Can we anticipate the impacts of great subduction zone earthquakes and volcanic eruptions on sediment generation and transport across landscapes and seascapes?

 

Subduction-zone land- and seascapes, spanning the offshore trench to the volcanic arc, are shaped by myriad processes. Storms and earthquake-shaking mobilize rock, sediment and soil from slopes, which are continuously transported seaward by the ebb and flow of flooding rivers and offshore currents.  Such catastrophic and punctuated erosional pulses across land- and sea-scapes can initiate complicated responses and continuous adjustments that persist for years or even decades following the events that precipitated the geomorphic cascade. Slope failures from volcanic sector collapse, earthquake land-level changes, and storms can all dam river channels, leading to either continuous adjustments in response to changes in sediment supply, or outburst floods that rapidly alter river channel morphology – both of which can impact downstream communities. The generation of large volumes of detritus from subduction-zone disturbances can modify river networks for decades to years, changing both their forms and processes in ways that may produce more frequent flooding and promote channel widening.  

 

Understanding these disturbances and their cascading impacts have enormous practical importance because they pose substantial risks to the ecosystems, communities, and infrastructure lying in their paths.  Despite this, there are still key uncertainties as to when catastrophic surface disturbances might be initiated, where the detritus produced by these events might go, and how long and far the cascading impacts that are produced by these disturbances might extend.  This knowledge gap has, in part, persisted because of an inability to observe the dynamics of processes, and understand these dynamics through computationally demanding numerical simulations. However, developments in the ability to observe the initiation, transport, and long-term impact of these events, and to simulate the physics of these processes at scale now promise to narrow this knowledge gap.  High resolution space-born imaging methods now allow us to locate where and when events are initiated, and in some cases, characterize rates of motion. Sub-orbital plane and drone-based platforms, coupled with computer vision developments, allow detailed characterization of downstream impacts produced by disturbances. Submarine drone and continuous monitoring technologies have very recently allowed us to capture seascape changes produced by sediment density currents that may be initiated by earthquake-generated submarine landslides.  Simultaneously, developments in computer hardware now provide petaflop-scale computation to researchers, while developments in numerical methods allow accurate simulation of multiphase physics of the flows produced by disturbances and cascading impacts. Many of these advances are accelerating in a way that will allow us to address the key fundamental questions that underlie our ability to understand these hazardous events: What are the fundamental controls on the initiation and runout of landslides, turbidity currents, and volcanic mudflows?; and, How do surface processes produce cascading and persistent impacts as material is transported across the land- and sea-scape?

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