Figure 10 [TCS]
Figure 10: 210Po-210Pb dating results from 3 eruptions on the EPR and Gorda Ridges. Ages are given as eruption windows (black bars), which represent unavoidable uncertainty in the extent of initial Po degassing. Heavy dashed lines show likely eruption intervals. Po is completely degassed upon eruption at subaerial and shallow submarine volcanoes. We are not certain this occurs at oceanic depths of 2–3 km, so we report an “eruption window” based on a conservative minimum degassing estimate and 100% degassing. The 2-month window we currently report is based on observations at 9°50'N EPR (panel a), although the still preliminary data from 10°44'N EPR (panel c) may allow us to narrow eruption window widths because 3 of 4 samples were >75% degassed of Po upon sample collection. Errors in maximum age (gray horizontal bars) refl ect data regression and analytical errors (see the eruption window inset). Sample collection dates are depicted by a --|, coinciding with cruises to those areas (vertical gray bars). Absolute and relative times are given at the base of the plot. Note the difference in error on maximum ages for Gorda samples taken in April and August 1996 (ages overlap for all samples in panel B but early sampling led to much higher resolution ages). The young lava flow image is a video frame grab from Alvin dive 3935 of the FIELD expedition (provided by Robert Zierenberg). An example ingrowth curve and the seismic record that led to the Gorda event response are also shown, tied to calendar time and sample ages.