So far, you have learned about forces from within the crust (endogenic forces) and the surface forces which cause weathering and erosion (exogenic forces). In this chapter, we will look at the balance that exists between the two forces and what happens when these forces are thrown off balance due to the rising and sinking of the Earth’s crust. This is known as isostasy. This chapter is for Higher Level students only.
KEY WORDS
l Endogenic forces l Exogenic forces l Isostatic movement l Isostatic equilibrium l Isostatic rebound l Fluvial readjustment
l River rejuvenation l Knickpoint l Paired terraces l Incised meanders l Entrenched meanders l Coastline of submergence
LEARNING OUTCOMES
What you MUST know l A definition of isostasy l Coastlines of emergence and submergence l Adjustment to base level of a river (fluvial readjustment) l Landscape development and peneplain development
Introduction
From your study of physical geography so far, you know that the Earth’s crust is in a continuous cycle of landform creation and destruction. Landforms such as volcanoes and fold mountains create vertical rises in the Earth’s crust. These are gradually worn down overtime by denudation (weathering and erosion).
• Forces from within the crust which form tectonic landscapes, such as fold mountains and volcanic plateaus, are referred to as endogenic forces.
• Forces which breakdown these landforms on the surface (weathering and erosion) are referred to as exogenic forces.
GEO DICTIONARY
Endogenic forces: forces from within the Earth. Convection currents cause plates to collide separate and slide past, creating vertical landforms on the surface
Exogenic forces: forces on the surface. Weathering and erosion leads to the breakdown of landforms created by endogenic forces
PATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT 245
l Coastline of emergence l Raised beaches l Raised cliffs l Raised wave-cut platforms l Peneplain
