Origin, characteristics, and behaviour of lahars following the 1990 eruption of Kelud volcano, eastern Java (Indonesia)
Origin, characteristics, and behaviour of lahars following the 1990 eruption of Kelud volcano, eastern Java (Indonesia)
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1990 年爪哇东部克卢德火山喷发后火山泥浆的起源、特征和行为（印度尼西亚）
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
S. Bronto
中科院分区：
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作者：
J. Thouret;K. Abdurachman;J. Bourdier;S. Bronto
与20世纪大部分的克卢德火山（东爪哇）喷发相反，1990年2月10日的普利尼亚火山喷发并没有伴随着湖爆发火山泥流。 然而，在1990年2月15日至3月28日期间，至少发生了33次喷发后火山泥流。它们横扫了11个排水系统，并以4-11 m s-1的估计平均峰值速度行进了24公里。矿床（体积≥30 000 000 m3）位于火山周围的火山岩裙上，距喷口2 km约7 m厚，距喷口10 km约3 m厚。 沉积物中细微但显著的沉积学差异与四种流动类型有关：（a）早期块状沉积物粗糙，分选不良，轻微粘结，通常为反级配。据推测，他们记录热火山泥流，包括火山碎屑流沉积物的浮石和火山渣，可能是由降雨径流的热近端火山碎屑流沉积物的快速再活化。沉积特征，如碎屑近平行于层理和厚的，不均匀的床，表明这些流动是层流。(b)丰富的、分选很差的矿床包括非粘性的、碎屑支撑的、反级配的矿床和未级配的、细粒的和粘性基质支撑的矿床。这些床显示分层和垂直分离/密度分层，表明脉冲泥石流的不稳定特性。它们被解释为沉积从流波段在下游的中间距离，包括喷发前沉积物。沉积学证据表明，在渐进加积过程中的不稳定流动特性。(c)细粒，分选不良和未分级的存款被解释为记录后期超浓缩的溪流，形成在溢流的减弱阶段，并转化为下游的溪流。(d)未分级的，粗糙分层的存款是由流动之间的过渡流高浓缩流和溪流，更远的下游（远至27公里，从通风口）。在Kelud，流动和行为的转变发生在距离源仅10公里的范围内，在冲积扇的顶点。水流特性的快速变化归因于低细颗粒含量和不稳定流态，这可能是由于：（a）由于靠近喷口的河道坡度突变以及河道横截面和粗糙度的变化，推移质快速沉积;（B）非粘性沉积物中的粉砂+粘土含量非常低。这些沉积物与水混合产生了溪流。
Abstract In contrast to most twentieth-century eruptions of Kelud volcano (eastern Java), the 10 February 1990 plinian eruption was not accompanied by lake-outburst lahars. However, at least 33 post-eruption lahars occurred between 15 February and 28 March 1990. They swept down 11 drainage systems and travelled as far as 24 km at an estimated mean peak velocity in the range of 4–11 m s–1. The deposits (volume ≥30 000 000 m3) were approximately 7 m thick 2 km from vent, and 3 m thick 10 km from vent, on the volcaniclastic apron surrounding the volcano. Subtle but significant sedimentological differences in the deposits relate to four flow types: (a) Early, massive deposits are coarse, poorly sorted, slightly cohesive, and commonly inversely graded. They are inferred to record hot lahars that incorporated pumice and scoria from pyroclastic-flow deposits, probably by rapid remobilization of hot proximal pyroclastic flow deposits by rainfall runoff. Sedimentary features, such as clasts subparallel to bedding and thick, reversely to ungraded beds, suggest that these flows were laminar. (b) Abundant, very poorly sorted deposits include non-cohesive, clast-supported, inversely graded beds and ungraded, finer-grained, and cohesive matrix-supported beds. These beds display layering and vertical segregation/density stratification, suggesting unsteady properties of pulsing debris flows. They are interpreted as deposited from segments of flow waves at a middle distance downstream that incorporated pre-eruption sediments. Sedimentological evidence suggests unsteady flow properties during progressive aggradation. (c) Fine-grained, poorly sorted and ungraded deposits are interpreted as recording late hyperconcentrated streamflows that formed in the waning stage of an overflow and transformed downcurrent into streamflows. (d) Ungraded, crudely stratified deposits were emplaced by flows transitional between hyperconcentrated flows and streamflows that traveled farther downvalley (as far as 27 km from the vent). At Kelud, the transformation of flow and behavior occurs within only 10 km of the source, at the apex of the alluvial fans. The rapid change of flow behavior is attributed to the low fines content and to the unsteady flow regime, which may be due to: (a) the rapid deposition of bedload, owing to the break in channel gradient close to the vent and to changes in channel cross-section and roughness; and (b) the very low silt+clay content in the non-cohesive deposits. These deposits mix with water to produce streamflows.