Mendocino Fracture Zone Cruise
August 24 - 31, 2000
Over 300 km off the California-Oregon Coast
August 28, 2000: Day #5
Log Entry: High seas and winds have kept us from working for two days. The winds have topped out at over 40 knots. The seas began with increasing white caps and then huge lines of rollers. The sun never left us though. We could enjoy the sunshine and watch the seas crash against the broad bow of the boat. Sleeping has been a challenge with the sounds and movements of the ship. We used the time to try and catch up on our sleep and our bookkeeping.
Our real-time navigation system preserves a map of where the vehicle was at every mark point. Comments written during the dive and the frame-grabs from the video can also be tied in with the navigation. The result is that we can "replay" the dive from the series of frame-grabs and observer comments. We have added to this replay our descriptions of the samples that have been examined in detail on board ship. This replay process is constantly being improved. We have found software to permit us to review the frame-grabs quickly for any dive
Some new scientific insights have become apparent during this replay process. The dive up the Mendocino Ridge has yielded a vague stratigraphy of ocean crust. If you only consider the grab samples, we obtained gabbros near the bottom and basalts near the top. The rock cores are all sheared volcanic rocks. Was this just a bias from choosing the best looking rocks to core or does it say something about the distribution of rock types? We don't know yet.
The second major insight is that the basement of the Gorda Escarpment does appear to be an extension of the Mendocino Ridge. The rock cores as well as the grab samples are dominated by volcanic breccias, but cobbles of weathered gabbro and basalt have also been found. When we finally get the ROV back into the water on Tuesday, our target will be the contact between this basaltic basement and the overlying sediments.