Preconditioning by sediment accumulation can produce powerful turbidity currents without major external triggers
Preconditioning by sediment accumulation can produce powerful turbidity currents without major external triggers
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DOI：
10.1016/j.epsl.2021.116845
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发表时间：
2021-03-03
影响因子：
5.3
通讯作者：
Lundsten, Eve
中科院分区：
文献类型：
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作者：
Bailey, Lewis P.;Clare, Michael A.;Lundsten, Eve
浊流主导着沉积物向深海的输送，并且可能会破坏关键的海底基础设施。人们通常推断，强大的浊流是由重大外部事件引发的，比如风暴、河流洪水或地震。然而，浊流触发的基本模型仍然缺乏充分验证，很少有研究能够准确记录精确的流动时间。在此，我们分析了在加利福尼亚近海的蒙特雷峡谷内对强大（速度高达7.2米/秒）浊流所做的最详细的一系列测量结果。在仪器部署的18个月期间，直接监测到了14次浊流。虽然水流确实在季节性沉积物供应增加的时段较为集中，但没有观察到一致的触发机制。我们将蒙特雷峡谷（一个由沿岸漂沙供给的沙质峡谷头部）的浊流时间与其他仅有的通过直接监测精确测量了大量（>10 - 100次）水流的系统进行了比较；这些系统包括斯阔米什三角洲（一个沙质峡湾头部三角洲）和刚果峡谷（与刚果河以泥为主的河口相连）。一种常见的季节性模式浮现出来，从而形成了一种关于在沉积物堆积区域（如峡谷头部或河口）通过边坡失稳引发浊流的预处理和触发的新模型。在这个模型中，仅仅是快速或持续的沉积物供应就能够产生升高的孔隙压力，这种压力可能会持续存在，从而使边坡易于失稳。一旦经过预处理，一系列较小的外部扰动，比如中等强度的风暴浪，会导致局部孔隙压力变化，从而成为有效的触发因素。因此，重大外部触发因素并非总是强大浊流触发的必要条件。（C）2021作者。由爱思唯尔出版社出版。
Turbidity currents dominate sediment transfer into the deep ocean, and can damage critical seabed infrastructure. It is commonly inferred that powerful turbidity currents are triggered by major external events, such as storms, river floods, or earthquakes. However, basic models for turbidity current triggering remain poorly tested, with few studies accurately recording precise flow timing. Here, we analyse the most detailed series of measurements yet made of powerful (up to 7.2 ms(-1)) turbidity currents, within Monterey Canyon, offshore California. During 18-months of instrument deployment, fourteen turbidity currents were directly monitored. No consistent triggering mechanism was observed, though flows did cluster around enhanced seasonal sediment supply. We compare turbidity current timing at Monterey Canyon (a sandy canyon-head fed by longshore drift) to the only other systems where numerous (>10-100) flows have been measured precisely via direct monitoring; the Squamish Delta (a sandy fjord-head delta), and the Congo Canyon (connected to the mud-dominated mouth of the Congo River). A common seasonal pattern emerges, leading to a new model for preconditioning and triggering of turbidity currents initiating through slope failure in areas of sediment accumulation, such as canyon heads or river mouths. In this model, rapid or sustained sediment supply alone can produce elevated pore pressures, which may persist, thereby predisposing slopes to fail. Once preconditioned, a range of minor external perturbations, such as moderate storm-waves, result in local pore pressure variation, and thus become effective triggers. Major external triggers are therefore not always a prerequisite for triggering of powerful turbidity currents. (C) 2021 The Authors. Published by Elsevier B.V.