Geomorphology is a science of the evolution, classification and mapping of the landforms. Evolution of the landforms depends on the geological time scale and not on the human time scale. Geomorphology significantly contributes in the development and management of the natural environment.
On the basis of factual and functional aspects, geomorphological investigations could be of following types:
1. Physiognomic Geomorphology (Evolution of the Landforms):
The study of geomorphological investigations on the sequence of the landform development under million of years is called ‘Physiognomic’ geomorphology.
2. Dynamic Geomorphology (Morph-dynamic Characteristics of Landforms):
The geomorphological investigations concerned with the erosional and depositional processes and the minor changes caused in the landforms by these processes through weathering, mass movement, with the water action, glacier and wave action are placed under this type.
3. Static Geomorphology (Geomorphic Features of Existing Landforms):
This type of geomorphological investigations are mainly concerned with the classification and mapping of the present day landforms. This type significantly contributes in evaluating the hydrological and agricultural potentials and also the pedological engineering and ecological characteristics of each landform unit.
4. Integrated Surveys:
This type of geomorphological investigations involves the intricate relationship up existing between landforms and the other elements and surface and ground water. Such type of studies may also reveal the impact of natural environment on the human activities and inversely the effect of human activities on natural environment.
Geomorphic Features of the Hot Indian Arid Zone:
Indian Arid Zone—on the basis of ifs evolutionary history, form, pattern and characteristics of the drainage, depth, size and nature of the sediments, slope and erosional/depositional/salinity hazards, has been divided into fourteen major landform units.
The salient geomorphological characteristics of these landform units are following:
1. Sand dunes:
There are six types of dunes, belonging to the old and new dune systems. The dunes belonging to old dune systems are stabilized obstacle, parabolic, longitudinal and transverse dunes of 10 to 80 m heights. The dunes of new dune system are active shrub-coppice and barchans dunes of 90 cm to 2m and 3 to 10 m heights respectively.
2. Sandy undulating aggraded older alluvial plains:
The intense Aeolian activities have created undulations in the form of sand sheets of 20 to 300 cm thickness, longitudinal and transverse dunes of 90 cm to 5 m height and sand hummocks and ridges of 30 cm to 1 m height over the flat alluvial plains. Within the sandy deposits, a weakly developed layer of calcium carbonate has been observed in some parts of the arid zone.
3. Sandy undulating interdunal plains:
This is more widespread than the flat interdunal plains. Intense Aeolian activities have created undulations on the alluvial surfaces of this unit in the form of sand sheets of 100 to 400 cm thickness, sandy hummocks of 1 to 2 m height and low longitudinal and transverse dunes of 3 to 5 m height.
4. Flat interdunal plains:
It mostly occurs between the stabilized coalesced parabolic, longitudinal and transverse dunes. Texture of the surface sediments varies from loamy sand to sandy loam and loam in pockets.
5. Flat buried pediments:
This is flanking rocky or gravelly pediments covered with 1 to 3 m deep alluvial sediments with less than 1° slope. These are mainly transported by stream channels from the adjoining hills and pedimented surfaces and are partly developed in situ. These alluvial sediments are underlain by hard rocky strata.
6. Sandy undulating buried pediments:
The mode of formation of this is similar to that of the flat buried pediments but later on it is been affected by intense Aeolian activities which created sand sheets of 50 to 200 cm thickness and sand dunes of 2 to 10 m height and at certain places even of 20 to 40 m height.
7. Flat aggraded older alluvial plains:
This is most extensive and occurs predominantly in the eastern part of the arid zone. These plains are covered with the alluvium of varying thickness. Within the alluvial deposits, a thick alluviated layer of calcium carbonate has developed in the form of nodules and is locally known as Kankar pan.
The coating of calcium carbonate is usually on the parent weathered material occurring below the alluvial deposits. The depth of the Kankar pan varies from 7 to 180 cm. The nature die sediments varies from loamy sand to sandy loam and also loam but certain places in pockets silty clay loam are found.
The major hilly tract of the Rajasthan arid zone is the Aravalli mountain range which occurs along its eastern boundary. The chief rocks of this tract are the metamporpic quartzite, slate, phyllite, micaschist the Aravalli and Delhi age.
Around Sirohi, Abu and Erinpura, the hills are composed of Erinpura granite and pegmatite of Algonkian age. These hill ranges generally have narrow ridges, conical shape, and high relative relief. The hill slopes are covered with colluvial debris.
9. Piedment plains:
The hills of different formations are flanked at their b uses by piedment plains, and are composed to thick colluvial debris derived from the adjoining hills. The total thickness of the sediments varies from 10 to 25 m in the upper part and 3 to 5 m in the lower part.
10. Rocky or/and gravelly pediments:
This occurs along the base of the rhyolitc, sandstone and limestone hills. The slope varies from 3° to 8° in the upper part, 1° to 3° in the middle part and 0°8′ to 1° in the lower art The vast gravelly pediments around Kolayat and Bap are the ideal examples of the desert pavements.
11. Saline flat aggraded older alluvial plains:
This occurs mainly in southern and northwestern parts of the Indian arid zone. The salinity has developed due to the excess irrigation in the medium to heavy textured flat aggraded older alluvial plains. The salinity is due to the impeded drainage conditions.
12. Shallow saline depressions:
At Sambhar, Kuchaman, Didwana, Lunkaransar, Jamsar, Bap, Thob, Pachpadra, Sanwarla and around Pokaran and Jaisalmer large and small saline depressions of different shapes and sizes occur. The Sambhar saline lake covers the largest area. These saline depressions are the gathering grounds of the salts and evaporites.
13. Graded river beds:
The Luni is the only river in the hot Indian arid /one, which forms the bulk of arid region. Its total length is 500 km with a total catchment of 348664 sq. km. Its greatest peculiarity is that it tends to increase its width rather than depth. Its major tributaries are the Jojri, the Guhia, the Bandi, the Sukri, the Jawai and the Sagi.
14. Younger alluvial plains:
These plains occur in narrow strips along the courses of the Luni and the Ghaggar and their tributaries. The texture of the sediment varies from sand to loamy sand and sandy loam to loam. The depth of the sediments ranges from 10 to 20 m and kankar pan is absent.
The geomorphology is a binding element in the integrated surveys and controls the distribution and development of the natural resources. The integrated surveys in different parts of the Indian arid zone have revealed that landforms act as an environment where soil develops, surface and groundwater circulate, vegetation grow and the man tills of his field.