Geomorphic cycle pdf

If three or more radiating glaciers cut headward until their cirques meet, high, sharp pointed and steep sided peaks called horns form. Glaciated valleys are trough-like and U-shaped with broad floors and relatively smooth, and steep sides.

There may be lakes gouged out of rocky floor or formed by debris within the valleys. There can be hanging valleys at an elevation on one or both sides of the main glacial valley.

They are long ridges of deposits of glacial till. Terminal moraines are long ridges of debris deposited at the end toe of the glaciers. Lateral moraines form along the sides parallel to the glacial valleys.

The lateral moraines may join a terminal moraine forming a horse-shoe shaped ridge. When glaciers melt in summer, the water flows on the surface of the ice or seeps down along the margins or even moves through holes in the ice.

These waters accumulate beneath the glacier and flow like streams in a channel beneath the ice. Such streams flow over the ground not in a valley cut in the ground with ice forming its banks. Very coarse materials like boulders and blocks along with some minor fractions of rock debris carried into this stream settle in the valley of ice beneath the glacier and after the ice melts can be found as a sinuous ridge called esker.

The plains at the foot of the glacial mountains or beyond the limits of continental ice sheets are covered with glacio-fluvial deposits in the form of broad flat alluvial fans which may join to form outwash plains of gravel, silt, sand and clay.

Drumlins are smooth oval shaped ridge-like features composed mainly of glacial till with some masses of gravel and sand. The long axes of drumlins are parallel to the direction of ice movement. They may measure up to 1 km in length and 30 m or so in height. Wind is one of the dominant agents in hot deserts. The wind action creates a number of interesting erosional and depositional features in the deserts.

Gently inclined rocky floors close to the mountains at their foot with or without a thin cover of debris, are called pediments. Plains are by far the most prominent landforms in the deserts. In times of sufficient water, this plain is covered up by a shallow water body.

Such types of shallow lakes are called as playas where water is retained only for short duration due to evaporation and quite often the playas contain good deposition of salts. Weathered mantle from over the rocks or bare soil, gets blown out by persistent movement of wind currents in one direction. This process may create shallow depressions called deflation hollows. Deflation also creates numerous small pits or cavities over rock surfaces. The rock faces suffer impact and abrasion of wind-borne sand and first shallow depressions called blow outs are created, and some of the blow outs become deeper and wider fit to be called caves.

Many rock-outcrops in the deserts easily susceptible to wind deflation and abrasion are worn out quickly leaving some remnants of resistant rocks polished beautifully in the shape of mushroom with a slender stalk and a broad and rounded pear shaped cap above. Sometimes, the top surface is broad like a table top and quite often, the remnants stand out like pedestals.

When the wind slows or begins to die down, depending upon sizes of grains and their critical velocities, the grains will begin to settle. Dry hot deserts are good places for sand dune formation.

Obstacles to initiate dune formation are equally important. There can be a great variety of dune forms Crescent shaped dunes called barchans with the points or wings directed away from wind. Parabolic dunes form when sandy surfaces are partially covered with vegetation.

That means parabolic dunes are reversed barchans with wind direction being the same. Seif is similar to barchan with a small difference. Seif has only one wing or point. Longitudinal dunes form when supply of sand is poor and wind direction is constant. They appear as long ridges of considerable length but low in height. Transverse dunes are aligned perpendicular to wind direction. These dunes form when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind direction.

Soil erosion is of four types which are as follows:- Wind Erosion :-Winds carry away vast quantity of fine soil particles and sand from deserts and spread it over adjoining cultivated land and thus destroy their fertility. This type of erosion is known as wind erosion. It takes place in and around all desert regions of the world. These areas are subject to intense wind erosion.

Sheet Erosion :-Water when moves as a sheet takes away thin layers of soil. This type of erosion is called sheet erosion. Such type of erosion is most common along the river beds and areas affected by floods. In the long run, the soil is com- pletely exhausted due to removal of top soil and becomes infertile.

Rill Erosion :-The removal of surface material usually soil, by the action of running water. The processes create numerous tiny channels rills a few centimeters in depth, most of which carry water only during storms. Gully Erosion :-When water moves as a channel down the slope, it scoops out the soil and forms gullies which gradually multiply and in the long run spread over a wide area. This type of erosion is called gully erosion.

The land thus dissected is called bad lands or ravines. In our country, the two rivers Chambal and Yamuna are famous for their ravines in U. Soil Formation Soil consists of rock and sediment that has been modified by physical and chemical interaction with organic material and rainwater, over time, to produce a substrate that can support the growth of plants.

Factors of soil formation are:- Parent material: soil formation depends on the mineral material, or organic material from which the soil is formed.

Soils will carry the characteristics of its parent material such as color, texture, structure, mineral composition and so on. For example, if soils are formed from an area with large rocks parent rocks of red sandstone, the soils will also be red in color and have the same feel as its parent material. Time: Soils can take many years to form. Younger soils have some characteristics from their parent material, but as they age, the addition of organic matter, exposure to moisture and other environmental factors may change its features.

With time, they settle and are buried deeper below the surface, taking time to transform. Eventually they may change from one soil type to another. Climate:Two important climatic components, temperature and precipitation are key.

They determine how quickly weathering will be, and what kind of organic materials may be available on and inside of the soils. Moisture determines the chemical and biological reactions that will occur as the soils are formed. Warmer climate with more rainfall means more vegetative cover and more animal action.

It also means more runoff, more percolation and more water erosion. They all help to determine the kind of soils in an area. Steep, long slopes mean water will run down faster and potentially erode the surfaces of slopes.

The effect will be poor soils on the slopes, and richer deposits at the foot of the slopes. Also, slopes may be exposed to more direct sunlight, which may dry out soil moisture and render it less fertile. Organisms:The source and richness of organic matter is down to the living things plants and animals that live on and in the soils.

Plants in particular, provide lots of vegetative residue that are added to soils. Their roots also hold the soils and protect them from wind and water erosion. They shelter the soils from the sun and other environmental conditions, helping the soils to retain the needed moisture for chemical and biological reactions. Fungi, bacteria, insects, earthworms, and burrowing animals help with soil aeration.

The major assumption which Davis made was that the erosion starts only after the uplift has stopped. The uplift is complete and has stopped.

Immediately erosion of the uplifted block sets in. The streams follow initial irregularities available without adjusting to the structure. These are consequent streams. The floors of the valley suffer down cutting while the summits remain almost unaffected.

At this stage, the vertical erosion slows down and the horizontal action increases. A characteristic feature is the erosion of mountain tops at a faster rate than lowering of the valley floor. The subsequent streams gain importance now. A gentle gradient, accentuated by horizontal action and deposition, reduces the erosion intensity. A thick layer of sediment represents the earlier erosion activity. Relicts of mountains or monad knocks are dotting the water divides and a featureless plain—peneplane is produced.

The Davisian cycle affords a genetic classification and nomenclature of landscape, as compared to a morphological one and provides the means of expressing texture and the build of a landscape. The consideration by Davis of change in base level as indication of the initiation of a new cycle has certain advantages.

Two, the base level changes during glaciations are accommodated. In a way, the geographical cycle proposed by Davis is backward looking as it considers complete suspension of uplift after the erosion has set in.

There are no logical grounds for the assumption that flat slopes are old and steep slopes are young. Other variables controlling the slope are nature of soil material and the bedrock, climate, vegetation and the downslope factors acting at the slope foot.

An ideal Davisian cycle would take millions of years to complete. What about the earth movements during the cycle? Too much of generalisation in the Davisian cycle presents an inadequate framework for landform interpretation. There is little evidence to prove that landforms actually evolve to an end product or peneplane. Penck made certain deviations from the views of Davis. One, the erosion does not remain suspended till the uplift is complete.

In fact, he said, the geomorphic forms are an expression of the phase and rate of uplift in relation to the rate of degradation, and that interaction between the two factors, uplift and degradation, is continuous. Two, the rate of uplift keeps changing. Penck proposed three types of valley slopes on the basis of erosional intensity acting on crustal movements.

A short summary of this paper. Download Download PDF. Translate PDF. Ajay Kumar extension assistant professor M. Davis was geography professor at Harvard University. He wrote about his model from , travelled and spoke widely.

Like his contemporaries in natural science he was strongly influenced by Charles Darwin On the Origin of the Species and Charles Lyell Principles of Geology , although used evolution as a notion of history inevitable progress or change over time rather than a process and took a deterministic rather than probabilistic view of evolution like Darwin.

This is the first model of landscape evolution to gain widespread acceptance within the discipline. The cycle of erosion was a model for stream erosion and landscape development proposed by William Morris Davis in the late 19th century. Davis' Stages in the fluvial cycle of erosion published in defined a young, mature, and old sequence in the development of river valleys and the landscape the rivers were eroding.

His basic concept includes a rapid tectonic uplift, followed by cessation of the land, which allows the rivers and streams to reduce the surface to a level close to sea-level.

The concept of peneplanation was a part of his model. In his model Davies picked up ideas of John Wesley Powell about limitation of erosion on land and concluded that sea level is the ultimate base level for subaerial erosion. Further he suggested that streams always have at least some gradient and temporary base levels, such as inland-lakes, are controlling points upstream of them.

It has three stages of its model i. Davis stated that the cycle begins with the uplift of mountains. Rivers and streams begin to create v-shaped valleys in their younger stage and during the first stages, the relief is steepest and most irregular in nature. Next, the streams are able to carve wider valleys in mature stages and then begin to meander, leaving only gently rolling hills in old age.

Developments in the sciences of geology and geomorphology, especially the plate tectonics revolution of the s and 70s, have confirmed the preliminary nature of the model. Walther Penck worked — in Argentina as a geographer, and is best known for his contributions to the field of geomorphology. In particular, he opposed key elements of the Davisiancycle of erosion, concluding that the process of uplift and denudation occur simultaneously, at a gradual and continuous rate.

Walther Penck, the German geologist, put forward his thesis of landform evolution in His main work was in the German language which was translated into English Czech and Boswell Penckcriticised and opposed the cycle concept of Davis. In fact, Davis and Penck saw geomorphology through different eyes. Davis attempted the explanatory description of landscape, adopted another standpoint that the main purpose of geomorphological research is to obtain information that might contribute to the understanding of crustal earth movements.

Penck did not agree with Davis' assumption of very rapid uplift of a land surface followed by a long period of crustal stability.