Quaternary Volcanic Ashes in the Narugo and Onikobe Volcanic Areas

Abstract

A. The Narugo volcanic areaThe original form of Kata-numa which seems as explosion crater is supposed to be a paleo-lake formed by the crustal deformation. The mudflow materials and volcanic ashes erupted out under the fluviatile-lake environments.The volcanic ashes from the Narugo volcanoes covered the mudflow materials and terrace plains except the present river bed. These ashes are classified into two main volcanic ashes depending upon the soil colors. One of them is the black volcanic ash, and the other is the brown volcanic ash. The soil color of the black volcanic ash is presumed to have been derived from the colored minerals and humus.B. The Onikobe volcanic areaThe original form of the Onikobe basin was formed by the crustal deformation, and deposited the lacustrine sediments in the paleo-lake. The first eruption of the volcanic ejecta occurred under the fluviatile-lake environments. The volcanic ashes from the Onikobe volcanoes accumulated on the outer mountains, inner volcanic bodies and terrace surfaces except the present river bed.However, the volcanic ashes in the Katayamajigoku and Arayu areas include the plant leaves. These ashes are supposed to have been deposited on the bottom of the paleo-lake in early Quaternary age. Under the polarized microscope, no mineral fragments are recognized in these ashes. This is a remarkable point of the characteristics compared with the volcanic ashes of the other areas investigated. This reason is supposed that the alteration of the volcanic ashes has been accelerated by the solfataric action and subterranean heat etc.