VIRTUAL VS ACTUAL 3D AND THE ANCIENT MISSISSIPPI RIVER IN ILLINOIS

The Prairie Research Institute hosts an annual outreach event in March for students (K-12), their teachers and parents, and the general public. ISGS exhibits showcase the geology of Illinois as part of the event. One exhibit showcases the glacial geology of Illinois and the ancient buried landscapes now covered by glacial and post-glacial deposits. Engaging the passively-interested passersby and communicating the character of ancient landscapes or the types and distribution of geologic materials can be a challenge. Our goal is to generate interest, enthusiasm, and an appreciation for the framework upon which we work, live, and play. Virtual and actual three-dimensional models help us tell the story.

The fact that Illinois has been repeatedly visited by continental glaciers is apparent to the trained eye. However, to the untrained eye most of the state may appear flat. The paucity of natural geologic exposures and the subtle character of post-glacial landforms mask the underlying complexity. The visual impact of how the ancient buried landscape was altered by each subsequent glacial event is a surprise to both the trained and untrained eye. Discussing how these changes influenced the complexity and distribution of the materials at or near land surface follows easily.

A 3-dimensional model of the ancient Mississippi River valley was constructed from a bedrock topography map of Illinois and an adjacent area of eastern Iowa. Using a GIS, raster images for the bedrock topography of both maps were converted to contour lines (5-foot interval). The two vector data sets were stitched together and a 20-foot contour interval was selected for the 3-dimensional bedrock surface. Each contour interval, cut from masonite became a layer in the stepped ‘actual’ model.

The vector layers from the ‘actual’ model were used to ‘build’ a virtual model that was ‘painted’ with geologic maps to show sequence and distribution of materials. An automated slide show of successive snapshots of the virtual layers demonstrates the evolution of the modern Mississippi River valley from the valleys of the ancient Mississippi River. Interactive manipulation of the virtual model allows the user to exaggerate, remove, or make transparent various layers to reinforce the learning experience or to graphically answer questions.