How was a thousand kilometre cable-breaking submarine flow triggered by an exceptional Congo River flood?

刚果河特大洪水是如何引发数千公里电缆断裂的海底水流的？

• 批准号: NE/V004387/1
• 负责人: Daniel Parsons
• 金额: $ 37.81万
• 依托单位: University of Hull
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV004387%2F1
• 关键词: How; was; thousand; kilometre; cable

This proposal seeks to understand how a prodigious 1,250 km runout submarine sediment avalanche (turbidity current) was triggered on 14th January 2020, by the largest flood in 50 years along the Congo River. This submarine flow broke two seabed telecommunication cables that underpin data traffic to West Africa causing the internet to slow from Nigeria to South Africa. These submarine cables had not previously broken in the last 20 years. This flow also caused a series of oceanographic moorings to surface, placed along Congo Submarine Canyon by a NERC project (NE/R001952). Cable breaks and surfaced moorings show that this remarkable flow ran out for over 1,200 km, as measured along the canyon axis. Moreover, the flow continuously self-accelerated, such that it reached front speeds of >8 m/s, some 1,150 to 1,250 km from its source at the mouth of the Congo River. This is the longest runout turbidity current yet monitored in action, and the only monitored flow to continuously self-accelerate for over a thousand kilometres. It is important to understand how such powerful and very long runout turbidity currents are triggered, especially for hazards to strategic seabed cables, including cable routes that are planned for 2020-21 off West Africa. The January 14-16th submarine flow is not associated with an earthquake, and it occurred during a period of low wave heights. However, it does coincide with an extreme flood of 80,000 m3s-1 observed in December 2019 along the Congo River. It is thus also important to determine how the frequency of submarine flows will be effected by future climate and hydrological changes in the Congo Basin. Here we seek to understand how this exceptional river flood triggered a thousand kilometre submarine flow, by conducting a detailed survey of the Congo River mouth. We will use the geomorphology of that river-to-submarine-canyon transition to understand how the offshore flow was triggered by the river flood, for example by mapping landslide scars, or testing a hypothesis that river bedload was driven over a single steep avalanche face. This is an urgency grant because evidence of how the Jan 2020 flow was triggered (e.g. seabed failure scarps) will be buried or wiped-out by the next peak discharge of the Congo River in Oct 2020.There are extremely few direct measurements of the most powerful turbidity currents that run out for hundreds to thousands kilometres to the deep ocean, and the few measurements available previously produced step changes in understanding. Indeed, there has only been one previously directly-measured turbidity current on this scale, which is the Grand Banks event in 1929 that broke all ~20 cables across the N. Atlantic. The Grand Banks event ran out for over 800km, but decelerated from 19 m/s to 3 m/s, rather than continuously accelerating as in the Jan 2020 event. Moreover, the Jan 2020 event already has much more detailed measurements from the timing of offshore moorings, with further data to come via recovery of these moorings and 12 OBS (with hydrophones and geophones) on a NERC cruise. This Jan 2020 event is thus a rare and extremely valuable opportunity to understand how far large-scale flows operate, linked to exceptional river floods with much longer (50-100 year) recurrence intervals. The main gap in our understanding of the Jan 2020 event is what happened at the river mouth, and this is key for predicting flow frequency and links to climate change. The geomorphology of the river to canyon-head transition is currently unknown. For example, UKHO bathymetric charts mainly use data collected in the 1890s. Here we will use swath multibeam echosounder systems to survey the river to canyon transition at much higher resolution and in three dimensions, thereby documenting its geomorphology in unprecedented detail. Past work shows how a single multibeam bathymetric survey can produce major insights into turbidity currents triggering at river mouths.

该提议旨在了解刚刚在2020年1月14日触发了1,250公里的跳运潜艇雪崩（浊流）是如何被刚果河沿线50年来最大的洪水触发的。这种海底流量破坏了两条海底电信电缆，这些电信电缆支撑了到西非的数据流量，从而导致互联网从尼日利亚到南非放缓。这些海底电缆以前在过去20年中并没有断裂。这种流程还引起了一系列海洋模型表面，沿着NERC项目（NE/R001952）沿着刚果海底峡谷放置。电缆断裂和浮出水的系泊表明，正如沿峡谷轴所测量的那样，这种显着的流量超过1200公里。此外，流动不断地自动加速，使其达到距刚果河口源的前速度> 8 m/s，约1,150至1,250公里。这是尚未在作用中监测的最长的跳出浊度电流，也是唯一的监测流动流，可连续自动加速超过一千公里。重要的是要了解如何触发如此强大且非常长的浊流，尤其是对于战略海床电缆的危害，包括计划在西非2020-21的电缆路线。 1月14日至16日的海底流与地震无关，并且发生在低波高度的时期。但是，它确实与2019年12月在刚果河沿线观察到的80,000 M3S-1的极端洪水相吻合。因此，确定如何通过刚果盆地的未来气候变化来影响海底流的频率也很重要。在这里，我们试图通过对刚果河口进行详细调查，了解这种特殊的河流洪水如何引发一千公里的海底流。我们将利用该河流到苏贝亚河 - 综合河过渡的地貌来了解如何触发河流洪水的近海流量，例如，通过绘制滑坡疤痕或检验假设，即河床上载有河床是在单个陡峭的雪崩脸上驱动的。这是一项紧迫的赠款，因为证据表明2020年1月流动如何（例如，海底故障疤痕）将被2020年10月在刚果河的下一个峰值排放而被掩埋或淘汰。几乎没有直接测量最强大的浊流，这些浊流最少，这些浊流耗尽了数百万到千公里的深海，以前可用的测量量很少，并在以前产生了几千公里，并衡量了几个衡量标准。确实，在这个规模上，只有一个以前直接测量的浊度电流，这是1929年的大银行活动，在整个N. Atlantic中打破了所有约20条电缆。大银行活动的比赛时间超过800公里，但从19 m/s下降到3 m/s，而不是像2020年1月的活动那样不断加速。此外，2020年1月的活动已经从离岸系泊设备的时间安排中进行了更详细的测量，并在NERC巡航上通过恢复这些系泊设备和12个OBS（带有氢气和地理器）进行进一步的数据。因此，这项2020年1月的活动是一个罕见且极为宝贵的机会，可以理解大规模流动的运作程度，与更长（50 - 100年）复发时间更长（50 - 100年）相关的河流洪水。我们对2020年1月事件的理解的主要差距是河口发生的事情，这是预测流量频率和与气候变化联系的关键。目前尚不清楚河流到峡谷头过渡的地貌学。例如，UKHO测深图主要使用1890年代收集的数据。在这里，我们将使用Swath Multibeam Echosounder系统以更高的分辨率和三个维度来调查河流过渡到峡谷过渡，从而以前所未有的细节记录其地貌。过去的工作表明，单个多微型测深调查如何产生对河口触发浊流的主要见解。

项目成果

Carbon and sediment fluxes inhibited in the submarine Congo Canyon by landslide-damming

• DOI: 10.1038/s41561-022-01017-x
• 发表时间: 2022-09
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: E. Pope;M. Heijnen;P. Talling;R. Jacinto;A. Gaillot;Megan L. Baker;S. Hage;M. Hasenhündl;C. Heerema;C. McGhee;Sean C. Ruffell;S. Simmons;M. Cartigny;M. Clare;B. Dennielou;D. Parsons;C. Peirce;M. Urlaub