ESSAY OUTLINE 1

Question: State the geological conditions that limestone has which allows for karst landscape formation.

- Chemical Composition: composed largely of the mineral calcite (calcium carbonate: CaCO3). Limestone often contains variable amounts of silica in the form of chert or flint, as well as varying amounts of clay, silt and sand as disseminations, nodules, or layers within the rock. The primary source of the calcite in limestone is most commonly marine organisms. These organisms secrete shells that settle out of the water column and are deposited on ocean floors as pelagic ooze or alternatively is conglomerated in a coral reef. It is alkaline in nature.

*Hence soluble by surface and groundwater.
Though it must be present near or at the surface and less than 50 feet of loose soil covering this soluble rock.

- Porosity: Low porosity due to the compaction of the sediments under high pressure during its formation.

*provides mechanical strength to support karst features such as caves. Consolidation also affects the surface slope development where weak limestone, due to lack of mechanical strength resulting from high porosity.

- Rock Jointing:
-Types of Rock Jointing: Presence of styolites, vertical joints and extensive bedding planes due to the processes of lithification.

- Permeability: High permeability due to the bedding planes, styolites (due to iron oxide content) and vertical joints which act as avenues of weakness.

*Jointing MOST IMPORTANT FACTOR because they permit rocks to holds more water and facilitate groundwater circulation through the system by increasing permeability, which is more important than porosity in the formation of karst.

- Specific Location: Travertine is a banded, compact variety of limestone formed along streams, particularly where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution that is supersaturated with chemical constituents of calcite. Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells.

*High relief is necesary in order that there can be development of verticaland underground circulation of drainage. Space must be available for these movements of water hence the height of the karst area above the sea level or above the level of through-flowing rivers must be great enough for a full circulation of underground water to develop. SPECIFIC location is then important.

Other factors that are undermined by the more important factors stated above in relation to karst formation:

- Rock Hardness: Relative hardness rating a H:3 on the Moh’s scale (comparable to that of a penny)

- Rock Texture: The texture varies from coarse to fine. Most limestones have a granular texture. Their constituent grains range in size due the variation in chemical composition where Limestone being a sedimentary rock has a mixture of rock components in them.

- Rock Colour: Pure limestone is white or almost white. Because of impurities, such as clay, sand, organic remains, iron oxide and other materials, many limestones exhibit different colors, especially on weathered surfaces.