Recent Activity at Loihi Volcano

Events during 11 Aug to 17 Aug 1996

Current Geologic Activity and Research at Loihi

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15-16 Aug 1996: A report on the first shore-based chemical anaylses on fresh lavas from loihi collected on the Event response Expedition last week (by UH Scientist Mike Garcia):
The recent expedition to investigate the cause of the seismic event at Loihi returned the freshest glass ever observed from this volcano. All previous Loihi samples have had a coating of some secondary material on the glass, produced over time by the rock having sat on the sea floor. Several of the new samples collected during the PISCES V dives last week are pristine. Initial petrographic and geochemical results (described below) support the hypothesis that these glassy lavas were produced during a recent (July 1996) eruption of Loihi.
Petrographically, these samples are weakly vesicular, olivine basalts. This is a feature that is typical of Loihi's tholeiitic basalts. Loihi also has erupted alkalic basalts in the past but they are usually aphyric and strongly vesicular. Few alkalic lavas have been erupted recently on Loihi (<5% of the surface flows; Garcia et al., 1995), suggesting that the source for Loihi lavas is drifting closer to the center of the Hawaiian hotspot rising up from a fixed location in the Earth's mantle. This reasoning is based on the fact that tholeiites are produced from higher melting temperatures in the mantle than alkalic lavas.
Three of these samples were selected for electron microprobe analysis to determine the composition of their glass rinds. This is a rapid and reliable method for examining the composition of submarine basalts. Here are the results:

Microprobe Analyses of Glasses from the Recent Loihi Seismic Event/Eruption

UNPUBLISHED DATA OF MIKE GARCIA. CONTACT HIM DIRECTLY BEFORE USING THIS DATA (garcia@soest.hawaii.edu)

Sample  SiO2  TiO2  Al2O3  FeO   MnO  MgO  CaO   Na2O  K2O  P2O5  Sum

P286-1& 48.75 2.63  13.72 11.79  0.14 6.91 12.05 2.53  0.45 0.24  99.21

P286-2  49.0  2.56  13.79 11.47  0.16 6.85 11.75 2.48  0.39 0.20  98.65

P286-3& 48.90 2.65  13.75 11.87  0.15 6.91 12.00 2.55  0.46 0.23  99.47

P286-4  48.85 2.62  13.61 11.58  0.15 7.01 12.15 2.60  0.43 0.21  99.21

P286-5  48.95 2.64  13.89 11.93  0.15 6.80 12.08 2.60  0.44 0.22  99.70
 
P286-6& 48.90 2.68  13.80 11.82  0.15 6.72 11.94 2.56  0.46 0.24  99.27

P287-1  49.10 2.62  13.79 11.89  0.16 6.87 11.95 2.52  0.40 0.20  99.50

P287-2  49.40 2.62  13.74 11.90  0.16 6.93 12.00 2.51  0.40 0.19  99.85

Tow-yo% 49.20 2.63  13.53 11.91  0.17 6.88 12.05 2.53  0.43 0.22  99.55

NOTES:
& = samples plotted in data figure
% = glass recovered from TOW-YO cast #3

To learn more about these lavas and the results of these chemical analyses mean, visit our Rock Geochemistry web page. The figure below shows how the composition of these new lavas, plotted as red symbols, compare to previously analyzed Loihi lavas

14 Aug 1996: We have a post-cruise summary on-line from the cheif scientists of the recent R/V KOK event response expedition. It is too long to post to this page, but is available on a separate document.

12-13 Aug 1996: Not much new to report, as the equipment and samples have just been completely off-loaded and the science party is recovering from a long week at sea. In the very near future, Fred Duennebier will have available a Cruise Summary, which will be posted to this site. At that time, we hope to also make available info on post-expedition analytical plans for samples collected.
Some of the rock samples that appear youngest and will therefore be analyzed for application of the 210Po-210Pb age dating technique, have already been mounted for electron microprobe analysis at UH. Major element compositions should be available within the next few days and will help us determine the range of rock compostions in the sample set.

11 Aug 1996: The R/V KOK returned to Honolulu harbor yesterday evening.

Rocks collected during the expedition were examined, described and photographed the day after the ship returned to port. Images are available for you to see in our Rock Gallery, courtesy of Kevin Johnson, who rushed them up to UH from the ship and Ken Rubin, who quickly photographed them and prepared this exhibit.

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Last page update on 8 Oct. 1996