What causes magma in the lower mantle of earth to rise upward toward the crust

the moons gravitational force acts on the magma

the core of earth expand

the density of the magma decreases

the volume of the magma decreases

Decompression melting also occurs at mantle plumes, columns of hot rock that rise from Earth's high-pressure core to its lower - pressure crust. As the denser tectonic plate sub ducts, or sinks below, or the less-dense tectonic plate, hot rock from below can intrude into the cooler plate above.