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Difficulty: Very hardLandform Evolution by Running Water and Underground Water

In the geomorphic development of a karst landscape, groundwater percolating through well-jointed limestone dissolves calcium carbonate to form distinct subterranean and surface features. Which of the following sequences correctly orders the evolutionary stages of these landforms from initial surface solution to the most advanced stage of cavern collapse?

  1. A
    Terra rossa formation → Blind valley truncation → Stalactite formation → Oxbow lake development
  2. Swallow hole (gripe) → Doline → Underground cavern excavation → Polje with karst windowAnswer
  3. C
    Gorge formation → Interlocking spur development → Cavern collapse → Stalagmite growth
  4. D
    Mechanical frost wedging → U-shaped trough excavation → Doline formation → Stalactite growth

Answer

The correct sequence begins with a swallow hole (gripe), followed by doline expansion, underground cavern excavation, and ultimately the formation of a polje with a karst window.
The correct answer accurately outlines the progressive development of limestone terrain under the action of underground water. Surface runoff enters enlarged joints at a swallow hole, expands surface hollows into dolines, excavates subterranean caverns through carbonation, and eventually causes roof collapses that expose underground streams via karst windows and form extensive flat-floored poljes.

Step-by-Step Solution

1
Identify the primary chemical weathering process
Groundwater reacts with carbon dioxide to form weak carbonic acid, dissolving calcium carbonate along limestone joint planes.
Karst landforms develop predominantly through solution (carbonation) by underground water.
2
Trace the initial surface entry points of water
Surface streams disappear underground via sinkholes or swallow holes (gripes).
Joint enlargement at the surface diverts surface runoff into subterranean drainage systems.
3
Analyze intermediate subterranean and surface collapse features
Solution hollows enlarge into dolines, while continuous subterranean solution hollows out massive caverns.
Subterranean stream flow enlarges underground passages along bedding planes and vertical joints.
4
Determine the advanced/mature stage landforms
Cavern roofs collapse to expose underground rivers (karst windows) and create expansive flat-floored depressions (poljes).
Extensive structural collapse of roof rocks marks the late stage of karst landscape evolution.

Key Concept

Karst Geomorphology and Subterranean Landform Evolution
Estimated Time:1m 30s
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Topics

Landform Evolution by Running Water and Underground Water

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