MBARI Ridges 2005 Expedition
Juan de Fuca Leg: August 7–18, 2005
Gorda Leg: August 22–September 2, 2005
August 12, 2005
Tiburon dive 878, East Blanco Depression, Blanco Fracture Zone
Update by Bob Embley; photos and movie by Bill Chadwick.
Bob Embley writes:
Today’s dive was in a deep basin at the western end of the Blanco Fracture Zone, where the ocean floor generated by the Juan de Fuca Ridge to the north slides by the Pacific plate born on the Gorda Ridge to the south. The primary purpose for the dive was to search for hydrothermal activity in this basin and to collect the chemosynthetic fauna that inhabits them. Such fauna could explain some anomalous discontinuities in the genetic lineage of the animals inhabiting hydrothermal vents on the Gorda Ridge and those of the Juan de Fuca Ridge.
The Blanco Fracture Zone is the undersea equivalent of the San Andreas Fault. The sliding motion, known as “strike-slip”, can move plates for hundreds of kilometers past one another over time. These long fault zones can also “leak” lavas in places where the fault zone bends or is offset. This creates the strange undersea terrain we saw on today’s dive. We explored volcanic hills whose lavas have been broken and ground up by numerous earthquakes along faults that criss-cross the basin. The lavas are old and in stark contrast to the young lavas we saw on yesterday’s dive.
We knew from dives made almost a decade ago that there was hydrothermal activity in this basin so our first goal was to return to that site. To our delight, we found the warm springs early in the dive and we were able to take samples of the warm fluid being emitted through the iron-rich yellow mounds that made small fairy-castle structures growing out of the side of the slope. The image to the left is a yellow chimney at a warm spring. The red laser dots are 30cm apart for scale.
As a bonus we relocated the “Party Hat” vent fluid collector we had deployed almost 9 years ago and recovered it and the temperature recorder attracted to it. Maybe we’ll be able to recover the temperature record from it when we return to shore! Although there was no sign of the larger chemosynthetic fauna we were hoping to see on this dive there is a lot more to explore here and other similar places along the fracture zone and this dive was a great start!