Monterey Bay Aquarium Research Institute

Mendocino Fracture Zone Cruise
August 24 - 31, 2000
Over 300 km off the California-Oregon Coast
Logbook

August 24, 2000: Day #1


ROV Tiburon with the coring sled attached, ready for the day's mission.

Log Entry: We began our dive at this site just after lunchtime and on the same day that we left Eureka. Because of the late start, we decided to shorten the dive track to begin at a depth of about 2000 m. This was about half-way up the wall of the Gorda Escarpment. The plan was to go up the north-facing wall and over the summit of the ridge by the end of the dive. The short dive time meant we had to budget our time carefully and only try for a single drill core. We landed on a site of massive basaltic units perfect for drilling. After looking around for only a short time, we selected a site that looked like a faulted wall of basalt. The drilling was slow and the barrel jammed after about 30 minutes. Nonetheless, we recovered several inches of silicified basalt. The grab sample from the same site has a similar silicic coating with slickensides. In the frame grab you can see one of the faulted walls in the background.

The beautiful massive exposures at our initial site led us to assume that there would be continuous rock all the way to the summit. We were wrong, wrong, wrong. Much of the wall was in fact coated with sediment of variable thickness. We found lumps of mafic rock protruding from the sediment and coated with a soft white mineral. As we neared the summit of the ridge, every boulder was inhabited by benthic fauna. Some of the more interesting were the king crabs fighting to be king of the hill. Just over the top of the ridge we found a layer of siliceous mudstone sticking out of the sediment, which may correlate with similar layers in the ODP drill core. The only way we got this one to the surface was to put it on top of the drillsled.


Four crabs playing king of the rock at the top of the ridge.

Many of the rocks were broken up or ground into fault gauge. Much of the wall was obscured by sediment. At the end of the dive we were satisfied with our efforts, though. We had collected 7 grab samples, four pushcores of sediment or precipitates and one drillcore along with the animals that could be scraped from the rocks. So the easy answers we were after still elude us. Tomorrow we head for the Mendocino Ridge where we hope the geology will be simpler



A grab sample from a site halfway up the wall of the Gorda Escarpment, this area was covered with silicified basalt. 

"The Big Kahuna," a layer of siliceous mudstone sticking out of the sediment that may correlate to previous core samples

Today's Menu

Breakfast:
Chilled fruit
Oatmeal with raisins & brown sugar
Eggs to order
Omelettes to order - Ham/mushrooms/bell pepper/cheese/onion
Hash browns
Pancakes
Blueberry-Lemon muffins
Bacon or sausage

Lunch:
Tortilla soup
Tossed salad/Fruit salad
Taco Bar
Refried beans
Spanish rice
Cut corn
Doug's famous fresh salsa & chips 

Dinner:
Salad bar
Tortilla soup
Teriyaki chicken
Spinach ravioli
Broccoli w/caper sauce
Garlic bread
Spanish rice
Strawberry rhubarb pie


Next Day