My experiments with volcanoes

by Thomas Augustus Jaggar

The twenty-eight percent of earth surface which lies above the sea in continents is made up of siliceous sediments of shallow water basins, with quartz as the dominant mineral, their strata wrinkled, and eroded into mountain ranges. Desert and lake or river bottoms make up most of the remainder. This material, when ancient, was changed by heat and infiltration into what are called gneisses, schists, and granites; and the process of granitization is among the metamorphic processes. It is a process of deep burial, heat, gases, and water which has always been a puzzle, and may affect ancient volcanic lavas wherever they have covered the land. It is a process of solution of silica, and its deposition is by steam and other vapors.

In the same way volcanic action by the outpouring of lava through cracks is a process of solution of the deeper crust of the earth by hot gases, largely burning hydrogen. Lavas emerging from Etna or Mauna Loa are melted earth crust, dissolved and brought up by this same hydrogen and by other gases from the walls of profound cracks leading down to the earth core. Volcanism and metamorphism are thus the same process, namely the action of gases up cracks through deep earth crust. But metamorphism acts on continental sediments, whereas modern volcano eruption acts through sea bottom and sea shore faulting, very ancient features of the earth and distinct from continents. In Hawaii no metamorphic rock fragments have been found.

Such primitive oceanic fault fissures extend under continents remnant from the time of evolution of continents. They bring up the metamorphic hot gases, which in siliceous sediments, make granites and gneisses and schists with the aid of groundwater. Geology has no knowledge whatever of whether this metamorphic process affects the hard rock under the oceanic muds, because geology has never collected a piece of that rock. Geology however knows inclusions and explosive fragments from oceanic volcanoes, and it does not find there granite and gneiss and schist. However, generalization does not apply to continental volcanoes like those of Italy and Africa.

The beginning of fossils on continents is commonly considered to have been 500 million years ago, and this may be extended another 1,500 million years for the most ancient identifiable continental rocks, and an estimated total thickness of 120,000 feet to the bottom of the most ancient sediments on earth. We know nothing of thickness of most ancient volcanic deposits under the oceanic mud.

This brings us to the great German explorer Stübel, who mapped volcanoes of the Andes, founded a museum of his work in Leipzig, and published monographs on the Andes. He wrote a final book, including material on Mount Pelée, on the “genetic differences of volcanic mountains.” But such modern continentalists as Daly and Bucher in America have disregarded Stübel. Daly is the authority on a shallow earth shell and substratum of basalt, and Bucher of Columbia University is a specialist on continental sediments and granitization.

The point is that Stübel made a profound generalization which nobody has proved wrong. The earth is at least 3,000 million years old, and when oceanic fault blocks sank and received condensing atmospheric water and continental fault blocks remained high and became eroded, there was already a thick shell of volcanic lavas. For volcanism was the most ancient process on the earth’s surface. It had always brought gases up cracks from the core, making atmosphere, water, and extrusions. Stübel, called the extrusive shell on the outside of the primitive crust the globe’s armorplate. The primal gas escape, whatever the ancestral turbulence inside, had to come up cracks and make volcanic deposits. It is commonly presumed that the very thick inside crust formed rapidly by cooling and solidifying from outside the core inward, and from inside the atmosphere outward. The latter surface was eventually under water cooling over most of the earth and under air cooling over the small continental area, a marked difference of temperature and pressure for the two areas.

Seismometry teaches that most of the crust is of fairly uniform density. Therefore, presumably, a thick crust was arrived at early. There was obviously a time of conflict between the weighting of the crust by its heavier accumulations next to the core, by its lighter accumulations exteriorly under water and air, and finally by its external armor plate of unknown comparative weight, made of volcanic lava. For all we know, this might have been volcanic pumice. Rapidity of crust thickening is speculative.

Right here there is an element of mystery in speculation as to which has to accommodate comparison with the moon, the merging of atmospheric condensation with volcanism, and the merging of suboceanic condensation of lava with pristine eruption. This is too hard a nut to crack, in our current ignorance of rock under sea bottom muds. But Stübel’s insistence on a coating of lava armor plate over both continents and sea bottoms as the earlier volcanism, and an external veneer on the earth, is unavoidable. If it were all basalt like the present oceanic volcanoes, we should find basalt in continents underneath the granites. We do not do so. If it were all light weight granitizing by segregation of silica, we should find commonly granite and obsidian fragments within oceanic lavas. We do not do so. We have to conclude then that our sections, topographic and geologic, do not go deep enough. And as for the ocean bottoms, we have no sections at all. But Stübel was right. An unknown volcanic eruption period had to precede geologic volcanoes.

The question of ancient greenstones in Africa, Scandinavia, and Canada is much discussed, for there were old volcanic lavas in many places; mixed with gneisses, schists, and granites. They were not a deep layer, but presumed to be ancient remnants of interspersed lavas among sediments. They are one more evidence that volcanic eruption goes back to the time of the most ancient rocks on continents and that its lavas were affected by metamorphism. But no continuous deep stratum of greenstones is known. At depths of fifty miles, under continents only, is the Mohorovicic change to denser rock. This is an echo surface in earthquake waves, but it is absent over the whole Pacific. It may be the top of the armor plate.

Justice Holmes wrote that the Constitution of the United States was an experiment. That all law of the nation works salvation by prophecy based on experiment. The experiments were extended to the Bill of Rights and all the amendments to the Constitution. I feel that geology—in view of its extreme ignorance of submarine rocks, ores, metals, oils, spring waters, temperatures, magnetism, gravity, and gases for most of the earth—needs a bill of rights and numerous amendments to its constitution. Its salvation by prophecy needs to be based on experiments with instruments, drill rigs, and anchored laboratories in this vast area. These experiments, superficially, have been conducted by oceanographic sampling of bottom materials, by gravity pendulums operated in submarines, by cameras on sea bottoms, and collections of bottom waters, by tests of radioactivity of bottom materials, by echo sounding to determine thickness of muds, by volcanology on oceanic islands, by topographic surveying of the bottom, and by all the excellent work of the oceanographic and geologic stations and their seismographs, with some studies of marine chemistry, physics, and biology. The conclusions in this book amount to only one small prophecy based on experiments with volcanoes. But the rock under deep ocean mud is still uncollected.