Crystal Cave is a marble karst cave within Sequoia National Park, in the western Sierra Nevada of California. It is one of at least 240 known caves in Sequoia National Park. Crystal Cave is in the Giant Forest area, between the Ash Mountain entrance of the park and the Giant Forest museum. The cave is a constant 48 °F (9 °C). It is accessible by Park Service guided tours only. Tickets are not sold on-site, but must be bought at the Foothills or Lodgepole Visitor Center. The study of karst is considered of prime importance in petroleum geology since as much as 50% of the world’s hydrocarbon reserves are hosted in porous karst systems.
Map of Crystal Cave
Karst topography is a landscape formed from the dissolution of soluble rocks such as limestone, dolomite, marble, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. The cave formed in the marble because carbonate rocks, limestone and marble (metamorphosized limestone) dissolve in acid. The acid comes from rain water. As rain falls through the air, it reacts with carbon dioxide along with sulfur oxides, nitrogen, and other natural compounds to form weak acids. As these acids percolated through carbonate rocks, the water slowly dissolves the stone. Weak points along bedding planes dissolve fastest forming cracks. Once the ground water dissolves the cracks to a critical width, the flow of water becomes turbulent increasing the rate that the limestone is dissolved. Even more water is then channeled though these widened cracks eventually creating the cavern.
Caves often form on several levels and the topmost caves are the oldest. Crystal Cave formed in a ridge between Yucca and Cascade Creeks. It began forming about 1.15 million years ago as water from Yucca Creek percolated down through the marble exiting on the other side of the ridge into Cascade Creek. As the creeks on either side of the ridge eroded further down, the level of cave formation moved down as well. So the oldest caves are above the most recently formed caves. The cave tour enters the lowest and youngest portion of the cave system. The lower levels are through to have formed about 0.56 million years ago.
Stalactites, Stalagmites and Columns
Stalactites and stalagmites are common features in caves, formed when the acidic water reaches an open area, resulting in the carbon dioxide leaving the water and thus depositing calcite (calcium carbonate). An easy mnemonic to remember is:
A stalactite grows from the cave ceiling, so it has to hold on “tite”. A stalagmite grows from the cave floor with all of it’s “mite”.
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 (≈4 to 5 mm diameter), 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.
The same water drops that fall from the tip of a stalactite deposit more calcite on the floor below, eventually resulting in a rounded or cone-shaped stalagmite. Unlike stalactites, stalagmites never start out as hollow “soda straws.” Given enough time, these formations can meet and fuse to create pillars of calcium carbonate known as a column.
Speleothems
Cave formations are known to cavers as speleothems. They are formed by mineral-rich water dripping and seeping through caves. This water deposits minute amounts of minerals, usually calcite and aragonite, over thousands of years to form these speleothems. In the photo above you can see a smooth area towards the bottom and speleothems toward the top of the photo. The smooth areas indicate the water was moving quickly while the lacy speleothems beside the smooth area indicate the water was more stationary.
Dog Tooth Spar
Dogtooth spar is a larger crystal formation that, as it’s name implies, resembles dogs teeth. In this particular case there are few crystals but the resulting formation results from still water.
Drapery Speleothems
A Curtain or Drapery is a calcite formation in the form of a wavy or folded sheet hanging from the roof or wall of a cave.
A curtain forms when water runs down the roof or the wall of the cave. If the ceiling is nearly horizontal, the water will form a stalactite, if the wall is nearly vertical, the water will form a sinter gallery. But if the angle is in between – about 45° – the water will not fall down, but run down the wall. It will always use the same path. While the water runs down the wall it losses carbondioxide (CO2) to the atmosphere of the cave and as a result deposits calcite in a thin vertical line on the wall. This line grows and grows, and very soon there is a small rim. Once there is this small rim the water has no possibilty to leave this path. It always follws this path like a train follows its tracks.
Flowstone Speleothems
Soda straws, stalactites, stalagmites and columns are called dripstone because they are deposited by dripping water. Flowing water can also deposit calcite down a wall or across a floor. This is called (surprise!) flowstone. Flowstone looks like a pile of mud but is actually solid calcite.
Sparkling White Lights
The sparkling yellow, white and silver patches on the walls just beyond the limit of light are microbial communities. The sparkling effect is due to drops of condensation reflecting your cave light. The most abundant phylotypes found in these patches are members of the Proteobacteria (a major group of bacteria including many pathogens), Actinobacteria (a group of Gram positive bacteria) and Nitrospira (nitrite-oxidizing bacteria). Different color patches appear to have different dominant species, many of the other species are new to scientists and have not been identified. Two of the more commonly reported genera are Streptomyces and Nocardia, none of the ancient group the Archaea have yet been isolated from these patches. This is also an example of Rimstone, also called gours, which is a type of speleothem (cave formation) in the form of a stone dam. Rimstone is made up of calcite and other minerals that build up in cave pools. The formation created, which looks like stairs, often extends into flowstone above or below the original rimstone.
Marble Hall
Crystal Cave’s beautiful marble cavern is a sight not to be missed. It is the largest cave in the system. There are many tubes in the cave, most of which are roughly circular. They extend from horizontal to vertical. One tube about three and a half feet in diameter terminates on the ceiling of Marble Hall, extending upward at a steep angle. On the outside of the cave, about 100 feet above and east of the main entrance, there is a small opening in slumped marble. Behind the slump this becomes a rudely circular tube six feet wide and five feet ten inches high above a partial filling of soil. The tube descends into the mountain at an angle of about six degrees, and at twenty-eight feet from the entrance it turns sharply to the left and narrows to four feet eleven inches in diameter, and forty-two inches high above the fill. From this point on the fill rises almost to the ceiling. Flutes on walls and ceilings indicate a downward or in-leading current of water formerly flowed through it.
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