Discuss the impact of weathering on landforms

Weathering controlled landforms are those whose formation is dominated by process.Erosional,depositional and complex varieties may be identified.Erosional varieties are formed when the weathering selectively attacks bedrocks.If the transporatation complex is linked to the weathering process then an erosional,weathering generated landform may be recognised.example:-removal in solute form of bedrock,removal of material by action of lichen and algae.Depositional types are formed when transportation process,form landforms,acts on the results of weathering.Example:-scree.

In Complex type weathering plays a major role but unrelated transport process actually generate relief.Example:-tor.

erosional forms:-

a)Microforms:-Smaller erosional landforms can not be atributed to a single process.chemical alteration may exploit an existing weakness (perhaps a set of microcracks) and may be associated with biological weathering ,often due to lichen colonisation.uder a suitable conditions salt crystalisation may act to exploit the weakness.

        In pit development,the hollow begins with dissolution of dark coloured minerals and is rounded by the removal of the small grains and mineral fragments.

          In case of differential weathering forms ,diferent composition occur next to each other.the contrast in degree of weathering is enhanced by mechanical and biochemical actions of the lichens.Example;-There may be marked depressions along band  that contain mica,hornblende and other mafic minerals.

            honey combs form has the tendency to widen inwards and the holes tend to occur at sites of microcrack development and their growth is encouraged by lichen activity,at coastal location it's due to salt crystallization.

Mesoforms:-

A rounded boulder(or corestone) is sphereoidal weathering and is typically developed in igneous rocks.Initially square ,joint bounede blocks develop with grus in the cracks which later develop into rounded boulders.Other theory include weathering pattern influenced by microcracks arrangement especially rectangular.Other ideas involve chemical weathering,pressure release and development of Liesegang rings.

       solution channel are common on exposed sloping surface of soluble rock such as hard limestone.the group term is called rillenkarren & dimensions vary.Biological weathering by algae may be important.similar channels sometimes called 'flutes' may be found on les soluble rocks like granites and sandstone are most typical of karst region.

   Large weathering pits  in temperate regions starts as small depressions periodically filled with rain and organic debris.On the granite rocks the acid solution brings enlargement.On quartz rich sandstone iron precipitate and aid lichen growth, with mineral destruction through action of hyphae.At other places salt crystallization &/or bio-chemical weathering aid weathering pit formation.

A flake (a sheet of fairly uniform thickness  is formed in all environments & in all rock types (like granite sandstone and limestone  and by a variety of process including chemical weathering (especially hydration),insolation,pressure release,salt crystallization and natural fires.

A rough surface is an area of individual depression(1-5 m deep) that we have merged and is often found on gneiss where hollows develop at mica-rich sites and at most locations which favour chemical weathering enhanced by typical prescence of micro-cracks.

Macrofroms:-

Enhanced chemical weathering at the base of the rock outcrop may bring relatively rapid and local retreat of the face with the development of overhangs or rock shelters.Example:-Haytor rocks,Dartmoor,south-west England.

Depositional forms:-

Scree is a deposit of angular rock fragments resting against step slope and is a product of frost shattering  and gravity.the fossil nature of snowdonian screes(north wales) is indicated by their partial burial beneath a veneer of later soil.

Complex landforms:-

Tor is an eposed mass of blocky or rounded rocks,generally undistributed and is widely found on massively jointed crystalline rocks (i.e.,granites etc.).apart from weathering ,rock properties and erosional processes contribute significantly.Physical weathering (frost action) guided by joint density and chemical weathering by fluid action.It may have emerged as a major component of an incised etchplain which is still evolvong.We find 2 types of joint structure.

Lateritic landscapes ,lateritic mantles between 10 - 150m. thick and consisting of highly weathered material rich in secondary forms of iron and or aluminium and depleted in silica,are found in 30(degree)N - 30(degree)S.their thickness and character,particularly development of upper hardened horizons/duricrusts which provide parent material for landform development.It is supported by erosion as well as weathering.