Professor J. D. Dana explored the same region in 1887, and was fully persuaded that the material thrown out was connected with the historic event of 179o. "The distribution of the ejected stones, ashes and scoria all around Kilauea seems to show that the whole bottom of the pit was in action ; yet the southern, as usual, most intensely so." The heavy compact basalts and their large use indicate that the more deep seated rocks along the con duit of the volcano had been torn off by the violent projectile action. "It was an explosive eruption of Kilauea such as has not been known in more recent times." of the neighborhood, usually of a gray color and somewhat vesi cular. Some carry olivine and all appear to belong to early periods of formation. The tuffs and many stones make up the bulk of the cliffs to the south of the caldera.
The recent (19o7) map of Kapapala shows finely the distribution of this eolian deposit to the south and southeast. Not less than twenty square miles have been covered by it; ex tending for five miles southerly and southwesterly, or as far as to the ancient cone of Koae. There are several volcanic cones such as Kearaarea or Kamakaia in the midst of extensive fissures, both old and new. To the south of Koae are many large sand dunes that have been blown from the ash accumulations.
On the other side of the fissures as one follows the regular road to Kau from Kilauea for nearly four miles, there are numer ous patches of fine-grained drab tuff from two or three to six or more inches in extent with scoriaceous pieces and pisolitic spherules which are less conspicuous than the others, but of the same general character and age.
Similar materials may be seen at the saw mill for koa lumber two miles from the Volcano House, and for four or five miles towards Glenwood, so that the entire area covered by the debris of explosive eruptions is estimated at more than sixty square miles. They are six feet thick in the new road around Kilauea iki. The following section has been made out : At the surface, small gravel stones with soil ; Gravel two feet thick ; Sand, becoming black below ; Another foot thickness of sand; Pumice, a few inches thick, sometimes in pockets ; Rubble stones, some as large as cobbles; Underlying rock.
The black seams are suggestive of a vegetable growth, indi cating a lengthy period when plants were able to spread naturally from the surroundings, only to be covered later by the volcanic rain.
fhe enormous area thus covered with explosive material ren ders it probable that the comparatively mild discharge of 1790 was inadequate to account for so extensive an inundation. There must have been several such discharges, perhaps recurring during centuries of time. Only a tithe of the stones spread over the sur face would have been needed to destroy a much larger detach ment than that suffocated in 179o. It would seem more con sonant with the facts to connect the prolific tuffaeous and scoriae ous discharges with the days of Liloa rather than of Keoua; and perhaps Keanakakoi may have been the vent through which the discharge came.
Certain observations made in 19o5 may be significant here : Opposite Keanakakoi in the pit of Kilauea there was formerly exhibited upon the maps a "sulphur bank," now mostly covered by the black ledge. A narrow promontory still extends westerly to the south of Halemaumau, terminating at Kapuai and only slightly elevated, and covered with eolian debris. At the south west end of the wall from Poli o Keawe there is an abrupt change from basalt to scoriae, and as you climb to this rock from the gravel a marked fault appears with a S.W. direction. On look ing backwards there is a noticeable dip of the layers towards the old sulphur bank—perhaps of ten degrees. The fault seems to be the same with that figured by Professor W. H. It seems apparent that the tuffs came from Keanakakoi, unless they represent the inward slope of the material blown out from Kilauea, such as falls toward the vent in tuff cones. Most of the cliff encircling the south curve of Kilauea is composed of similar materials.
Dr. Brigham speaks of several shallow pits in this tuff that were made by the falling down or washing into fissures the finer parts of the sand and gravel. All these facts impress one with the magnitude and unusual character of the materials erupted about Keanakakoi.
While there has been uncertainty about the date and origin of the various Kau accumulations of dust, it is refreshing to be able to present the views of Mr. E. D. Baldwin, obtained recently as the result of his survey for the Kapapala map. He finds that much of the fine volcanic ash has been derived from a Kilauean source ; while there were earlier discharges in lower Kau and at Ka Lae not thus accounted for. These have been mentioned elsewhere in connection with the history of Mauna Loa.