Test: Geomorphology - 4 - UPSC MCQ

• At higher gradients, downward, vertical erosion is more dominant. This produces V-shaped valleys. As gradients decrease, downward erosion is less dominant, and lateral erosion begins to dominate, forming meanders.

• As the debris or silt is deposited, it reduces the depth available for the water to flow, and thus the bed is raised. Floodplains are created as a result of both erosion and deposition. Material is also deposited on the sides forming raised banks called levees.

• Floodplains are created as a result of both erosion and deposition. When the river flows normally its bed is raised through accumulation of deposits. Material is also deposited on the- sides forming raised banks called levees. When the river reaches the sea. the fine materials it has not dropped yet are deposited at its mouth, forming a fan-shaped alluvial area called a delta.

• When the river reaches the sea, the fine materials it has not dropped yet are deposited at its mouth, forming a fan shaped alluvial area called a delta.

• Vertical erosion is dominant in upper reaches because of

1) high speed of river,

2) low sediment load,

3) high gradient and

4) bed erosion

Basically river rejuvenation is a term used when the river starts becoming young again (back from an old stage). Incised meanders are formed when the river (in its upper courses) develops deep valleys and gorges. And existing meanders are vertically eroded by the rejuvenating stream. Water acts as a lubricant in landslides.

These are found in the lower course of a river.

• Formation of floodplains and levees was not affected by the sediment load. Formation of an ox-bow lake is as follows.

• The water twists and turns when the river enters the plain, leading to the formation of large bends called meanders.

• Along the sides of the meander, there is continuous erosion and deposition that makes the ends of the meander loops come closer and closer.

• In due course, the loop breaks off from the river and forms a cut-off lake, also called an ox-bow lake.

1. Tectonic Earth movements, where the slope of the land changes, and the stream is tipped out of its former course.

2. Head-ward erosion of one stream valley upwards into another, or

3. Lateral erosion of a meander through the higher ground dividing the adjacent streams.

• A wind gap is a valley through which a waterway once flowed but is now dry as a result of stream capture. Water gaps and wind gaps often provide practical routes for trails, roads and railroads through mountainous terrain. Examples of wind gaps in the Blue Ridge Mountains of Virginia include Swift Run Gap, Rockfish Gap, and Buford’s Gap.

• Since deltas have a large sediment deposition, they prevent ships from anchoring close to the shores. There is not enough depth in the water.

• Alluvial fans Water flowing from a higher level breaks down into foot slope plains of low gradient. Normally very coarse load is carried by streams in the upper reaches. It becomes too heavy to carry and is deposited in a low to high cone-shaped deposit called alluvial fan.

• There is no stratification of river load as all the material (fine and coarse) is dumped together.

• Streams make alluvial fans eventually shift course, forming many channels called distributaries.

• Deltas They are like alluvial fans but are formed at different locations, i.e. near the sea.

Deltas occur near the sea mouth, i.e. very close to mean sea level, which can be the lowest elevation possible.

Conditions favourable for Delta Formation

• Active erosion of the river in its upper course to provide extensive gravel, sand and silt to be eventually deposited as deltas.

• The coast should be sheltered preferably tideless, else delta will be washed away.

• There should be no strong current running at right angles to the river mouth, as it can wash away the sediments. Any large lake in the way of the river course can filter off the sediments, thus unfavourable for delta formation. The sea should be shallow adjoining the delta as the sediments will disappear in the deep waters of the sea. This is why a continental shelf is preferred.

Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms. Stalagmites rise from the floor of the caves. The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.

Coastlines of Emergence

• These are formed either by an uplift of the land or by the lowering of the sea level.

• Bars, spits, lagoons, salt marshes, beaches, sea cliffs and arches are the typical features.

• The east coast of India, especially its south-eastern part (Tamil Nadu coast), appears to be a coast of emergence. The west coast of India, on the other hand, is both emergent and submergent.

• The northern portion of the coast is submerged as a result of faulting and the southern portion, that is the Kerala coast, is an example of an emergent coast.

Coastlines of Submergence

• A submerged coast is produced either by subsidence of land or by a rise in sea level. Ria, fjord, Dalmatian and drowned lowlands are its typical features.

• Lagoons sheltered by sandbars or barrier islands are called coastal lagoons. Coastal lagoons form along coastal plains - flat or gently sloping landscapes.

• The size and depth of coastal lagoons often depend on sea level. When the sea level is low, coastal lagoons are swampy wetlands. When the sea level is high, they can look like coastal lakes or bays.

• A catcher beach should not be confused with a dumping ground or heavily trashed public beach.

• A catcher beach typically receives its accumulations of debris due to its shape and location in combination with high-energy waves, storms or winds.

• A specific example of a catcher beach can be found along the shores of Gore Point, Alaska.

• The geography of this location makes it a very high-density catcher beach, as it sticks out like a hook into the Gulf of Alaska current.

• Sometimes the oasis may be abnormally large. Tafilalet Oasis in Morocco is a large oasis with an area of about 13,000 sq. km.

• Animals and even humans live in big oases. In desert areas, the location of the oases is of critical importance for trade and transportation.

Seif: a long, narrow sand dune or chain of dunes, generally oriented in a direction parallel to the prevailing wind or a direction resulting from two or more winds blowing at acute angles,to each other. The dune crest consists of a series of peaks and gaps, and the steep, or slip, face may change sides of the dune according to changes in wind direction.