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Yep that is right, stalactites fall down.. and stalagmites crawl up.

When I was in senior school I remeber weeks of our geography lessons being spent discussing these things, and it was sooo boring! Last week the kids at CLAS had great fun playing with them, and asking questions and taking photographs of them.

I hope to take Asha tomorrow to the river to look at ice a bit more, but in the mean time, some information for you on ICE, Stalactites and Stalagmites.

So what is the point of icicles then?

However, stalactites aren’t the only natural formations that look like elongated carrots. Once the researchers had found a mathematical representation of the stalactite’s shape, they began to wonder if the solution applied to other similarly shaped natural formations caused by dripping water.

So the team decided to investigate icicles. Although other scientists have studied how icicles grow, they had not found a formula to describe their shape.

Surprisingly, the team found that the same mathematical formula that describes the shape of stalactites also describes the shape of icicles.

“Everyone knows what an icicle is and what it looks like, so this research is very accessible. I think it is amazing that science and math can explain something like this so well. It really highlights the beauty of nature,” Short said.

The finding is surprising because the physical processes that form icicles are very different from those that form stalactites. Whereas heat diffusion and a rising air column are keys to an icicle’s growth, the diffusion of carbon dioxide gas fuels a stalactite’s growth.

Short, a doctoral candidate in UA’s physics department, Baygents, a UA associate professor of chemical and environmental engineering, and Goldstein, a UA professor of physics and the Schlumberger Professor of Complex Physical Systems at the University of Cambridge in England, published their article, “A Free-Boundary Theory for the Shape of the Ideal Dripping Icicle,” in the August 2006 issue of Physics of Fluids. The National Science Foundation funded the research.

As residents of cold climates know, icicles form when melting snow begins dripping down from a surface such as the edge of a roof. For an icicle to grow, there must be a constant layer of water flowing over it.

The growth of an icicle is caused by the diffusion of heat away from the icicle by a thin fluid layer of water and the resulting updraft of air traveling over the surface. The updraft of air occurs because the icicle is generally warmer than its surrounding environment, and thus convective heating causes the air surrounding the icicle to rise. As the rising air removes heat from the liquid layer, some of the water freezes, and the icicle grows thicker and elongates.

“At first, we focused only on the thin water layer covering the icicle, just like we did with stalactites,” said Short. “It was only later that we examined the layer of rising air, which is technically more correct. Strangely though, both methods lead to the same mathematical shape for icicles.”

The resulting shape turns out to be described by the same mathematical equation that describes stalactites. One could call it the Platonic form.

The team wanted to compare the predicted shape to real icicles. Because icicles are scarce in Tucson, the scientists naturally turned to the Internet. They were able to compare pictures of actual icicles with their predicted shape.

The team found that it doesn’t matter how big or small the actual icicles were, they could all fit to the shape generated by the mathematical equation.

“Fundamentally, just like in the early stalactite work, it’s a result that implies that the shape of an icicle, at least in its ideal, pristine form, ought to be described by this mathematical equation. And we found, examining images of icicles, that it is a very good fit,” senior author Goldstein said.

original article

Stalactites are formed by the deposition of calcium carbonate and other minerals, which is precipitated from mineralized water solutions. Limestone is calcium carbonate rock which is dissolved by water that contains carbon dioxide forming a calcium hydrogencarbonate solution. The chemical formula for this reaction is:[1]

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 cave it will drip down. When the solution comes into contact with air the chemical reaction that created it is reversed and particles of calcium carbonate are deposited. The reversed reaction is:[1]

Ca(HCO3)2(aq) ? CaCO3(s) + H2O(l) + CO2(aq)

An average growth rate is 0.13 mm (0.005 inches) a year. The quickest growing stalactites are those formed by fast flowing water rich in calcium carbonate and carbon dioxide, these can grow at 3 mm (0.12 inches) per year.[2]
Greek stalagma (“???????????”), “drop” or “drip”) is a type of speleothem that rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate.

The corresponding formation on the ceiling of a cave is known as a stalactite. If these formations grow together, the result is known as a column.

When touring caves with stalactites and stalagmites you might be requested to not touch the rock formations. This is generally because the formation is considered to still be growing and forming. Since the rock buildup is formed by minerals solidifying out of the water solution onto the old surface, skin oils can disturb where the mineral water will cling, thus affecting the growth of the formation. Oils and dirt from the hands can also stain the formation and change its colour permanently.

Icicles will form when ice or snow is melted by either sunlight or some other heat source (such as heat leaking from the interior of a heated building), and the resulting melted water runs off into an area where the ambient temperature is below the freezing point of water (0°C/32°F), causing the water to refreeze. Over time continued water runoff will cause the icicle to grow. If an icicle grows long enough to touch the ground (or its corresponding ice spike growing up from the ground) then it is called an ice column.

Icicles can pose both safety and structural dangers. Icicles that hang from an object may fall and cause damage to whatever is below them. In addition, ice deposits can be heavy. If enough icicles forms on a object, the weight of the ice can severely damage the structural integrity of the object and may cause the object to break.

http://en.wikipedia.org/wiki/Lavacicle

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