Question

causes of interuption of fluvial cycle of erosion​

Answer 1

Answer:

Explanation:

Causes of Interruption in the Cycle of Erosion:

1. Interruptions due to vulcanicity and climatic changes (accidents):

The chapter of any cycle of erosion is closed due to permanent interruptions caused by volcanic erup­tion and climatic changes. The widespread volcanic fissure flows cause upwelling and pouring of immense volume of basaltic lava which covers larger areas and obliterates surface drainage and reliefs which results in the permanent interruption and closure of the existing chapter of existing fluvial cycle of erosion.

The fresh cycle of erosion may start only when the fissure flow ceases, lavas are cooled and solidified, new surface is formed and new sets of streams are initiated. It may be pointed out that such interruptions in the fluvial cycle occurred over Indian peninsula during Cretaceous pe­riod when Deccan lava flows covered vast areas of the Deccan plateau including Chotanagpur plateau and even southern parts of the Vindhyan upland causing closure of the Jurassic cycle of erosion. The new Tertiary cycle was initiated only after the Deccan trappean lavas were cooled and solidified and monsoon climate set in.

Climatic interruptions (accidents) occur due to major changes in the climate of the concerned region, for example, if the fluvial cycle of erosion in a humid region is passing through mature stage, and there is sudden climatic change leading to onset of either extreme dry conditions or extreme cold conditions, then the cycle of erosion is interrupted to such an extent that the chapter of current cycle of erosion is closed and another set of cycle either arid cycle (if the climate becomes extreme hot and arid) or glacial or periglacial cycle (if the climate becomes glacial/periglacial or subglacial) sets in.

It may be mentioned that if there are minor changes in the climate, then the chapter is not closed, rather it (cycle) is either augemented or slowed down. Suppose, if the climate becomes more humid leading to increased amount of rainfall, then the sur­face runoff and stream discharge will automatically increase which would cause local interruption in the cycle by accelerating the rate of erosion (case of rejuvenation), the effects of which may spread over larger areas.

2. Interruptions due to base level changes:

Any change in the base level of erosion (deter­mined by the sea level) causes interruptions in the cycle of erosion or may initiate new cycle whether the previous cycle is complete or not. Changes in base level of erosion are basically of two types i.e., positive change (due to rise in sea level) and negative change (due to fall in sea level).

The base level changes caused due to sea level changes are eustatic (wide spread). Base level of erosion also changes due to tectonic factors i.e. subsidence of landmass causes positive change whereas upliftment of landmass is responsible for negative change. It may be mentioned that such type of subsidence or upliftment of landmass may be or may not be related to sea-level.

Positive change of base level (or rise in base level) shortens the cyclic time. Secondly, positive change of base level of erosion is indicative of accelerated alluviation (deposition) whereas negative change causes acceler­ated erosion (rejuvenation). It is evident that rejuvena­tion is the most important factor of interruption in the fluvial cycle of erosion and genesis of polycyclic (multi-cyclic) reliefs and hence it needs detailed dis­cussion.