– Formation:
– Tubes form when calcium carbonate or calcium sulfate dissolved in water comes out of solution and is deposited.
– In soda straws, each drop deposits a ring of mineral at the tip before falling and being replaced by a new drop.
– Stalagmites or flowstone may form where water drops hit the cave floor.
– Soda straws are fragile and easily crushed, hence rarely seen within arms reach in show caves.
– Kartchner Caverns in Arizona has well-preserved soda straws due to restricted access.
– Outside the cave environment:
– Straws can form beneath man-made structures and grow faster than in natural caves.
– These forms, known as calthemites, have different chemistry derived from concrete or other calcareous materials.
– Calthemite soda straws can grow up to 2mm per day, significantly faster than speleothem soda straws.
– Calthemite straws are lighter and have thinner walls compared to speleothem straws.
– Changes in drip rate over time can cause variations in the diameter of calthemite straws.
– References:
– Hill and Forti (1997) discuss speleothem growth rates and cave minerals in their book.
– Rivenburg (1999) mentions Kartchner Caverns in an article about Arizona’s caves.
– Smith (2016) explores calcite straw stalactites growing from concrete structures in Cave and Karst Science.
– Macleod et al. (1990) investigate concrete degradation in a major road bridge from a mineralogical perspective.
– Additional references provide insights into calthemite formation and growth rates.
– Subtopic 4:
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– Subtopic 5:
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A soda straw (or simply straw) is a speleothem in the form of a hollow mineral cylindrical tube. They are also known as tubular stalactites. Soda straws grow in places where water leaches slowly through cracks in rock, such as on the roofs of caves. Soda straws in caves rarely grow more than a few millimetres per year and may average one tenth of a millimetre per year. A soda straw can turn into a stalactite if the hole at the bottom is blocked, or if the water begins flowing on the outside surface of the hollow tube. Soda straws can also form outside the cave environment on exposed concrete surfaces as a type of calthemite, growing significantly faster than those formed on rock.
