Table 3. Comparison of Propagation Timescales teq Based on Scaling the Experimental Results of Lacerda [1987] and the Numerical Results of Ogden et al. [2008], With Jet Collapse Timescales tcoll for the Systems of This Studya System Pr(0)/Pa teq,s tcoll,s Laboratory nitrogen jet 100 0.15 x 10-3 0.2 vulcanian 100 1 65 Mount St. Helens 100 54 84 Mount St. Helens 150 78 93 Mount St. Helens 250 80 104 aIf teq <= tcoll, we estimate a Mach disk shock has time to form at its equilibrium location.