25 - Caves and Karst (w/ Brian Redder!)
25. Caves and Karst (w/ Brian Redder!)
Much like myself, many animals that live deep within caves have no skin pigment, eyesight, and have slow metabolism. What is the importance of these habitats? What is limestone? How are caves formed? Let’s learn to be scientifically conversational.
General Learning Concepts
1) What is a cave and what is the essential chemistry?
a. What is a cave? Rocks are made up of grains or crystals of different minerals. Most rocks have pores of varying sizes, from visible to invisible to the eye, but rarely are these pores large enough to walk into. When they are, that space is called a cave.
b. What is karst? Karst is a landscape that arises from when underlying rock is soluble (capable of being dissolved by water) which often makes it associated with limestone. This leads to an area that is known for having sinkholes, caves, springs, and so on. About 13% of the world’s surface is capable of being called karst. [2]
c. What is limestone? Limestone is a bit of a catch-all term for a variety of sedimentary rocks (these rocks often start as sediments carried in rivers and deposited in lakes and oceans) which tend to be comprised of a chemical called calcium carbonate / calcite (often associated biologically with bones, teeth, shells). Pure limestone is white in color but impurities like clay, sand, organics. [2] [3]
d. What is pH? A direct function of the free hydrogen ions present in the sample. We tend to think of pH in terms of acidity with food. The scale ranges from 0 – 14 with 7 being considered neutral (as pure water has a pH of 7). Lower than 7 is acidic; higher than 7 is basic (alkaline).
2) Timeline of cave formation
a. Cave Types: Because cave can be defined somewhat ambiguously, it is important to note there are several types of caves.
i. Solution Cave: Primarily what we’ll speak of today. Formed from carbonate and sulfate rocks by the passage of slowly moving ground water to form tunnels and caverns.
ii. Lava Cave: Tunnels or tubes that are formed because the outside of the lava cools and hardens while the hot, inner lava continues to move. This leaves a “tube” that resembles a cave.
iii. Sea Cave: Constant kinetic energy of the ocean exerts pressure of rocks lining the shores of oceans. Additionally, often smaller parts of sediment are carried along with the tides which help exert further forces to chip away these rocks on the shores.
iv. Glacier Caves: Melting water can excavate drainage tunnels in ice; not to be confused with ice frozen in solution caves or lava caves.
b. Basic steps to formation of a solution cave: Rain water holds carbon dioxide from the air soil and turns into a weak acid (carbonic acid) that dissolves limestone, leaving spaces that can become enlarged enough to form a cave. This generally happens in locations in which are just below the water table and are capable of forming horizontal passages. When the water reaches locations with massive amounts of air present again, the carbon dioxide will equilibrate from the water, thusly making the water less acidic. Then, the calcium carbonate re-precipitates and is deposited as drip-stone. [2]
c. Large: The largest solution cave known to date is Hang Sơn Đoòng (Mountain River Cave) in Vietnam. Originally discovered in 1990 by a local man Ho Khanh in the Phong Nha-Ke Bang National Park, the cave was lost for another 18 years. Estimated age is 2 – 5 million years old. It’s more than three miles long, with numerous chambers large enough to hold an entire city block of New York skyscrapers. Being the world’s largest cave, Son Doong contains many appropriately gargantuan formations, including the 200-foot “Hand of the Dog,” which might be the world’s largest stalagmite. Son Doong is also distinguished by two large dolines, areas where the cave roof collapsed, that let in light and created conditions for dense prehistoric flora to grow in the middle of the cave. Controversially, some wish to make a cable car ride through Son Doong. [2] [3] [4]
3) Caves and Ecology (Ecology: relationship of one organism to another and their surroundings)
a. Nutrients and Energy: There are a variety of critical small molecules, elements, and essential nutrients required for life.
i. Water: Water allows for biochemistry to happen. Additionally, it is important for some organisms who choose to live their life cycle in the water. It is used for the formation of caves. Running water sources bring nutrients from far-away locations into the cave.
ii. Carbon sources (food): Often, carbon sources or food sources such as green plants that photosynthesize are not available deep in the cave. Therefore, food sources usually grow earlier in cave structures or are carried by wind or current. Food can be retrieved in the form of droppings from animals that leave the cave to find nutrients and come back.
iii. Light: Light is not available to the same degree across the cave.
b. Zones: There are different zones in the cave that provide totally different environments.
i. Entrance Zone: The beginning of the cave and the end of the “outside”.
ii. Twilight Zone: Light diminishes; plant life becomes sparse.
iii. Transition Zone: No light; changes in moisture and temperature still happen.
iv. Deep Zone: No light; relative high humidity; low evaporation rate. Near constant temperature.
c. Common Cave Flora and Fauna: Bacteria are responsible for turning inedible foods into simple foods and nutrients that are important for cave ecology. Bats are cave visitors that come and go; other examples are bears, skunks, moths, and people. Those who live in caves but could also live outside include earthworms, some beetles, cave crickets, some frogs and salamanders, and crustaceans. Finally, those who live in the caves and cannot live outside include cave snails, cave worms, cave spiders, cave millipedes, cave insects, cave fish, and more. The difference is that these animals may have slower metabolism, no sight, or no skin pigment. [2]
4) Fun Tidbits
a. Mite vs. kites: Stalagmites grow upward from the care floor, generally because of water dripping from the overhead stalactites.
b. What is a soda straw? Hollow mineral cylindrical tube, also known as tubular stalactites. Water slowly moves (falls) but deposits a ring of minerals that eventually becomes a tube or straw shape. If the hole is blocked, it can become a stalactite. This is similar to a lava tube but with the natural mineral properties of water.
5) Solicited Questions
a. How do caves form underwater? This process is actually quite similar to our previously described formation section. The acidic water responsible for dissolving calcite and carving tunnels and channels becomes submerged. Changes in the water table impact the water levels in these places.