My experiments with volcanoes

by Thomas Augustus Jaggar

The epoch-making significance of this experiment was not understood until later. Calculation of the angle of slope of the pipe, where it went down into the liquid and hit on the bottom, showed that vertically the liquid was about fifty feet deep. With the aid of soldiers from the Kilauea Military Camp, this experiment was repeated several times; and each time the lake was found to be the same depth.

This conclusion was later verified by sudden subsidences of the liquid lava until the cliffs bordering the liquid were fifty feet high. The eastern grottos turned into cascades, with the liquid pouring down a well. The liquid lake had become a river pouring over a ledge of its own bottom, across from the western source wells to the eastern sinkholes. These latter were fountaining grottos when the lakes were full, but they exhibited internal rectangular upright sinkholes when the lake level was down. This was verified repeatedly, and the phenomena of source wells at the west and cascading sinkholes at the east were confirmed and photographed. It thus became evident that the lava lakes were nothing more than convectional lava flows over pasty solidified substance of their own bottom sediment. Convection means rising foam, loss of gas, and sinking gas-free heavier liquid.

In other words, the bench magma capped with overflows on the marginal platforms was a paste, cooled from the top and bottom and sides and making the saucer of streaming liquid. It was this paste which constituted the swelling heart of the bench magma. The fountaining of gas bubbles escaping from solution robbed the lava of heat and caused it partially to solidify, always at a depth of about fifty feet. Thus there were necessarily three substances: The deep lava fizzing with self-heating gases (later proved to be inflammable hydrogen, carbon monoxide, sulfur, and inert nitrogen and argon), the streaming foam into which the deep lava expanded, and the semi-solidified refuse of the foam created at the bottoms and banks of the liquid lava when it cooled from bright yellow heat (about 1150° Centigrade) to a dark-red heat (about 900° Centigrade).

The streaming across the bottom from west to east meant that during six months of rising lava, some 600 feet in the last half of 1916, the lava column was a cylinder of semicooled lava, maintained by upward pressure of the deep lava bubbling up in the western crack between the cylinder and Halemaumau wall. Meanwhile, at all times, the lakes were nothing more than streams of foam fifty feet deep and skinned over on top, congealing on their bottoms and shores and cascading down sinkholes in the eastern wall cracks of the cylinder. A convectional circulation was what maintained the rising, foaming, heating, and cooling and the changes in density of the liquid as it lost its gas. Thus the entire fountaining phenomenon of the lava lakes was due to the self-heating of what is known as exothermic reaction of gas escaping from solution in molten basalt. Much of this is actually the burning of hydrogen in air, creating a convectional circulation wherever the deep lava can find an outlet.

Ordinarily these outlets are along cracks or rifts in the slope of the mountain, where they are seen to break out in gassy fountains 500 feet high, and often to flow along the crack to a cavity where they cascade downward when less foamy and heavier. A lava flow is always solving a problem of foaming and liquefying, just as does champagne or beer.

There still remains the unsolved problems of how much of the deep lava is gas and whether it is mere pressure which holds the gases in solution, as in soda water. The alternative is for the deeper magma to be entirely gas, oozing up cracks in the globe, and reacting with oxygen from the air and solid rock, percolating from the core of the earth upward, and melting its walls.

In a sense, the entire decade to 1920 was an experiment. The results of that decade showed that the mountain swells and shrinks in tides with the passages of the sun and moon, but that Kilauea Mountain and Mauna Loa Mountain are all parts of what might be called Hawaii Island Mountain. The island of Hawaii is above an old ocean bottom 18,000 feet deep and is only the end of a ridge 1,700 miles long, which even at its lowest end, Midway and Ocean Islands, is still 12,000 feet high above the smooth mud-over-rock ball of the Pacific Ocean bottom. All the evidence shows the ridge to be a pile of lava flows over a crack, with a veneer of coral. If, then, the relatively small Kilauea dome is swelling and shrinking in sympathy with the sun, the long Hawaiian ridge is doing the same thing to a much greater degree.

Michelson has shown that the solid rock of the globe rises and falls in a tide about one foot every half day. As I have said, our daily measurements in 1912 showed that the lava in Halemaumau had a daily tide and that the larger movements reached maxima in June and December and minima in the intervening months, which proved it must be a solar effect. This was very exciting information and suggested a long train of experiments, which were to be successful in the next decade, based on the idea that the whole mountain swells as shown by leveling. This extends out to a radius of twenty miles from Kilauea Crater, and probably extends all the way to the seashore.

The actual measurement of a lava tide in Halemaumau was done during July and August 1919. R. H. Finch had just come from Washington to be my assistant. Oliver Emerson of Honolulu was another assistant, and two Harvard youths, Sumner Roberts and Charles Thorndike, who had been on war missions in submarine chasers, sent word through their parents that they were anxious to do something dangerous around an active volcano. I jumped at the chance to employ them to help me measure the lava tide.

The north lake in Halemaumau was quite accessible, and we organized night and day shifts for surveying measurements from a canvas shelter on the actual bench lava near the lake. For twenty-minute periods, each observer critically measured a number of monuments on the bench magma and glowing places of the lake edge. Then a new measurement was started by leveling the transit. This sequence was kept up night and day for a lunar month, namely twenty-eight days. One of the monuments was a fixed Halemaumau benchmark, equipped at night with a lantern and used as a datum for the fluctuating lake points.