By the end of this chapter I will be able to: zz zz
Syllabus Link: 1.6
understand that over time different forces act to alter the balance of the lithosphere; explain how isostasy has impacted on fluvial processes;
zzidentify features of rejuvenation from Ordnance Survey maps, diagrams and photographs; zzdescribe the formation of one feature associated with rejuvenation, giving named examples; explain how isostasy has impacted on coastal landscapes;
zz zz zz
zz identify coastal features formed by isostasy from diagrams and photographs;
understand how subaerial processes lead to the erosion of the landscape and the formation of peneplains;
explain and be able to identify from diagrams the stages in the cycle of landscape formation.
Chapter 1: Plate Tectonics
Isostasy refers to the adjustment the earth’s crust undergoes as it either sinks into or rises up from the mantle.
How Glaciation Causes
Isostatic Movement During the ice ages, ice accumulated on the surface of the earth. The weight of the ice on the earth’s crust caused the crust to sink into the mantle (Fig. 11.1(a)).
Crust Mantle A-Z
Isostatic readjustment: The sinking downwards of land due to the weight of ice.
Isostatic rebound: When land moves upwards following the melting of ice sheets.
When the ice melted, the crust rose slowly upwards, a process called isostatic rebound (Fig. 11.1(b)). Rebound from the last ice age is ongoing today, for example, in the Gulf of Bothnia, Finland.
Fig. 11.1(a) The crust sinks slowly into the mantle under the weight of glacial ice.
Crust Mantle
Fig. 11.1(b) When the ice has melted, the crust rebounds.
The Impact of Isostasy on
Fluvial Processes The post-glacial upward movement of continents led to falling sea levels which impacted on fluvial processes. Sea level is generally regarded as being the base level for rivers and is the lowest level on a river channel to which erosion can occur. The long profile of rivers shows them as having steep gradients in the upper stage and gentle gradients in the lower stage. (Fig. 11.2(a))
Steep gradient Gentle gradient Land 164 Fig. 11.2(a) The long profile of a river. Sea Ice
