Developing a Global Listening Network for Turbidity Currents and Seafloor Processes

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This ambitious project can make a major step-change in understanding of seafloor processes and geohazards by developing a listening network based on low-cost hydrophones (via acoustic noise in water column) and geophones (via ground shaking). This type of low-cost network has unusually widespread applications, but here we aim to answer fundamental questions about how submarine mass-flows (turbidity currents and landslides) are triggered, and then behave. These hazardous and often powerful (2-20 m/s) submarine events form the largest sediment accumulations, deepest canyons, and longest channel systems on our planet. Turbidity currents can runout for hundreds to thousands of kilometres, to break seabed cable networks that carry >95% of global data traffic, including the internet and financial markets, or strategic oil and gas pipelines. These flows play a globally important role in organic carbon and nutrient transfer to the deep ocean, and geochemical cycles; whilst their deposits host valuable oil and gas reserves worldwide. Submarine mass flows are notoriously difficult to measure in action, and there are very few measurements compared to their subaerial cousins. This means there are fundamental gaps in basic understanding about how submarine mass flows are triggered, their frequency and runout, and how they behave. Recent monitoring has made advances using power-hungry (active source) sensors, such as acoustic Doppler current profilers (ADCPs). But active-source sensors have major disadvantages, and cannot be deployed globally. They can only measure for short periods, are located on moorings anchored inside these powerful flows (which often carry the expensive mooring and sensors away), and they need multiple periods of expensive research vessels to be both deployed and recovered. We will therefore design, build and test passive sensors that can be deployed over widespread areas at far lower cost. These novel sensors will record mass-flow timing and triggers; and changes in front speed (from transit times), and flow power (via strength of acoustic or vibration signal).We will first determine how submarine mass flows are best recorded by hydrophones and geophones, and how that record varies with flow speed and type, or distance to sensor. Our preliminary work at three sites already shows that hydrophone and geophones do record mass-flows. Here we will determine the best way to capture that mass-flow signal, and to distinguish it from other processes. This will form the basis for then designing and field testing a new generation of low-cost smart sensors, which return data without expensive surface vessels; via pop-up floats and satellite links. Advances in technology make this project timely, as they allow on-board data processing by smart hydrophones to reduce data volumes, which can be triggered to record for short periods at much higher frequency. We will test the new smart sensors, and use them to answer two major science questions. First, do submarine flows in different settings show consistent modes of behaviour? Second, what triggers submarine flows in river-fed systems, and how are they linked to major river floods, earthquakes, and tropical cyclones? To do this, we will place these new sensors along the Congo Canyon (dilute river, passive margin, no cyclones) off West Africa, and the Gaoping Canyon (hyperpycnal river, active margin, frequent cyclones) offshore Taiwan.These sensors have other widespread applications. Low cost warning sensors would be a major advance for offshore hazard assessment, and leaks from CCS facilities or gas pipelines. Sensors that record landslides would be a step change for tsunami warning systems, or threats to valuable seabed infrastructure. This proposal is also particularly timely, because of advances in technology now allow on-board data processing and communication between smart sensors, which can be triggered to record for short periods at much higher frequency.