Supplement your information with examples from different countries where migration has proved to be advantageous.

Magma forms by partial melting of upper mantle and crust. partial melt means that only a fraction of the available material forms a melt, and that the remainder stays solid. the partial melt rises because of its lower density and ascends through he crust. this is so conclusive mean the answer would be magma igneous rocks or balistic magma.

The fact that the earth goes through natural cycles for example the ice age some scientists belive that it is just another cycle