Woods Hole Oceanographic Institution
|When:||Friday, Nov. 18, 2011, 10:30 a.m. to 11:30 a.m.
Join us for coffee beginning at 10:00 a.m.
|Where:||Seminar Conference Room, 10100 Burnet Road, Bldg 196-ROC, Austin, Texas 78758|
|Host:||Nick Hayman, UTIG|
More than two-thirds of the Earth's volcanic output occurs in the ocean basins, much of it along the global mid-ocean ridge system. As no active mid-ocean ridge eruptions have been directly observed, our knowledge of eruption dynamics (eruption rates, flow velocities) in this environment are extremely limited. Eruption dynamics represent a primary parameter controlling length scales of volcanic deposition and provide some of the best indicators of the state (e.g., overpressure) of crustal magma storage reservoirs. Lava flow morphology provides a useful, but qualitative proxy for eruption dynamics. I will describe a novel geospeedometer for mid-ocean ridge eruptions, CO2 degassing and vesiculation, that allows me to place quantitative constraints on eruption duration and flow rates. We use ion microprobe to measure dissolved volatiles in glasses from a suite of samples collected at ~200 m intervals along a 2.5 km long flow path within the 2005-06 eruption. The range of CO2 concentrations along the flow path is nearly as large as observed in a collection of individual samples representing tens of flows along the ridge crest. Using vesicle size distribution analyses we find that the range in CO2 reflects degassing from supersaturated conditions near eruptive vents towards equilibrium at the distal end of the flow by diffusion-controlled vesicle growth. Volatile concentrations and vesicle properties are used to constrain dynamic models of degassing and provide estimates of flow duration and time/distance-dependent flow rates. In addition to CO2 degassing, this sample suite provides information on the nature of geochemical variability within mid-ocean ridge eruptions and the causal links to physical processes to volcanic emplacement.