Geography/Geology 352: Geomorphology

KARST PROCESSES & LANDFORMS

A. Introduction

• karst connotes an assemblage of landforms and a set of processes

• agenda:

  • examine the impact of driving forces and the resisting framework on the development of karst

  • explore karst hydrology

  • review karst landforms

  photo: USGS http://pubs.usgs.gov/circ/circ1182/pdf/15WCFlorida.pdf

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B. The Driving Forces

1. The Solution Process

• Main reaction:

CaCO₃ + H₂O + CO₂ = Ca⁺² + 2HCO₃^-

2. Factors Controlling the Solution Rate

a. amount dissolved CO₂

• partial pressure of CO₂ in air: as the PCO₂ increasese, the quantity of CO₂ absorbed by water increases

• temperature: cooler water is capable of dissolving more CO₂ that warmer water at a given PCO₂

• biological processes: decaying humus is an important source of CO₂

b. climate

• temperature, precipitation, biological activity

• runoff generation is the most important effect of climate

 

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C. The Resisting Framework

1. Lithology and structure - ideal conditions for a fully developed karst landscape requires limestone that is:

a. fairly pure (over 60% calcite for some karst; over 90% calcite for fully developed karst landscape)

b. very thick

c. mechanically strong

d. massively jointed

2. Porosity and permeability

a. porosity: percentage of pore spaces in a given volume of rock or soil

• primary porosity: intergranular voids

  affected by:

  • grain size distribution

  • particle shape

  • degree of packing

• secondary porosity: voids due to joints, faults, fratures or bedding planes

  • promotes circulation by increasing permeability

• porosity is important only if rocks are also permeable

b. permeability: ease with which rock or soil transmits water

 

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D. Karst Hydrology

1. Surface Drainage - dry valleys and disrupted surface drainage

2. Subsurface Drainage

a. Model 1

• vadose zone (zone of aeration)

• phreatic zone (zone of saturation)

• water table reflects overlying topography

• diffuse aquifers

groundwater flow follows Darcy's Law:

V = volumetric flow rate
h = head
L = distance between 2 measurement
      points
K = hydraulic conductivity

Q = discharge
K = hydraulic conductivity
I = hydraulic gradient
A = cross-sectional area

b. Model 2

• no water table

• collection of conduits that function like a 3-dimensional river system

• conduit aquifers

  • groundwater flow determined by gravity; may be turbulent

   

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E. Karst Landforms

1. Dolines (sinkholes)

a. dissolution sinkholes
image source: USGS http://ga.water.usgs.gov/edu/sinkholes.html

b. collapse sinkholes
image source: USGS http://ga.water.usgs.gov/edu/sinkholes.html

photo: A.S. Navoy. USGS Landslide Hazards Program, Landslide Images http://landslides.usgs.gov/learningeducation/imagepreviews.php

2. Uvala

3. Poljes

4. Karst valleys

5. Cockpit & tower karst

6. Caves

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F. Summary