**Bring a ruler**
The Lesson - Going Underground ...well, sort of...
It's really amazing what you can find when you step off the path. When I did, I immediately spotted the possible presence of stalagmites and stalactites. But what's the difference?
A stalagmite is an upward-growing mound of mineral deposits that have precipitated from water dripping onto the floor of a cave. Most have rounded or flattened tips. Stalagmites are typically composed of calcium carbonate, but can also consist of "exotic" items such as mud, peat, pitch, sand, and amberat (crystallized urine of pack rats).
On the other hand, a stalactite is a type of formation that hangs from the ceiling of caves, hot springs, or man-made structures such as bridges and mines. Any material that is soluble (dissolved in a solution), or can be deposited as a colloid, or is in suspension, or is capable of being melted, may form a stalactite. Stalactites may be composed of similar materials as noted in the description of stalagmites.
The definition of "speleothem," in most publications, specifically excludes secondary mineral deposits in mines, tunnels, and other man-made structures. For example, a "secondary" mineral is one which is derived by a physicochemical reaction from a primary mineral in bedrock or detritus, and/or deposited because of a unique set of conditions in a cave; i.e., the cave environment has influenced the mineral's deposition.
Calthemites, which occur on concrete structures, are created by completely different chemistry to speleothems. They are a secondary deposit derived from concrete, lime, mortar or other calcareous material outside the cave environment. Calthemites grow on or under man-made structures and mimic the shapes and forms of cave speleothems.
Calthemites are usually the result of hyperalkaline solution (pH 9–14) seeping through a calcareous man-made structure until it comes into contact with the atmosphere on the underside of the structure, where carbon dioxide (CO2) from the surrounding air facilitates the reactions to deposit calcium carbonate as a secondary deposit. CO2 is the reactant (diffuses into solution) as opposed to speleothem chemistry where CO2 is the product (degassed from solution). It is most likely that the majority of calcium carbonate (CaCO3) create calthemites in shapes which, mimicking speleothems, is precipitated from solution as calcite as opposed to the other, less stable polymorphs of aragonite and vaterite.
Calthemites are generally composed of calcium carbonate (CaCO3) which is predominantly coloured white, but may be coloured red, orange or yellow due to iron oxide (from rusting reinforcing) being transported by the leachate and deposited along with the CaCO3. Copper oxide from copper pipes may cause calthemites to be coloured green or blue. Calthemites may also contain minerals such as gypsum.
The growth rate of calthemite stalactite straws, stalagmites and flowstone, is very much dependent on the supply rate and continuity of the saturated leachate solution to the location of CaCO3 deposition. Calthemite straw stalactites precipitated (deposited) from hyperalkaline leachate have the potential to grow up to ≈200 times faster than normal cave speleothems. For example, one calthemite soda straw has been recorded as growing 2 mm per day over several consecutive days, when the leachate drip rate was a constant 11 minutes between drips. When the drip rate is more frequent than one drop per minute, there is no discernible deposition of CaCO3 at the tip of the stalactite (hence no growth) and the leachate solution falls to the ground where the CaCO3 is deposited to create a calthemite stalagmite. If the leachate supply to the stalactite straw's tip reduces to a level where the drip rate is greater than approximately 25 to 30 minutes between drops, there is a chance that the straw tip will calcify over and block up. New straw stalactites can often form next to a previously active, but now dry (dormant) straw, because the leachate has simply found an easier path through the micro cracks and voids in the concrete structure.
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Questions - please note that all answers must be completed. I don't expect you to be a geologist; however, I do expect that you read the lesson and apply your learning. Generic, incorrect, incomplete or "armchair-type" answers may result in a deleted log. I read and respond to all answers.
Note: Group answers will not be accepted, so please send as individual responses.
1. After getting to GZ (read the description), look up.
a) Describe what you see in terms of the geology: colours (chemicals), textures, size (length, width). Be as detailed and specific as possible - refer to the lesson to help you out.
b) Based on your observations, name the geological feature.
c) In your own words, describe how this/these geological features(s) were formed.
2. Look up at the ceiling. For the item identified in Q1, name it, measure it (cm please), and estimate the drip rate and how long the structure has likely been "growing". Explain your reasoning.
a) Send, but don't post, a photo of the structure you measured.
3. Mandatory photo to determine you were on-site. With your log, upload a photo of you / your GPS standing at the entrance to the tunnel - where the graffiti is. Take a photo with said graffiti and not the EC. Do not photograph any spoilers. Thanks!
Thanks for visiting! Please send your answers via the messaging service and I will reply. Please - no spoilers of any kind in the logs. And finally....Group answers will not be accepted - individuals must submit their own responses, including photos. Cheers!