8 LANDFORMS RESULTING FROM WEATHERING IN EAST AFRICA

 Although weathering is all about wear and tear of the earth’s surface, in the process it leads to the formation of landforms, especially within the karst regions.

Karst regions are regions made up of limestone rocks.

These landforms include;

Glikes and clints:

These are formed during the process of carbonation where by rainfall dissolves CO2 in the atmosphere to form weak carbonic acids.

These carbonic acids act on limestone rocks to form calcium carbonates or converted to a more readily dissolvable form of calcium bi carbonates.

In areas where limestone rocks alternate with rocks with different minerals, the weak CaCO3 are removed in solution to form ditch-like depressions called grikes while the hard resistant rocks remaining behind form round topped ridges called clints e.g. at Kajjansi near Kampala.

Stalactites.

These are features found mostly in karst regions (areas with limestone rocks).

They are protrusions found on the roof of a chemically weathered limestone cave.

Stalactites are therefore formed when rainwater mixes with carbon dioxide in the atmosphere to form weak carbonic acids.

These carbonic acids dissolve the limestone rock on the roof of the cave and the solution starts dripping on the floor.

When water evaporates, dripping stops and finger like projections are left on the cave and are called stalactites. 

Best examples are found at Nyakasura in Fort-Portal in kabarole district in Uganda and Tanga in Tanzania.

Stalagmites

These are formed together with stalactites in the karst regions.

A stalagmite is a landform that arises from the floor of the cave due to the accumulation of materials deposited on the floor from ceiling drippings.

These are therefore formed on the floor of the cave by dripping water from the roof of the cave.

When water evaporates from the dissolved calcium carbonate, it leaves behind a dry and compact mass of limestone protruding upwards and this forms a stalagmite and are also found at Nyakasura.

Pillars.

A pillar is an upright shaft or structure of stone or any other mineral relatively slender in proportion to its height and can be of any shape in section.

Pillars are formed hen stalagmites and stalactites meet in a limestone cave. They appear as vertical stands of calcium carbonates.

Underground caves.

These are natural hollows formed under ground by rivers. They are formed when a river flowing into a karst region disappears underground hence removing the limestone rocks in solution.

They are formed due to the solution. Solution is the removal of rock in solution by acidic rain.

Some rocks are chemically weathered by being dissolved in water for example limestone and after weathering off such rocks, it forms impressive features like widened hollows for example the caves at Nyakasura.

Sinkholes.

A sinkhole is a depression or hole in the ground caused by some form collapse of the surface area. 

Sinkholes occur due to erosion or underground water. They start developing longtime due before it actually appears.

Most of the sinkholes occur due to karst processes of chemical dissolution of carbonate rocks.

The formation of sinkholes involves the process of erosion or gradual removal of slightly soluble bedrock such as limestone by percolating water, the collapse of cave roof, or a lowering of water table.

Sinkholes often from through the process of suffusion for example groundwater may dissolve the carbonate cement holding the sandstone particles together and then carry away the lax particles gradually forming a void or sinkhole.

Exfoliation domes

An exfoliation dome is a large dome-shaped form, developed in massive homogenous coarse-grained rocks especially granite by exfoliation.

Exfoliation is a term used to describe the peeling away of sheets of rock millimeters to meters in thickness from a rock’s surface due to a range of physical and chemical processes during exhumation and weathering.

Therefore, if a form of mechanical weathering in which curved plates of rocks are stripped from the rock below.

Exfoliation domes therefore a result of physical weathering by exfoliation. The rapid heating and cooling especially in the areas of high temperatures cause expansion and contraction of rocks.

The outer most layer of the rock is eventually detached from the original and it peels off.

This leaves behind a round topped rock called an exfoliation dome. Best examples are seen at Mubende along Mubende- kyenjojo road.

Arenas

these are lager circular depressions on the earth’s surface. They are formed in areas of alternating bands of hard and soft rocks.

So the soft rocks are weathered away leaving behind the hard and resistant rocks.

The soft rocks are removed leaving behind circular depressions which may or may not be filled with water to form arenas.

Examples can be seen on the slopes of mountain Rwenzori in the areas of Ntoroko.

Tors

these are remnants of weathered rocks rooted in the bed rocks.

These appear onto the earth’s surface as basaltic remnants.

They are common in jointed rocks which are weathered deep and when denudation forces remove these debris, tors remain as resistant rocks bedded in as un-weathered.

Best examples can be seen in Kenya at Kitmikaye near Seme, Bismark rock in Lake Victoria near Mwanza.

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