Global magma production rates on Earth are about 20–25 cubic kilometres per year (4.8–6.0 cu mi/a).
It is often easier to measure magma supply rates when they are normalized for an exposed surface area as it is often difficult to delimit an intrusion.
Not all volcanic bodies are equally well exposed, and it is often impossible or difficult to measure magma supply rates exactly.
Furthermore, volcanic flux rates often vary over time, with distinct lulls and pulses.
[4] The magma supply rate is used to infer the behaviour of volcanic systems which erupt periodically, as well as to describe the growth of the continental crust and of deep-seated magmatic bodies such as plutons.