Denudation chronology

Denudation chronology

Denudation chronology involves description of landforms evolution through successive stages of geological time or Cyclic time involving larger geological time on larger spatial scale.

According to R J Small ”the meaning and concept of the denudation chronology is to add identify, date and interpret planation surfaces developed in past cycles and sub cycles of erosion”. denudation 1

Denudation chronology is based on the concept of “Palimpset topography” which means such a surface which bears the influence of geomorphological process of past geological period after partially erased initial imprints (landscapes) in the beginning following the dictum “present is the key to past”.

Model of denudation chronology

denudation 2

denudation 3

Fig : Schematic diagram of landmass denudation- in this model the average surface elevation is reduced by one half every 15 million years.

Strahler devised the model of the denudation process and ascertained the time required to reduce the land mass to peneplain. The basis of model is described below:

-An uplifted mass of about hundred km with has been assumed as arisen from the sea

-The uplifted block has a broadly Domed Summit. It is bordered by low areas at or below sea level which receives the sediment.

-With decreasing elevation, the rate of denudation itself diminishes in a constant ratio such that one half of the available land mass is removed in each 15 million years period. This time may be called as the ‘Half-life’ of the available mass.

– Thus after a lapse of 15 million years the average elevation will have been reduced to 2.5 km as shown in figure .

– At the end of 30 million years average elevation and denudation rate are again reduced by one half to one fourth of the critical values.

– Now three fourth of the mass is eroded and average altitude is down to 1.25 km.

– As average elevation declines, the intensity of change is proportionately diminished (stage B through D )

– In stage E, an average elevation of about 3000 m is attained after about 60 million years. The land surface now can be described as Peneplain.

Criticism

Denudation is not a linear and static process but is interrupted by process of up-liftment or hastened erosion due to other factors. Hence the model of denudation is unpredictable.

Conclusion

Denudation chronology is thus a contemporary record of sediment and solute flux through River system, representing the mass removed from the continental surfaces, have been used to estimate rates of denudation.

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