Third special report of the Hawaiian Volcano Observatory of Hawaii National Park and the Hawaiian Volcano Research Association: Ash formations of the island Hawaii

The purpose of the study was to determine the areal extent of the various volcanic ash formations, to describe them petrographically and to develop means of discriminating them. The ash formations, long known in a general way, had been only casually observed by geologists. Their interpretation and separation from other surficial materials has been much retarded by great differences in the degree of weathering and appearance of the same material in arid and in humid parts of the island. The wide distribution of ash formations in contrast to lava flows led to the hope that they could be discriminated and correlated and used as key horizons to work out the major events in the geologic history. It was believed that critical study of the effects of weathering on the ash formations, together with systematic tracing from regions of typical expression to others where the features were less typical and more obscure, would throw light on the stratigraphic relations and historical significance of the various units.