Heat flow on earth is declining with time as natural radioactivity continues to be spent.

Convection of earth’s core and mantle do not produce steady heat transfer from earth’s core to the surface.

There is enormous diversity of heat flow at earth’s surface at any one time.

Jessop & Lewis 1978

Since volcanism is driven by higher than average heat flow, volcanism comes and goes as heat flow changes in time and place. Overall, heat declines, but in any time or place, it can vary markedly in both directions. Super-eruptions result from very high heat flow conditions.

There is a huge fundamental earth scientific debate about the origin of heat flow, hot spot volcanism and related phenomena: Plumes vs Plates.

It is also possible to look at the geologic record of large eruptions--a recent study of this was made by Mason et al 04.

Volcanologists agree that super-eruptions lie in the earth’s future, but the time and place is uncertain.

Geol Soc London