Mendocino Fracture Zone Cruise
August 24 - 31, 2000
Over 300 km off the California-Oregon Coast
August 25, 2000: Day #2
Log Entry: The day dawned beautifully with clear skies and blue seas. Last night after collecting two gravity cores the ship steamed to the west about 46 miles to the Mendocino Ridge. This shallow ridge, just south of the Escanaba Trough comprises the western end of the Mendocino Fracture Zone. Our plan is to follow the course of an earlier ROV dive, the Navy's ATV, which collected samples here in 1995. Included in this earlier sample suite were rocks that originally formed within the lower oceanic crust. Samples of such oceanic gabbros are rare for the Pacific Ocean and their uplift history might also provide clues for the regional tectonic story.
The dive started at the deepest point, in a sediment filled basin at 2800 m. Odd-looking sediment balls in the basin were immediately dubbed "bioballs". Driving south, we found a massive outcrop of layered and massive rock surrounded by sediment that offered an ideal site for drilling a rock core. The 11-inch core proved to be an heavily veined volcanic rock, not a gabbro. Boulders and cobbles distributed along the faulted walls of the Ridge provided more sites for grab samples and two additional cores (both of these were volcanic also with beautiful veins of quartz and chlorite). The last core refused to come out of the hole with the barrel. The skillful Tiburon pilots carefully plucked the rock core from the borehole and dropped it into one of the push core quiver.
Much of the north flank of the Mendocino Ridge is covered by sediment and talus. We sampled some large boulders that were 500 to 1000 meters below the top of the ridge. The source of the boulders could not be found, however. When we went to the top of the ridge all we found were round pebbles and cobbles. The Oregon State contingent has suggested that the Mendocino Ridge was above sea level at some point. This would explain both the absence of the source of the boulders and the reason for the cobbled summit. The flank of the Ridge was also apparently a brittle star convention, with the occasional boulder providing highly populated high-rise locations. Another unusually common creature that we have seen on both our dives is the octopus-the last count was over a dozen specimens of the dark-eyed creatures.
We had a successful day of sampling with three rock cores, 10 grab samples and four push cores-two with sediment and two with pebble samples. Tonight we will steam back to the east to dive on the westernmost Gorda Escarpment.
Oatmeal w/raisins & brown sugar
Eggs to order
Omelettes (ham/mushroom/bell pepper/cheese/onion)
Pancakes - Blueberry pancakes
Split pea soup (made from scratch!)
Baked Alaska true cod
Hopin' John's blackeyed peas
Split pea soup
Top serloin roast
Mashed potatoes & gravy
Mushroom rice pilaf