My experiments with volcanoes

by Thomas Augustus Jaggar

Isostasy was devised by Dutton and pounced upon by the mathematicians, until they had gravity proving the whole world thin-crusted over an understratum of plastic lava. The seismologists on continents agreed, finding a density change, but with no evidence of fluidity. The world became, mathematically and petrologically, a sphere built of layers all the way down to the heavy fluid hot core, which was conveniently imagined to consist of iron and nickel, because some bolides of the solar system made of those metals occasionally fall on the earth.

All my experience of volcanoes and of deep oceans militated against a thin crust, a shallow underlayer of basalt to feed volcanoes, and a nickel iron core. The core is heavy, and sixty-two elements are heavier than iron. All reason seemed against the notion that the vast volcanic sea bottoms are a thin crust wrinkling under contraction. Reason found every evidence on both earth and moon for a thick peridotite or olivine crust, broken into ancient blocks, bounded by long lines of fracture, the blocks variously settling and scraping against each other from time immemorial, actuated by volcanic forces from the core. The whole of volcanology points toward sinking and down-faulted ocean basins, alongside the remnant upstanding continents which are the minor feature of the primitive earth surface. Water condensed and filled hollows. The processes of the core that made all this were volcanism—mother of air, ocean, seabottom, land, and life. The crust was thick enough to make cracks 2,000 miles long on a globe 8,000 miles in diameter. If there was a balancing of weights as in “isostasy,” it was between high silica in continental lava and low silica basalt that spread under the oceans. This is not static, but is a continuing process of a kinetic, or changing, earth.

This excursion into theory is intentional, so that in the middle of this book the geologically trained reader will understand that experience of volcanoes in Hawaii, the Caribbean, New Zealand, Alaska, Italy, and Japan had made me a rebel against conventional geology. The reason is that the great submerged mountain range of the long Hawaiian Archipelago is different from the mountain ranges of Europe and Asia and must be accounted for in global history. How would the three decades 1921 to 1950 confirm expectation that the deep ocean bottom is the most important and volcanic thing in geology, just as it is the biggest thing?

Routine observation and photography at Halemaumau pit reached a climax of recording brilliant fiery events in March 1921, and it changed to the recording of explosive steam in May 1924. The first of these fireworks, after lava flows from a rift in the Kau Desert, draining the pit and fluctuating with the ups and downs of the pit lava, occurred in 1919–1920. This was a return to Halemaumau of effervescence in frothy volumes, so that the pit was overflowing on five sides. On March 20, 1921, occurred the most intense display of brilliancy, culminating the gradual rising of the lava column to outflow following 1918.

Then came, in the later months of 1921, a sinking away and recovery of the lava. In 1922 came a sinking again, with the lava breaking out in the Chain of Craters of the eastern rift, as though it had been blocked by freezing in the southwest rift and was forced over to split open the old cracks of the mountain to the east. This was confirmed in 1923 by another outbreak in the forest adjacent to the sixth crater, Makaopuhi, which with Napau pit beyond, had been the scene of the 1922 outflows.

This action was all extended in April 1924 to the shoreline end of the eastern rift, thirty miles away from Halemaumau, when the Kapoho country cracked open with many earthquakes, and a block of the mountain settled beneath sea level. Coconut palms at the beach were left in a lagoon of sea water eight feet deep. Seventy-five earthquakes in a day frightened away Filipino plantation laborers; railway and roads were ruptured, with new cliffs forming nine feet high; and all of this followed a monumental sinking of Halemaumau bottom, from a vast sea of lava to a tumble of debris in two months.

It was evident that between 1920 and 1924 the fracture of the long curved rift athwart Kilauea cauldron from the Kau Desert to the east point of the island was draining the lava out under the ocean to the east. Forty miles from the shore, the submarine slope is covered by 18,000 feet of water.

What is the result? The whole of Kilauea Mountain is charged with groundwater, which trickles warm through the beach at Pohoiki and partly warms ponds near Kapoho. Obviously this groundwater of the southeastern lobe of the island mountain surrounds the shaft of Halemaumau at some undefined depth, and the rising and falling glassy lava in the shaft ordinarily glazes itself with a water-tight skin, and may be thought of as a crusted tube. About this tube the groundwater shows only as the lazy steam of the little vents of the pit margins. On May 10, 1924, came the collapse of the Halemaumau pit walls, introducing an explosive steam eruption such as had not been seen by five generations of Hawaiians.

The adventures of this period were glorious ones for the scientists. First should be mentioned the amazing subsidence which occurred suddenly at 2 A.M. November 28, 1919, just as Mrs. Jaggar looked across Kilauea Crater at the outline of crags and lava lakes making a glowing dome where Halemaumau pit should have been. We felt a lot of little earthquakes and saw the dome of lava heapings, with glowing lakes on top, sink slowly and majestically and leave the old familiar glowing pit. For almost the whole of 1919 this had been a dome, with overflows, now here, now there. At ten o’clock only the evening before, old Alec had conducted tourists to the top of the dome, where they looked down at the clover-leaf lakes. If it had started to go down while they were there—and any of us might have been there—it is awesome to think of the inevitable fiery engulfment.

After watching the sinking, which was followed by puffs of dust and smoke and some avalanche noise, we took a car to the pit at once. And when we got there in the early morning hours we found the pit enlarged to 2,000 feet across, with the pattern of the lava lakes still apparent at the bottom, indicating that the entire cylinder had lowered as a unit to a depth of about 700 feet. Red hot avalanches were tumbling inward with a roar, from the veneer of lava plastered on the wall. By the forenoon of that day the liquid lava started to pour up and inward as a ring of bubbling fountains all around the edges. What this ring represented was the wall crack between the subsided cylinder of semisolid lava, now pushing upward, and the funnel of rock wall outside. This V-shaped filling grew wider as the uprising progressed, and so the ring lake became wider, while the top of the harder column became a ring of crags and the space inside became a quiet lava puddle supplied by inflow from the ring lake. The whole column of ring crags with the lagoon inside and the brilliantly fountaining lake outside rose with unheard of rapidity during the next three weeks.