Developed by Paul Howell (phowell@alleg.edu), Department of Geology, Allegheny College, Meadville, PA 16335.
Discipline: Geology
Isostasy is a state of gravitational balance among the objects which comprise the surface of the earth. To a first approximation, continents "float" on the earth's surface because they are lighter than the underlying mantle material. This is just like ice cubes floating in a glass of water–the ice is less dense than the water, so it floats. Bobbers is a graphical simulation of isostasy that lets you experiment with the physical controls which govern the state of balance. These are the density and thickness of the floating objects (continents or blocks of wood or icebergs...) and the density of the supporting medium (or media).
Bobbers1 represents a simple system with two bobber blocks floating in an ocean. Sliders and textfields control the dimensions of the bobbers, and their balance (elevation and mass) is continually recalculated and redisplayed. Parameters may be varied from realistic to the absurd (both flying and sunken continents). Exercises for class work emphasize visual problem solving and developing a feel for the (sometimes) non-intuitive behavior of floating continents. Bobbers2 is an extension to the two bobber model by creating a single continent with ten segments, each fully adjustable. This can be used to simulate mountain belts, sedimentary basins or any irregular floating object. Sediments can be added to any continental block which is underwater (an additional load which further depresses the bobber). Bobbers3 (under development) is a more complex segmented continent which allows much greater flexibility over additional loads placed on the continent (overthrust belts, sediments or continental ice sheets) and allows the continental segments to be linked flexurally to allow adjacent blocks to help support the additional load.
Courses that use the application at Allegheny College include Physical Geology and Historical Geology.
This application was developed under NeXTstep release 2.2.
