Actun Tunichil Muknal EarthCache

Actun Tunichil Muknal is known locally as Xibalba or ATM.

It is a cave which is about 5 kilometers long and consists of a long river passage for approximately 3 kilometers and which is a famous Maya archaeological site that includes skeletons, ceramics and stoneware.

Attention: The cave cannot be entered by your own. You have to hire a guide or book a respective tour (recommended). In addition to that, it periodically closes when rainfall causes the river's water level to rise and potentially flood parts of the cave.

Actun Tunichil Muknal is part of the Tapir Mountain Reserve, a protected area of approx. 28 square kilometers, and is located in the foothills of the Maya Mountains. These mountains are mainly made of Paleozoic era granite, Cretaceous limestone and sediments.

Millions of years ago, most of the landmass of Belize was covered by a broad, shallow tropical sea. One of the major rock types deposited in this sea was limestone. This limestone had its origin either from biological materials like corals and mollusks or in some cases could be precipitated directly from the seawater. "Some" years later, these limestone formations were uplifted on the northern flanks of the Maya Mountains and were partly dissolved by water. This process of solution produced a distinctive type of landscape characterized by caves, sinkholes and a lack of surface drainage called Karst. Inside the caves the solution process is still ongoing. On the one hand rivers continue carving out the cave beds, on the other the acidic rainwater still enters the caves from above building speleothem.

But how did the various speleothem types like stalagmites, stalactites and flowstones compose?
From the chemical point of view, limestone is the chief form of calcium carbonate rock. The rainwater which travels through the rock contains carbon dioxide and forms a weak acidic calcium bicarbonate solution. As soon as this solution reaches an edge it comes into contact with air. The chemical reaction that created it is reversed and particles of calcium carbonate are deposited. Speleothem is created. It should not be touched since the rock buildup is also formed by minerals. Skin oils can alter the surface tension where the mineral water clings or flows thus affecting the growth of the formation and/or a permanent color change. The average growth rate is very little: For example stalactites grow only 0.13 mm a year.

	Stalactite A dripstone type of formation that hangs from the ceiling of caves. All limestone stalactites begin with a single mineral-laden drop of water. When the drop falls, it deposits the thinnest ring of calcite. Each subsequent drop that forms and falls deposits another calcite ring. Eventually, these rings form a very narrow (0.5 mm), hollow tube commonly known as a soda straw stalactite. Soda straws can grow quite long, but are very fragile. If they become plugged by debris, water begins flowing over the outside, depositing more calcite and creating the more familiar cone-shaped stalactite.
	Stalagmite A dripstone type of formation that rises from the floor of a cave. Stalagmites are formed by water drops that fall from the tip of a stalactite depositing more calcite on the floor below. Unlike stalactites, stalagmites never start out as hollow soda straws.
	Stalagnate/Pillar/Column A dripstone type of formation that goes from the ceiling to the floor. Stalagnates are formed when a stalactite and a stalagmite meet or when a stalactite reaches the floor of the cave.
	Flowstones A type of formation that is composed of sheetlike deposits of calcite formed where water flows down the walls or along the floors of a cave. They are the most common speleothem and may form in any type of cave where water enters that has picked up dissolved minerals. There are two common forms of flowstones: Tufa and travertine. Tufa is usually formed via the precipitation of calcium carbonate and is spongy or porous in nature. Travertine is a calcium carbonate deposit often formed in creeks or rivers. Its nature is laminated and it includes such structures as stalagmites and stalactites. Typical flowstone appearances are draperies, curtains, bacon, rimstone dams or stone waterfalls.
	Crystals A type of formation that is created by the removal of bedrock, rather than as secondary deposits. Typical cave crystals are Dogtooth spar (large crystals), Frostwork (needle-like), Moonmilk (white and cheese-like) and Anthodites (flower-like clusters)

In order to log this earthcache you have to answer the following questions:

1. How does the entrance of the cave look like?
2. Given the information in the listing combined with your observation: How long does it take for mother nature to create the seen stalactites?
3. If you hike through the cave, you can see a color that clearly differs from the limestone's red and brown tones. What color is it and what is the mineral's name? Ask your guide if you are not sure.
4. In the inner chamber ("The Cathedral"), what happened to the majority of the Maya artifacts - geologically?

Two optional, none-geological questions/tasks:

5. How often do you have to cross the Roaring Creek River until you reach ATM?
6. As taking photos in the cave is prohibited and you most probably will leave your equipment at the parking place take a photo of you and/or your GPS device at the starting point of the trail before you started or after you finished your trip. If you do the latter your smile normally will be far bigger :-)

Please send me your answers through my profile. You can immediately log and do not have to wait for an answer. I'll get in touch with you if something is strange.

Sources:
[1] http://www.wikipedia.com
[2] http://www.belize.com

Images:
[1] http://experiencebelize.com
[2] http://www.flickr.com
[3] http://www.astra28.eu
[4] http://www.speleomyszkow.pl
[5] https://elyserioux.wordpress.com
[6] http://wiki.lubbockareagrotto.org