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This section provides descriptions of the most prominent and distinctive geologic features and processes in Timpanogos Cave National Monument and vicinity.
Charleston Fault Zone
In addition to the large thrust fault, the Charleston Thrust zone also includes an east- west trending corridor of faults and folds. Structural analysis and mapping in American Fork Canyon demonstrates that the zone contains an array of low- angle thrust faults and highangle reverse (faults with the hanging wall being pushed up relative to the footwall typically at angles greater than ~30º) and normal faults. From local cross cutting relationships, it appears the thrust faults formed first, followed by reverse faults and some normal faults, and finally by a majority of normal faults, a few of which reactivated reverse fault surfaces. The overall pattern of faulting and folding in the area indicate that the zone is a left- lateral strike- slip (analogous to the San Andreas Fault of California where blocks slide past each other along a fault surface) system superimposed on a preexisting imbricate thrust fan (Paulsen and Marshak 1998). Movement on the Charleston Thrust appears to have occurred in the Late Cretaceous- Tertiary time Sevier - Laramide Orogeny. Its surface trace is overlapped east of the Wasatch Mountains in the Uinta Basin by rocks of earliest Tertiary age, placing a latest age bracket on the last fault movements in the area (Baker, Huddle, and Kinney 1949; Baker and Crittenden 1961; Paulsen and Marshak 1998).
The trace of the Charleston Fault in the Timpanogos Cave Quadrangle is believed to lie concealed in the hanging wall of the Deer Creek Fault, an east- west trending, south- dipping, mid- Tertiary normal fault which crosses the quadrangle near its northern boundary. All but a small area in the northeast corner of the Timpanogos Cave quadrangle is therefore occupied by rocks of the upper plate of the Charleston Fault, characterized by the thick facies.
Cave Formation and Speleothems
Once the caves formed, minerals dissolved in the saturated water began to precipitate, drop by drop, to create the spectacular array of speleothems, or cave formations, present at Timpanogos Cave National Monument.
Bullock (1942) described three distinct geological epochs of cave formation for Timpanogos Cave. The first is the faulting phase where the preliminary fissures were formed to focus the second phase or excavational epoch wherein water dissolves rock away along the fissures. Three faults were involved and all indications point to recent (in geologic time) movement along them (St. Clair et al. 1976). The structural orientations of Hansen and Middle Caves are the same, N55ºE, whereas the orientation of Timpanogos Cave is 10º northward from the other two, N45ºE. This indicates that Hansen and Middle Caves were most likely developed along the same set of faults whereas Timpanogos Cave was developed along a different fracture (White and Van Gundy 1974). Dissolution was accomplished by pirating of surface water streams infiltrating the fractures within the rock, and groundwater flowing downslope focused along the linear features (St. Clair et al. 1976). The third and final phase of ongoing cave development involves the deposition of sediments and speleothems in the caves.
The caves consist mainly of high, narrow passageways in a linear arrangement, described below (figure 2). The caves are somewhat less developed and excavated than might be expected in a typical karst landscape, the reason for this could be the high concentration of dolomite in the Deseret Limestone around the formation of the cave. Dolomite dissolves much slower than pure limestone (White and Van Gundy 1974). Other reasons could be a lack of sufficient water or properly oriented fractures for dissolution. Additional rooms may remain to be discovered in the Timpanogos cave system.
The caves are composed of a variety of morphologies which indicate their origin in relation to the water table. Vadose origin (above the water table) and phreatic origin (below the water table) cave passages display different features as a function of the role of thoroughgoing water movement. Vadose origin passages show features indicative of ephemeral, fast moving water such as waterfall shafts, stream slots and meanders, small scallops, and directionality of passages to maintain a consistent gradient. Phreatic origin passages, on the other hand, show rounded cross sections, no preferred directionality of passages, an absence of sediment derived from outside the cave, and very gentle scallops indicative of slow water movement.
The Timpanogos Cave system may show both types of passageways, though a vadose origin is questionable. Scallop development in the caves indicates an approximate direction of water flow opposite that of the nearby American Fork River, possibly indicating that the caves formed at a sufficient depth, such that both the location and direction of flow in the American Fork River had no apparent bearing on cave development.
Dissolution is possible when there is enough subsurface water flow to remove dissolved bedrock and keep undersaturated water in contact with the soluble walls. Dissolution rates vary directly with flow distance, chemical saturation, and temperature and inversely with initial fracture width, discharge, gradient and pressure of carbon dioxide in solution. An average maximum rate of dissolution, or wall retreat, is 0.01 - 0.1 cm/year. Solutionally enlarged high- angle faults tend to produce fissure- like passages with lenticular cross sections and very angular intersections, hence Timpanogos cave is an angular karst feature (Palmer 1991). The cave is angular, but does not vary much in elevation; the maximum elevation difference between the mouth of Hansen Cave to the southwest end of Timpanogos is only 19 m (61 ft) (White and Van Gundy 1974).
There are some alluvial sediments deposited in flat beds within the caves about 2.4 m (7.9 ft) thick (St. Clair et al. 1976). These sediments are primarily sand and yellow silt (White 1971).
In addition to the cave at Timpanogos National Monument, the landforms of the Wasatch Mountains provide unique examples of alpine karst landforms. There is little soil cover on the precipitous slopes of American Fork Canyon and bare rock ledges are common, making the exposure of the bedrock geology extremely apparent (White and Van Gundy 1974). Less soil is available to pick up carbon dioxide, but the colder temperatures at this altitude allow more solubility of carbon dioxide into the groundwater dissolving the rock into karst landforms (Jasper, personal communication 2006).
At the high altitude of Mt. Timpanogos, rinnenkarren (lit. German for truck ruts, solutional features carved on limestone faces like furrows) and pinnacle karren (solution furrows with intermittent pillars), as well as solutional pans (dissolved depressions) are forming in the Bridal Veil Falls Limestone of the Oquirrh Group during snow melt.
The Deseret Limestone, in addition to hosting the cave system, also supports a pinnacle karst landscape with a relief of several meters (tens of feet) along the canyon walls. The rough pinnacle surfaces indicate that this may be a remnant of Pleistocene climatic conditions because they are weathering rapidly under current conditions (White 1971; White and Van Gundy 1974). Other carbonate units at Timpanogos Cave National Monument, the Maxwell, Fitchville, and Gardison formations do not display much solutional sculpturing (White and Van Gundy 1974).
Trace elements such as nickel, iron, and manganese, play the role of artist in the caves, splashing shades of green, yellow, orange, brown, pink, and black in otherwise white minerals. However, it is the tremendous diversity and number of helictites which makes the Timpanogos Cave system special. Helictites are small speleothems which twist and turn into strange, fantastical shapes as they grow from the cave walls.
The Timpanogos Cave complex is exceptionally well mineralized (figures 4 and 5). More than 42 different types of cave formations have been identified (Horrocks and Tranel 1994). The walls display intricate sculpturing with common wall and ceiling pockets. In addition to this sculpturing, incredible speleothems decorate the cave walls. Even the grandest speleothems begin with a single drop of water saturated with dissolved minerals (figure 6).
The usual calcite dripstone deposits give way to complex helictites and other erratic forms (White 1971). Sample analysis revealed that only three minerals are responsible for the variety of erratic speleothems found in the caves: calcite (CaCO3), aragonite (CaCO3), and hydromagnesite (4MgCO3·Mg(OH)2·4H2O) (White and Van Gundy 1974). Aragonite, a calcium carbonate mineral, is common in all areas as needles and anthoditic forms. "Moonmilk," composed of hydromagnesite, occurs locally as tufts of material on the tips of dripstones.
Trace elements may lend their color to the deposits. Nickel in calcite is thought to be responsible for unusual yellow stains whereas nickel in aragonite may result in a unique green cast (White 1971). Trace amounts of iron and manganese often lend a brown or orange cast to the speleothems. Copper and lead also contribute to the vast array of colors in the caves.
The common flowstones and dripstones are typically coarse- grained and white or light brown. They appear to be entirely composed of calcite. Monocrystalline dripstone or soda straw varieties are not commonly present in Timpanogos Cave system (figures 7 and 8). Flowstones in the cave complex can vary in color from deep chocolate brown (such as in the Cascade of Energy) to deep clear yellow. Some of the flowstones are faintly luminescent, but most are unusually lacking in luminescence (the emission of light by a substance that has received energy from an external stimulus) (White and Van Gundy 1974).
There are at least 16 different types of erratic speleothems in the Timpanogos Cave complex. Most of these are different morphologies of dripstone and flowstone. The erratic forms are calcitic helictites, aragonitic helictites, globulites, and spicular aragonite. These forms can occur together, such as in the Chimes Chamber, or separately. Calcitic helictites have smooth exteriors, are often curved and twisted. They form anastamosing branches. Frostwork anthodites tend to be linear, jutting from the walls at all angles. They have rougher surfaces than the calcite helictites. Some calcite can be intergrown with the aragonite in these forms (White and Van Gundy 1974).
Small clusters of acicular aragonite crystals, herein called, spicular aragonite are also known as anthodites. They appear as bush- like clusters of crystals radiating from a common "stalk." Common in the caves are several globular or nodular forms of speleothems. Some appear as spherical lumps on the tips of other crystals. They are incredibly variable in their morphology. Also found tipping aragonite spicular crystals is a loose, white, powdery moonmilk composed of hydromagnesite (White and Van Gundy 1974).
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