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首页> 外文期刊>地質調查所月報 >Essential material of the March 31, 2000 eruption of Usu Volcano: Implication for the mechanism of the phreatomagmatic eruption.
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Essential material of the March 31, 2000 eruption of Usu Volcano: Implication for the mechanism of the phreatomagmatic eruption.

机译：2000年3月31日的基本要素爆发USU火山：对Phreatomagmatic Buluption的机制的影响。

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The 2000 eruption of Usu Volcano, Japan, started with a phreatomagmatic explosion at the northwest foot of the volcano on March 31. This first explosion was the largest and the most important one. After a course of petrographical and geochemical analyses, we identified essential materials in the eruptive products that consist of various types (essential, accessory, accidental) of rock fragments. In the March 31st eruptive products, there is a pumice fall (Us-2000pm) with maximum grain size of 2 cm. It is considerably fresh in appearance and its magnetite composition is not similar to those of all pumices from Usu Volcano. Therefore, we conclude that the pumice is not accidental (e.g., resedimented deposits of the 1977 product) but essential. In the ash fall, we found fresh volcanic glass (Us-2000g) with many needle microlites and spherical microbubbles. This type of glass composed of about a half of the March 31st ash. Because the Us-2000g glass is similar to the Us-2000pm pumice in petrological characters, this glass is also essential material. The March 31st phreatomagmatic eruption is characterized by the following special features; (1) a large amount of essential material is in the products; (2) black (ash-rich) and high eruption cloud was maintained for hours; (3) spontaneous fragmentation is inferred at deeper level than the aquifer. Thus, we propose that this eruption is a kind of phreatoplinian eruption. We also discuss the relationship between the magma of the 2000 eruption and those of the pre-2000 eruptions. Deduced from similarity of zoning profiles of plagioclase phenocrysts and of oxygen isotopic compositions, we conclude that the Us-2000 magma is also a member of the series of magmas since the 1663 eruption.
机译：2000年爆发珠山火山，日本，开始了射气岩浆爆炸在火山脚下西北3月31日的这第一次爆炸是最大和最重要的一个。岩相学和地球化学分析的课程后，我们发现在由岩石碎片的不同类型（必需，附件，意外）的喷发产品的基本材料。在3月31日发疹产品，有一个浮石下降（US-2000pm）具有2cm最大粒径。它在外观上相当新鲜和磁铁矿成分不是类似于从珠山火山所有浮石的。因此，我们得出结论，浮石并非偶然（1977年产品例如，resedimented存款），而且是必要的。在落地灰，我们找到了新的火山玻璃（US-2000克）与许多针microlites和球泡。这种类型的玻璃约在3月31日的火山灰构成的一半。由于美国-2000克玻璃类似于岩石字符美2000pm浮石，这种玻璃也是必不可少的材料。 3月31日爆发射气的特点是由以下特殊功能; （1）大量的基本材料的是在产品; （2）黑色（灰丰富）和高喷发云保持为小时; （3）自发碎片在比含水层更深的层次推断。因此，我们建议，这种爆发是一种phreatoplinian喷发。我们还讨论了2000年喷发的岩浆和那些2000年以前爆发之间的关系。从分区斜长斑晶，氧同位素组成的简档的相似性推断，我们得出结论，我们-2000岩浆也是由于1663喷发串联岩浆中的一员。

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