Hard to believe we’re coming to the end of this very productive survey here in the Gulf of Alaska rescuing Ocean Bottom Seismometer (OBS) instruments that we deployed in the summer of 2018. The entire time onboard the Marcus Langseth has been a wonderful experience working with very interesting and dedicated people in the scientific party and Langseth crew. We’ll be returning to port in two days, and hopefully the weather is as nice in Kodiak as when we sailed on August 26th.
Leaving Coast Guard Base Kodiak on Monday afternoon, August 26th. Beautiful day to set sail!
My role in this endeavor has been to monitor and assess the performance of the hull mounted Simrad EM122 multibeam echosounder and the Knudsen 3.5 kHz subbottom profiler. The multibeam echosounder maps bathymetric soundings in a swath below the ship as we travel along, and the Knudsen profiler details sediment layers underlying the seafloor. Both of these data sets will provide more detailed surficial and subsurface information of this area than has been previously collected. Our primary mission has been to recover OBS units that have rested on the seafloor collecting seismic data since the summer of 2018, however we took advantage of transits to each OBS station to collect bathymetric and reflectivity information using these remote sensing instruments. And because the weather cooperated with us (with the exception of a very interesting weekend storm!!), we’ve also had time to run two mapping surveys: One detailing the fore-arc trench fault system south of the Shumigan Islands, and another directly over the epicenter of the January 2018 m7.9 earthquake that shook the area. Both the multibeam system and subbottom profiler have performed extremely well, even in dicey weather, and have given us a wealth of information that will contribute to the understanding of subduction zone processes occurring south of Alaska.
View of new multibeam data looking ENE along the Aleutian Trenchaxis. Note the intricate fault patterns on the incoming subducting plate.
Along the way we’ve also found time to enjoy ourselves playing in cribbage and ping pong tournaments, and most importantly, the galley crew has served us excellent meals and desserts! As we complete this second mapping survey over the next 24 hours or so, I’ll be reflecting on all the fun and interesting conversations I’ve had with everyone here and will always cherish this time I’ve spent onboard the R/V Marcus Langseth. Lastly, yesterday we had a good omen appear on our starboard side, the most spectacular rainbow I think I’ve ever seen!!
– Bill Danforth, USGS Woods Hole, Massachusetts