To travel from Ketchikan, Alaska to our field area in the western Aleutians requires us to steam 1700 miles – nearly the entire width of Alaska (and Alaska is big). By any mode of transportation, this is a long trip, but especially by ship. Research ships generally go a maximum speed of 10-11 knots (11.5-12.5 miles per hour). Although we are moving slow, at least we are able to keep traveling around the clock thanks to the mates and ship’s crew. Progress can be helped or hindered by currents and winds, so that even if the ship is going 10 knots through the water, our speed over the ground may be slower or faster. We have already experienced a wide range of weather conditions on our journey from flat calm and sunny yesterday to 15 foot seas and 55 knot winds today (definitely prefer the former).
But the long trip is not all bad! For one, it allows everyone to get their sea legs and organize for the work ahead, including testing equipment. It also gave us a chance to do a little underway science. We were able to map the seafloor just offshore of Ketchikan and image the shallowest sediments below the seafloor. This is done by sending out high-frequency pings from an instrument mounted to the hull of the ship and recording returning signals that have bounced off of the seafloor and layers below the seafloor. We crossed part of a spectacular system of channels in the seafloor that carry sediments eroded from the steep mountains flanking the coast out into the sea, where they form huge sediment deposits on the deep seafloor called sediment fans. The sediment fans offshore Alaska are some of the largest of their kind in the world. But the sediment transport system that creates the channels and sediment fans is disrupted by plate tectonics (Walton et al., 2014). As the Pacific Plate moves north at ~44 mm/yr with respect to North America (Elliott et al., 2010), these seafloor channels are severed from their sediment supplies onshore and carried north, as shown by the interesting work of Maureen Walton and collaborators.
We continue west and expect to arrive in our study area on Monday morning.
Donna Shillington, NAU
Elliott, J.L., Larsen, C.F., Freymueller, J.T., Motyka, R.J., 2010. Tectonic block motion and glacial isostatic adjustment in southeast Alaska and adjacent Canada constrained by GPS measurements. J. Geophys. Res. 115, doi:10.1029/2009JB007139.
Walton, M.A.L., Gulick, S.P.S., Reece, R.S., Barth, G.A., Christeson, G.L., Van Avendonk, H.J.A., 2014. Dynamic response to strike-slip tectonic control on the deposition and evolution of the Baranof Fan, Gulf of Alaska. Geosphere 10, 680-691, doi: 610.1130/GES01034.01031.