Explosive release of gases and rocks from the top of molten rock bodies (magma)

Gases dissolved in molten rock (“magma”) leave the magma as it crystallizes to form solid, igneous rocks underground. Near Cloncurry in western Queensland, Australia, there is evidence in ancient rocks that this process occurred extremely rapidly, which is highly unusual. Pipe-like bodies of fragmental rock, cemented by small rock pieces and minerals precipitated from these gases, are found extending out from the tops of crystallized igneous rocks. We calculated ‘fluidization’ velocities of particle and gas transport in these pipes to be > 10m/s, approaching the velocities sometimes observed in volcanic eruptions. These processes are important to explain some of the features of copper-gold deposits in the region and elsewhere in the world.