ORDER OF EVENTS IN THE HISTORY OF MOHOKEA.
Several events can be clearly discriminated in the history of the Mohokea caldera.
T. The formation of the cone of Mauna Loa. This is really composite, but may be treated as a unity for convenience. Basalt came from below and flowed over the edge of the primeval crater till the whole dome, seventy-five by fifty-three miles in two dia meters and 13,65o feet altitude, had been formed, composed of millions of layers gradually superimposed upon one another. The altitude must have been even greater, so as to allow for the falling in of the surface to develop the caldera of Mokuaweoweo.
2. After the material ceased to flow over the surface, two styles of eruption commenced or continued to be manifested ; those high up, allowing streams of molten lava to flow away quietly, and those starting from comparatively low levels, dis charging with violence. The base of the cone was filled by these ruptures of the basaltic sheets and the discharge of streams of melted lava. The irregularities of the southern edge of the cone between Kilauea and Punaluu were produced at this time. Mo hokea was the most important of these displays. The three inter montane valleys sank down in the usual style of the breaking of the superior crust from a caldera. Perhaps, because of the great size of the pit, all the fragments could not be absorbed by the inner fiery fluid ; two rows of blocks were crowded up, and the work of fracture ceasing, the great masses of rock were elevated and held in position. It is to be noted that the faults are at right angles to those running seaward from, the apex of Mauna Loa. This agrees with the theory of W. L. Green, that the discharges of the lava from the interior of the cone always take place at the intersection of the cross-fissures. Very much lava flowed away at this time, including the three valleys mentioned and the crust adjacent as far as to Kapuna.
3. Two great eruptions, separated by a long interval of time, threw out into the atmosphere enormous clouds of ashes. The
intermediate period was long enough to allow of the invasion of plants over the sterile area of silt. Because of the occurrence of this ash entirely around the circumference of Mauna Loa, it seems most likely that the vent was at Mokuaweoweo. A gi gantic cloud rose above the trade winds and spread out on all sides, while the particles too heavy to be carried great distances fell to the ground. Three recent eruptions of a similar nature are on record—from Krakatoa in 1883, from Tarawera in i886, and in 1907 at Vesuvius. I have estimated that 2,00o square miles of the island of Hawaii were covered by these ashes. These are preserved, but they must have been strewn much beyond these limits and lost in the sea. Could any one have observed the skies at this time he would have seen repeated the sky glows, the Bis hop's rings, and the green sun. This must have been an ex plosive eruption—a style of discharge denied to Hawaiian vol canoes by the early writers.
4. Several flows of pahoehoe will be described presently over lying the ash, some of them from the Mohokea depression itself.
5. More or less connected with them are several discharges of aa.
6. Last of all, I should not fail to recall the disastrous earth quakes of 1868, whose epicentrum lay in the vicinity of this cal dera. No more severe shocks have ever been experienced since the country has been settled by people of European descent. The quakes were observed at Kona, Kahuku, Waiohinu, Kilauea, and Hilo. All were severe, but the greatest devastation was wrought in the vicinity of Mohokea. Can it be that the seat of the seismic disturbances lay beneath Mohokea ? The chief discharge of lava was on the flank of Mauna Loa several miles west of Mohokea, and there was another from Kilauea in the opposite direction.