Preconditioning and triggering of offshore slope failures and turbidity currents revealed by most detailed monitoring yet at a fjord-head delta

Abstract

Rivers and turbidity currents are the two most important sediment transport processes by volume on Earth. Various hypotheses have been proposed for triggering of turbidity currents offshore from river mouths, including direct plunging of river discharge, delta mouth bar flushing or slope failure caused by low tides and gas expansion, earthquakes and rapid sedimentation. During 2011, 106 turbidity currents were monitored at Squamish Delta, British Columbia. This enables statistical analysis of timing, frequency and triggers. The largest peaks in river discharge did not create hyperpycnal flows. Instead, delayed delta-lip failures occurred 8–11 h after flood peaks, due to cumulative delta top sedimentation and tidally-induced pore pressure changes. Elevated river discharge is thus a significant control on the timing and rate of turbidity currents but not directly due to plunging river water. Elevated river discharge and focusing of river discharge at low tides cause increased sediment transport across the delta-lip, which is the most significant of all controls on flow timing in this setting.

Dispersion, Accumulation, and the Ultimate Fate of Microplastics in Deep-Marine Environments: A Review and Future Directions

“…"; Galy et al, 2007;Zavala et al, 2012;Sparkes et al, 2015). Secondly, turbidity currents may form due to externally or autogenically triggered collapse of sediment accumulations, such as at submarine canyon heads that trap littoral sediment transport (e.g., Xu et al, 2002;Paull et al, 2018;Smith et al, 2018), rapidly prograding delta fronts (e.g., Clare et al, 2016;Obelcz et al, 2017) or on open continental slopes (e.g., Nisbet and Piper, 1998;Talling et al, 2014;Soutter et al, 2018). Such failure-generated flows may be highly concentrated, contain a heterogeneous sediment mixture, and have the potential to run-out significant distances, eroding and entraining seafloor deposits from open slopes, or within a canyon or channel along their path (e.g., Piper and Savoye, 1993;Stevenson et al, 2015;Allin et al, 2016;Hunt, 2017;Mountjoy et al, 2018).…”

Lessons learned from the monitoring of turbidity currents and guidance for future platform designs

“…Three submarine channels connect the delta lip to channel lobes in water depths of up to 200 m ( Figure 2C: Hughes Clarke, 2016). Repeat seafloor surveys, and water column monitoring has revealed extremely frequent (>100/year) turbidity currents during seasonal peaks in meltwater discharge (Hughes Clarke et al, 2012;Clare et al, 2016). Here we focus on a seafloor frame containing and upward-looking ADCP (installed on the terminal lobe of one of the channels in 2011; Figure 2C), and multi-point moorings installed in 2013 and 2015 to measure flows that attained velocities of up to 3 m/s (Hughes Clarke, 2016; Hage et al, 2018).…”

Major modification of sediment routing by a large Mass Transport Deposit in the Gulf of Lions (Western Mediterranean)

“…They can play a significant role in the movement and transfer of sediment at river mouth deltas or canyon heads at hourly or yearly time scales (Biscara et al, 2012;Clare et al, 2016 ;Kelner et al, 2014;Mazières et al, 2014;Obelcz et al, 2017;Smith et al, 2007), but also at geologic time scales on canyons and whole margin development (Micallef et al, 2012;Sultan et al, 2007). This is particularly the case for large mass transport deposits that instantaneously redistribute huge volumes of sediment, in the order of several km 3 .…”

“…1) and did not created any distal positive relief, (2) seabed rejuvenation by rapid burying related the high sedimentation rates that persisted at the base of slope until 18.5 kaBP (Bonnel et al, 2005; Lombo Tombo et al, 2015), i-e during ca. 1.5 to 3.5 ka after the emplacement of the RWMTDT, and by the development of the neofan avulsion lobe and channel-levee on top of it.At river mouth subaqueous deltas or upper slopes under high sedimentation rates sliding seems to be a frequent quasi intrinsic process of sediment movement and transfer but resulting morphologies are quickly buried and obscured, sometimes within days to years(Biscara et al, 2012;Clare et al, 2016 ;Kelner et al, 2014;Mazières et al, 2014;…”