Monterey Bay Aquarium Research Institute

West Coast Expedition
July 20 - August 30, 2002
West Coast of North America
Logbook

August 18, 2002: Day #30


Fig. 5 is a vent in the Sasquatch hydrothermal field that had fluids with temperatures near 200 C. The ROV is collecting fluids in a gas-tight water sampler.

Debra Stakes writes: Our dive plan for today almost repeats our dive from yesterday, but with better outcomes (we hope). We want to find a good site to place a borehole for a seismometer and collect. We begin at the Homerpro beacon that we left at the end of yesterday’s dive. After a quick reassessment of this aborted coring site, we decide that this big piece of talus is in fact a bad place for a seismometer. The greatest challenge has been finding a place flat enough for the ROV to be stable for the multiple hours required to core a borehole. We shift our strategy to finding flat spots, not fault scarps. This change of strategy pays off, as I remember the contact seen yesterday with flat pahoehoe flows ponded up against older pillow basalts (Fig 1). The flat floor and beautiful pillows make a great target. We sit and core for hours (Fig.2) (most of the dive) but are rewarded with our first top quality corehole seismometer site. The site is marked with the homerpro acoustic beacon, sealed with a plug the same size as the seismometer (Fig 3). This site will wait until next year for an instrument to be deployed. A benefit of the coring process is that we also recover a beautiful core of fresh basalt from the pillow (Fig 4). After we finished drilling, we returned to the Sasquatch vent field to collect a fluid sample (Fig. 5), some worms and an altered rock.



Figure 1 shows the site we select for a borehole. This is placed at the contact between the older pillow lavas and younger sheet flows.

Figure 2 shows the ROV with the coring sled doing its job to create a 6.985 cm borehole for a seismometer.


Figure 3 shows the borehole marked with a plug to keep out the mud and potential biological inhabitants.

Figure 4 is the basalt core recovered by our coring sled. The borehole was made using a corer-reamer bit. This bit cuts a 3.175 cm core and also reams the hole to almost 6.985 cm in diameter.

 

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