What is the theory of continental drift? Talk about the supporting data.(Answer in 200 words)
Answer: Running water is considered one of the most important geomorphic agents bringing about the degradation of the land surface. There are two components of running water. One is overland flow on the general land surface as a sheet and another is linear flow as streams and rivers in valleys. SignRead more
Answer: Running water is considered one of the most important geomorphic agents bringing about the degradation of the land surface. There are two components of running water. One is overland flow on the general land surface as a sheet and another is linear flow as streams and rivers in valleys. Significance of running water in the evolution of landforms:
- Most of the erosional landforms made by running water are associated with vigorous and youthful rivers flowing over steep gradients.
- With time, stream channels over steep gradients turn gentler due to continued erosion, and as a consequence, lose their velocity, facilitating active deposition.
- There may be depositional forms associated with streams flowing over steep slopes. But these phenomena will be on a small scale compared to those associated with rivers flowing over medium to gentle slopes.
- The gentler the river channels in gradient or slope, the greater the deposition. When the stream beds turn gentler due to continued erosion, downward cutting becomes less dominant lateral erosion of banks increases and as a consequence, the hills and valleys are reduced to plains.
- Overland flow causes sheet erosion. Depending upon irregularities of the land surface, the overland flow may concentrate into narrow to wide paths forming rills, gullies, and ultimately valleys.
Depositional Features of Running Water
| Feature | Characteristics | Diagram |
| Alluvial Fans | Alluvial fans are formed when streams flowing from higher levels break into foot slope plains of low gradient. Normally very coarse load is carried by streams flowing over mountain slopes. This load becomes too heavy for the streams to be carried over gentler gradients and gets dumped and spread as a broad low to high cone-shaped deposit called an alluvial fan. |  |
| Deltas | Deltas are like alluvial fans but develop at a different location. The load carried by the rivers is dumped and spread into the sea. If this load is not carried away far into the sea or distributed along the coast, it spreads and accumulates as a low cone. Unlike in alluvial fans, the deposits making up deltas are well very sorted with clear stratification. |  |
| Floodplains, Natural Levees and Point Bars | Deposition develops a floodplain just as erosion makes valleys. Floodplain is a major landform of river deposition. Large-sized materials are deposited first when the stream channel breaks into a gentle slope. Thus, normally, fine-sized materials like sand, silt, and clay are carried by relatively slow-moving waters in gentler channels usually found in the plains and deposited over the bed and when the waters spill over the banks during flooding above the bed. Natural levees are found along the banks of large rivers. They are low, linear, and parallel ridges of coarse deposits along the banks of rivers, quite often cut into individual mounds. Point bars are also known as meander bars. They are found on the concave side of meanders of large rivers and are sediments deposited in a linear fashion by flowing waters along the bank. |  |
The study of running water in the evolution of landforms helps us understand and appreciate the diversity of landforms on the surface of the earth.
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Continental drift theory, given by Alfred Wegner in 1912, suggests that all the continents are formed from a single continental mass 'namely PANGAEA' surrounded by mega ocean 'namely PANTHALASSA'. He argued that around 200 million years ago PANGAEA broke into various continents. Evidences in supportRead more
Evidences in support of the continental drift theory:-
The Jig-Saw-Fit (matching of continents):-
The shorelines of South America and Africa facing each other have remarkable and unmistakable match.
The rocks of same age across the oceans:-
radiometric dating methods have correlated the rock formation in different continents.
eg- marine deposits along the coastline of south america and africa are of the Jurassic age.
Tillite:
The glacial tillite found in Gondwana system of sediments has its resemblance to six different landmasses of the Southern Hemisphere.
Placer Deposits:
The placer deposits of gold in the Ghana coast do not have source rock in the region.
Distribution of Fossils:
identical species of plants and animals adapted to living on land or in freshwater are found on either side of the marine barriers.
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The Continental Drift Theory had some limitations they are mentioned below:
- Wegener was unable to clarify why the drift started.
- the forces described by wegner that propelled the movement of continents were, too weak to move continents.
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