Schematic melting model for the Pu‘u ‘Ō‘ō eruption.  (a).  The uppermost portion of the Hawaiian mantle plume is stippled with red and blue blobs that represent small-scale, long-lived compositional heterogeneities.  These heterogeneities are shown with a large-scale radial zonation, but other geometries are possible (e.g., bilateral asymmetry).  As this mantle rises to the surface, melt percolates upwards in steady-state equilibrium with the residue.  (b).  The transfer of melt from pores into chemically isolated channels to supply eruptions at Lō‘ihi, Kīlauea and Mauna Loa in the past may have created patches of recently depleted mantle beneath Hawai‘i (small black ovals).  The Pu‘u ‘Ō‘ō eruption, illustrated by the small vent, dashed melt pathway and inverted fractal “tree”, represents a current example of this process.  Initally, the Pu‘u ‘Ō‘ō eruption may have tapped fresh mantle that was never melted beneath Hawai‘i (small elongate region at the base of the fractal “tree”).  The small-scale, long-lived compositional heterogeneities from (a) are simplified to light red and blue bands for clarity.  (c). When melt is extracted into channels to supply a given eruption, such as Pu‘u ‘Ō‘ō, it must be drained from an ever increasing volume in order to sustain the flow of melt to the surface.  As the eruption continues, the volcano might tap melt from more distal areas and tend to encounter a greater number of patches of melt from recently depleted mantle (medium elongate region that overlaps with the black ovals).  (d).  As this process continues, the volcano might sample chemically and isotopically heterogeneous pockets of melt from fresh mantle (in addition to melt from recently depleted mantle), and thus, efficiently transmit the geochemical signatures of long-lived, small-scale compositional heterogeneities from the volcano’s source region to the surface (large elongate region that overlaps with the black ovals and the shaded area).