Factors

= Factors of isostasy =

Isostasy is the result of differences in density between the lithosphere and the asthenosphere, and how the surface layers of the Earth can yield under the weight of large mass (Mussett and Khan 2009). The average density of the lithosphere is between 3400 and 4400 Kg/m3, while the density of the asthenosphere is between 4400 and 5600 Kg/m3. The less dense lithosphere therefore “floats” on top of the denser asthenosphere. This gets a bit more complicated when dealing with areas that are topped by mountain ranges. A mountain can be thought of like an iceberg in the ocean, the volume underneath the surface is greater than that above. So this means that mountains have “roots” that keep them balanced (figure 1). These roots essentially thicken the continental crust beneath the mountains up to 70Km compared to the average of 30Km (Ollier 2006).

Figure 1

Figure 2

The roots of mountains diminish as the mountains are eroded. The idea that the mountains are floating obeys Archimedes’ Principle, which states that if an object is placed in liquid, the part under the surface displaces an amount of liquid equal to its weight (Mussett and Khan 2009).