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:
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
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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This page created and maintained by Ken Rubin,© krubin@soest.hawaii.edu
Last page update on 8 Oct. 1996
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