Mantle convection - is when the plates move around the asthenosphere and the magma moves in circular patterns due to heat.
Movement of tectonic plates is related to convection currents in the earth's mantle. Tremendous heat and pressure within the earth cause the hot magma to flow in convection currents. These currents cause the movement of the tectonic plates that make up the earth's crust.
Lack of water, and food, being in the vast desert means hard food and little rain this leads to many organisms struggling to live, also being forced to drink dirtier water means you could catch a disease more easily