2-9. Hualalai Volcano [J. Hammer]
Successful interpretation of the stratigraphic, structural, and
petrologic complexities of the North Kona terrain on the flank of Hualalai has
critical implications for understanding the primary depositional growth of the
submarine flanks of oceanic volcanic islands, structural evolution of Hualalai,
and development of large slumps elsewhere in the Hawaiian chain. New data on the will closely interface with the
abundant existing data and several in-progress studies on Hawaiian volcanoes
and with ongoing slope-stability and petrologic studies in Hawaii. Thorough study of the geologically
young, but seemingly inactive North Kona area should perrnit instructive
comparisons with the new dive data on geometrically similar slump and
compressional structures at Hilina (Kilauea volcano), South Kona (Mauna Loa),
Laupahoehoe
(Kohala), and Waianae (Oahu) .
The lithologic sequence of lavas and volcaniclastic rocks on the
mid-slope benches, if studied in detail, may provide critical information on
(1) the early growth of Hualalai, (2) frequency of large submarine slumps from
another active Hawaiian volcano, (3) further information on the relative role
of extensional slumping versus distal compression and uplift in generating the
submarine benches on the offshore flanks of several Hawaiian volcanoes, and (4)
any possible involvement of rocks from Mauna Loa volcano.
Studies on the west (Mauna Loa-Hualalai) side of Hawaii Island,
where there are multiple young landslide features (especially South Kona.
Alika, and North Kona), provide an opportunity to compare and contrast with the
existing detailed Hilina and Nu'uanu results. The North Kona bench complex
(Fig. 2-9-1), first recognized by the USGS GLORIA side-scan surveys (Lipman et
al., 1988) and then in more detail from SeaBeam bathymetry (Chadwick et al.,
1993) involves multiple geometrically-intricate proximal mid-slope benches and
basins, and a distal region containing scattered small blocks and hummocks (up
to 1 km across and 100 m high). In contrast to the Hilina slump, no extensional
block fault structures are preserved on land; any such faults originally
present may have been completely buried on the steep slopes draped by young
lavas between the northwest rift zone of Hualalai and the Kealakekua fault that
roughly coincides with the northem extent of lavas from Mauna Loa.
The North Kona benches may be related to Hualalai volcano: in
addition to the well defined northwest rift zone that was active during the
tholeiitic shield stage of this volcano, a south rift zone has been traced
10-15 km south of the Kealakekua fault by on-land gravity data (Kauahikaua and
Hildenbrand, 2000), indicating that Hualalai extends well to the south of its
present surface exposures (which are overlapped by Mauna Loa lavas just north
of the Kealakekua fault. Because tholeiitic volcanism ceased at Hualalai at
>100 ka, it seems unlikely that lavas from Mauna Loa will interfinger at
deep ocean depths of the lower North Kona benches. Although Hualalai has been
in the post-shield alkalic stage for > 100,000 years, it continues to erupt
on average every few hundred years (most recently in 1801) and is among the
potentially most hazardous of Hawaiian volcanoes because of the substantial
population living on its slopes and the likely high flow velocities likely from
its low-viscosity alkalic lavas.
The deeper parts of several of them provide exceptional places to
search for lavas that may extend our view of Hualalai magmatism back in time.
This would provide new views on the evolution of the Hawaiian plume. Evidence
may also be obtained on the relative proportions of pillow lava vs
hyaloclastite involved in construction of the submarine flanks of large oceanic-island
volcanoes, a current topic of controversy.
Year 2002 dive targets:
(1) Midslope Bench
Dives in the North Kona region will complement two 2001 Kaiko
dives (K218 and K219 to the north and south, respectively) to the lower and
mid-slope benches on the submarine flank of Hualalai, bringing the coverage of
this region closer to that already accomplished for other Hawaiian volcanic
flank regions. One objective is to
sample a the northern extension of a the bench investigated in the Kaiko dives.
Are the lithologic units
continuous along the length of the
bench? Samples collected near the
Hualalai submarine rift zone will augment the growing collection of Hualalai’s
shield-stage volcanicsm.
(2) Alika Slide
The Alika slide deposit west of Mauna Loa is an obvious feature in
large scale (1: 4x106) bathymetry maps. It is inferred to have formed about 105 ka and may be the
youngest of the large landslides around the Hawaiian Islands. Samples will be analyzed to determine
the lithologies of materials involved in the slide, test the hypothesis that
these materials were shed from Hualalai.
One idea proposed in 2001 and yet untested for
the North Kona region is that large blocks such as this one are exceptional places to search for lavas that may extend our
view of Hawaiian magmatism back in time. This could provide new evidence
pertaining to the evolution of the Hawaiian plume.
(2) ?Slide deposit?
An
arcuate block directly down slope from and 0.44 km to the west of the summit of
Hualalai is similar in morphology to blocks in the Hilina and Laupahoehoe
slumps, which are derived from Kilauea/Loihi/Mauna Loa and Kohala volcanos,
respectively. Observations and
samples of this block will be used to determine weather this material is
derived from a slump, landslide, or volcano-spreading, and whether the material
originated at Hualalai or Mauna Loa. Evidence will be gathered on the
relative proportions of pillow lava and hyaloclastite involved in construction
of the submarine flanks of large oceanic-island volcanoes, a current topic of
controversy.
Work plan:
We will use submersible visual/video data to interpret the structure of the North Kona bench and more distal slide blocks, and their relation to volcano spreading along a basal detachrnent. Samples will be analyzed chemically and petrographically in order to determine compositions and eruption depths of pillow lavas and the fragments in volcaniclastic rocks. Analytical methods will include major and minor elements for bulk-rock samples by XRF and INAA methods, glass compositions by electron-probe, and ion-probe analysis, and volatile contents by FTIR measurement. Results could also permit informative comparisons on the subaerial-submarine, and tholeiitic alkalic transitions, especially with the detailed data emerging from the Hawaii Scientific Drilling Project for Mauna Kea.