Steam-driven eruptions are explosions that frequently occur in volcanic and geothermal areas. They are powered by the sudden release and expansion of steam and liquid water trapped under high pressure within the pore spaces of host rocks. We have experimentally studied how the strength of rock hosting steam and liquid controls the nature of explosions based on examples from Lake Okaro (New Zealand). Specifically, we used experiments to estimate the relative amounts of energy that goes into breaking rock up, versus that required for ejecting particles upwards and outwards. Here we report the main methodological approach and results of petrophysical properties analyses, decompression experiments and estimation of explosivity of water, respectively.