How does the lava get so hot. Travis Dear Travis, Lava gets hot because it starts out in a hot place and then loses little heat on the way to the surface. Lava starts as solid rock in the mantle. Rocks in the mantle and the core are still hot from the formation of the Earth about 4.6 billion years ago. When the Earth formed material collided at high speeds.
Rocks are good insulators so the heat has been slow to dissipate.
Under the right conditions the hot rocks melt to make magma. The magma is well insulated under layers of rock until it reaches the surface.