2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 12
Presentation Time: 11:40 AM


MALAHOFF, Alexander, Oceanography/HURL/SOEST, University of Hawaii at Manoa, 1000 Pope Road, MSB 319, Honolulu, HI 96822, GREGORY, Todd S., BOSSUYT, Arnaud, DONACHIE, Stuart, HOU, Shaobin and ALAM, Maqsudul, malahoff@hawaii.edu

Loihi submarine volcano is a hot spot volcano located at a water depth of 990 m, 34 km south of the Island of Hawaii, constructed through volcanism along a summit rift that terminates at the southern end at a water depth of 5,500 m. Hydrothermal activity & the presence of microbial mats at numerous vents mark the summit & upper portions of the south rift of Loihi. An intense period of earthquake activity ever recorded beneath Loihi took place between July 16 & August 10, 1996 with up to 140 earthquakes per day & magnitudes of up to 4.5. Visual observations of the Loihi summit using the submersible Pisces V after the earthquakes showed a fractured, faulted terrain covered by talus & the complete disappearance of a 300-meter high hydrothermally active summit cone into a newly formed 300-meter deep, 1,000-meter-wide pit crater. The pit crater formation resulted from the collapse of about 150 x 106 cubic meters, or about 380 x 106 tons of rock into the volcano. The now exposed dike system was observed to be hydrothermally altered with sufficient heat remaining to generate new vigorous vent systems at the base of the dike system on the floor of the newly-formed pit crater at a water depth of 1,300 m, as well as along the rim of the crater at a depth of 1,000 m. The collapse of the summit led to the formation of a westerly-directed hydrothermal plume emanating from Pele’s Pit & a series of hydrothermal vents with temperatures up to 160°C & extensive bacterial mats. In order to sample & maintain microbial vent assemblages at their ambient pressure & temperature, we fabricated a “seamless” total system comprised of submersible-mounted samplers, a helium-activated sample transfer system & a battery of one-liter Teflon-lined stainless steel bioreactors. The bioreactors have successfully maintained ambient temperature & pressure of the hydrothermal vent fluids collected from hydrothermal vents in the pit crater. The bioreactors can sustain pressures to 150 atm & temperatures over 165°C. The system was deployed during October 2001 Pisces V submersible operations on Pele’s Pit during which the maximum vent water temperature measured was 90°C. Analysis of the hydrothermal fluids showed the presence of a diverse vent community.