Knowledge Bank

The viscosity of water can be of major significance to the geology of the mantle wedge. As water dehydrates from a subducting slab, it rises and interacts with the overlying rock of the mantle wedge. The flow rate of water from the slab can lend insight into magma flow below volcanic arcs. In order to measure the viscosity at high pressures (2-5 GPa), a hydrothermal diamond anvil cell (DAC) was used. Brownian motion and viscosity of a fluid can be determined by measuring the displacement of particles in suspension. Prior to using the DAC, analogous experiments were run at room temperature and 1 atmosphere. These analogous experiments resulted in viscosities close to the published values of 1x10-3 Pa·s. Problems were encountered with the high pressure experiments. Only low pressures were obtained. The data that were obtained at low pressures indicates that the Brownian motion technique is valid. There are modifications to the experiment that can be done in the future to possibly obtain better results.