking.

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Caving – also known as spelunking in the United States and Canada and potholing in the United Kingdom and Ireland – is the recreational pastime of exploring wild cave systems (as distinguished from show caves). In contrast, speleology is the scientific study of caves and the cave environment.

The challenges involved in caving vary according to the cave being visited; in addition to the total absence of light beyond the entrance, negotiating pitches, squeezes, and water hazards can be difficult. Cave diving is a distinct, and more hazardous, sub-speciality undertaken by a small minority of technically proficient cavers. In an area of overlap between recreational pursuit and scientific study, the most devoted and serious-minded cavers become accomplished at the surveying and mapping of caves and the formal publication of their efforts. These are usually published freely and publicly, especially in the UK and other European countries, although in the US, these are generally private.

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Both ‘stalactite’ and ‘stalagmite’ originate from the Greek word stalassein meaning ‘to drip’. The first use of both words goes back to the 17th century. Both stalactites and stalagmites are also called dripstones as they form from minerals in dripping water.

Stalactites are the mineral formations that hang down like rock icicles, while stalagmites rise up from the floor. The word stalactite comes from the Greek word for "dripping," stalaktos, which in turn comes from the verb stalassein, "to trickle," which is how stalactites are formed. Water comes down through the top of the cave, bringing rock minerals with it that eventually form those pointy stalactites.

A stalagmite is the pointed formation that rises from the floor of a cave. When you go spelunking, or cave exploring, you'll have to avoid the areas where stalagmites have formed.

Stalagmites are thin piles of mineral deposits that have fallen from the roof to the floor of a cave. They're sometimes connected to the stalactites that dangle down from the top. Because stalagmites form from drops of water combined with minerals, they get their name from the Greek stalagmos, "a dropping," and share a root with stalactite — the Greek stalassein, "to trickle."

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When lichen and moss growing on a rock create an environment that causes rocks to break down both physically and chemically.

Biological weathering also means organic weathering. It is the disintegration of rocks as a result of the action by living organisms. Plant and animals have a significant effect on the rocks as they penetrate or burrow into the soil respectively. Biological weathering can work hand in hand with physical weathering by weakening rock or exposing it to the forces of physical or chemical weathering.

For instance, some plants and trees grow within the fractures in the rock formation. As they penetrate into the soil, and their roots get bigger, they exert pressure on rocks and make the cracks wider and deeper that weaken and eventually disintegrate the rocks. Microscopic organisms can also produce organic chemicals that can contribute to the rock’s mineral weathering.

Biological weathering is a very common type of weathering that we see around us. There are many small animals that bore hole in the rock and live inside it. Over the time, they burrow and widen cracks and end up breaking rocks apart. Then there are bacteria, algae and lichens produce chemicals that help break down the rock on which they survive, so they can get the nutrients they need. They produce weak acids which convert some of the minerals to clay. We, humans, are also responsible for biological weathering. As we construct more homes, industries, dams, power plants, roads, we rip the rocks apart.

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When water collects in the cracks of a rock, it can freeze when temperatures drop. The ice expands and the pressure can split the rock. In cold, mountain regions, one can even hear gunshot-like cracks as rocks are split apart by frost.

A mechanical process, freeze-thaw weathering causes the ?joints?(cracks) in rocks to expand, which wedges parts of rocks apart. Because water expands by about 10% when it freezes, this creates outward pressure in rock joints, making the cracks larger.

Joints occur naturally in rocks as a result of their formation. Fractures that are not offset, joints do allow for the entry of water into rocks.

In climates where temperatures dip below freezing in the winter, moisture in the joints of rocks solidifies as ice. Over time, after several cycles of freezing and thawing, joints get large enough that bit of rock start to fall off in smaller pieces. This breakdown of rock happens faster at higher altitudes, where many freeze-thaw cycles can occur during the year.

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Haloclasty is a type of physical weathering caused by the growth of salt crystals. The process is first started when saline water seeps into cracks and evaporates depositing salt crystals. When the rocks are then heated, the crystals will expand putting pressure on the surrounding rock which will over time splinter the stone into fragments.

Salt crystallization may also take place when solutions decompose rocks (for example, limestone and chalk) to form salt solutions of sodium sulfate or sodium carbonate, from which water evaporates to form their respective salt crystals.

The salts which have proved most effective in disintegrating rocks are sodium sulfate, magnesium sulfate, and calcium chloride. Some of these salts can expand up to three times or more in volume.

It is normally associated with arid climates where strong heating causes strong evaporation and therefore salt crystallization. It is also common along coasts. An example of salt weathering can be seen in the honeycombed stones in sea walls.

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When water collects in the cracks of a rock, it can freeze when temperatures drop. The ice expands and the pressure can split the rock. In cold, mountain regions, one can even hear gunshot-like cracks as rocks are split apart by frost.

A mechanical process, freeze-thaw weathering causes the joints? (cracks) in rocks to expand, which wedges parts of rocks apart. Because water expands by about 10% when it freezes, this creates outward pressure in rock joints, making the cracks larger.

Joints occur naturally in rocks as a result of their formation. Fractures that are not offset, joints do allow for the entry of water into rocks.

In climates where temperatures dip below freezing in the winter, moisture in the joints of rocks solidifies as ice. Over time, after several cycles of freezing and thawing, joints get large enough that bit of rock start to fall off in smaller pieces. This breakdown of rock happens faster at higher altitudes, where many freeze-thaw cycles can occur during the year.

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Physical weathering is also known as mechanical weathering. It is a process, initiated by humans, plants or animals, which breaks down rocks and minerals on the surface of Earth. It changes just the shape or size of the rocks and minerals. Chemical weathering, on the other hand, happens when the chemical composition of the rock and soil changes, forming new chemical combinations and a different internal structure.

Physical weathering is also called as mechanical weathering. This is the process where rocks breakdown without altering their chemical composition. Physical weathering can occur due to temperature, pressure or snow. There are two main types of physical weathering. They are freeze thaw and exfoliation.

Freeze-thaw is the process where water goes into the cracks of the rock, then freezes and expands. This expansion causes rock to break apart. Changing temperature also causes rocks to expand and contract. When this happens over a period of time, rock parts starts to break down. Due to the pressure, cracks can be developed parallel to the land surface which leads to exfoliation.

Physical weathering is prominent in the places where there is little soil and few plants. For example, in desserts surface rocks are subjected to regular expansion and contraction due to temperature changes. Also, in mountain tops, snow keeps melting and freezing which causes physical weathering there.

Chemical weathering is the decomposition of rocks due to chemical reactions. This changes the composition of the rock. This often takes place when rain water reacts with minerals and rocks. Rain water is slightly acidic (due to dissolution of atmospheric carbon dioxide, carbonic acid is produced), and when the acidity increases chemical weathering also increases. With the global pollution, acid rains occur now, and this increases chemical weathering more than the natural rate.

Other than water, temperature is also important for chemical weathering. When the temperature is high, the weathering process is also high. This releases minerals and ions in rocks into surface waters. There are three main types as to how the chemical weathering occurs. They are solution, hydrolysis and oxidation. Solution is the removal of rock in solution due to acidic rain water. This is sometimes called carbonation process, since the rain water acidity is due to carbon dioxide. Hydrolysis is the breakdown of rock to produce clay and soluble salts by acidic water. Oxidation is the breakdown of rock due to oxygen and water.

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Decaying leaves and plant matter give out carbon dioxide, which is also present in the air around us. Carbon dioxide dissolves in water to create carbonic acid through a process called carbonation. This acid can, over time, dissolve rocks, especially limestone. Limestone is a soft rock that consists mainly of calcium carbonate, which reacts with rainwater, dissolving away to create huge caves and cave complexes.

Carbonation is the chemical reaction between carbon dioxide present in the air, and the hydration compounds of the cement in concrete structures. The rate of carbonation depends on the physical characteristics such as the design, on-site preparation, production and protection, as well as external factors, such as the location and degree of exposure to contaminants and other environmental factors. Carbonation may lead to the corrosion of the reinforcement steel and deterioration of concrete structures.

The carbonation process starts immediately when concrete is exposed to air. Carbon dioxide (CO2) penetrates the concrete through the pores where it reacts with the calcium hydroxide and the moisture in the pores to form calcium carbonate. The carbon dioxide combines with the pore water to form a dilute carbolic acid which acts to reduce the concrete’s alkalinity.

Carbonation reduces the concrete’s natural alkalinity from pH13 to about pH8. Whereas a high pH provides a passivation layer around the steel, at pH below 9.5, the passivation layer breaks down and exposes the reinforcement steel to the corrosive effects of water and air.

When steel rusts, it expands in volume and exerts force on the surrounding concrete, causing the concrete to crack and spall at a rate that increases exponentially if the corrosion is not prevented.

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When salt water that collects on the rough surface of rocks, or seeps into cracks, evaporates, it leaves behind salt crystals. Over time, these crystals alter the rock, forming hundreds and thousands of tightly joined pits called honeycombs that are a classic example of both physical and chemical weathering.

Honeycomb weathering occurs throughout the world, but the origin remains a matter of controversy. Wind erosion, exfoliation, frost shattering, and salt weathering have been proposed as explanations, although few attempts have been made to substantiate these hypotheses with chemical or mineralogical studies.

Chemical analyses and field observations indicate that honeycomb weathering in coastal exposures of arkosic sandstone near Bellingham, Washington, results from evaporation of salt water deposited by wave splash. Microscopic examination of weathered surfaces show that erosion results from disaggregation of mineral grains rather than from chemical decomposition. Thin walls separating adjacent cavities seem to be due to protective effects of organic coatings produced by microscopic algae inhabiting the rock surface. Cavity walls are not reinforced by precipitation of elements released by weathering, as has often been suggested at other locations. Honeycomb weathering develops rapidly and can be observed on surfaces that were planar less than a century ago.

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