Figure 6 from  Geophysical Investigations conducted by the U. S. Geological Survey on Fletcher's Ice Island (T-3) during the International Geophysical Year.

From Page 13: "Ice being blown from the shot hole. Charges used for seismic bottom reflections ranged from 1 to 50 pounds, Usually 1 or 2 pounds of explosive were sufficient to provide high quality records. Larger charges were sometimes used since the poor condition of the available explosives made it dangerous to break apart cases which were solidly frozen."