Figure 5
The influence of porosity and hydrothermal alteration on rock strength. (a) Density as a function of porosity (%) and oxygen isotope compositions (δ18O) as a proxy for degree of alteration for the variably-altered rocks collected from the Merapi dome. The unaltered but porous samples from the 2006 eruption are also shown (black symbols; F = fresh). Dotted lines are aids to help visual orientation. (b) Uniaxial compressive strength (MPa) as a function of porosity (%) and oxygen isotope compositions (δ18O) as a proxy for degree of alteration for the variably-altered rocks collected from the Merapi dome. Rock strength decreases as a function of degree of alteration and porosity (see also Supplementary Fig. S1) implying that edifice stability is controlled by a combination of porosity and hydrothermal alteration (see inset). HDS high dome stability, IFI increased flank instability.
