MODELING COLLAPSE STRUCTURES IN THE CLASS ROOM WITH SIMPLE MATERIALS

The use of simple physical models often enhances the class room experience for geology students. This can be particularly true for nonscience majors in general education classes. Many geology instructors use simple materials to demonstrate faulting and folding, or more complex ideas such as the different types of seismic waves. Often, hard to follow diagrams are used to enhance an oral description of complex geologic phenomena. A physical model using simple, readily available materials, can be used to demonstrate the development of different collapse structures. This model consists of a box constructed of a layered cardboard base with clear plexiglass sides. The cardboard base contains a cut-out depression into which an inflatable rubber bladder is inserted. Tubing leads from the bladder to an external air source. Sifted flour is layered over the rubber bladder in order to mimic earth materials. Layers of flour tinted with different colors of dry tempera paint can be used to mimic a layered sedimentary structure. This model can be used in two modes. First, if flour is layered over an uninflated bladder, inflation followed by deflation can be used to model caldera forming eruptions. This scenario reproduces radial fractures developed by bulging (inflation) followed by the development of a circular collapse structure as the bladder is deflated. This scenario models the filling and eruption of a magma chamber during caldera development. In the second mode, flour is layered over an already filled bladder. A collapse structure develops upon deflation of the bladder. This mimics the collapse of caverns and the development of sinkholes in a karsted terrain.