Laboratory investigations of viscous effects in replenished magma chambers

Some laboratory experiments are described which investigate the dynamical effects of replenishment of a magma chamber containing high viscosity magma by hotter, denser and much more fluid magma. In the experiments a layer of hot KNO₃ solution is emplaced beneath cold glycerine, which has a viscosity 3000 times greater. Less dense fluid is released immediately and continuously from the interface as a result of crystallization in the lower layer and rises as plumes through the overlying glycerine. Further crystallization occurs in the plumes, and the crystals fall out; but there is little mixing between the two fluids and a layer of depleted KNO₃ solution forms at the top. The experiments demonstrate that interfacial processes begin to dominate where there are large viscosity differences between adjacent fluid layers as would be the case in a rhyolitic magma chamber replenished by basaltic magma.