My experiments with volcanoes

by Thomas Augustus Jaggar

The results of all these tests showed that rigid beds carried the arching force and that soft beds were most invaded and pushed aside by the wax. The steepness of curvature of arch varied with the load. An inclined pipe formed an irregular lens thickest away from the incline. In a hard bed ruptured on a downbend, concentric fractures around a dome let the lava up to higher strata.

On the crest of a hard bed the fractures are like the spokes of a wheel, but they do not make dikes; they yawn open upward. Liquid wax tended to spread as a thin sheet in soft layers of strata, stiffer wax tended to arch up in a steeper dome. Rapid injection made a higher and smaller dome than slow injection.

Compared with the arching up the whole long mountain oval of the entire Black Hills dome, with granite on the crest, this intrusion of wax only imitates the small domes of lava intrusion or injection, where the injection carries the energy or stress. Indeed, in nature, even the lava lenses are influenced by the buckling that is going on in the strata under stresses of crust warping. For the warping crust of the earth is always pulling the trigger and straining the strata. The lava rising from below seeks out the weak places and assists the buckling, as well as following the most incoherent mud or shale beds.

When it comes to the big oval of the whole Black Hills uplift—swollen up like the Rocky Mountains during millions of years and within which the lava injections were only an item—we are dealing with a push from below or an expansion that swelled up the pre-Cambrian ancient rocks as well as the later granites. Such swellings were doubtless made again and again in Massachusetts. There, also, we find lavas and granites and Red Beds and glacial boulders, older than the Appalachian Mountains, as well as younger. The younger Triassic lavas are definitely erupted between fault blocks.

All that our experiments showed was what melted stuff will do in strata under weight, when the force of melted stuff overcomes that pressure to find a place for itself, although the weight may be more or less lifted by big arching that is taking place on a big scale. The arching is bigger than the hydraulic or gas pressure squirting.

There is another possibility besides buckling. This is faulting, or movement of deep crust blocks the boundaries of which do not appear. The deep crust is a movable mosaic above the core, and this movement renews itself, now here, now there. Dutton shows that we may think of the Rocky Mountains this way all the way out to the Pacific coast. We may have the core fluids sucking down the blocks, the volcanic fluids pushing up the local strata. And the volcanic fluids in cracks are the degenerate gassy top remnants of the core fluids which man has never seen and which are 1,800 miles down.

The boundaries of the crust blocks do not appear because the whole first shell of the globe is buried under lavas and intrusions and crystals and mud, meaning by mud, countless dumpings of lakes and rivers and seas through 3,000 million years. Such is the kind of thinking started by making wax injections.

It will be seen from the experiments that whether we are imitating underground heat with a Bunsen burner to start a geyser, or overground cold with delta apparatus to simulate a glacier, we are dealing with erosion of the earth’s surface. Erosion started with the first attack on lava by the atmosphere or by sea water. Never was the pristine lava anything like the magma inside the globe; it snapped and chilled and oxidized. Whether we call it basalt or obsidian, it degenerated. Moreover, it degenerated in the outer crust when it loosed its gases, heated itself and the rock wall, found groundwater and free air, and started oxidation new to it. Thermal action is just as much concerned with erosion as is rainfall or snow. Therefore, whether injecting wax and swelling strata or imitating geysers and ripplemarks, we were experimenting with volcanoes, for the crust of the earth is fundamentally volcanic. For the purposes of this book these facts demand reiteration.

In what are called geosynclines, or earth sags, the great beds of strata are accumulated. They are the dirt washed from highlands into midland seas. They are strata of sandstone, mudstone, or limestone; thin films in comparison with the fire-made earth crust. It was the wrinkling of basin fills by expansion or end push that built Himalaya and Appalachia. The mountains are etched out of foldings and overthrusts and faults by rotting and water transport. Pressing the strata endways to wrinkle them is called mountain building, much better named strata wrinkling. The thickest of them reached twelve miles vertically, but what is that to the earth’s crust of 1,800 miles? The crust lifts and lowers fault blocks. The little strata basins expand with heat on their bottoms and get pulled and pushed by underground lava intrusions. Also they get squeezed by global contraction between crust blocks, and shoved up and down by the agelong wobbles. The biggest wobble was the downdrop of the great oceans over fault blocks when the crust first cracked and settled over the core. Those oceans have shifted and adjusted in waves of global action ever since. The crust has kept the earth a sphere while lavas erupted and weighted down the blocks. This block wobble extends into the innermost continents. Eruptions up the cracks migrated from the continental seas to the shores of the present oceans. They changed composition as they did so, because they changed from under-air eruptions to under-sea eruptions, fifteen pounds pressure to 600 atmospheres pressure. From erosion eruptions with enormous heat, to deep sea eruptions with enormous chilling and pressure. And the latter are the volcanoes of the present day, mostly concealed except for the islands and sea borders.

Meantime, the crust blocks continue to wobble up and down, and quakes continue to creak under the rock tides of sun and moon pulls. The creaks and wobbles are our big earthquakes, tidal waves, and eruptions. Such big accumulations of eruptions as the Cordillera or the Hawaiian Ridge is a terrific weight in a few million years. Both heaps have been at it since Miocene time, or for about 18 million years, banging down through the crust blocks on top of the core. Whether such balancing of heavy weights on top of the crust blocks is due to change of lava weights or sediment basins, six to twelve miles of rock vertically, the down squeeze and underflow is called by the Greek word isostasy. It means standing level and is a poor word because the earth’s crust never stands still. The blocks are eternally adjusting and creaking over a fluid core, the globe is whirling, the sun and moon are pulling, the volcanoes are erupting, and the solar system is shooting through space. Terra firma is never static. And our little atmospheric lives on top of it never stand still. We are hot, and we ourselves do a great deal of eroding.