FeMO3 Dive Cruise 2008
Report Day 10 -- Wednesday 1 October 2008 -- Exploring Loihi's North Rift
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FeMO3 Dive Cruise 2008 |
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Jason’s work day began in Pele’s pit working around the hot water vents that sponsor the growth of so many bacteria, but the second half of dive J2-368 is devoted to exploring the North Rift roughly parallel to a dead submarine cable.
The cable was used to connect an instrument package containing a seismometer, hydrophone and pressure sensor to the power grid on the Big Island. The package was nicknamed HUGO for Hawaii Undersea Geological Observatory. A receiving station collected the data coming ashore from the instruments. Unfortunately the rough lava of the North Rift damaged the insulator on the cable and the power failed only 11 days after it was put down. While it was active HUGO’s instruments were very effective at picking up the sound and shake of earthquakes as well as the sound of humpback whales. HUGO was recovered in 2002 by the Jason and the R/V Thomas G. Thompson, but the cable was left behind.
The rock samples that the biologists and geochemists are looking for must be from recently erupted lava that is still glassy. Volcanic glass (obsidian is an example) forms when the lava cools so quickly that crystals have no time to form. This glass provides a source of iron and manganese for bacteria. If the glass is very fresh it also indicates that the rock is suitable for chemical analysis. Because glass quickly weathers to clay, the presence of fresh glass means that the rock was recently erupted and not yet badly weathered by the environment. The chemicals found in the glass reflect the mineral composition of the source magma and provide an estimation of the depth of in the Earth that magma came from.
The north slope of Lo’ihi has many more animals attached to the seafloor; animals like deep water corals, sea pens and crinoids. These animals attach themselves to the seafloor as larvae and grow in place catching plankton for food. They can’t move to hunt so they must wait for the plankton to drift onto their tentacles. Their presence on the north slope indicates there is probably more food on this slope than on the south slope. This makes sense because the north slope is both closer to the Big Island (a potential source of food) and up current from the South Rift.
Shawn Doan onboard the R/V Thomas G. Thompson
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