PDS_VERSION_ID        = PDS3
RECORD_TYPE           = STREAM

OBJECT                = TEXT
  PUBLICATION_DATE    = 2009-11-15
  NOTE                = "Geologic setting description"
END_OBJECT            = TEXT
END

Lanai Lookout, Koko Crater

Koolau volcano on the island of Oahu, experienced most of its volcanic
activity between 2.9 and 2.1 Ma. Much younger (0.8-0.06 Ma) alkalic basalts of
the Hawaiian Volcanics top the older theoliitic deposits, and the chemical
signature of these younger lavas suggests that they have a slightly different
source than the older deposits. There is, however, no typical alkalic cap on
Koolau. Koolau has been fiercely eroded, and more than half of the original
mountain has collapsed and is now on the ocean floor. Koko Crater is a cinder
cone that was formed during one of the later eruptions of Koolau. It is
estimated to be about 24,000 years old. Most of the material in Koko crater is
glassy, palagonite ash that was originally of basaltic composition, although
it has been altered by weathering, and the palagonite itself is an alteration
product of basaltic glass. Tantalaus Ash is a tephra deposit of glassy,
angular basaltic scoria associated with Koolau volcano. Formation of the
non-accretionary lapilli may have been due to rounding in a highly turbulent
fountaining regime, or fragmentation within the neck, as in a strombolian
eruption (that is, the fragmentation front moves within the neck over time).

References: 
Fekiacova, Z., Abouchami, W., Galer, S.J.G., Garcia, M.O., and Hofmann, A.W.,
2007. Origin and temporal evolution of Ko'olau volcano, Hawai'i: inferences
from isotope data on the Ko'olau Scientific Drilling Project (KSDP), the
Honolulu Volcanics and ODP Site 843, Earth Planet. Sci. Lett. 261, 65-83.

Allen, C.C., Gooding, J.L., Jercinovic, M., Keil, K., 1981. Altered basaltic
glass: A terrestrial analog to the soil of Mars. Icarus 45, 347-369.