Page 475 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 14 Weathering, Karst Landscapes, and Mass Movement 439
cave formed by chemical processes is a cavern. Mam- moth Cave in Kentucky, one of the largest caverns in the United States along with Carlsbad Caverns in New Mexico, is the longest surveyed cave in the world at 560 km. GeoReport 14.4 explains the role of amateurs in many of the cave discoveries.
Cave networks are found in many regions of Canada. Notable examples include Castleguard Cave in Banff National Park, Alberta, that descends over 20 km into rock beneath the Columbia Icefield; caves in Nahanni National Park in the Northwest Territories; and the Gargantua Cave in southeastern British Columbia. The lat- ter has the largest known cavern in Canada, being 290 m long, 30 m wide, and 25 m high. Small caves are frequent in karst landscapes across Canada, such as in the gyp- sum karst of Cape Breton, Nova Scotia (Figure 14.21). For more on caves in Canada, see the Canadian Cave and Karst Information Server at www.cancaver.ca.
Caves generally form just beneath the water table, where later lowering of the water level exposes them to further development (Figure 14.22). As discussed in
▲Figure 14.20 tower karst, Li River valley, China. [Keren Su/Corbis.]
◀Figure 14.19 Deep-space research using cockpit karst topography. Cockpit karst topography near Are- cibo, Puerto Rico, is the setting for earth’s largest radio telescope. The discolouration of the dish does not affect telescope reception. The suspended movable receivers where the signals focus are 168 m above the dish. [Bobbé Christopherson; inset Cornell University.]
Chapter 11, speleothems are formations consisting of mineral deposits inside caves and occur in various characteris- tic shapes. Dripstones are speleothems formed as water containing dissolved minerals slowly drips from the cave ceil- ing. Calcium carbonate precipitates out of the evaporating solution, literally one mo- lecular layer at a time, and accumulates on a spot below on the cave floor.
Thus dripstones are depositional features—stalactites growing from the ceiling and stalagmites building from the floor. Some- times a stalactite and stalagmite grow until they connect and form a continuous column (Figure 14.22b and c). Flowstones are sheet-like formations of calcium carbon- ate on cave floors and walls (Figure 14.22d). Soda straws are a type of thin, long stalactite (Figure 14.22e). For more on caves and related formations, see www.goodearthgraphics
.com/virtcave/virtcave.html.
The exploration and scientific study of caves is spe-
leology. Scientists and explorers estimate that some 90% of caves worldwide still lie undiscovered, and more than 90% of known caves have not been biologically surveyed, making this a major research frontier. Cave habitats are unique, nearly closed, self-contained ecosystems with simple food chains and great stability. In total darkness, bacteria synthesize inorganic elements and produce or- ganic compounds that sustain many types of cave life,
▲Figure 14.21 Cape Breton, NS, gypsum karst. The lowland areas contain gypsum beds that were dissolved, producing an irregular hummocky terrain. Isolated flats are the remnants of the original, bevelled slope on the intervening sandstone and shale. Underlying the steeper, interior hills beyond is resistant volcanic rock. [Raymond Gehman/Documentary Value/Corbis.]