U.S. Geological Survey Open-File Report 2010-1173
A caldera is a large, usually circular volcanic depression formed when magma is withdrawn or erupted from a shallow underground magma reservoir. It is often difficult to visualize how calderas form. This simple experiment using flour, a balloon, tubing, and a bicycle pump, provides a helpful visualization for caldera formation.
(click on the title page to start the video)
This report is presented in MP4 format; the latest version of Apple QuickTime or similar software is required to view it. Get QuickTime (free download) to view this movie.
Venezky Dina, and Wessells, Stephen, 2010, Caldera demonstration model: U.S. Geological Survey Open-File Report 2010-1173 (video).