Presentation on theme: "Karst Landscapes Dev. due to: Hard jointed limestone… restricts path of water flow Low water table……….. stagnant water not shape landscape High rainfall……………"— Presentation transcript:
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 non- existant. 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.