Karst Hydrology 121 Section A-Identifying and Protecting Cave Resources
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Part 2-Conservation, Management, Ethics: Veni-Karst Hydrology 121 Section A-Identifying and Protecting Cave Resources Karst Hydrology: Protecting and Restoring Caves and Their Hydrologic Systems GeorgeVeni Cavers tend to be conscientious. We try to tread softly through passages to limit our impact. We clean up and restore caves that have been impacted by others. We fight to preserve and protect caves and their contents from outside impacts like urbanization. We work to improve our restoration and protection methods, and, through vehicles like this book, share that information as much as possible. Many of the adverse Many orthe adverse impacts a cave may suffer and the means to prevent impacts a cave may or alleviate them are determined by the cave's hydrology. This chapter suffer and the means provides hydrologic information and guidelines to assist cavers in protect- ing and restoring caves. It teaches the basics of how caves forn1 and how to prevent or water moves through caves and their surrounding landscapes. The chapter alleviate them are also examines common hydrologic problems and impacts on caves, and determined by the what problems can be solved by individual and group actions. cave's hydrology. The following sections are meant to reach cavers of all experience levels. References are cited for those wanting details. Specific recommendations are included, but the focus is on general principles to help guide cavers through situations that cannot be covered within this chapter. The Basics of Karst Hydrology How Water Enters, Moves Through, and Exits Caves The movement of water through caves is closely tied to the question of how caves form. Moore and Sullivan (1997) provide a good basic over- view, while White (1988), Ford and Williams (1989), and Klimchouk and others (2000) offer highly detailed information. Gillieson (1996) offers less detail but more emphasis on cave management. Despite their wide variety of origins, caves or cave areas can be classi- fied in one of three groups: carbonate, evaporite, and pseudo karst (Figure 1). Caves in carbonate rocks form primarily in limestone, but some also occur in dolomite and marble. Caves in evaporite rocks usually form in gypsum but also in halite in exceptionally arid climates. Caves in both carbonate and evaporite rocks form primarily by water dissolving away the bedrock. The landscapes where such solutional processes are dominant are called karst. It is beyond the scope of this brief chapter to discuss all cave types in detail. Limestone caves will be emphasized since they are the most common. The typical limestone cave begins to form where water enters the rock along a fracture or bedding plane and slowly flows downward and laterally until discharged from a spring at a lower elevation. While pure water has little ability to dissolve limestone, water entering the ground is charged with carbon dioxide from the atmosphere and soil to form carbonic acid. Over millennia, the weak acid enlarges fractures and bedding planes. As the openings become larger, water drains more efficiently. These increasing 122 Cave Conservation and Restoration Pseudokarst volumes of water then enlarge the openings at faster rales. This process George Yen; self-accelerates. Eventually, one flow path toward the spring dominates the local drainage pattern and captures flows from smaller channels. When it Caves and karst-like becomes large enough for human exploration, we call that conduit a cave. features that do not form In the more common situation, a cave map looks like a branching surface primarilyby the stream. The tips of the hydrologic network typically include fractures, dissolution of the rock sinkholes, and swallets that capture surface water and route it underground. are called pseudokarst. In the subsurface, each branch flows downstream to join other branches, Several types of eventually fonning limbs and then the trunk of the underground drainage pseudokarst feafures network which discharges from a spring (angular and curvilinear passages, occur. Major types Figure I). include the following: Geologic and hydrologic factors often prevent the development of such • Sea Caves. Formed ideal flow systems, which usually occur in relatively flat-lying, highly- where waves pound on fractured rocks that sit atop relatively impermeable rocks. cliffsand preferentially Local geologic factors frequently affect cave development. Low fracture enlarge fractures, frequency and/or continuation of the limestone deep below spring levels zones of softer rock, or result in cave networks that extend deep below the water table. Caves in areas where wave dipping rocks may branch asymmetrically, capturing most waler from the action is concentrated. updip direction. Figure 1 shows some other examples of how hydrogeologic factors that (Cootinued 00 ",xl page! create a cave relate to the cave's shape. Braided or anastomotic passage patterns indicate slow or ponded conditions. Rectilinear mazes may suggest development by flooding or seepage through a caproek. Figure 1. A summary Ramiform and spongework patterns, such as in Carlsbad Caverns, did chart of how cave not form epigenically by water flowing down from the surface, but morphology reflects hypogenically by rising hydrogen sulfide gas mixing with groundwater hydrogeologic origin to form sulfuric acid, \vhich in turn dissolved the limestone to create (from Palmer 1991). caves. TYPE OF RECHARGE VIA KARST DEPRESSIONS DIFFUSE HYPOGENIC SINKHOLES SINKING STREAMS INTO POROUS (LIMITED DISCHARGE IGREAT DISCHARGE THROUGH SANDSTONE SOLUBLE ROCK FLUCTUATION) FLUCTUATIONI DISSOLUTION 8'1' ACIDS OF DEEP-SEATED SOURCE OR SINGLE PASSAGES AND BY COOliNG OF THERMAl BRANCHWORKS CRUDE 6A/\NCHWOAKS. MOST CAVES ENLARGED WATER (USUALLY SEVERAL LEVELS) USUAlLY WITH THE FURTHER ElY RECHARGE MOST CAVES FORMED BY & SINGLE PASSAGES FOLLOWING FEATURES FROM OTHER SOURCES MIXING AT DEPTH SUPERIMPOSED: 00 w ~ ~\~-~ ~ ,/f!; >- ~"< i ~\ >- ~ /IA ; ~ ISOLATED FISSURES in ANGULAR FISSURES, \ AND RUDI"'ENTARY NETWORKS, 0 PASSAGES IRREGULAR NETWORKS FISSlJHES. NETWORKS II: NETWORKS SINGLE PASSAGES, FISSURES 0 00 PROFILE: z --=" "- " '. u. ~ 0 ~< .--- w ..... -'i IJf -/?}t.~ "z ~ !~1 "->- J~ ~ .\ >- 0 I / SHAF'T ANO CANYON RAMIFORM CAVE'S, W "m CURVILINEAR ANASTOMOSES. COMPlEXES,lNTEASTRATAl RARE SINGLE-PASSAGE /\NO >- SPONGEWORK Z PASSAGES ANASlOMOTIC MAZES SOLUTION ANASTOMOTIC CAVES « PROFILE: Z ~ :E :l 0 z0 0 < .' ..••~~.. '. .. ~i•. ~ ''J( ,". .~' ~ • • w ~~ •• ~ ", . ~ ~ RUDIMENTARY RUDIMENTARY RAMIFORM & SPONGE WORK SPONGEWOAK SPONGEWORK BRANCHWORKS " SPONGEWORK CAVES Part 2-Conservation, Management, Ethics: Veni-Karst Hydrology 123 Beyond the Cave: Water in the Drainage Basin (Con,nued) For most of the 20th century, scientists argued whether caves form above, below, or at the water table, or even whether \vater tables actually exist in • Tectonic Caves. Humanly enterable karst. \Ve now know that caves form in all of those situations, and that karst fractures that occur water tables do exist. Caves are integral parts of karst aquifers and are a where large sections part of an interconnected series of voids that transmit water down through of bedrock separate, the vadose zone (the area above the water table) and into the phreatic zone such as by one side (the water-saturated area below the water table), and eventually out of the slumping down a spring. Aquifers are reservoirs of water held underground in whatever hillside or valley. voids exist in the rocks and soil. In karst, these voids make up complicated networks of fractures, bedding planes, some pore spaces, and of course, • Talus Caves. caves. Humanlyenterable The area that feeds all water into a stream, spring, or cave is called the spaces that occur beneath and within drainage basin. Valley ridgelines define the drainage basin boundaries for piles of large fallen surface streams. All water that enters the basins must eventually flow rocks. through these streams. Groundwater drainage basins do not always con- form to the boundaries of surface basins. Karst groundwater basins arc • Suffosion Features, notorious for crossing below surface basin boundaries, but they still These include caves function by similar principles. Rather than surface water flowing down a and sinkhole-like topographic surface, groundwater flows down from "ridges" to "valleys" or depressions that form troughs in the water table where flow is concentrated. Significant cave by the localized streams often flow along these troughs. downward movement Subsurface flow converges on large conduits because of their greater of fine, unconsolidated material through or ability to transmit water. Even hypogenic caves, which form independently below locally denser or of water entering the ground from the surface, capture local flO\v paths better-cemented from the surface to form drips, domes, pools, and streams. Figure 2 material. illustrates how water that seeps or floods into sinkholes, fractures, and sinking streams flows down troughs in the water table to merge into single • Volcanic Pseudo- large cave streams, and discharges from the same spring, It should there- karst. Lava tubes fore be clear that caves, plus the rate, volume, and quality of water that are the most extensive flows through them, and the materials carried in the water, directly reflect type of volcanic the conditions and activities on the surface in the cave's drainage basin. pseudokarst. Lava tubes form where Cave Chemistry and Speleothems molten lava drains from beneath a cooling, Some of the water