October 11- October 17, 2003
October 14, 2003
David Clague writes:
After the late end to yesterday’s dive, we started up a few hours later than usual so everyone could get some sleep. By 8:30 we were diving on a large cone on the south flank of Rodriguez Seamount. This volcanic cone is one of the largest cones known on any seamount with a volume of 2.6 cubic kilometers, and a height of more than 500 meters. The long-lived eruption that constructed this cone lasted at least several decades at a reasonable eruption rate, and perhaps two or three times as long since the lava is thick and pasty and most likely erupted at rates well lower than Hawaiian volcanoes. The cone consisted entirely of explosive eruption deposits, with blocks of lava enclosed in volcanic sandstone. The dive continued to the north and explored a second cone. This cone was constructed of pillow lava—the first we have seen on Rodriguez. A third cone once again consisted of fine-grained explosive eruption deposits. We have been studying the deposits from submarine explosive eruptions for several years, so these deposits will expand our knowledge of the lava compositions and physical conditions required for explosive eruptive behavior. We collected 25 rock samples and nearly as many animal samples during this dive, which kept us busy in the lab for several hours labeling, describing, preserving, and archiving samples. Most of the geological results from this dive will be forthcoming when we have a chance to study the samples under the microscope and chemically analyze the rocks. The chemistry will tell us a lot about how, where, and when Rodriguez Seamount lava formed and how it erupted. After the dive was completed and while the science party was working on the recovered samples, the ship did a small survey around an acoustic beacon to evaluate the navigation system used to track the remote vehicle Tiburon on the bottom. In general, we determine where the ship is located using GPS (Global Positioning System) and then determine where the vehicle is relative to the ship using an acoustic system mounted on the ship. Both locations are plotted in real time on base-maps of high-resolution bathymetry so the scientists know where the vehicle is observing and collecting samples in reel time. The data collected will be analyzed when the ship returns to home port to determine if adjustments are required to the system.
We will dive on additional volcanic cones tomorrow to evaluate the uniformity or variability of lavas compositions and eruption products on Rodriguez. The weather, after such a difficult start, has been improving each day and today the seas were calm and the winds were light. It was the first day when the sea was not speckled with whitecaps, for which we are all grateful.