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Publication Date

January 1985

Keywords

United States, Regional Speleology, Geology

Description

MS Thesis of Roy Jameson, West Virginia University, 1985. Fractures influence cavern development by promoting bedrock collapse. Fractures also localize solution, thus guiding flow paths and promoting the growth of blind fissures or the j i u fragmentation of bedrock. Observations in branchwork caves in West Virginia suggest a method of inferring the locations of the early flow paths along fractures (structural segments) and of analyzing their subsequent enlargement. Detailed mapping and morphologic analyses of structural segments in the Union Limestone (Mississippian Greenbrier Group) in the North Canyon of Snedegar Cave, indicate stage I phreatic growth as ungraded tubes. Flow was guided mostly by bed partings (37%), systematic joints (29%), or bed-joint intercepts (20%). Thrust faults and their intercepts with joints guided 11% of the 1382 feet of inferred tubes. The stage I tubes lay on two levels separated by joint conduits. At the end of stage I, flow paths formed a complex network with several closed loops. Stage II began with the earliest onset of vadose conditions. Low-discharge streams incised the apices of the ungraded tubes, forming narrow trenches. Lower parts of the ungraded conduits grew under closed-conduit flow in -pressure loops. Where stage I flow paths branched in a downstream direction, the higher downstream paths were abandoned, because stream depth was insufficient for flow to continue past high points. This process reorganized the flow system into three active conduits and three abandoned tubes. The active conduits became canyons (the North Canyon, the Headwall Passage, and the Saltpetre Maze Passage) as the streams cut down, removing pressure loops and grading the floors of the narrow trenches. The joint conduits between the two levels enlarged as shafts. Stage III began with the introduction of clastic sediments. The sediments promoted undercutting, leading to the development of wide undercut surfaces. Wide trenches formed beneath these surfaces. A partial grading of the floor between the two levels was effected in the North Canyon by headward incision and lowering of the lip of the shaft, combined with a flow-path diversion. Collapse produced wedge-shaped breakdown where undercutting was extensive below bedrock bounded by faults, joints, and the narrow trenches. Open Access See Extended description for more information.

Subject: topical

Regional Speleology; Geology

Subject: geographic

United States

Type

Article

Genre

Thesis / Dissertation; serial

Identifier

K26-04284

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