Lava is hot for two primary reasons: Pressure and radiogenic heating make it very hot deep in the Earth (about 100 km down) where rocks melt to make magma. The rock around the magma is a good insulator so the magma doesn't lose much heat on the way to the surface.

Is magma hotter than lava?

Magma is hotter than lava, depending on how recently the lava reached the surface and if the magma and lava are from the same magma chamber below the...

What causes magma to heat up?

As the denser tectonic plate subducts, or sinks below, or the less-dense tectonic plate, hot rock from below can intrude into the cooler plate above. This process transfers heat and creates magma.