CHAPTER 1 THE TECTONIC CYCLE
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Transcript CHAPTER 1 THE TECTONIC CYCLE
Karst Landscapes
AS Geography
Learning Outcome
• Understand the processes involved in the
formation of Karst Landscapes.
• List examples of Karst regions.
• Describe the surface and underground
landforms in a Karst region.
• Explain the life cycle of a Karst landscape.
Karst topography
Exposed limestone
Landscape created by water
Dissolving of carbonate rock
Examples of Karst Regions
• The Burren, Co Clare
• Marble Arch, Co
Fermanagh
• Kras, South-West
Slovenia
• Guilin, Guangxi
Region, China
Limestone & Carbonation
• Limestone is permeable
Rain takes in carbon dioxide as it passes through the
atmosphere
Carbon dioxide (CO2) dissolves in rainwater (H2O)
Forms weak carbonic acid (H2CO3)
The carbonic acid reacts with the calcium carbonate (CaCO3) in
the limestone
This forms calcium bicarbonate (Ca(HCO3)2), which is soluble
in water
This solution percolates through rock
It removes the calcium carbonate
Fissures in rock become enlarged
Underground drainage system develops
Karst Landscapes
SURFACE LANDFORMS
Limestone pavement
Exposed area of limestone
Rugged and bare landscape with flat areas of
rock surface
Formation of a Limestone Pavement
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
Solution; water containing the carbonic acid
dissolves the permeable limestone
Joints and cracks (i.e. bedding) are widened by
this process
e.g. the Burren, Co Clare
Features of limestone pavements
Clint: section of a limestone pavement
separated from adjacent sections by
grikes
Grike: vertical fissure that develops along
a joint in limestone
Karren: small hollow that forms on the
surface of a limestone clint
Swallow Holes
• A river disappears underground in a limestone
region
Formation of Swallow Holes
River reaches an area of permeable rock
Disappears down through grikes
Grikes made bigger by solution (carbonation)
Forms swallow hole (sinkholes)
2.
Dry valley = remains of
river valley
downstream from
sinkhole
River of resurgence =
where river
reappears at the
surface
Pairwork Quick Questions
• Explain the process of carbonation.
• Explain the term ‘permeable’.
• Name two surface landforms in a limestone
region.
• Which part of the limestone pavement would
you walk on?
• Give two other words used to describe a
swallow hole.
Learning Outcome
• Lesson 2
– Recap on Karst landscapes & examples
– Recall the surface landforms in a Karst region
– Complete & Label diagram showing all Karst
features
– Watch video clips explaining the formation of
Karst landforms
– Homework; Page 84 Q 1, 2 & 3.
Karst Landscapes
VIDEO CLIPS
Karst Landscape
UNDERGROUND LANDFORMS
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
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 the stalactites hanging down
from the roof of the cave
Stalactites are hollow mineral tubes, like drinking straws
They are very thin and fragile
Stalagmites
Water droplets fall to the cave floor
Drops of water lose carbon dioxide and deposit calcite
Over time deposition of calcite form the stalagmites growing upward
from the cave floor form directly below stalactites
Stalagmites are thicker than the stalactites
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
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
Pairwork; OS Map Task
• OS Map of the Burren Area, page 82
– Give a grid reference for the Ailwee area
– Identify the height of the limestone terrace shown
on the map
– Locate and identify two swallow holes found on
this OS map extract
Cycle of Erosion in a Karst Topography
Three stages:
Youthful
Mature
Old age
Youthful stage
Rivers flowing on the surface
Erosion of impermeable rock
Then erosion of permeable rock (limestone)
Chemical weathering (carbonation)
Formation of swallow holes
Mature stage
Dry valleys on the surface
Swallow holes
Old age stage
Weathering
Removal of limestone
Older more resistant rock left prominent – hums
Rivers once again flow over the surface
Quick Revision Questions
• Name the main weathering process effective on
limestone
• List the three parts of a limestone pavement
• Name another surface landform found in a
limestone region
• Name four underground landforms in a limestone
region
• Describe a stalactite
Exam Questions
• With reference to the Irish landscape, examine how
the process of weathering has influenced the
development of any one limestone feature. (30m)
• Examine with reference to an example you have
studied, the formation of one rock type and how it
produces a distinctive landscape. (30m)
• Explain with the aid of diagrams, how any two
underground landforms, found in a Karst region are
formed. Give a named example of each in your
answer. (40m- OL)