The amount of heat they are exposed to has a lot to do with the inferences and observations that they make on the density of the earth's core. The inner core is the most compact due to the fact that they have a lot of direct exposure to heat and the gravity of the earth pressung down on it. The inner core is less subjected to those conditions.
These are called Subduction zones.
I would say that probably classifying natural disasters and their impact on man would most likely be considered by William Hughes as true geography as rather than just describing earth's features it would show the impact of earth's processes on man.
