The JOIDES Resolution research drillship, a key vessel in the Integrated Ocean Drilling Program (IODP), was docked in Victoria this summer for three months of refit work before heading out on two cruises in July and September.
The Juan de Fuca Plate is a hot-spot of scientific ocean drilling. Since ODP expedition 139 in 1991, numerous boreholes have been drilled in the Northeast Pacifc and several of them where equipped with CORK (Circulation Obviation Retrofit Kit) hydrologic observatories. These CORKs enable geoscientists to observe changes in subsurface pressures and temperatures caused by earthquakes, storms, hydrothermal convection and regional plate strain. NEPTUNE Observatory is collaborating with IODP to provide live connections to CORKs in deep-sea boreholes at NC node locations Cascadia Basin, Clayoquot Slope and our planned future node at Middle Valley.
During the Juan de Fuca Hydrogeology Expedition 327 (July 5–September 5) in the mid-plate area near our Cascadia Basin node location, two new CORKs were installed in boreholes drilled about 360, and 530 meters deep into the ocean floor. In addition to scientific instruments that measure pressures and temperatures, these CORKs are equipped with fluid samplers that collect pore water samples from the sediment covered oceanic crust. These samples will be recovered in the future and analyzed by geochemists and marine microbiologists. In September 2009, the CORK installed in ODP borehole 1026B was connected to NEPTUNE. It is the first CORK observatory with real-time access to its temperature and pressure data. The 1027 area near the centre of the Juan de Fuca Plate is important for several of Ocean Networks Canada’s research projects, including Ocean Crustal Hydrogeology, Seismograph Networkand the West Coast “Tsunami-meter”.
Advanced CORK Installation
After a 3-day port call with celebrations, ship tours and a short lecture series, the JOIDES Resolution embarked on expedition 328 (Cascadia ACORK; September 9-19) led by Earl Davis (Pacific Geoscience Center) to install a new Advanced CORK observatory (ACORK 1364) in the Cascadia subduction zone, 75 km off the coast of Vancouver Island. This ACORK will help scientists monitor changes in pressure associated with this seismically active setting, and better understand how gas hydrates form. Earl Davis is the Principal Investigator for the Ocean Crustal Hydrogeologyresearch project. Also joining the expedition was Martin Heesemann, Ocean Networks Canada staff scientist for Plate Tectonics and Earthquake Dynamics. In 2011, the new ACORK will be connected to our network, which will provide power and real-time data collection over the coming decades.
ACORK 1364, which extends 300 m into the seafloor, is equipped with five pressure gauges, which monitor fluid pressures at the seafloor and in the sediments 155, 205, 245 and 295 meters below the seafloor. The pressure gauges, located on the CORK head above the seafloor, are connected by hydraulic tubes to external screened sections. These screens allow pressure fluctuations within the pore fluid of the sediments to be transmitted to the pressure gauges, while keeping the mud out. If a seismic event causes compression of the sediments beneath the seafloor, the fluid pressure rises in the sediment pore spaces surrounding the CORK. This pressure increase is felt not only in the surrounding sediment, but also passes through the screens and into the hydraulic tubes. These changes are then measured by pressure sensors attached to the top of each tube in the instrument bay section of the ACORK head.
The ACORK casing itself is empty down to a seal at the bottom. This will allow it to be instrumented with a variety of devices in the future, depending on the needs and interests of scientists trying to understand tectonic processes and crustal hydrogeology in this area.