In order to provide new insights into the relationship between plutonism and volcanism, numerical simulations involving heat transfer computation were used to estimate the conditions required for the formation of large magma chambers within plutons that grow by vertical stacking of sills. Large magma chambers can develop within plutons if sill accretion rates exceed 10−2 m/yr. For 10 km thick plutons, the volumes of eruptible magma are large enough to feed the most voluminous silicic explosive eruptions only if magma fluxes exceed 10−2 km3/yr. Emplacement rates required for the formation of a crystal mush from which a melt layer could be extracted by compaction are only slightly lower than the emplacement rates required to directly forming reservoirs of magma that are hot enough to be eruptible. The long-term average pluton emplacement rates inferred from the geochronological data (10−3 m/yr) are too low to allow for the formation of large magma chambers. However, some shallow laccoliths were emplaced much more rapidly and super-eruptions of 103 km3 of ignimbrites associated with caldera collapse are evidence of the existence of large shallow magma chambers. Taken together, magma fluxes estimated on the basis of geochronological data on plutons and laccoliths, and on the basis of current large-scale deformation in magmatic provinces, the occurrence of super-eruptions, and the results of numerical simulation suggest that the growth of plutons is a multi-timescale process with large magma chambers developing during the episodes of highest magma fluxes.