Every since my first visit to the Gulf of Alaska aboard the JOIDES Resolution drilling ship in 1992, I have been interested in the origin of the numerous volcanic seamounts that pepper the seafloor in the Gulf of Alaska. Many of the seamounts occur in long chains that lead southeast from the Gulf of Alaska down to the west coast of the U.S. and Canada. These seamounts are thought to have formed as the Pacific Plate moved over a group of hotspots that are now off the coast of Oregon, Washington, and British Columbia. As the Pacific Plate moves toward the northwest it acts like a conveyor belt and carries the seamounts with it. As one seamount is carried away from a hotspot, another forms in its place, so the older the seamounts are, the farther they have been carried by the plate. The result of this process is the long seamount chains we see today in the Gulf of Alaska (see Location Map), with the oldest seamounts at the northwest ends of these chains and the youngest at the southeast ends.
|Location Map. This location map shows some of the many chains of volcanic seamounts (black blobs) in the Gulf of Alaska. Only a few of these seamounts have been studied, but we are mostly interested in the ones that formed at the Cobb hotspot. The current location of the Cobb hotspot under Axial Seamount on the Juan de Fuca Ridge is shown. The thin line connecting Axial Seamount with Patton Seamount shows how the plate moved over the hotspot during the past 30 million years (m.y.). About 33 m.y. ago Patton Seamount was above the hotspot, but as the Pacific Plate moved to the northwest it carried Patton Seamount with it.|
Making a map of Gulf of Alaska seamounts
In July of 1999, four of us from OSU (Bob Duncan, Martin Fisk, Laura Snow, and myself) visited Patton Seamount aboard the research ship Atlantis on an expedition supported by the NOAA/NURP West Coast Undersea Research Center in Fairbanks, Alaska. The Atlantis carries the Alvin submersible, which we planned to use for our geological and biological sampling program, but our first step was to create a map of the seamount so that we would know where to go. Not much was known about the shape of Patton Seamount before our visit, and we needed to find good rock outcrops to sample. So first we made a map using the SeaBeam swath bathymetry system on the Atlantis. Swath bathymetry systems are able to measure the depth of the seafloor over a wide swath all at the same time, rather than at just one point at a time like a typical depth finder. So we were able to cover the entire seamount in less than day of survey time. When we were done we had a detailed map of the cliffs, spires, and flat areas of the seamount, and could select interesting-looking areas to explore with the Alvin submersible.
In June-July 2002, four of us from OSU (Martin Fisk, Mike Rowe, Chris Russo, and myself) returned to the Gulf of Alaska to map and sample several additional volcanic seamounts. This second expedition was supported by the NOAA Office of Ocean Exploration. The OE program maintains an excellent website that includes details about our 2002 expedition.
Finally, in July-August 2004, four of us from OSU (Jason Chaytor, Denise Giles, Paul Walczak, and myself) and Rachel Teasdale from Chico State returned again to the Gulf of Alaska to map and sample several volcanic seamounts in the Bowie hotspot chain, just north of the Cobb hotspot chain. The Bowie chain is obvious in the Location Map above, it sweeps NW-SE across the northern Gulf of Alaska. This third expedition was also supported by the NOAA Office of Ocean Exploration. They maintain another excellent website that includes details about our 2004 expedition.
|Bathymetric map. This is a 3-dimensional perspective (looking north) of our bathymetric map of Patton Seamount, with two smaller seamounts in the foreground. Deep areas are blue and shallow areas are red. Patton Seamount is about 10,000 feet tall and 20 miles wide. If you have a fast connection click on this link to download a video (28 MB) fly-around of Patton Seamount.|
Diving with Alvin on Gulf of Alaska seamounts
We conducted eighteen Alvin dives on five seamounts, and sampled a variety of volcanic rocks and marine life. We are still working on the rock samples, and will post some of our results here. Biologists from the National Marine Fisheries Service in Kodiak, Alaska, the University of Alaska, and Woods Hole Oceanographic Institution, are working on the biological samples. Below are some images and video showing the seafloor. We also conducted an interview for the Arctic Science Journeys radio show giving some of our impressions what is was like to dive in Alvin on Patton Seamount.
|Geology. This is a an image of the type of rocks we found on Patton Seamount. Most of the rocks are fist- to head-sized. If you have a fast connection, click on this link to download a video (7.5 MB) of some footage of the Alvin submersible sampling rocks on the slopes of Patton Seamount.|
|Biology. This is an image of some of the abundant life found on the seafloor on Patton Seamount. If you have a fast connection, click on this link to download a video (12 MB) of more marine life.|
This page was last updated on
21 December 2005
by Randy Keller
Department of Geosciences
Oregon State University