MODELING LAVA DOME COLLAPSE USING CORRELATION BETWEEN POROSITY AND UNCONFINED COMPRESSIVE STRENGTH

Unconfined compressive strength (UCS) is a strong control on lava dome stability and can be used to model domes and study the possibility of their collapse. Connected porosity measurements were taken on rhyolite cores from the Tarawera and Ngongotaha lava domes and subsequent strength tests determined the UCS for each core. The data were then analyzed to produce a negative exponential function relating UCS to connected porosity. The relationship between these two variables make it possible to examine changes in lava strength from changes in porosity. The exponential function, along with data on the porosity, thickness and density of the Cordón Caulle obsidian flow and Unzen lava dome, was used to generate models for lava dome collapse. These models compare estimated UCS of the rock to the load of the lava dome and predict the risk of collapse. Higher dome load relative to estimated UCS will create less stability and increase the risk of collapse. Despite the exclusion of other relevant factors, e.g. tensile strength and seismicity, it is concluded that porosity, via UCS, is significant to provoking collapse.