STRATIGRAPHIC, TEXTURAL, AND GEOCHEMICAL ANALYSIS OF A PYROCLASTIC DENSITY CURRENT DEPOSIT IN THE AKAROA VOLCANIC COMPLEX, NEW ZEALAND

The recorded 1199~1200 A.D.eruption is the largest among all the Changbaishan volcano eruptions in history.It can be subdivided into two phases of Plinian eruption,the first is named the Chifeng phase and the second the Yuanchi phase.The eruptive pattern of the Chifeng phase is: Plinian column(the Chifeng pumice fall deposits) → pyroclastic flow(the Changbai pyroclastic flow deposits) → lahar(the Erdaobaihe lahar deposits) mainly triggerd by pyroclastic flow.The eruptive pattern of the Yuanchi phase is from Plinian column(the Yuanchi pumice and ash fall deposits) → pyroclastic flow(the Bingchang pyroclastic flow deposits).The total volume of both the first and the second Plinian falls has been estimated at about 120 km~3.The bulk volume of the Changbai pyroclastic flow deposits was(estimated) about 8 km~3;that of the Bingchang pyroclastic flow deposits about 0.5 km~3 and of the(Erdaobaihe) lahar deposit about 2 km~3.The author deals with mainly the sequence and distribution of the pyroclastic deposits of the 800 a.B.P.eruptions.

Pyroclastic fall

Peléan eruption

Pumice

Lahar

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Citations (7)

Study of Distal Pyroclastic-flow Stratum from Tianchi Volcano in 1215 (±15) Eruption: Pyroclastic-flow Over Water

Acta Geologica Sinica - English Edition (2013)

Bo Zhao Jiandong Xu Chuanyong Lin

Abstract In this paper, we describe three strata at the distal part of the pyroclastic‐flow from the Tianchi volcano in 1215 (±15) eruption. One of the strata with crosslayers that are different from typical pyroclastic‐flow strata may come from a ground‐surge. The grain‐size and scanning electron microscopy (SEM) analysis was performed to study the origin of the pyroclastic‐flow. Characteristics of grain‐size distribution show that it is similar with the ash cloud. Through the SEM analyses, we found some quench structures with less damage on the surfaces of the vitric pumices. These phenomena indicate that there has been hydration in the transportation processes at the distal of pyroclastic‐flow. It has partly changed the transportation mechanism of pyroclastic‐flow, which transitions form dense flow to diluted flow. This paper develops a new distal pyroclastic‐flow model in the Tianchi volcano that can be divided into three stages, i.e. the quench stage, expanding stage and depositing stage.

Pyroclastic fall

Peléan eruption

10.1111/1755-6724.12031

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The evolutional history of the eastern and the central area of Kuju volcano group.

JOURNAL OF MINERALOGY PETROLOGY AND ECONOMIC GEOLOGY (1991)

Takehiro Ohta

Geological field work of Kuju volcano group in central Kyushu has been carried out to construct the evolutional history of the volcano group. Especially, at the eastern and the central area, the evolutional history after a large pyroclastic eruption, which occurred 30, 000-35, 000 y. B. P. to generate pyroclastic flows, has been clarified using a tephrochronological method. Eleven tephra layers are recognized around Kuju volcano group. These layers are in descend-ing order ; Komekubo crater scoria-fall, Kuju-1 ash-fall, Danbaru scoria-fall, Kuju-1 weathered ash, Kuju-2 ash-fall, Kikai-Akahoya ash-fall, Kuju-2 weathered ash, Kuju-3 weathered ash, Kuju-1 pumica-fall, Kuju-4 weathered ash, Miyakono scoria-fall. Kikai-Akahoya ash-fall were erupted from Kikai caldera, which is situated at the southern Kyushu, about 6, 000-6, 500 y. B. P. The other tephras may have originated from Kuju volcano group. Kuju-1 pumice-fall was accompanied with the 30, 000-35, 000 y. B. P. pyroclastic eruption. Danbaru scoria-fall was erupted 3, 000-5, 000 y. B. P. The evolutional history of the central area is as follows: At 30, 000-35, 000 y. B. P., a large quantity of pyroclastic materials erupted from a presumed eruption center, which situated between the Kutsukakeyama dacitic mountain and Yuzawa andesitic tablelands. After this eruption, the greater part of the central area had been formed by extrusions of lavas and pyroclastic rocks before Kikai-Akahoya ash-fall deposition (6, 000-6, 500 y. B. P.). From 6, 000-6, 500 y. B. P. to 3, 000-5, 000 y. B. P., Mimatayama dome lava erupted. The activity of the central lava domes (e. g. Kujusan lava dome) occurred after 3, 000-5, 000 y. B. P. This activity was accompanied by Kuju-1 ash-fall. After this activity, phreatic explosion and fumarolic activity occurred, and fumarolic activity continued until now. The evolutional history of the eastern area is as follows: The activity of eastern area began after 30, 000-35, 000 y. B. P. Before Kikai-Akahoya ash-fall deposition, andesitic lavas effused north of Hiijidake. After this period, all of Hiijidake mountain and the lower part of Taisensan mountain were formed by a large quantity of lavas and a small amount of pyroclastic falls. Kuju-2 ash-fall was deposited simultaneously. About 3, 000-5, 000 y. B. P., Strombolian eruption occurred at Taisen-san, forming Danbaru and Komekubo scoria cones accompanied by the deposition of Danbaru scoria-fall. After this activity, dacitic lava erupted at the southern edge of Komekubo crater, then Komekubo crater scoria-fall erupted from the crater. Finally, Kuroda-ke dome lave erupted at the eastern end of Kuju volcano group. The volcanic output rates are calculated for three periods; 32, 000-6.300 y. B. P., 6, 300-4, 000 y. B. P. and after 4, 000 y. B. P. At the central area, the rate for 6, 300-4, 000 y. B. P. is the largest (0.256km3/k. y.). At the eastern area, the rate became greater from 0.017km3/k. y. through 0.452km3/k. y. to 0.635 km3/k. y.

Pyroclastic fall

Scoria

Volcanic ash

Peléan eruption

Caldera

Pumice

10.2465/ganko.86.243

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Citations (4)