This EarthCache is located within a small adit/tunnel that is most likely related to the mining and quarrying activities that have occurred in the Meldon area over the centuries. Although there is water within, good walking boots should be more than sufficient if you are careful with where you place your feet. There is no chance to get lost, as you will see when you get there, and the tunnel appears to be perfectly stable, but as always you hunt for this one because you want to and as such do so entirely at your own risk.
This EarthCache will take you on a short trip underground, where you will see some of the layers of rock that are found in the Meldon Area, and the resultant speleothems. Scientifically speleothems are a category of cave formations, or decorations, that formed after the cave itself had been created. Although they can vary in appearance, and how they form, the chemical composition follows only a few different formulas, which reflect the location and rocks that they form from.
The process is started with water on the surface filtering through the soil, absorbing carbon dioxide, turning the water into a weak carbonic acid. This weak acidic solution passes through the rocks and where there are rocks that contain calcium, such as limestone, the acid dissolves a small amount of this calcium. When this solution exits the rock, into the cave, the dissolved carbon dioxide is released and because of this the solution cannot hold as much dissolved calcium. As a result the calcium is then precipitated, creating the speleothems. Most commonly this calcium is deposited in the form of the mineral calcite (CaCO3).
This chemical composition makes up the majority of speleothems, but as well as the calcite the solution can dissolve other minerals from different rocks that are present. These additions to the solution affect the colour of the speleothems, and they can range from pure white all the way to black.
Clear or pure white is the result of pure calcite that do not have any other minerals dissolved in the solution.
Pink is formed from the rock dolomite and is actually not calcite at all, but the process happens in much the same way.
Green is formed by impurities of glauconite, which is normally in the form of potassium iron silicate. This is typically dissolved from clays or shale.
Reddish Brown is formed by iron oxides and as a result looks 'rusty'. This iron commonly comes from ironstone, which is easily identifiable by its rusty looking colour.
Grey and Black is formed most commonly by manganese, but can also be a result of lead. These minerals can be found within a number of rocks.
Although the basic chemical composition of most speleothems are the same, the way they are deposited leads to vastly different appearances, and as such are categorised into different formations. There are four main categories, which can be further subdivided.
Dripstones
These are the 'typical' speleothems and is the category that most people will associate with this process. They are formed, as the name suggests, by solution falling from the rock above and landing on the ground below.
Straws are a thin walled hollow formation that is called this because they resemble a drinking straw. The solution dripping from the ceiling deposits a microscopic ring of calcite crystal. Over time these rings continue to form and the straws continue to grow.
Stalactites are a formation that grows, like straws, down from the cave roof. Nearly all stalactites start their 'life' as a straw, which are subsequently blocked with calcite or impurities. Over time the stalactite thicken and lengthen as a result of the solution running down their outer surface.
Stalagmites are solid dripstones that grow upward from the cave floor, and are usually associated with a stalactite or straw on the roof above that the solution is falling from.
Columns and Pillars are formations that result when stalactites or stalagmites extend from floor to roof.
Flowstone
These form where the solution doesn't drop down from the roof, but runs down a rock face, to the cave floor.
Shawls form when solution trickles down the rock, resulting in a narrow strip of calcite that hangs away from the rock, much like the dripstones. As the solution runs along the same path the strip of calcite grows downwards and eventually creates a thin sheet.
Flowstones are formed when solution runs over the surface of the rock, creating a wide layer of calcite. Over time the layer thickens, sometimes creating impressively thick flowstones.
Pore Deposits
These deposits form where solution enters the cave through the pores and cracks with the rocks, and because of this droplets dp not form. As a result they are not subject to gravity, so they can create some amazing speleothems. Although it is not certain, it is thought that they are a combination of capillary action and hydrostatic pressure.
Helictites create irregular growths that grow in any direction and are not affected by gravity. The evaporating solution creates a minute layer of crystal and slowly a capillary tube slowly develops. This draws further solution and the capillary tube grows, extending the helictite. The result of this type of formation are wonderful tube like structures that can twists any way, defying gravity.
Cave Corrals are similar to helictites, but the capillary tubes do not form. This means that the resulting deposit grows over a large area and has a rough texture, with no discernible 'structure' to it.
There is also a fourth group, pool deposits but I have not included them here because they require a pool to form, which this EarthCache location does not have.
To log this EarthCache go to the posted coordinates, enter the cave, and send me a message or email answering these following questions
1) On the left hand side of the large fallen rock there is evidence for human activity, what is this?
2) What types of speleothems can you identify within the cave?
3) Describe the colour of the calcite material forming the speleothems.
4) What mineral do you think is responsible for the colour?
5) Looking at the rocks in the cave, can you see any evidence for where this mineral may have come from?