KILAUEA BETWEEN 1841 AND 1849.
In the interval between the discharges of 1840 and 1849 two novel features are developed. The first relates to the production of a central lava lake resting in a basin of its own cooled material. The second is concerned with the encirclement of Halemaumau by an igneous canal, coinciding nearly with the edge of the next black ledge to be formed.
In February, 1842, Mr. Coan writes: "When within four or five rods of the great lake, unaware of our near proximity to it, we saw directly before us A vast area of what we had supposed to be solid lava moving off to the right and left. We were at first a little startled, not knowing but all was about to float away beneath us, especially as the lavas for a mile back were almost insupportably hot, and gases and steam were escaping from nu merous openings. On looking again, we perceived that the whole surface of the lake was from six to fifteen feet above the level of the surrounding lava, although at my last visit it was from sixty to seventy feet below. Within six feet of this embankment we could see nothing of the lake, and in order to examine it we climbed the precipice some fifty feet. The explanation of this strange condition of things is this : when the liquid contents of the lake had risen to a level with the brim there was a constant and gradual boiling over of the viscid mass, but in quantities too small to run off far. Consequently it solidified on the margin, and thus formed the high rim which confined the lavas. Twice, or at two points while we were there, the liquid flood broke through the rim and flowed off in a broad, deep channel which continued its flow until we left the volcano. The view was a new one, and thrilling beyond description." In July, 1844, Mr. Coan describes a vast overflow at Halemau mau, from which rivers of lava proceeded adjacent to the black ledge on either side. The beginning of the process consisted in the welling from below of so much liquid that the outlines of Halemaumau were obliterated. The streams were described as two deep canals five to fifteen rods wide, one hundred feet deep and two miles long; it was a lake having two outlets at its opposite points, each one following the margin of the black ledge and com ing within half a mile of each other under the northern wall of the caldera.
Mr. Coan had the company of his son, Titus Munson Coan, who noted the conditions already mentioned, and spoke also of a small lake upon the floor of the pit at about the middle of the west side. A diagram accompanied Mr. Coan's letter, a mere out line, but having all the essential features indicated two years later by Mr. Lyman.
There were fissures along the course of the canals, one of them two hundred feet deep, and in one place the lava plunged down a precipice of fifty feet. The character of this display was not explained at the time. In June, 1846, Mr. Coan reported that the central parts of the floor had been elevated four or five hundred feet since 1840, so that some portions of it are higher than the black ledge. Professor Dana thinks from this statement that in 1844 the lower floor was less than one hundred and forty feet deep, except along the wide canals.
The observations of Rev. C. S. Lyman in July, 1846, explain the rapid obliteration of the lower pit. See our Plate 3o re storing the condition of the caldera after the rude sketch of Mr. Lyman. He found the conditions reported by Mr. Coan. By
instrumental measurements he proved that the black ledge still re tained the level of six hundred and fifty feet below Uwekahuna as given by Wilkes. But there was a "canal nearly up to the black ledge, and in some places quite," encircling the pit, though in some parts obliterated. Along the inner margin of a part of the canal was a continuous ridge of angular blocks of compact lava often fifty or one hundred feet high, which Mr. Lyman considered "once constituted a talus, or accumulation of debris" on the slope of the black ledge of 184o; the floor with this margin of blocks had been elevated till this ridge overtopped the edge of the escarpement at whose incline it had been accumulated. He adds : "The pheno menon seems inexplicable on any other hypothesis than that of the bodily upheaving of the inner floor of the crater." "When visited by the Exploring Expedition of 1840, the surface of the Great Lake was between three hundred and four hundred feet below the black ledge, and measured only a thousand by fifteen hundred feet in diameter. Consequently in six years the lake had not only increased in size, but it had actually risen in height as much as it had been previously depressed by the out-draining of lavas in the eruption of 1840. This gradual rising of the solid embank ment of the lake contemporaneously with the lake itself, together with the filling tip of the whole interior of the crater, is doubtless to be attributed to the combined effect of repeated overflowing to gether with the upheaving agency of subterranean forces." The lake at the southern end seems to have been raised upon a rim ten to twenty feet high, with the diameters of 2,000 and 2,400 feet. The lavas were in gentle ebullition, tossing up broken jets five to fifteen feet and, frequently encrusted, and had a general movement southwesterly. Sticks of wood thrown into the liquid immediately disappeared, but were instantly followed by a sudden outburst of flame and smoke.
The "Furnace" marked on the map was the beginning of a dome, ten or twelve feet high with walls a foot thick, compared by a later writer to pie-crust ; inactive in July but "in full blast" six weeks later in August. Brigham compares this to one of the "hornitos" described by Humboldt in the malpays of Mexico.
On December 7th, Mr. Coan found the lake full and active. On July, 1847, the great lake had filled up and overflowed a considerable area around its rim, and it was easy to dip up the viscid matter with sticks and ladles. Early in 1848 a thick crust formed over Halemaumau and was raised into a dome covering the whole lake. This increased in size and by August was almost high enough "to overtop the lower part of the outer wall of Kilauea and look out upon the surrounding country." This meant two hundred or three hundred feet elevation, traversed here and there by fissures through which it was possible to descry the glowing of the subterranean fires. Occasionally lava was pressed sluggishly through these apertures, rolling in heavy and irregu lar streams down the sides, spreading and cooling over the slopes or at the base. Thus this dome has been formed partly by up heaval and partly by igneous accretion. This is the first account of a dome over Halemaumau.
Still later in the autumn of 1848 an extraordinary inactivity pre vailed throughout the crater. No fire was visible, even in the night.