Abstract Landslides are among the most frequent and dangerous mass removal processes around the globe. They can be triggered by different phenomena such as earthquakes, extraordinary rains, glacier outbursts, volcanic activity, among others. In this study, we reconstruct the origin and potential cause of a rock avalanche that occurred in the Cotahuasi canyon in southern Peru. The head-scarp is a cirque carved during the Last Glacial Maximum and is formed by Alpabamba ignimbrites and Upper Barroso Formation volcanics. Slope failure removed a minimum volume of 1.13 km3 generating a dry rock avalanche that was immediately confined into the Cachana valley, where it traveled 11 km downstream before reaching the Cotahuasi river. There, it did run for another 3 km towards the opposite Mungui mountains with minimum speeds of 72 m/s. The transversal Mungui range forced the avalanche to laterally spread upstream and downstream along the Cotahuasi river, as well as upstream the Pampamarca tributary prior to its final stop. The resulting deposit (H/L = 0.16) developed hummocky topography and formed a 10 km long and ≤100 m high dam that impounded two temporary lakes. At their maximum capacity, these lakes could hold ~1.6 × 108 m3 of water prior to overtopping the dam. The dam-breakout generated a catastrophic flood (massive layer forming terraces) that traveled for tens of kilometers and likely as far as the sea. The debris flow deposit could be well-documented up to a distance of 20 km from the breach with the presence of 4 to 50-m-thick terraces with a minimum volume of 0.72 km3. After this distance, the deposit disappears, likely due to post-emplacement erosion by the river itself. Considering the missing volume at the head-scarp cirque (~3.85 km3) and the sum of the minimum volumes of the rock avalanche and debris flow deposits (~1.85 km3), circa forty percent of the material must have been removed by glacial and fluviatile activity since the time of its original emplacement.

中文翻译：

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秘鲁科塔瓦西河沿线的更新世岩崩、筑坝和次生泥石流

摘要 滑坡是全球最频繁和最危险的大规模拆除过程之一。它们可能由不同的现象引发，例如地震、特大降雨、冰川爆发、火山活动等。在这项研究中，我们重建了发生在秘鲁南部 Cotahuasi 峡谷的岩崩的起源和潜在原因。头饰是在末次盛冰期雕刻而成的圆环，由阿尔帕班巴火山岩和上巴罗佐组火山岩形成。边坡破坏至少消除了 1.13 平方公里的体积，产生了干燥的岩石雪崩，该雪崩立即被限制在 Cachana 山谷中，在到达 Cotahuasi 河之前向下游移动了 11 公里。在那里，它确实以 72 m/s 的最低速度向对面的 Mungui 山脉又跑了 3 公里。横向的 Mungui 山脉迫使雪崩沿 Cotahuasi 河的上游和下游横向蔓延，并在最后一站之前向上游 Pampamarca 支流蔓延。由此产生的沉积物 (H/L = 0.16) 形成了丘状地形，形成了一个 10 公里长、≤100 米高的大坝，蓄水了两个临时湖泊。在它们的最大容量下，这些湖泊在超过大坝之前可以容纳约 1.6 × 108 立方米的水。大坝溃决产生了一场灾难性的洪水（形成梯田的巨大层），其传播范围达数十公里，可能远至大海。泥石流沉积物可以在距裂口 20 公里的范围内得到充分记录，其中存在 4 至 50 米厚的阶地，最小体积为 0.72 平方公里。在这段距离之后，沉积物消失了，可能是由于河流本身的入位后侵蚀。考虑到头棱环的缺失体积 (~3.85 km3) 以及岩崩和泥石流沉积物的最小体积之和 (~1.85 km3)，大约 40% 的物质必定已被冰川和河流侵蚀活动自其最初进驻之时起。