Thousands of denuded volcanoes have been examined all over the world, yet the remnant necks rarely exceed a mile in diameter, and the larger ones were caused by the coalescence of several vents and by a combination of explosion and collapse. The absence of denuded volcanic necks even approaching a third the diameter of Crater Lake is in itself a powerful argument against the explosion theory.
To return to the evidence offered by the form of Crater Lake, it may be recalled that usually explosion craters are funnel-shaped, especially if the walls are composed of fragmental deposits. Cylindrical craters have been cored by strong blasts of gas, as at Vesuvius in 1906, but these are relatively small. The singular paucity of lithic detritus round Crater Lake, Krakatau, Santorin, and similar calderas shows that coring of cylinders miles across is possible only in theory. Precipitous walls bordering large volcanic depressions must be taken as a sign of engulfment.
7. The concluding arguments of Smith and Swartzlow relate to the post-caldera eruptions of Wizard Island. That a volcano may resume activity after the collapse of its summit is only to be expected. Neither the subsequent activity nor the character of the material erupted has any bearing on the mode of origin of the caldera itself.
From the foregoing, the conclusion is inescapable that Crater Lake cannot have been formed by explosive shattering of the top of Mount Mazama. We may now pass to a preferred explanation which is fundamentally different. In this explanation, we begin with the knowledge that only a small fraction of the 17 cubic miles of solid rock which have disappeared is to be found as fragments among the ejecta.
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