Although the
geologic nozzles have no geology or geography in common, they are
united by the equations of fluid mechanics. In each case, flow
through a constriction is important, e.g., the conduit of Old Faithful
is irregular in shape (a video of the conduit will be shown), the
rapids are in regions of the river constricted by debris flows, and the
lateral blast at Mount St. Helens was like the discharge of a rocket
nozzle. Some geologic fluids have very low sound speeds: dusty
gases, and boiling water, for example. Because of this, flow
fields can transition between subsonic and supersonic
conditions. The analogy between shallow water flow
(subcritical, supercritical, hydraulic jumps) and gas flow (subsonic,
supersonic, shock waves) allows the processes to be compared and
contrasted.