One of the key reasons for Federation was to achieve a united defence force which could better protect Australia. Around the 1880s, the Australian colonies had become increasingly concerned over the close proximity of foreign powers.
Split and merge into it. Answered by The Community. Making the world better, one answer at a time. Dissolved gases trapped in the magma provides the force that causes magma to erupt to the surface. Magma is molten material before it reaches the surface and is lava.
Slab Pull. This force occurs as a subducting plate sinks into the hot mantle beneath it. The subducting plate, usually basalt, is denser than the material it is subducting into, purely due to its difference in temperature. As the plate sinks into the mantle, it acts to pull the rest of the plate behind it.