DEPOSITIONAL MECHANICS OF TURBULENT NUEES ARDENTES (SURGES) FROM THEIR GRAIN SIZES

被引：14

作者：

BRISSETTE, FP ^{[1
]}

LAJOIE, J ^{[1
]}

机构：

[1] UNIV MONTREAL,DEPT GEOL,MONTREAL H3C 3J7,QUEBEC,CANADA

来源：

BULLETIN OF VOLCANOLOGY | 1990年 / 53卷 / 01期

关键词：

D O I：

10.1007/BF00680320

中图分类号：

P [天文学、地球科学];

学科分类号：

07 ;

摘要：

The ability of turbulent nuees ardents (surges) to transport coarse pyroclasts has been questioned on the basis that settling velocities of coarse fragments in the deposits are much too high for them to have been supported by turbulence in a dilute gas suspension. A computer model is used to evaluate the settling velocity of pyroclasts in suspensions of varying concentration and temperature. Since suspension of grains in low-concentration surges occurs if the shear velocity exceeds the settling velocity, the shear velocities related to the 16th and 84th percentiles, and the mean of the grain-size distribution are compared in surge deposits of the Vulsini, with the shear velocity necessary to move the coarsest grain on the bed surface (the Shields criterion). The results show that the settling velocities do not vary significantly in gaseous suspensions having volume concentrations lower than 15%, and that an increase in concentration to 25% is not sufficient to decrease the settling velocity of the coarser fraction, if it represents flow shear velocity. It is shown that the settling velocity of the mean grain size (M(z)) best depicts the shear velocity of a dilute turbulent suspension. Applying the results to the May 1902 paroxysmal nuees ardentes of Mount Pelee shows that the estimated mean velocities are well within the observed velocities, and sufficient to support all the clasts in dilute, turbulent suspensions.

引用

页码：60 / 66

页数：7

共 29 条

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