Figure 6a. High pressure face of a failed window; note the small opening 
through which the compressed water penetrated into the conical 
fracture cavity on the low pressure face of window. 
Figure 6b. Low pressure face of a failed window; note the conical fracture 
cavity from which the cone-shaped plug was ejected by the 
compressed water entering the cavity through the small hole at 
its apex. 
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