UNH Ocean Seminar

Monitoring Turbidity Currents: You Don’t Need to Be Active, but It Really Helps If You Listen

John Hughes Clarke


Friday, Apr. 2, 2021, 3:09pm

Turbidity currents are a global submarine phenomenon moving sediment over lengths scales of 100’s of kilometers, rivalling the worlds river systems. Their activity builds the continental margins and transports significant volumes of carbon into the deep sea. Such events however, are frustratingly infrequent, and usually catastrophic and thus observing their characteristics has remained elusive.

The glacially fed fjords of British Columbia have long been recognized to be one of the few sites globally where turbidity current activity is both more frequent and accessible. A 17-year monitoring program has been in place that has allowed precise monitoring of the episodic formation, growth and evolution of the seabed channels and depositional lobes formed by turbidity currents. At the delta front locations, where the flows are much more active and predictable, vessel-based active acoustic imaging has successfully been utilized to examine the nature of the flow themselves. To capture the less frequent, but most significant flows, in-situ monitoring has been attempted using moored ADCPs. The results however, have been disappointing as these flows are usually acoustically impenetrable.

As an alternate approach, a passive acoustic monitoring program was implemented that “hears” the flows as they go by. This evolved out of an opportunistic 2013 experiment which demonstrated that they have a distinctive signature. In 2019, a multi-sensor array was installed along the active channel and one major flow was captured. The results of analysis of this event will be presented.


John Hughes Clarke has degrees in geology and oceanography and has spent the last 35 years using active acoustics to investigate modern sedimentary processes in shelf and deep sea environments. He currently works within the Center for Coastal and Ocean Mapping where he undertakes research and teaching on aspects of multibeam surveying that are most critical in support of national mapping programs.