533 



Figure 2 Is taken from a report by Schllchter, Schneider 

 and Cole on the Measurement of Bubble-Pulse Phenomena. It 

 shows the appearance of the dome^ radial plumes and columnar 

 plumes at different times and for different Initial charge 

 depths . The charge weight used is 290 lbs . for this series of 

 shots . 



One of the difficulties in interpreting pictures of the 

 type shown in Figure 2 is the fact that the top of the dome is 

 used as a reference point rather than the water surface which 

 is necessarily obscured. If, however, the height of the plume 

 is plotted against time, it is easy to extrapolate this to zero 

 height and thus find the time of emergence of the plume from 

 the surface, called the plume time in Figure 3' Similarly, sur- 

 face velocities can be found by extrapolating differentiated 

 height vs . time curves . The results have been plotted by the 

 above mentioned authors and are shown in Figure 3- It is seen 

 that vertical plume velocities are high for charges at depths 

 for which the plume time coincides with the gas globe period, 

 or sum of periods . This shows that hi._,h plume velocities occur 

 when the gas globe reaches the water surface in a collapsed 

 state. Furthermore, the Jog in the plume time curve corres- 

 ponds with the maximum expansion and the subsequent contracting 

 phase of the gas globe. This means that for charges at these 

 depths it is necessary to wait about an additional half period 

 for the plumes to appear. 



It is seen, therefore, that a reasonably satisfactory 

 account of some of the visible surface phenomena can be given 

 by referring them to the behavior of the gas globe, and that 

 plumes of a similar appearance occur if the explosion bubble 

 breaks surface in the same phase of its oscillation after one 

 or two or even three complete periods . Thus the occasional 

 observation of a high columnar plume characteristic of a 

 shallow explosion occurring in the case of a relatively deep 

 explosion is explained by the critical combination of circum- 

 stances which permits the gas globe to oscillate through two 

 or three periods and arrive at a depth near the surface in the 

 same phase as if the charge were statically detonated at that 

 point . 



It is also clear from Figure 1 that the time of appearance 

 of the plumes is not very sensitive to the charge depth and 

 jumps discontinuously from short times to longer times as the 

 depth is increased. Observation of these times therefore does 

 not lead to a good indication of the actual depth of explosion. 



