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Difficulty: Very hardLandform Evolution by Running Water and Underground Water

During the structural evolution of a karst drainage basin, percolating meteoric water enriched with dissolved carbon dioxide descends vertically through unsaturated jointed limestone until it reaches an impermeable stratum. Which of the following correctly identifies the dominant process operating at the water table interface and the resulting subterranean landform?

  1. Chemical solution enlarging horizontal conduits along bedding planes to form phreatic cavernsAnswer
  2. B
    Corrasion (mechanical river abrasion) carving out vertical V-shaped gorges below the limestone layer
  3. C
    Metamorphic recrystallization forming crystalline marble pillars within subterranean hollows
  4. D
    Downslope gravitational mass movement slumping subterranean roofs into surface dry valleys

Answer

Chemical solution enlarging horizontal conduits along bedding planes to form phreatic caverns
The correct answer identifies chemical solution enlarging horizontal conduits along bedding planes to form phreatic caverns. As carbonated water descends through joints in permeable limestone and reaches the saturated water table, its flow becomes predominantly horizontal along bedding planes. The continuous solvent action of carbonic acid dissolves calcium carbonate, expanding horizontal fissures into extensive subterranean caverns.

Step-by-Step Solution

1
Analyze the rainwater movement and chemical agent in karst environments.
Meteoric water absorbs carbon dioxide to form weak carbonic acid (H2CO3H_2CO_3), which dissolves calcium carbonate (CaCO3CaCO_3) in limestone.
Limestone dissolution is driven primarily by chemical carbonation rather than mechanical stream abrasion.
2
Determine the physical behavior of groundwater at the water table interface.
Vertical percolating (vadose) water reaches the saturated (phreatic) zone and shifts to horizontal lateral flow along bedding planes.
Water cannot easily penetrate deeper impermeable strata, concentrating solvent activity laterally.
3
Identify the resulting geomorphic feature created at this horizontal interface.
Persistent chemical solution along horizontal planes excavates extensive subterranean cavern networks and cave systems.
Phreatic cavern evolution along bedding planes is the primary landform developed where horizontal groundwater flow dominates.

Key Concept

Karst Cavern Evolution and Underground Water Solution Processes
Estimated Time:2m 0s
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Topics

Landform Evolution by Running Water and Underground Water

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