Plate Tectonics with Wax
Amongst a myriad of protests plastered on the rear of a rusted Volkswagen Bug, a bumper sticker commands: "Stop Plate Tectonics!" Those lobbying for the cessation of all things may feel a connection with such a call to arms. Most laugh at the absurdity of the possibility of stopping the inexorable wandering of our planet's restless crust. But for the exception of the occasional earthquake or volcano eruption, we typically witness few large scale changes in the Earth's crust; the earth's time scale dwarfs the life span of a human being millions of times over. But undeniably, the earth moves, shaping the very land masses upon which we now live. Despite that an Easterner does not typically wake up one day and discover that the East Coast has suddenly become the West Coast, there is no reason to expect that in another hundred million years or so, the North American plate won't be oriented in a direction opposite to its current configuration. And through all these tectonic tribulations, mountain ranges form as plates slowly smash together while rifts appear as they drift apart. Unfortunately, humans lack the time to witness the full extent of this fascinating creation/demolition derby.
The dynamics of the Earth's crust tell a large portion of the history of this planet. Wax-tectonics experiments shave away millions of years of field research by simulating portions of Earth's drama in the laboratory. Our experiment examines the rich world of ocean floor spreading over the course of minutes, in contrast to a time scale of millions of years. Our experimental apparatus is only three feet long, one foot wide and 4 inches deep. It is heated from below so that the wax melts and cooled from above to optain a crust which is then pulled apart. While peering into the wax tank, one can observe and characterize many phenomenon witnessed to be occurring on the planet. At this snappy pace, under controlled experimental conditions, these phenomenon can be measured, and the factors which contribute to the behavior or the wax system determined. And, remarkably, these phenomena seem to scale to the Earth. That wax spreading patterns should form and be similar to the Earth is fascinating, and lead to deeper questions of dynamics in general. So we question: Why stop tectonics when the alternative is so much more interesting?"
(Originally written by Will Bertsche and slightly modified by Eberhard Bodenschatz, 1998)
The evolution of wax-microplates is observed from above. A picture is taken every 15 seconds, the image size is 3.3mm accross and the pulling speed is 35 microns/sec. The dark line is the rift. An offsetted spreading center is formed in image (A). As time progresses (A to D) a microplate is formed and rotates counter clockwise and increases in size. In image (E) the microplate breaks off and is frozen into the newly formed crust (D). The spiral shape can be explained by a model that works both for wax and earth.