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Figure F19. Plot of calculated vesicle contents in basalts from Site U1349 as a function of pressure and water depth of eruption (modified after Wallace, 1998). Gray rectangle = vesicularity range. Degassing curves with different proportions of H2O and CO2 dissolved in the melt (fig. 11 in Wallace, 1998) show calculated vesicularity of each melt as a function of eruption pressure (water depth). The diagram is useful to bracket possible eruption depth for highly vesicular basalts. Assuming low H2O (<0.4 wt%) contents in MORB-like melts and high vesicle abundance (up to 75 vol%), one can conclude that the possible range of eruption pressures relevant for Site U1349 basalts was <15 bar (<150 mbsl).

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