Karst Landscapes
Dev. due to:
Hard jointed limestone… restricts path of water flow
Low water table……….. stagnant water not shape landscape
High rainfall…………… supply underground water
Carbonation Limestone consits of mainly calcium carbonate (insoluble). Rainwater
absorbs carbon dioxide & forms a weak carbonic acid. This changes calcium carbonate to
calcium and bicarbonate atoms (soluble) which can be washed away in solution.
Landforms
Limestone pavement: Examples: Black Head, Burren, Co. Clare and Marble Arch
Uplands, Co Fermanagh -A large flat area of exposed limestone with no soil. Carbonation
worked on the joints --- widened and deepend to form grikes. Grikes were seperated by
flat topped blocks called clints. Water rests on the clints and cause hollows called karrens
and their edges become fluted. Process: Carbonation & Solution.
Swallow Holes: Large cone shaped cavities on a stream bed. Associate with streams
diappearing underground. Formed by carbonation & solution weathering the rocks. Water
trickles through a crack & enlarges it. Aided by abrasion & hydraulic action. These create
underground passages, as the rock is divided by joints and bedding planes when the
underlying rock is eroded the top collapses Eg. Slieve Elva and Poulnabunny Co Mayo.
Downstream is left a dry valley where the river used to once run
Processes: Collapse, faulting, carbonation & solution
Closed Depressions Hollows in the grouund ranging from 2 metres to 100s metres in
depth & diameter.
Doline: smallest… circular…due to joints widened or cave roof collapsing.
Uvula: where several dolines combine or an underground cavern collapses.
Polje: largest enclosed depression. Has steep sides, flat floor & several kilometers in
area. Caused by several Uvulas combining or downfaulting in the limestone due to
tectonic activity. May be further added to by glacial ersoion. Eg. Carran
Depression
Dry Valley: Valley carved out by a river but is now dry.
1)
Meltwater streams from galciers cut the valley. Stream disappeared when ice
melted.
2)
River disappeareed down a swallow hole.
Turlough Seasonal lakes…. Hollows in limestone… Due to fluctuations in water table.
Underground Landforms
Caves & Caverns: Large underground passage. Acidic (ph5.6) groundwater flows along
cracks & dissolves limestone through carbonation. Enlarged over time & eroded further
by hydraulic action & abrasion. Most caves formed in zone of saturation as flowing
ground water dissolves the limestone. Meltwater from melting ice sheets at end of Ice
Age released vast amount of meltwater and boulders that enlarged them into enormous
caverns. Many are currently dry due to water table falling. Eg. Ailwee caves.
Speleothem/Dripstone Features
Stalactites: Water containing atoms of calcium and bicarbonate drips from the ceiling,
as it drips the carbon dioxide is released reversing the process of carbonation and what
remains crystalises into calcite rings forming straw stalictites. Originally hollow but
straw gets blocked - carrott shaped stalactite. Dunmore Co. Kilkenny
Stalagmite: Water drips to the floor & deposits of calcite build up. Shapeless due to
dripping effect. (solution & evaporation) Mitchelstown Co Cork
Stalagmite & Stalagtite meet to form pillars. Craig, Co Kerry
Curtains: Form similar to stalactites but on slanted ceilings. Grows out from the wall.
Eg. Ailwee caves.
Karst Cycle:
Tower Karst Landscape
Isolated tower like hills seperated by flat areas of alluvium. Represents old age stage
of Karst weathering.
Youthful stage: Rivers cut through rock onto underlying limestone.
Surface streams erode rock. Joints & bedding planes opened & widened. Some
streams disapper underground.
Mature stage: Dry valley, turloughs formed. Surface drainage nonexistant. Underground drainage creates caverns & tunnels. Roof begins to collapse to
form Poljes. Reached the impermeable rock.
Old Stage: Landscape lowered. Large scale collapse of underground
landforms. Tower like hills of limestone called hums remain. Caverns & underground
drainge system eliminated. Surface drainage recommences creating flat alluvial
floodplains.