A crustal block with mean density 3000 kg m^3 is initially in is ostatic equilibrium with the surrounding rocks whose density is 3200 kg m^3, as in the figure

(a). After subsequent erosion the above-surface topography is as shown in

(b). The distance L remains constant (i.e. there is no erosion at the highest point A) and Airy-type isostatic equilibrium is maintained. Calculate in terms of L the amount by which the height of A is changed. Explain why A moves in the sense given by your answer.

p= 3200 A P=:3000 (a) L p=:3000 (b) p= 3200