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International Research
big pillows. The thickness of the sedimentary layers is estimated
to be ~0.5-2 m from the sub-bottom profiler measurement.
The thickest sedimentary layers among our dives are observed
in this portion.
The submersible climbed a very steep slope of 60-70° of the
hummocky ridge of elongate and knobby pillows directing
downslope with a thin sedimentary carapace. The summit of
the hummocky ridge is cut by faults running NNE and NNW,
which expose truncated pillow lobes.
3.3 Dive #1090
The dive traversed the western flank of the valley ~3 miles
north of #1088 (Fig. 2). The submersible landed on a small
ridge with large pillows and lava tubes, with diameters ~1.5 m,
which is covered by thick sediment of ~0.5 m. N-S trending
fissures having sharp edges suggesting very fresh crack surfaces
are developed. We found a large depression along the ridge,
formed when basement collapses or subsides due to tectonic
movement, with its floor covered with sediments.
The western lava flow plain with greater than 500-m in width
is associated with a thick sediment blanket consistent with low
backscattering intensity of the sidescan sonar image. The area
has a series of ridges and valleys with several meters high undulation.
Direction of these ridges and valleys are NNW-SSE.
Some fissures are trending N-S, with width ~5 m and depth
greater than 10 m. They look fresh because cut sections of pillows
and lava tubes are exposed on the sharp fissure walls. The
N-S fissures cut the NNW-SSE trending structures and are
17 04'N
(a)
#1090
(b)
#1090
-3800
-3700
WF
SR
-3700
-3600
17 02'N
-3600
-3600
Eastern Margin
-3400
Bumpy
#1089
-3400
#1089
Western Margin
17 00'N
Smooth Surface
#1088
-3500
#1088
WF
-3400
SR
-3400
VC
-3500
144 48'E 144 50'E 144 52'E
144 48'E 144 50'E 144 52'E
Figure 2: (above) (a) Sidescan sonar
backscattering image of the median valley
in the 17°N segment center (data from
Asada et al., 2007). Light color shows high
backscattering intensity. (b) Bathymetric
map with 20-m contours. Red, blue, and
yellow lines show Shinkai 6500 dive tracks
#1088, #1089, and #1090, respectively.
Symbols on the dive tracks point to sampling
sites. SR: small ridge, WF: western
flank, VC: volcano complex.
(a)
(c)
(b)
(d)
Fujiwara et al. Figure 2
Figure 3: (right) Photos of lava flow
morphology taken during Shinkai 6500
dive #1088. (a) Jumbled lava flows near the
landing point. (b) Pillow lavas on the small
ridge. (c) Folded sheet lavas on the western
flank of median valley. (d) Pahoehoelike
lavas on the western flank of median
valley.
InterRidge News 26 Vol. 17, 2008