CONTROLS ON HIGH VARIATION IN SINUOSITY AND AVULSION IN NEIGHBORING DEEP-SEA CHANNELS IN THE GULF OF ALASKA
Variations in sinuosity may be the result of differences in sediment routing and proximity to sediment sources. Both systems receive glacial sediment, but tidewater and temporal lobe glaciers bring the Surveyor flux directly to, or near to, the ocean. There is little to no fluvial influence on sediment transport in this system. Glacially carved troughs act as conduits across a ~100 km wide shelf and only small canyons are present on the continental slope. Valley glaciers supply the Baranof system via rivers across the coastal plain and islands. The shelf is < 50 km wide with no glacial troughs, and canyons twice the size of those in the Surveyor system. The shorter shelf transit is likely to increase the overall flux and amount of coarse sediment across the shelf edge and is interpreted to be responsible for the formation of larger canyons and higher sinuosity compared to the Surveyor system.
The fan gradient and geology at the channel terminus could be additional components influencing sinuosity, as well as avulsion. With a terminus in the Aleutian Trench and the steep gradient of the outer trench swell, the Surveyor Channel may not experience backfilling of the main channel, and therefore has no need to avulse. The Chirikof Channel could be in a similar situation with a terminus in the topographically low Aja Fracture Zone. However, the Horizon Channel encounters significant topography within 100-200 km of the shelf edge, and forms lobes on the abyssal plain at its terminus. Normal lobe deposition could instigate main channel backfilling and avulsion. We will explore controls on these processes and systems using 2D seismic reflection, refraction, and bathymetric data, including a new dataset collected in June 2011 under the U.S. Extended Continental Shelf program.