Although geological and geophysical measurements at active ridges have provided indirect samples and remote images and ophiolites have provided fossil evidence, the lack of direct sampling of in situ physical and chemical properties severely hinders our understanding of subsurface magmatic systems at mid-ocean ridges. In contrast with the ridge setting, substantial information has been gained from direct sampling of Kilauea Iki lava lake. We reanalyze time series physical and petrological data from both in situ sampling and remote seismic and electromagnetic imaging of this lava lake in order to gain insights into the evolution of an enclosed basaltic magma body with many characteristics similar to a mid-ocean ridge magma chamber. Although the analogy is imperfect, our analysis of observations from Kilauea Iki suggests that at a mid-ocean ridge (1) a fine structure exists at the top of the magma body in the form of horizontal segregation veins (i.e., sills), (2) sustained convection within the magma chamber is highly unlikely, (3) a ''dry-out'' zone above the magma body and below the deepest penetration of hydrothermal circulation may exist, (4) with high magma supply (e.g., the East Pacific Rise), where quasi steady state melt zones are present, the magma chamber must be completely replenished very frequently (at least every 300--600 years), and (5) the onset of rigid behavior of the basaltic partial melt does not happen at a unique ''critical'' crystal fraction. These results also show that significant differences may occur in interpretation of the rheology of a magmatic system depending upon the type of petrologic, seismic, or drilling data analyzed.