On November 27th, Hawaii’s Mauna Loa, the world’s largest volcano, began erupting and spilling lava from fissures as its first eruption in nearly four decades.
The magma that comes out of Mauna Loa comes from a series of magma chambers found between about 2 and 40 km beneath the surface. These magma chambers are only temporary storage places for magma and gases and not where the magma originally comes from.
The origin is much deeper in the Earth’s mantle, potentially more than 1,000 km deep. Some scientists think that the magma could come from a depth of 2,900 km, where the mantle meets the Earth’s core.
Scientists suggest that the mantle is not made of uniform rock. Instead, differences in the type of mantle rock cause it to melt at different temperatures. Mantle rock is solid in some places, while it starts to melt in other places.
The partially molten rock becomes buoyant and rises toward the surface. The rising mantle rock is what makes a mantle plume. Because the overlying pressure decreases as the rock ascends, it melts more and more, and eventually collects in the magma chamber. If there is a large enough opening at the surface, and enough volcanic gases have collected in the magma chamber, the magma is forced to the surface in a volcanic eruption.