Modeling subduction on the kitchen table

Abstract

A simple analogue model home setup with white school glue and natural black magnetic sand, successfully reproduces many of the main processes associated to subduction on planet Earth. This homemade model reproduces the spontaneous subduction of a dense, magnetic sand layer into a viscous layer of white school glue in a plastic kitchen container, all in a few minutes. Preparation of this experimental setup is simple, the materials are inexpensive or easy to obtain, and quantitative observations can be performed using cellphone cameras and freely available software on a personal computer. This very visual model setup brings the concept of subduction closer to the student of geosciences, and can be performed and analyzed at home. Once all the materials are set, spontaneous subduction of the magnetic sand layer takes place in a single event punctuated by one or two slab-tearing episodes, where the trenches quickly retreat (consuming as much as 15 cm2/s), while leaving nearby slab segments unsubducted. Rapidly retreating trenches induce toroidal flow of glue around the torn subducting slab, and cause large vertical-axis rotations of the unsubducted segments above, dynamically supporting, extending, and eventually bringing them into the vigorous poloidal flow of the subducting slab. Black magnetic sand impurities within the otherwise white glue allow precise tracking of the toroidal and poloidal flows. Complete detachment from the edges of the container changes the kinematics of the experiment from rapid trench retreat, to an stationary trench that pulls the remainder of the black magnetic sand layer into the trenches and causes thinning and opening of an extensional axis, reminiscent of spreading centers.