Explaining the extreme mobility of volcanic ice-slurry flows, Ruapehu volcano, New Zealand
Gert Lube et al., Volcanic Risk Solutions, Institute of Natural Resources, Massey University, Private Bag 11 222, Palmerston North 4442, New Zealand. Pages 15-18.
The near-invisibility of ice-slurry flows in the geological record belies their significant hazard at snow-capped volcanoes. These four-phase flows exhibit extreme rates of volumetric bulking and unusually high mobility. Lube et al. clarifies the mechanisms of their motion through two examples generated on 25 September 2007 at Mt. Ruapehu, New Zealand. Brief explosions through Crater Lake ejected 5700 cubic meters of acidic water that entrained 60 times this volume of snow as it traveled over a snow-covered glacier. The resulting ice slurry traveled up to 7.7 km. A co-generated second flow took a more tortuous initial path, before riding over the already frozen deposits of the first unit and beyond. For the first time, downstream evolution of the kinematic properties of propagating ice-slurry fronts could be characterized, as well as the longitudinal variation of the physical properties of their resulting deposits. The chemistry and composition of the deposits show that during flow, vertical percolation of water through the porous ice-particle-water-air mixture generated a basal zone of high internal pore pressure. This effect is particularly strong when a thick, high-density flow front forms, which races ahead of the tail, to control runout and consequent hazard.
Increased mid-twentieth century riverbank erosion rates related to the demise of mill dams, South River, Virginia
Jim Pizzuto and Michael O'Neal, Department of Geological Sciences, University
|Contact: Christa Stratton|
Geological Society of America