The sea bottom topography and the geological structure around the Kazan Retto in Sitito・Iozima ridge.
The detailed topographic and geological surveys have been carried out with Survey Vessel ’Takuyo’ and a unmanned automated survey craft ’Manbou' around the Kazan Retto in 1991～ 92. About the geological structure and the history of the volcanic activity at the Kazan Retto, the survey results are summarized as follows. (1) Because of the extent of the submarine erosion, the order of the volcanic eruptions around the Kita-Io Sima is①’the western longrise’，② Kita-Io Sima，③ Funka-Asane. Because of the records of the volcanic eruptions and the diastrophism, the growth of the coral reef around the volcanic islands, the recent activity level about the eruption of the volcanos in the Kazan Retto is high in order of① Fukutokuoka-no”ba，② Io Sima，③ Funka-Asane. (2) After forming the submarine staratovolcano, Io Sima has experienced the large collapse at the south part of the volcano, the forming a caldera on its top and the aggradation of them. The blank of the volcanism turned out at 500～ 800 year B.P. around Io Sima. Recently the western and northwestern part of the coast is upheaving lively, the sandy beach at’Ido-ga Rama' is expanding rapidly. The average upheaving velocities of cays are 12 cm/year at Kangoku Iwa, 16 cm/year at Kama Iwa, lOcm/year at Hanare Iwa and 0.5 cm/year at Higasi Iwa. (3) The volcanic activity of Minami-Io Sima has closed, Fukutokuoka-no・bavolcano is active now. For the short period the magma type has been changed into the alkalic magma type. Volcanic rocks released from Fukutokuoka-no-ba in 1992 belong in the alkaline rock series. The blank of the volcanism turned out at 200～ 450 year B.P. around Minami-Io Sima, then the coral reef grew around its coast.
| Main Author: | |
|---|---|
| Format: | Journal Contribution biblioteca |
| Language: | Japanese |
| Published: |
1994-03-24
|
| Online Access: | http://hdl.handle.net/1834/16078 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|