My Science School

When a river flows through low-lying plains, it slows down, carving out a meandering path with many U-shaped curves. Over time, some of these curves become cut off from the main flow of the river by the build-up of silt deposits, and form oxbow lakes. These distinctive, curved water bodies are close to a river but separate from it.

An oxbow lake starts out as a curve, or meander, in a river. A lake forms as the river finds a different, shorter, course. The meander becomes an oxbow lake along the side of the river.

Oxbow lakes usually form in flat, low-lying plains close to where the river empties into another body of water. On these plains, rivers often have wide meanders.

Meanders that form oxbow lakes have two sets of curves: one curving away from the straight path of the river and one curving back. The corners of the curves closest to each other are called concave banks. The concave banks erode over time. The force of the rivers flowing water wears away the land on the meanders concave banks.

The banks opposite the concave banks are called convex banks. The opposite of erosion happens here. Silt and sediment build up on convex banks. This build-up is called deposition.

Erosion and deposition eventually cause a new channel to be cut through the small piece of land at the narrow end of the meander. The river makes a shortcut. Oxbow lakes are the remains of the bend in the river.

Oxbow lakes are stillwater lakes. This means that water does not flow into or out of them. There is no stream or spring feeding the lake, and it doesnt have a natural outlet. Oxbow lakes often become swamps or bogs, and they often dry up as their water evaporates.

Credit: National Geographic Society

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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.

Credit: Britannica

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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.

Credit: Irish Tourism

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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.

Credit: phys.org

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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.

Credit: Wikipedia

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