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.
This hot, buoyant magma forces its way upward through the overriding crust. As it approaches the surface, the pressure from the overlying rocks decreases, and this allows hot gas to come out of solution, further pressurizing the magma. When it reaches the surface, a volcano is formed.