Chapter 9 Karst Landscape Karst topography Exposed limestone

Chapter 9: 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 (CO 2) 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 g. Colm 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