A global review of subaqueous spreading and its morphological and sedimentological characteristics: A database for highlighting the current state of the art

Subaqueous spreading, a type of extensional mass transport that is characterized by a ridge and trough
morphology, has been documented globally but is poorly understood. Subaqueous spreading is observed on
gently inclined surfaces (typically <3◦) when sediment bodies experience a sudden reduction of shear strength
along their basal plane during clay softening or liquefaction of sands or silty sand sediment. Historically,
spreading has been associated with very large landslides, but many unknown aspects of these mass movements
have yet to be clarified. Does spreading influences the large catastrophic failure? What are the sedimentological
and morphological aspects that contribute in initiating this process? These are some of the research questions
that spurred the present work. Here, we introduce a database that incorporates information from thirty-two case
studies, and use this to provide key insights into the sedimentary and morphological aspects of subaqueous
spreading that will assist in the identification of spreading elsewhere. We find that subaqueous spreading is most
common along passive glacial margins, but is also observed along active margins. The occurrence of contourites
interlayered with glaciogenic deposits is, in most cases, associated with landslides (or landslide complexes) with
spreading morphology. The database shows that seismic loading is commonly suggested to be the dominant
trigger mechanism, although more geotechnical observations and modelling analysis would be needed to support
this conclusion. We compare subaqueous spreading with terrestrial spreading, in particular to earthquake-related
lateral spreading and clay landslides. We find that subaqueous spreading shares the same driving processes and
potentially also some of the trigger mechanisms that are associated with the terrestrial spreading cases. Future
work will be required to address the association between spreading and its occurrence on some of the largest
landslides on Earth, its development mechanism, and its potential hazard implications.