My experiments with volcanoes

by Thomas Augustus Jaggar

An effect that was more volcanic, but similar in principle, was the visible vapor inside of Halemaumau, close to the lava lakes, which always increased when the lava lowered and let the groundwater seep inward. These visible vapors dwindled when the hot slag bubbled and rose, and acquired a brighter glow. No steam vapor rose from the glowing lakes. There was drying up of groundwater by increased volcanic heat, just as the cracks of the bigger crater had their moisture dried by the action of sunshine.

I shall have more to say on the subject of the seasons, the calendar effects on the plat of rising and falling lava, and especially the solar equinoxes and solstices. There appeared the hint of a daily tide-like rise and fall of the lava in the pit.

Finally, there arose the question of counting earthquakes, measuring their spacing in time and place, and seeing which belonged to Mauna Loa and which to Kilauea fault rifts. We had to plot earthquake frequency and size in relation to lowering lava, to day and night or to the seasons. The study of rhythmic swelling and creaking inside the great pasty mountains became an exciting quest. It gave promise of cycles from the hours of the day to the decades of the century.

We also discovered, by measuring vertical angles, that the inner floors rose and fell differently from the liquid lakes, hence the floors could be called the bench magma, as distinct from the liquid magma. This led to a bold experiment in 1917 when the liquid lava lakes became accessible, after a casual visitor, Mr. Walter Spalding of Honolulu, discovered an easy path down to the overflow floors at the edge of the north lake. Here the streaming slag rushed toward a glowing grotto, built up by spatter of a border fountain into a huge half-dome containing a glowing cavern hung with stalactites on the shore of the lake. The platform outside of the grotto was overflowed, and built up as the liquid lake rose, the platforms of overflow sloping away to the wall valley under the pit cliff. Thus the lake was at the top of an inner dome a thousand feet across, just as Halemaumau pit rim was at the top of an inner dome of Kilauea floor three miles across. The outer edge of Kilauea Crater is a big oval at the top of the outward sloping greater dome of Kilauea Mountain forty or fifty miles across.

When a little conelet formed on the northern or western floor platform inside Halemaumau, its slope around a splashing and fountaining crack would make a fourth innermost dome a few feet across in the series of progressively smaller cone-in-cone structures from the outer rim of the big mountain inward to the Halemaumau centers of eruption. We saw such a conelet cave in just where I had stood and tested a flame the day before. Quietly the cone collapsed into a fountaining well of boiling lava beneath. The ring-in-ring conception must be held in mind with regard to any volcano, for one thing which we discovered is that cones are not only built up and collapsed but they are also swollen up by internal percolation of cracks and expansion of the hot stuff. This tumefying, or swelling, is concerned with the experiment now to be described.

Even after Perret described his “floating island” of 1911 and I saw the triangular islands appearing like shoals in a mud flat and gradually rising into crags in 1916 and 1917, I remained incredulous of the possibility of a basaltic island floating. When solid lava cracked off in pieces from inner cliffs around the lava lakes, the fragments immediately sank. Furthermore, when solid crusts formed on top of the foaming and streaming slag, the shells, when they got thick enough, cracked up, tilted up, and slid down and foundered in the melt beneath. It was obvious that lava rock is heavier than lava foam. Hence as an island is a rock, it would not float. This raised several questions. Where was the bottom of the lava lake on which it rested? Did the lava lake have a bottom, and if so how far down was the bottom when the same lake rose 600 feet in Halemaumau pit between June and December of 1916? In other words, was the lake 600 feet deep in December?

What would be the answer at any time if a stiff iron pipe were thrust down vertically into the liquid lake as a sounding rod? No one had ever raised the question. Cross-section drawings had always depicted the liquid as extending downward indefinitely within a vertical tube. When the lake became accessible in 1917, it seemed to me that a long steel pipe might be shoved over the border rampart, end on, and allowed to bend and sink, or to strike bottom. If the pipe could be recovered by dragging it back, fusible samples of known melting point might show the temperature of the depths.

For the experiment, 200 feet of one-inch iron pipe, which was screwed together in a single long piece, was laid across the north floor of Halemaumau. Ten assistants were distributed along the pipe twenty feet apart, and I stood on the rampart with Alec at the edge of the central portion of the lava lake. This was a high bank ten feet or more above the streaming liquid lava. The men were instructed to lift the entire long tube and walk forward with it, so that it would plunge into the liquid lengthwise, arching down toward the center of the lake as it came past me. Alec helped guide the pipe over the bank, and the men came forward with it at a steady walk. The end of the pipe, covered with a screw cap, was plunged into the liquid lava, traveling toward the bottom at a good speed. The strong current toward the left dragged it somewhat, but not enough to prevent its sinking. After two and a half 20-foot joints of the pipe had plunged into the liquid at a slope of about fifty degrees, I could feel the pipe encountering the increasing resistance of a pasty bottom. Continued forward progress of the pipe caused it to stop and arch up, while the surface lava streamed past it, and its lower end was definitely stuck in the bottom substance of the lake.

I then gave the signal to the carriers to try to walk back to the place where they had started, with a view to pulling the pipe up and recovering the terminal length. The pipe trailed upward out of the lava lake like a red hot rope, then stuck and refused to come out. It came close against the bank where it was frozen solid in the stiff blankets of pahoehoe crust, which gripped it like hot iron.

The terminal length had been equipped internally with a spiral of spring steel, containing Seger cones which are used in the porcelain industry and which bear numbers indicating they melt at graded temperatures. This first thermometer by meltability was never recovered. The free lengths of pipe had to be unscrewed close to the bank, and four twenty-foot lengths were lost. In later tests we learned to keep the pipe oscillating back and forth so it would not freeze.