十和田火山発達史概要

概要

論文の詳細を見る
Critically reviewing the results of the geological investigations including those by the present authors, the historical development of the Towada Volcano, Northeastern Honshu, Japan is outlined. The stratigraphy of the volcano is summarized in Fig. 1 and the distribution of the selected pyroclastic layers of ash-fall and ash-flow types ejected from the Towada are shown in Fig. 2. Absolute ages measured of the younger pyroclastics are listed in Table 1. The characteristics in the distribution, deposition, and preservation of the pyroclastics of the Towada throughout its history are also disscussed briefly. Preceding the activity of the Towada Volcano, a welded tuff effused in close relation with the formation of the Tashirotai Caldea, which was the oldest event of the Hakkoda Volcanoes situated about 25 km north of the Towada. The welded tyff filled the surrounding lower areas of the muturely dissected topography developed on the Miocene terrrain in the northern part of the Backbone Ranges of Northeastern Honshu. Five stages of activity are recognized in the development of the Towada Volcano. The first stage is represented mainly by the andesitic volcanic breccia accompanied with lava flows, suggesting the growth of the strato-volcano which was destroyed in the next stage. In the second stage, intensive eruptions occurred repeatedly. Most of the pyroclastic layers distributed in the south central and southeastern parts of Aomori Prefecture, the northern part of Iwate Prefecture, and the northwestern part of Akita Prefecture are products of the second stage of the Towada Volcano. Four layers of ash-flow tuff are distributed in all directions in the area within 50 km from the volcano, in contrast to the extensive spread of volcanic ash-falls restricted to the eastern region. The volume of each ash-flow tuff is estimated to 30-50 kms. The Towada Caldera was formed during the second stage. The third stage is characterized by the basaltic andesite lava that extruded and built a volcanic cone in the southern part of the caldera. The cone was destroyed by the succeeding eruptions, and pumiceous ash layers spread in the eastern areas. A part of the ash layers accumulated thickly on the flank of cone was welded. The fourth stage is represented by the youngest volcanic cone built on the northeastern rim of the minor caldera developed in the later phase of the third stage. The andesite in the northeastern part of the caldera lake is thought to be an extension of the youngest andesite lava from its lithological character. The absolute age of the end of second stage is about 13, 000 yr. B.P., the third stage ended at about 4, 000 yr. BP., and the fourth stage at about 1, 500 yr. B.P. An ash-flow of the fifth stage effused abruptly at about 1, 200 years ago. It flowed down along the Yoneshiro River valley southwest of the Towada. The ash-flow tuff occupied the fluvial plains in the basins along the Yoneshiro River, and many human remains including large wooden buildings were found beneath it.
東北大学の論文
1972-03-10

十和田火山発達史概要

スポンサーリンク

概要

著者

関連論文

スポンサーリンク