Caves Trip Pre‐Trip Student Reading Materials CLIMBE 2009 Montreat College Table of Contents The Bat Cave…………………………………………………………………………….………………………….3 Worley’s Cave ….……………………………………………………………...…………………………........4 The Rock Cycle……………………………………………………………………………………………………..5 What is a cave? Types of Caves…………………………………………………………………………....6 Karst Topography………………………………………………………………………………………………..7 Passageways………………………………………………………………………………………………………..7 Zones……………………………………………………………………………………………………………………9 Cave Meteorology……………………………………………………………………………………………..…9 Cave Ecology………………………………………………………………………………………………………12 Cool Cave Facts………………………………………………………………....................................13 Glossary……………………………………………………………………………………………………………..15 2
The Bat Cave After hiking a mile up a steep trail through a mature hardwood forest, you will be rewarded with Bat Cave’s natural air conditioning: a cool moist draft that constantly pours out of vents on the side of the large cave. Bat Cave is the largest known granite fissure cave in North America. The main chamber is a dark cathedral more than 300 feet long and approximately 85 feet high. Fissure caves are formed by rock splits, boulder movements, and other motions of the earth, while most other caves are formed by water dissolving and abrading rock. While seeing this impressive cave opening is the attraction for most visitors, the rugged slopes around Bat Cave contain an equally important array of habitats and creatures. Hickory Nut Gorge is cloaked in cove hardwood forest, while Carolina hemlock and chestnut oak forest are found on the cliff tops and ridgeline. The forests harbor a number of threatened or endangered plants, such as broadleaf coreopsis and Carey’s saxifrage. The preserve has an abundance of spring wildflowers, including bloodroot, toothwort, trillium, and violets. One of the Conservancy’s goals in managing this preserve is to reestablish the critically endangered Indiana bat to its former habitat. The cave itself is closed to visitation at all times and the preserve is closed from October to mid‐April in an effort to allow the bats to hibernate undisturbed. If bats are disturbed during hibernation, they fly around and quickly use up the stored energy that they need to survive the winter. Three previously undescribed invertebrates ‐‐ a spider, a millipede, and an amphipod ‐‐ also live in the cave and are specially adapted to survive without sunlight and with a limited food supply. In warm months, you may see the crevice salamander sunning on exposed rocks. 3
Worley’s Cave Morril's Cave State Natural Area is located in Sullivan County. It has more than 37,000 feet of mapped passages on two levels. Morril's Cave is commonly called Worley's Cave locally and is known for its voluminous size with rooms more than 75 feet wide and 250 feet long with high ceilings that often exceeds 100 feet. It is noted for its beautiful formations within its eight to ten miles of passages. The lower level of the cave contains a perennial creek complete with various fishes, white crayfish, and salamanders. An unearthed prehistoric stonewall some six feet high, built of rocks of various sizes, is evidence that the cave was likely inhabited by aboriginal people. It is unknown when the first settler entered Worley's Cave, although it has been written that settlers surely would have encountered the cave by the beginning of the 1800's. Nothing is known of the cave until it became the property of Elias S. Worley. Locally, the cavern is often still referred to as Worley Cave. A large amount of saltpeter was mined from the cave early in the Civil War. A mill was operated in the early 1900's where the stream exits at the lower entrance of the cave. It was said that the stream's volume was "sufficient, even in severest drought, to turn the undershot wheel of a large mill. A local resident John Morril led many explorations of the cavern "near the turn of the century." Much confusion has arisen over the years about the proper spelling of the name. It has been called Morrell, Morrill, Morrils, Morrels, Mirrells, Worley's and even Worlie's Cave. The issue was resolved in 1980 by the U.S. Board on Geographical Names when it approved the name Morrell Cave. The Natural Areas Preservation Act however has not been amended to change it from Morril's Cave since it was designated in 1973. 4
The Rock Cycle The vast array of rocks found on Earth can be categorized into three types: igneous, sedimentary, and metamorphic. As magma from the core of Earth rises to the surface, it cools and crystallizes to form igneous rock. Igneous rock is a cooled molten rock and the most commonly found is granite. When igneous rock weathers and erodes into sediment, it undergoes a process known as lithification. This compacting and binding of sediment hardens into sedimentary rock. Sedimentary includes rocks such as sandstone and limestone (used in the formation of caves). When exposed to extreme temperatures and pressure, sedimentary rock “morphs” into metamorphic rock. Metamorphic literally means “changed in form,” and includes rocks such as marble and slate. Diagram C1: The Rock Cycle 5
Types of Caves The term cave is given to a natural underground open space or cavity formed by various geological processes. Usually, there is an implication that there is an open connection to the surface large enough for a person to enter. While some caves may measure a few hundred feet, others extend for many miles and reach hundreds of feet in depth. There are many different types of caves formed throughout the world including corrasional, ice caves, lava tubes, and sea or wind caves. Corrasional Caves are caves formed entirely by the erosion of flowing streams that carry rocks and other sediments, even wind‐
borne. There must be some zone of weakness or fault to allow the guiding of the water. Ice Caves occur on glaciers, with surface crevasses channeling streams underground melting pathways through the ice, often to resurge at the forward end. Lava Tubes are formed by volcanic activity and are the most common “primary” caves. As lava erupts from the volcano and flows downhill, the surface cools and solidifies while the hotter lava continues to flow out in the center of the newly formed tube. Thus, a hollow tube is eventually formed and left behind. Finally, Sea and Wind Caves are usually found along coasts and are formed by the wave action of water crashing in zones of weakness in the cliff‐side. The most common cave type is the solution (or limestone) cave. These solution caves are typically formed in soluble rock, usually limestone, which dissolves when in contact with rain or groundwater charged with natural acids such as carbonic acid. They are also characterized by mineral deposits known as speleothems: flowstone, stalactites, stalagmites, draperies, soda straws and columns. 6
Diagram C2: Speleothems Karst Topography Karst is the name for a landscape with topographic features formed by groundwater erosion, including features such as: caves, sinkholes, sinking (or disappearing) streams, and solution valleys. About 20% of the United States region is considered to be karst. Sinkholes are natural depression or holes, resembling funnels, in the surface of the earth. Generally, they are identified by their oval or circular shape and can be very small and localized or as large as a football field. Disappearing Streams are surface streams that drain rapidly and completely into a sinkhole. Solution Valleys are large depressions caused by the merging of several sinkholes. The largest and greatest numbers of caves are found in areas of extensive deposits of limestone. This highly soluble mineral is primarily composed of calcite (CaCO3). As precipitation penetrates the soil it combines with carbon dioxide to form carbonic acid, which then seeps through the cracks in the ground and erodes the landscape. After several years, the area is hollowed out producing passageways and caverns, or caves. 7
Passageways As groundwater is guided through the land and erodes the earth, several types of passageways are formed (See Diagram C2). The most common passageway is the branch‐work, which resembles dendritic (or tree‐like) stream patterns and are made up of passages that join downstream as tributaries. This type is formed near sinkholes where groundwater recharge occurs. Each passage or branch is fed by a separate recharge source and converges into other higher order branches downstream. Other types of passageways are not so simplistic. Angular Network caves form from intersecting fissures of carbonate rock that have had fractures widened by chemical erosion. These fractures form high, narrow, straight passages that persist in widespread closed loops. Anastomotic caves largely resemble surface braided streams with their passages separating and then meeting further down drainage. They usually form along one bed or structure, and only rarely cross into upper or lower beds. Finally, there are two types of caves that form random passageways with no specific pattern. Spongework caves are formed as solution cavities and are joined by mixing of chemically diverse water. The cavities form a pattern that is three‐dimensional and random, resembling a sponge. Ramiform caves form as irregular large rooms, galleries, and passages. These randomized three‐dimensional rooms form from a rising water table that erodes the carbonate rock with hydrogen sulfide enriched water. 8
Diagram C3: Passage Types Zones One might think that the complexity of a cave’s layout is limited to an entrance and the deeper dark passages. However, this is not so. Caves have a unique layout and include four distinct zones: an entrance, the twilight, the middle, and the dark. The entrance of the cave is very similar to the environment aboveground. There are varying temperatures and ample sunlight for green plants to flourish at the mouth of the cave. Trekking farther into the cave the amount of sunlight is greatly reduced and the temperatures vary slightly, inhibiting the growth of vegetation. This area is known as the twilight, so named for the resembling diffused light at dusk. At this point in the cave we experience a phenomenon known as luminous efficacy, or the building of rods in our eyes to aid in the adaption to the darkness. Together, the entrance and the twilight zones are collectively called the threshold. 9
Deeper into the cave, where light is completely absent but there are slight fluctuations in temperature, is the middle zone. The middle zone is the first encounter with complete darkness. Finally, the deepest zone is known as the dark zone. There is complete darkness in the dark zone; however, the cave is capable of maintaining a stable temperature of 54‐56°F year round. Diagram C4: Cave Zones Cave Meteorology Weather can be defined as the present state of the atmosphere in an area with respect to heat, wind, pressure, and moisture. Of these, heat is the most important since changes in heat quite often bring about changes in the others. On the surface, weather is driven by the sun, which heats some areas of the earth more than others. Temperature differences lead to pressure differences which lead to winds and precipitation. But what are changes in the weather of a dark, sunless cave caused by? To understand, we must first look at how heat enters the cave. Significant amounts of heat can enter a cave in four possible ways. Heat may enter from the overlying rock, from the underlying rock, from air flowing into the cave, or from water flowing into the cave. 10
First, let's look at how heat enters the cave from the rock above it. The flow of heat through the sandstone and limestone overlying a cave’s passages is extremely slow. Vast temperature fluctuations between day and night are not uncommon on the surface, but if we were to monitor the temperature only two feet below the surface on such a day, the fluctuation in temperature would be only about 1°F. Therefore, it does not stay warm long enough during the day, nor does it stay cool long enough during the night, to significantly change the temperature of the rock only two feet underground. The same principle holds true for seasonal temperature fluctuations as well, although the depth at which temperatures begin to stabilize is greater. Seasonal temperature fluctuations of 80°F are reduced to only l°F at a depth of about 50 feet. So if a cave's only source of heat was from the overlying rock, its temperature would approximate the mean annual surface temperature for its area. It appears this is rarely the case. Since the interior of the earth is a tremendously hot, molten mass, one would naturally assume that temperature would increase with depth below the surface. This change in temperature with depth is known as the geothermal gradient. In areas where the geothermal gradient is low, cave temperature is influenced mostly by the mean annual surface temperature. In areas with high geothermal gradients, cave temperature is influenced by the mean annual surface temperature and by heat from below. Caves in areas such as this tend to be warmer than the mean annual surface temperature. The same geothermal gradient which is responsible for the warm waters of Hot Springs is heating the cave! Caves with no connections to the outside world have no further sources of heat. Since the heat supplied by the rock is provided very evenly, and since changes in the amount of heat 11
reaching the cave can only occur over very long periods of time, the weather in such caves is very constant. But caves with open connections to the surface have two more possible sources of heat which can alter the weather inside the cave: airflow and water. Both are capable of transporting outside conditions into the cave environment. The effects of water on the cave temperature can be very slight. Water dripping into the cave normally has reached rock temperature by the time it reaches the cave atmosphere, so little heat exchange can take place. But in caves with active streams flowing in from the surface, large seasonal fluctuations in temperature can occur very deep into the cave, since it takes a long time for the water to heat or cool to cave temperature. The real weather (i.e. daily changes in the cave's atmospheric conditions) of Wind Cave, South Dakota is driven by the wind. Few caves experience the volume of airflow which Wind Cave exhibits. On average, almost 1,000,000 cubic feet of air enter or leave the cave per hour when the Walk‐In Entrance is open! That's enough air to completely fill a cave 10 feet wide, 10 feet tall, and almost 2 miles long! Since it takes a long time for a volume of air this large to warm or cool to cave temperature, temperature changes can occur surprisingly deep into the cave on days when the cave is inhaling. The Wind Cave Climate Study of 1984‐85 showed that with the Walk‐In Entrance open in the winter, temperatures could fluctuate by over 12°F as far into the cave as the Post Office (over 500 feet from the entrance). The entire Half‐Mile Tour route is almost always cooler than the 55°F deep cave temperature, mostly due to cold air brought into the cave during the winter. So much for constant temperatures at Wind Cave! Not only does inflowing air affect cave temperature, but it also affects cave humidity. The same study showed that humidity was lower whenever the cave inhaled. Natural cave humidity 12
is probably about 95%‐100%. Cold air is usually dry, and when it enters the cave environment and warms it becomes even drier. Some areas showed humidity as low as 60% on days when the cave inhaled. Humidity did not stabilize until the Temple was reached, over 2000 feet into the cave. This drier air evaporates water from the cave environment, further cooling the cave since evaporation requires large amounts of heat. Cave Ecology The stable conditions of the cave are what effectively provide shelter, protection, and food for a multitude of organisms. There are five specific types of organisms that utilize caves in various ways: accidentals, trogloxenes, troglophiles, troglobites, and phreatobites. Cave accidentals are organisms that randomly wander into the cave but do not reside within it. These include animals such as fish and rodents. Other organisms within the cave live in the cave for some period of time. Trogloxenes are cave “guests” and live near or just inside of the cave entrance. Bats are considered to be trogloxenes, because they are often found in caves but forage outside. Troglophiles, or lovers, spend their entire life cycle inside a cave, but can be found in other environments, for example salamanders. Troglobites are animals that live entirely in the dark parts of caves. Such creatures have become specifically adapted for life in total darkness and over time they have evolved to develop improved senses of smell, taste and vibration detection, while losing anatomical features that are superfluous without light, such as functioning eyes and pigmentation. Specific examples include the blind cavefish and cave crickets. The last group of organisms, known as 13
the phreatobites, is a group of small organisms that live in tiny spaces of caves where humans cannot travel (e.g. insects). Diagram C5: Cave Dweller Locations Cool Cave Facts Among Stone Age cultures, caves had great ritual significance. The Maya of Central America believed that caves were the gateway to the Underworld and, therefore, any rituals performed there would quickly gain the notice of ancestral spirits. So strong was this belief that some temples were carved to resemble caves, or in some cases, ‐‐>built over caves to encourage the spirits to interact with living priests. The Native Americans of the Northern Hemisphere also believed that caves were sacred places. Archaic and Woodland Indians sent their bravest warriors into the dark recesses of Mammoth Cave to mine epsomite and gypsum crystals. Those who returned were honored and the crystals they brought home with them became sacred heirlooms or sought‐after trade items of the tribe. In more modern times, caves have been used for a variety of purposes: refrigerated food storage during pioneer times, saltpeter mining and weapons storage during the 1800s, speak‐easies and hideouts for moonshine stills during the Prohibition and dance halls during 14
World War II. Cumberland Caverns in Tennessee still contains a large dining hall which is regularly used for parties, receptions and Scout camp‐outs. Other Cool Facts: •
Touching an "active" formation causes growth to cease in that area because dirt or oil from your skin prevents water from reaching the growing formation. Enough touches, and the formation will "die." •
Based on data turned in to the Tennessee Cave Survey (TCS), Tennessee currently has more discovered caves than any other state at over 8,400. Officers of the TCS guess that the state may harbor as many as 15,000 caves. However, because of differences in how state cave surveys define caves, this record is a hard one to pin down accurately. •
The deepest cave in the U.S. is the Kazumura in the Olaa Cave System. It is a lava tube cave in Hawaii and is recorded at 3614 feet deep. The longest in the U.S., and the world, is the Mammoth Cave System in Kentucky. It is recorded at 346.010 miles long. •
The Krubera Cave is the deepest cave in the world. Located near the coast of the Black Sea, its recent measurements extending to a total depth of 7188 feet (2191 m). It was the first cave to be explored to a depth of more than 2 km down. 15
Glossary •
Anastomotic Passage: Passages separating and then meeting further down drainage. They usually form along one bed or structure, and only rarely cross into upper or lower beds. •
Angular Network Passage: High, narrow, straight passages that persist in widespread closed loops from intersecting fissures of carbonate rock that have had fractures widened by chemical erosion. •
Branch‐Work Passage: Resembles dendtritic (or tree‐like) stream patterns and are made up of passages that join downstream as tributaries. •
Cave: A Large underground chamber, typically of natural origin, in a hillside or cliff. •
Cave Accidentals: Organisms that randomly wander into the cave but do not reside within it. •
Corrasional Caves: Caves formed entirely by the erosion of flowing streams that carry rocks and other sediments, even wind‐borne. There must be some zone of weakness or fault to allow the guiding of the water. •
Dark Zone: The farthest region of the cave, complete darkness. •
Disappearing Streams: Surface streams that drain rapidly and completely into the ground. •
Entrance: An opening, such as a door, passage, or gate, that allows access to a place. •
Geothermal gradient: The change in temperature in relation to the depth of a cave. •
Ice Cave: Occur on glaciers, with surface crevasses channeling streams underground melting pathways through the ice, often to resurge at the forward end. 16
•
Igneous Rock: (of rock) Having solidified from lava or magma. •
Karst: Landscape underlain by limestone that has been eroded by dissolution, producing ridges, towers, fissures, sinkholes, and other characteristic landforms. •
Lava Tube Caves: Formed by volcanic activity and are the most common “primary” caves. •
Luminous efficacy: The process of building rods in our eyes to aid in the adaption to the darkness. •
Metamorphic Rock: Geology denoting rock that has undergone transformation by heat, pressure, or other natural agencies. •
Middle Zone: Where light is completely absent but there are still slight fluctuations in temperature. •
Phreatobites: Small organisms that live in tiny spaces of caves where humans cannot travel. •
Ramiform Passages: Irregular large rooms, galleries, and passages, randomized three‐
dimensional rooms. •
Sea & Wind Caves: Found along coasts and are formed by the wave action of water crashing in zones of weakness in the cliff‐side. •
Sedimentary Rock: Geology that has formed from sediment deposited by water or air. •
Sinkhole: A cavity in the ground, especially in limestone bedrock, caused by water erosion and providing a route for surface water to disappear underground. •
Solution Cave: Caves created by dissolving limestone by acidic water. •
Solution Valleys: Large depressions caused by the merging of several sinkholes. 17
•
Speleothems: A structure formed in a cave by the deposition of minerals from water. •
Spongework passage: Formed as solution cavities and are joined by mixing of chemically diverse water. The cavities form a pattern that is three‐dimensional and random, resembling a sponge. •
Threshold: A collective term for the entrance and twilight areas of a cave. •
Troglobites: Cave dwellers. •
Troglophiles: Cave lovers. •
Trogloxenes: Cave visitors. •
Twilight: The middle area between light and darkness. 18