East Pacific Rise — Current Experiment Coordination — Responses [ISS]


1. PI-Project Information

Name: Marie-Helene Cormier, Spahr Webb, & Roger Buck
Institution: University of Misssouri – Columbia
Email address: CormierM@missouri.edu
Project Title: Testing Models of Magma Movement Along the East Pacific Rise Using Combined Geodetic and Numerical Experiment
NSF-OCE number: 0426575
Upcoming cruise ID and dates: R/V Atlantis, February 13-March 19 2007

2. Planned Sampling Requirements

  • 2.1. Types of Samples:
  • None. However, for a NSF-funded educational project, we may consider collecting one or two dredge samples. To avoid any problems with existing instrumentation at the seafloor, dredging would be conducted well away from the bulls eye area, and after careful examination of the sites where instruments have been deployed. In that respect, we are open to collecting samples during the leg for other scientists, if this did not require much more than a few hours (water column samples, etc.)

  • 2.2. Type of Sample Locality:
  • IF carrying out some dredging, location would be close to axis but in areas that would complement existing sample collections (away from bulls eye).

  • 2.3. Seafloor Collection Devices to be Used:
  • N/A

  • 2.4. Seafloor Experiments to be Deployed:
  • 20 Bottom Pressure Sensors (BPR) will be deployed by free falling, spaced about equally along the ridge axis from the Clipperton transform fault to the 9N OSC. The BPRs will be left at the seafloor for about 3-4 years (depending on ship scheduling). Our strategy is to deploy at least 2 BPRs for each "4th order ridge segment", and make sure that we will catch any eruption that might take place over the next 4 years between Clipperton and the OSC. That means that the BPRs will be deployed every 5 to 4 km along-axis.

    We are however considering a modification to that experiment: we may deploy a few BPR across-axis in the bulls eye area to sample vertical deformation related to magma movement in the across dimension.

    The BPR will be recovered with acoustic release system. The frequencies will be carefully selected with respect to other instruments already deployed nearby.

3. Planned Duration of Seafloor Experiments:

The bottom pressure sensors will be recovered about 3 years after their deployment, depending on ship scheduling (in 2009 or 2010). Ideally, we would be able to recover them after 1 or 2 years to check their proper functioning and to check whether they detected any eruption; however, we do not have (yet?) funding for doing this.

4. Constraints on Your Deployment Plans:

  • 4.1. Will vehicle operations be allowable in your experiment area? If so, with what restrictions for sampling or imaging (e.g., non-invasive observations or mapping).
  • Yes, there should not be any problem with vehicle operation. Note however, that BPRs will be about 3 meters high and include 3 glass spheres in their design.

  • 4.2. What is the proximity (meters distant) from your experiment(s) that future sampling can be done.
  • The BPR are designed with glass flotation spheres, so should not be touched by sampling vehicles. Dredging or rock coring operations should be avoided within ~100m from their deployment site. Other than that, there should not be any restriction to sampling in their vicinity.

  • 4.3. What is the proximity (meters distant) to which other in-situ instrument deployments can be made.
  • If deployed with video control, other instruments can be deployed very close (as close as 5 meters). However, the BPRs should not be moved, as they are designed to detect minute vertical motion of the seafloor (cm-scale), which we will interpret in terms of subsurface magma movement.

  • 4.4. Will you be using acoustic devices or moorings?
  • The total height of the BPRs will be about 3 meters, using a tripod concept. They will include 3 glass flotation spheres, and will be recovered with an Edgetech acoustic release. We do not anticipate any problem with the accidental release of the BPRs or other nearby instruments (safeguards are built in the Edgetech design).

  • 4.4. Are you looking for other experiments that can be co-located with your experiments?
  • Not specifically. However, any video images of the instruments in-situ on the seafloor would be very welcome, as a ground-truth for their geological context and proper position. Should we detect any eruption or magma movement with the BPRs, it might justify deployment of other experiments.

  • 4.5. Does your experiment require site protection? To what level of tolerance?
  • No

5. Other Issues?

Not for the moment.

Cormier experiment photo

The conceptual map from our proposal that shows where BPRs will be approximately deployed; the arrows mark the boundaries of the 4rth order segments from your paper [White et al., 2002].

All the BPRs will have glass floatation spheres, so we do need to select the exact deployment sites before going to sea and ensure they will not negatively impact other experiments. We are relatively flexible (+/- 1km) as to their positions in the along axis direction. However, in case of diking event, we expect that the maximum vertical displacement will occur close to the ASC; on the other hand, to ensure that the instruments would survive another eruption, they should be deployed outside the ASC. So within a few 100m from the ASC should be the right distance.

Cormier experiment photo 2

BPR measurements. TAK 13 Nov. 2006.