Submarine channel evolution: active channels in fjords, British Columbia, Canada

Seafloor channel systems are well developed in several British Columbia (Canada) fjords, including Knight, Bute and Toba inlets. The channels are active conduits for turbidity currents during episodic failures of delta fronts at the fjord heads. Recently acquired swath multibeam bathymetric data enabled a complete and detailed assessment of the form of these channel systems. Repeated multibeam surveys in Bute and Toba inlets (Mar. 2008 and Nov. 2010) indicate that the deeply incised channels may undergo accretion or erosion over a period as short as 2.5 years. Locally significant (> 15 m) bathymetric changes were documented in the channel systems, with bathymetric differences exceeding 5 m occurring along approx. 20-25% of the resurveyed channel lengths. Slope failure involving the upper delta front observed in Toba Inlet is a mechanism for the rapid initiation of new channel segments. Sediment accretion on the inner side of some channel bends indicates that point bars may form as lateral channel migration proceeds. Channel sidewall slumps are found at some outer channel bends and mounded deposits may occur at these sites. Lateral migration is accompanied by outer bend erosion, overall deepening of the channel and the development of terraces.