Russel Wallace : Alfred Russell Wallace (sic)
The violence of an explosion will depend largely on the amount of confinement and pressure to which the exploding compounds are subject, as well shown in the cases of Kilauea--where there is a constantly open vent and no violent eruptions--as contrasted with the numerous catastrophic explosions of long dormant volcanoes whose vents had become sealed up with cores of solid lava. But it is admitted that the crust of the earth has been growing thicker during all geological time. It is therefore almost certain that, in the remoter epochs volcanic phenomena were more frequent but less violent than they have become now that the crust is thicker, and, in its lower portions, at all events, denser and more consolidated. The usual argument, that, because the interior of the earth was somewhat hotter in early times, therefore volcanic phenomena were more violent, appears to me to be entirely fallacious. The liquid matter immediately below the crust would have been at the same temperature as it is now; and if there were a more abundant supply of aqueous vapour and other gases, the thinner and more permeable crust would have allowed of their constant and comparatively easy escape.
I do not remember to have seen this consideration referred to in any discussion of the question, and I therefore submit the argument to the consideration of physical geologists.
Alfred R. Wallace.