Karst Landscape
Karst topography
• Exposed limestone
• Dissolving of carbonate rock
Chapter 9: Karst Landscape
Examples of karst regions
• The Burren, Co. Clare and Marble Arch, Co. Fermanagh
Chapter 9: Karst Landscape
Formation
• Limestone is permeable
• Carbon dioxide (CO2) dissolves in rainwater
• Forms weak carbonic acid
• Percolates through rock – rocks dissolved by carbonation
• Fissures in rock become enlarged
• Underground drainage system develops
Chapter 9: Karst Landscape
Surface landforms
1. Limestone pavement
•
Exposed area of limestone
•
Rugged and bare landscape with flat areas of rock
surface
Chapter 9: Karst Landscape
Formation
•
Carbonation (chemical weathering)
•
Rainwater mixes with carbon dioxide in the air
•
Forms a weak carbonic acid
•
More carbon dioxide is absorbed when the water
percolates through the soil, limestone is dissolved
•
Joints and cracks (i.e. bedding) are widened by the
rainwater
•
e.g. the Burren, Co Clare
Chapter 9: Karst Landscape
Features of limestone pavements
•
Clint: section of a limestone pavement separated from
adjacent sections by grikes
•
Grike: vertical crack that develops along a joint in
limestone
•
Karren: small hollow that forms on the surface of a
limestone clint
Chapter 9: Karst Landscape
2. Swallow holes
•
River reaches an area of permeable rock
•
Disappears down through grikes
•
Grikes made bigger by solution (carbonation)
•
Forms swallow hole (sluggas/sinkholes)
•
e.g. Poll na gColm in the Burren, Co. Clare
Dry valley = remains of river valley downstream
from sinkhole
River of resurgence = where river reappears
at the surface
Chapter 9: Karst Landscape
Subsurface landforms
1. Caves
•
Swallow holes – river disappears underground
•
Carbonation – passages form large caverns
•
River erodes the rock of the cave by abrasion and
hydraulic action
•
Carbonation and solution dissolve permeable rock
(limestone)
•
Cave develops at or below zone of saturation
•
e.g. Ailwee Cave, the Burren, Co. Clare; Dunmore
caves, Kilkenny
Chapter 9: Karst Landscape
2. Dripstone features
Stalactites
•
Drops of water containing dissolved limestone seep down
through cracks/fissures in the cave roof
•
Drops of water lose carbon dioxide and deposit calcite
•
Over time deposition of calcite forms pillars hanging
down from the roof of the cave
Stalagmites
•
Water droplets fall to the cave floor
•
Drops of water lose carbon dioxide and deposit calcite
•
Over time deposition of calcite form pillars growing
upward from the cave floor form directly below
stalactites
Chapter 9: Karst Landscape
2. Dripstone features (continued)
Pillars
•
Stalactites and stalagmites grow towards each other
•
Eventually join to form a pillar or column
Curtains
•
Rainwater drips from a long crack in a cave roof forms a
continuous strip of calcite
Chapter 9: Karst Landscape
The Burren, Co. Clare
•
Covers approximately 250 square km of north-west
Clare
•
Formed during the carboniferous period, 355 to 290
million years ago
•
Formed of limestone rock
•
Features include:

limestone pavements

subsurface and dripstone features

e.g. Ailwee Cave
Chapter 9: Karst Landscape
Cycle of erosion in a karst topography
Three stages:
1. Youthful
2. Mature
3. Old age
Chapter 9: Karst Landscape
1. Youthful stage
•
Rivers flowing on the surface
•
Erosion of impermeable rock
•
Then erosion of permeable rock (limestone)
•
Chemical weathering (carbonation)
•
Formation of swallow holes
Chapter 9: Karst Landscape
2. Mature stage
•
Dry valleys on the surface
•
Sink holes
Chapter 9: Karst Landscape
3. Old age stage
•
Weathering
•
Removal of limestone
•
Older more resistant rock left prominent – hums
•
Rivers once again flow over the surface