Keck Expedition 2004
August 4, 2004 Day 6
Update for Wednesday August 4 - (by Debra Stakes)
The ROV pilots and the science party all slept in today after the long night completing the Nootka Broadband Site (see accompanying “Action on Nootka” by Taimi Mulder of the Canadian Geological Survey). At breakfast the Western Flyer is still steaming west, back to the Endeavour Segment. The ship is on station just about lunchtime and the ROV Tiburon is in the water just a few minutes before 1 pm. In the vehicle drawer is the new system to be deployed at Site KENE (Keck Endeavour Northeast flank) to replace the corehole seismometer that has been faithfully recording data for us during the past year (we hope). After each used system is brought on board the ship, there is a flurry of activity. The short period systems must have their time drift corrected before they warm up from the seafloor deepfreeze temperatures. The onboard clocks change their drift rates with temperature, so this is a time-critical measurement. After the glass sphere has warmed a bit, it is opened up and the data disks are labeled and removed. Then Andrew begins the data backup and quality control process. Over the next few days, this process will require long hours as both the sensors and loggers must be rebuilt to redeploy within 12 hours. The only way we can confirm that the hardware worked correctly during the previous 12 months is to look at the data after it is backed up. So all these tasks become equally important during the few hours after the recovery.
Site KENE was located only 10 minutes after the ROV arrived on the seafloor, thanks to our acoustic HomerPro beacons. Use of these acoustic markers has greatly speeded up all of the operations requiring revisiting a specific site. As soon as the vehicle gets within a few hundred meters of the instrument (which the surface GPS coordinates can do quite nicely) the ROV communicates with the beacon to get its range and bearing. It’s always exciting to catch the first glimpse of the instrument left to record data 12 months ago. The KENE sensor was being guarded by a very possessive crab and decorated with brittle starts. There are Canadian hockey pucks on the sensor handle that were used by the ROV ROPOS for the deployment last year. Taimi notes with disappointment that no one advised her to bring the hockey pucks this year for the replacement systems. The ROV spent less than 45 minutes on site to replace the KENE system. Two and a half hours later the ROV was descending to the KENW shortperiod seismometer site. The KENE and KENW sites are on the northeast and northwest flanks of the Endeavour spreading center. These flanks are built of elongate lobate flows pouring down hill. In 2002 and 2003 the boreholes were pre-drilled using the MBARI drillsled on two different ROV’s (MBARI’s ROV Tiburon in 2002 and the WHOI ROV Jason II in 2003). The KENW sensor can be seen extending from the borehole drilled into one of these pillows. In our quest to improve the methodology of our corehole seismometer installations, the pilots have brought down a hose to either vacuum or jet water into the boreholes and clean them out before reinstalling the sensors.
Two corehole sites were turned around today. Both of the systems were still running and the clock drift could be measured. Both of the loggers contained a full 12 months of data that is being backed up and checked tonight. We are trying to not become blasé about such success. It is built on years of work in Monterey Bay and precision in the installation of the systems here. The result is a high success rate and valid seismic network comprised of a minimum number of instruments. If all goes well the pilots will try for a new record and turn around three systems tomorrow. After each dive we check off the shrinking list of sites to visit. It’s been a very good day.