THE HISTORY OF THE EXPLORATION OFMAUNA LOA.
This term is applied to an immense dome seventy-four by fifty three miles in its two diameters as measured at the sea level, and 13,65o feet in altitude. Its mass extends downwards more than 16,000 feet farther to the level of the submarine plain at the bottom of the sea upon which the whole Hawaiian Archipelago is situated. That would be a cone 30,000 feet in height and as much as a hundred miles wide within which are one or more conduits leading to the reservoir of lava which supplied the ma terial for the various eruptions. It is probable that the cone may rest upon sediments of Tertiary age, like the sister island of Oahu.
The first word is equivalent to Mount, and the second signifies great or long. Some authors prefer to say Mount Loa rather than Mauna Loa. The natives call the caldera at the summit Mokuaweoweo. The great dome, so far as can be judged, is composed of overlapping sheets of basalt, both as and pahoehoe. Those at the surface are of known age, or certainly younger than those that are deep seated. There are no large canyons upon its surface produced by the erosion of streams, because the deposi tion of the sheets is so recent. Above io,000 feet there is scarcely any vegetation. The expanse is entirely composed of basalt showing evidences of many interlacing streams of lava. The surface is nearly level for the extent of four or five square miles.
Mr. Ellis who explored Hawaii in 1823 has nothing to say of Mokuaweoweo, while he writes fully of Kilauea. Pele is located definitely at Kilauea. I have not yet discovered any native tra ditions respecting eruptions from the larger volcano. It may be that the earlier explorers were not aware of the character of Mauna Loa. Ellis represents it as covered by snow throughout the year. It is uninhabitable, and therefore its eruptions would not usually be fraught with disaster to the inhabitants, and thus would be scarcely mentioned in the traditions. When Hawaii
shall have been studied carefully it will be possible to give the sequence of several pre-historic eruptions. One of these is Kea moku, an expanse on the north side of the mountain adjacent to and underlying the flow of 1843. The fact that it is distinguished upon the Government map indicates that the surveyors were im pressed by its recency. It starts from the cone of Kokoolau 8,000 feet high, and terminates at the altitude of 3,00o feet at the hill whose name is now applied distinctively to the flow itself. Its area is very much the same with that of the well known eruption of 1843, extending down hill for twenty-one miles, the first third of the way proceeding due north, and then to the northwest. The area of 1843 laps over the edge of Keamoku.
I find very nearly the same name applied to an aa flow on the opposite side of the mountain, along which the new Kau Volcano road runs for several miles. This is supposed to be connected with a broad stream starting just below Pun Ulaula seven miles east of Mokuaweoweo. Upon most of the maps this stream is represented to have the date of 1823, and to have been connected with the discharge from Kilauea of that date, described by Mr. Ellis. This gentleman, however, makes no allusion to the ex istence of any recent stream descending from Puu Ulaula in that year, nor does he have anything to say about eruptions from Mauna Loa. Our illustrations, Plates 14 and 26, will show the lack of connection between this early flow of aa and the eruption in Ponahohoa; and anyone who will take the pains to scrutinize this aa along the Kau Volcano road will be satisfied that it is much older than 1823. I have questioned Professor W. D. Alexander and Mr. W. E. Wall, the Government surveyors, upon whose maps this late date is given, and they do not recall their authority for this label. Hence I regard this flow as belonging to an unknown prehistoric date—but one of great importance.