LIMESTONE AND CHALK LANDFORM

Sedimentary rocks of organic origin, primarily formed from coral accumulation, result in unique landscapes known as karst topography. Largely composed of calcite (CaCO3) in its pure state, these formations are highly soluble in rainwater, creating distinct features that characterize karst regions globally. In its pure state, the rock consists of calcite, and when combined with magnesium, it forms dolomite. This distinctive composition contributes to the solubility of the rock, shaping karst landscapes.

1. Karst Features

• Precipitous Slopes: The karst landscape is often broken by steep and abrupt slopes.
• Absence of Surface Drainage: Unlike other terrains, karst regions lack surface drainage; most water flows underground.
• Underground Streams: Streams that briefly flow on the surface soon disappear underground, rendering the surface dry.
• Springs and Resurgences: Water penetrating the limestone re-emerges on the surface as springs or resurgences.

Structural Features

Formation of Surface Features

1. Swallow Holes: Small depressions on the surface formed by rainwater.
2. Sink Holes: Points of weakness where rainwater sinks into limestone, forming holes like Gaping Ghyll in Yorkshire.
3. Caverns and Gorges: Water sinking into limestone etches out caverns, and when the roof collapses, limestone gorges such as Cheddar Gorge are formed.
4. Dolines: Swallow holes coalesce to form larger holes known as dolines.
5. Uvala: Dolines merge to create uvala, expansive depressions often covered with clayey soil.
6. Polje: In Yugoslavia, large depressions called polje span hundreds of square miles, influenced by faulting. During the rainy season, the floor near the water table becomes temporary lakes.

2. Subterranean Features

1. Underground Passages: Streams descend through swallow holes into underground passages, forming caves.
2. Stalactites and Stalagmites: Calcium carbonate carried in solution creates formations like stalactites, descending from cave roofs, and stalagmites, rising from cave floors. When stalactites and stalagmites join, they form pillars.

Prominent Karst Caves

1. Batu Caves (Kuala Lumpur): A notable cave system in Malaysia.
2. Mammoth Caves (Kentucky): Extensive cave networks in Kentucky, USA.
3. Carlsbad Cave (New Mexico, USA): A renowned cave system in New Mexico.
4. Postojna Caves (Yugoslavia): Notable limestone caves in Yugoslavia.

3. Distribution of Karst Regions

• Causses in Southern France
• Pennines in Britain (e.g., Yorkshire and Derbyshire)
• Kentucky in the USA
• Yucatan Peninsula in Mexico
• Cockpit Country in Jamaica

4. Human Activities in Karst Regions

1. Vegetation and Settlements: Karst regions are mainly barren with thin soil, high porosity, and a lack of surface drainage, making vegetative growth challenging. Scattered settlements with sparse populations are common.
2. Resource Utilization: Lead, often found in conjunction with limestone, is extracted for use in the cement industry. Quarrying activities, such as those in West Malaysia, support cement works.

5. Chalk Landforms

• Little or no surface drainage
• Dry valleys, known as coombes, replacing former water-filled valleys
• Low-rounded hills in Southern and Southeast England, called Downs in North France
• Covered with short turfs and woodland