Eruption Processes Associated with the 2005-06 Volcanic Episode at the East Pacific Rise ISS

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Intellectual merit: This project involves the analysis of a dataset acquired from the East Pacific Rise (EPR) between 9 46'N and 9 56'N that will include: 37 TowCam deployments with over 150,000 seafloor images, 2 m/pixel DSL120a sidescan sonar and 10 m/pixel SM2000 bathymetry over the site of a new volcanic eruption, and a number of Alvin and Jason2 deployments that provide near-bottom observations and samples, all of which will have been collected within one year of that recent eruption. A number of questions related to eruption processes will be examined: . What is the size of the 2005-06 eruptions relative to estimates of previously studied mid-ocean ridge eruptive events? The conservatively estimated, preliminary volume of the 2005-06 eruption (~22 million cubic meters) is four to five times greater than that inferred for an eruption at that site in 1991-92, and places it among the upper one-third of documented eruptions on intermediate- to superfast-spreading mid-ocean ridges. Still, we have only a limited understanding of whether this eruption was of a typical or large size for this portion of the EPR. Using the plan-view pattern of volcanic deposits on the crestal plateau as a guide, it is hypothesized that this eruption was large for this portion of the EPR and, in places, paved over multiple generations of previous eruptions. The current project will investigate the mechanisms of lava transport for the 2005-2006 eruptions that can be used to infer eruptive histories for the EPR ISS. . What controls the along- and across-axis distribution of lava of the 2005-06 eruptions? The boundaries of the 2005-06 lava flows are considerably more complex than any previous representations of MOR eruptions. It is hypothesized that the sequence of flow lobes along the ridge axis relate directly to the location of active fissure segments. Once lava is erupted from fissures in the floor of the AST, flow paths across the crestal plateau might have been controlled by pre-existing seafloor topography, especially lava channels, which focused flow and impacted the distance to which the flows traveled. . How does the off-axis fissure eruption fit into current paradigms regarding the fine-scale segmentation of the ridge axis and its relation to melt bodies in the crust? A unique aspect of this most recent EPR volcanic phase is the eruption of lava from a discontinuous series of fissures located ~600 m east of the ridge axis on a narrow mound-like feature that extends between 9 52'-56'N. The fissure mound coincides with a fourth-order discontinuity in the ridge axis, and is located just inboard of the first significant inward facing normal fault east of the AST. It appears that there was ~coeval activity along this fissure mound and the adjacent EPR axis. A detailed map defining the extent of the off-axis fissure ridge will be constructed, and models will be explored to explain the relationship between the fault, off-axis fissure mound, ridge axis, and axial magma chamber for this predicted, but never before observed, phenomenon. Broader impacts: The proposed work will provide a critical context for understanding the seismic and hydrothermal signals that presaged the eruption, and the ongoing examination of how the ridge crest hydrothermal and biological processes respond to this most recent eruptive event. Detailed mapping of the eruption deposits will provide a baseline that will be crucial to interpreting a wide range of hydrothermal, biological, geochemical, and seismic processes being investigated by the EPR ISS community. The results of this work will be made broadly available through web-served GIS database that was created by the PI for the N. EPR. The project will partially support the PhD research of a MIT/WHOI joint program graduate student.