Monterey Bay Aquarium Research Institute

Gorda Ridge Cruise
August 5 - 21, 2002

August 13, 2000: Day #9

Dave Clague writes: Dive 194 was our first dive in the Escanaba Trough area. The dive was planned to map the vents and extent of a lava flow erupted near the western edge of the northernmost Escanaba Trough that was identified by high backscatter in both Simrad and AMS-60 side-scan data.

We began the dive near the edge of the flow, but landed in mud. After crossing what we thought would be the young lava flow, but where all we saw was a mud-covered bottom, we concluded that the flow was shallowly buried beneath sediments and that we were unlikely to be able to do any work on it with Tiburon.

We modified the dive plan and drove about 1 kilometer to the western valley wall to do a transect up the scarp. The scarp consists of sandstones and siltstones about halfway up from the bottom, with lava fragments as talus and finally as a flow sequence at the top of the nearly 700-m scarp. Many of the siltstone outcrops were near vertical and fractured so that they resembled dikes or pseudo-columnar jointing in thick flows or sills. The stratigraphy exposed in the scarp is similar to that within parts of the present-day Escanaba Trough, with thick turbidites from the continental margin overlain by surficial lava flows. Considering that these sedimentary rocks are younger than about one million years old, they are remarkably lithified. We collected about 10 sedimentary and 5 volcanic rocks, as well as rock chips in 5 pushcores. We also collected some non-vent fauna including a large sponge, a flytrap anemone, and the disc-shaped tunicate.

Monday's dive will be located at the Northern Escanaba hydrothermal site where the Ocean Drilling Program drilled a series of holes. Objectives are to collect water and temperatures of the fluids, vent fauna, and to map the hydrothermal deposits at these vents.

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