Question: What makes lava so hot ? And where does it come from

Kate Dobson answered on 9 Dec 2020:

Lava is molten rock that has been erupted, magma is the same material when it beneath the surface. Heat from the centre of the planet drives the entire system, the mantle (the region beneath the crust) flows very slowly making the tectonic plates move. Sometimes the forces in the plates build up causing the melt to be pulled out of the mantle (leaving most of the crystals behind) and move upwards. The chemistry of the magma controls how runny it is, but as that magma cools crystals start to grow and all magma (whatever chemistry it is) gets less runny. The lava that erupts at subduction zones (South America, Japan, Indonesia) has more water and less iron in it, which makes it thicker and cooler – these magmas are 500-800C when they reach the surface. Lava erupted in Iceland or Hawaii has less water and more iron making it runnier and hotter (up to 1200C when it erupts).