MONDACA VOLCANO LAHAR OF DECEMBER 3, 1762, MAULE REGION (35°28’S): ONE OF THE LARGEST VOLCANIC DISASTERS IN CHILEAN HISTORY

IF 0.9 4区 地球科学 Q3 GEOLOGY Andean Geology Pub Date : 2021-06-15 DOI:10.5027/ANDGEOV48N3-3361
J. A. Naranjo, F. Hevia, E. Polanco
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Abstract

The Mondaca volcano comprises a thick rhyolitic lava-field and a dome of similar composition, located near the Lontué River Valley headwaters in the northern part of the Southern Andes Volcanic Zone. It reaches a total volume of ~ 0.85 km, and it is formed by 4 subunits, named Mondaca 1, 2, 3 and 4, which correspond to successive rhyolitic blocky lava flows, emitted from a rounded dome structure. They present well-preserved flow structures and, in the surroundings, restricted to the south and east of the dome, pyroclastic fall, as well as block and ash deposits are also exhibited. Downstream, along the Lontué River, a laharic deposit is recognized. The lahar was produced after the collapse of an ephemeral ~0.44 km3 lake generated after the river obstruction by viscous lavas, during the 1762 first eruptive phase. Proximal lahar facies are well exposed between 5 and 30 km from their source. The profuse agricultural activity has completely obliterated the lahar's medium facies deposits along the Central Depression, but are well identified at the mouth of the Mataquito River, 180 km downstream, as a beige-coloured layer, interbedded within dark coastal beach-sands. The identification of overflows and super-elevation deposits formed during the debris flow emplacement along the Lontué River valley, allows to determine a high flow mobility, with estimated velocities that locally reached up to 114 km/h. Petrographic characteristics in addition to chemical composition of lavas from the volcano, pyroclasts and juvenile blocks of the laharic deposit, indicate that all they correspond to high K calcoalkaline rhyolites with subalkaline affinity. These backgrounds, together with the geographical continuity between the lavas and debris deposits along the Lontué and Mataquito rivers, verify facies correlation and common origin as the result of the 1762 Mondaca volcano eruption complex evolution. IN PR ES S Andean Geology 48 (3): xxx-xxx. September, 2021 doi: 10.5027/andgeoV48n3-3361 2 Although it was a mainly effusive eruption that could not be observed from Curicó, the collateral consequences would have been catastrophic over a vast area to the south of that city, and evidences one of the largest volcanic disasters in Chilean history. Probably because of the low density polulation at that time, the consequences could have been minor.
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1762年12月3日Mondaca火山泥流,maule地区(35°28′s):智利历史上最大的火山灾难之一
蒙达卡火山由一个厚的流纹岩熔岩场和一个类似成分的圆顶组成,位于南安第斯火山带北部的朗图瓦勒河谷源头附近。总体积约0.85 km,由蒙达卡1、2、3、4 4个亚单元组成,对应于连续流纹岩块状熔岩流,由圆形穹窿结构喷出。它们呈现出保存完好的流动结构,在周围,仅限于圆顶的南部和东部,火山碎屑坠落,以及块状和灰烬沉积也被展示出来。顺流而下,沿着朗图瓦勒河,可以辨认出一个熔岩沉积物。1762年第一次喷发期,黏性熔岩阻塞河流,形成了一个约0.44 km3的短暂湖泊。近端泥泥岩相在离源5 ~ 30 km处暴露良好。大量的农业活动已经完全抹去了沿中央凹陷的泥泥岩的中相沉积,但在下游180公里处的马塔基托河河口,可以很好地识别出一个米色层,与深色海岸沙滩砂互层。在lontu河谷的泥石流侵位过程中,溢流和超高程沉积物的识别可以确定高流动度,估计当地速度可达114公里/小时。岩石学特征及火山熔岩、火山碎屑和火山岩幼块的化学成分表明,它们均为高钾钙碱性流纹岩,具有亚碱性亲和力。这些背景,连同lontu河和Mataquito河沿岸熔岩和碎屑沉积物之间的地理连续性,验证了1762年Mondaca火山喷发复杂演化的相对比和共同起源。[j] .中国地质大学学报(自然科学版)。虽然这是一次主要的喷发,无法从Curicó上观测到,但附带的后果将对该城市南部的广大地区造成灾难性的影响,并证明了智利历史上最大的火山灾害之一。可能是因为当时人口密度低,后果可能很小。
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来源期刊
Andean Geology
Andean Geology 地学-地质学
CiteScore
3.90
自引率
0.00%
发文量
17
审稿时长
>12 weeks
期刊介绍: This journal publishes original and review articles on geology and related sciences, in Spanish or English, in three issues a year (January, May and September). Articles or notes on major topics of broad interest in Earth Sciences dealing with the geology of South and Central America and Antarctica, and particularly of the Andes, are welcomed. The journal is interested in publishing thematic sets of papers and accepts articles dealing with systematic Paleontology only if their main focus is the chronostratigraphical, paleoecological and/or paleogeographical importance of the taxa described therein.
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