Leg 2A-3 (Hana ridge and Kohara area)

K213: Kohala landslide (T. Kanamatsu)
 Sept. 10, 2001

Purpose of Dive K213
Smith et al., (2001) interpreted SeaBeam bathymetry of detail morphological structures on the northeast flank of Hawaii Island as indicating that debris of the Pololu landslide overlaps the newly identified benches of the newly identified Laupahoehoe slumps, all derived from Kohala volcano. The NW-SE striking benches the of Laupahoehoe slumps are at water depths of 3000 -5000 m. Basins on the bench are incompletely filled by sediment. The structure of the benches is considered to be analogous to the Hilina slump.
To determine the internal structure and rock types of the deep Laupahoehoe, bench dive 213 was planed to observe a rib on the lowest bench. The structure and lithology of the bench will be compared to that of the well-documented Hilina slump, on the south flank of Hawaii Island, to understand the formation processes of submarine benches on Hawaiian volcanoes. The dive observations and samples also may provide information on the early growth of Kohala volcano.

Dive Results
We landed in a water depth of 4471 m, at the foot of one of ridges of the lower bench, sloping to northeast. The dive climbed up the ridge, collected samples, and left the bottom at a depth 3315 m, at the end of the slope.
Two dominant lithology, were identified: lower of olivine-picritic basalt, and upper fine-grain volcanic breccia. The olivine-rich basalt is mainly characterized by small and irregular jointed exposures, but outcrops at 4050-4045 m depth, probably have flat and columnar-jointing surfaces, This suggests that the olivine-rich basalt is originated as lava sheet flows.
Most occurrences of the upper fine-grain volcaniclastics were seen as talus deposits, with matrix of brown mud. Some sedimentary structures were observed in the volcanic breccias. The contact between the two lithologies is unclear. The volcaniclastic breccia include angular clasts, in a matrix of very coarse sand to granule size. Most collected volcaniclastic basalt clasts were severely weathered concentrically.

Video highlight
11:35 - 11:38: angular jointed outcrop (sheet ?)
11:50-11:53: surface of sheet lava
11:57-59: jointed surface of sheet lava
13:43-45: cliff of talus deposits of volcanic breccia with matrix of soft sediments
13:48-13:50: out crop of volcanic breccia
Dive log
time depth (m) altitude (m) heading (degree) Narrative Sample
9:25 4338 300 191 kaiko detaches from launcher
9:35 4471 2.4 216 touch down on bottom - mud covered
9:37 4466 0.6 215 small rock chips on muddy surface
9:42 4464 2.4 222 approach small downward slope
9:43 4467 0 233 red pushcore in muddy sediments PC 1
9:47 4467 0.7 219 reflector straight ahead on sonar, 100 m ahead
9:50 4470 0.7 222 still on slight downslope
9:58 4468 2.5 219 climbing again - still all mud
10:01 4467 1.8 219 entering zone of increased reflectivity but no outcrop or even talus
10:05 4464 2.5 223 a rock! Mn coated
10:07 4461 3.3 219 more rocks, slightly platy, scattered in small area in mud
10:09 4461 1 221 sampling from small group of rocks. Very cemented. Sample #1a in box 2. Sample #1b in box 2 1a, 1b
10:11 4457 1.8 220 more and more scattered rocks
10:13 4448 1.9 219 bigger angular blocks sitting in mud
10:16 4421 2.5 231 sediment covered talus field
10:17 4414 230 steep outcrop - breccia? Lots of large angular blocks. May also be fractured, jointed sandstone. Lots of Mn coating
10:19 4414 2.1 232 sampling of same outcrop. Sample #2a put in box 3. 2a
10:22 4414 2.1 229 sample 2b in box 3. Sample 2c put in box 3. 2b, 2c
10:25 4399 3.6 218 moving up same outcrop, becomes less steep
10:27 4385 240 still in sediment covered outcrop
10:30 4355 220 muddy slope with scattered outcrop/talus
10:31 4342 208 steep outcrop - breccia? Less regularly jointed than last outcrop
10:33 4342 2.3 203 sampling outcrop. Lots of MnO. Could not sample
10:38 4340 3.1 203 trying again to sample. Sample #3a in box 4. Sample #3b in box 4. 3a, 3b
10:41 4328 4.1 229 moving up massive fractured outcrop
10:43 4298 219 less steep, still many outcrops
10:43 4293 219 cover sediment, lose outcrop
10:46 4275 1.6 222 muddy bottom, no rocks
10:50 4260 220 muddy bottom, no rocks
10:55 4240 221 muddy bottom, no rocks
11:00 4229 218 muddy bottom, no rocks
11:05 4207 1.6 220 muddy bottom, no rocks
11:10 4196 2 220 muddy bottom, no rocks
11:15 4183 219 muddy bottom, no rocks
11:16 4180 4.2 217 small isolated outcrop, similar to those below, maybe more irregular jointing/fracture patterns
11:17 4180 1.4 257 Sample #4a in box 5. Sample #4b in box 5 4a, 4b
11:20 4174 219 muddy bottom, no rocks
11:26 4143 1.2 219 muddy bottom, no rocks
11:27 4137 2.5 238 small rubbly outcrop/talus
11:30 4131 3.2 263 slightly bigger outcrop, same type of jointed/fractured rock
11:32 4133 313 sample #5 in box 6. 5
11:33 4125 3.3 237 more outcrop on left side of small ridge (to the right of kaiko)
11:35 4121 304 nice jointing. Sample #6 in box 7. 6
11:37 4115 1.7 286 still in big outcrop
11:38 4115 2.3 221 on top of small ridge - mud covered
11:39 4112 1.5 225 gravel and mud covered bench. Less mud than other areas may be the top of in-place rock
11:44 4086 2.2 220 mud with scattered blocks
11:45 4080 1.6 219 gravel and mud
11:47 4067 1.6 222 base of steeper slope, increasing rocks, on talus apron?
11:50 4050 2 272 Mn coated mantle sediment? No, it is hard - sheet flow maybe? Flat expansive outcrop
11:53 4050 1.4 257 sampling attempt at edge of outcrop. Sample #7 in box 8. 7
11:57 4044 3.3 222 outcrop rises up in small dome
11:59 4045 0.4 164 sampling attempt. Sample #8 in box 8. 8
12:00 4044 164 top of outcrop shows columnar jointing
12:01 4032 1.7 222 gravel and mud
12:03 4015 5.4 203 outcrop of breccias, steep
12:04 3990 4.6 199 out crop continues, breccias of outcrop covered by sediment
12:05 3975 2.5 192 sampling attempt at the end of outcrop sample#9a,b in box 9. 9a, 9b
12:08 3960 2.3 210 swarms of breccias at the right-hand side
12:09 3950 2.4 210 mud bottom with rock chips
12:10 3936 1.6 204 large breccias appears then mud bottom with rock chips
12:12 3912 1.8 202 large breccias accompanied with broken parts of it
12:14 3891 3.5 200 swarms of gravels on mud bottom
12:15 3880 1.5 202 rock fragments disappeared, reflection appear straight ahead on sonar
12:18 3869 1.6 199 mud bottom with rock chips
12:20 3860 3.3 201 proportion of rock chips increases
12:22 3861 0.9 197 going over mud bottom with rock chips whose proportion is sample as 12:20
12:23 3858 1.2 201 small domes of rock blocks
12:26 3845 3.1 192 blocks of rocks (talus ?) , Sample #10 in box2 10
12:29 3834 1.8 202 several benches of breccias (downward right-hand side)
12:32 3820 1.3 201 rock chips on mud bottom
12:33 3818 1.2 200 high reflection straight ahead on sonar
12:36 3808 1.9 200 going over mud bottom with rock chips
12:38 3799 2.5 201 large block of lava (?), sample #11 in box7 11
12:41 3791 5.3 200 steep outcrop of breccias
12:44 3766 2 203 proportion of rock decreases, then next outcrop appears, small dome
12:46 3757 1.4 231 sample from the dome, Sample#12a, b, c, d, e in box1 12 a, 12b, 12c, 12d
12:53 3753 1.8 205 mud bottom with rock chips
12:54 3730 2 210 mud bottom with rock chips
12:57 3717 2.1 212 fan shape high reflection on sonar (rock chips on bottom?), the slope turns downward for left side
12:59 3707 1.9 211 reflection on sonar left- side ahead
13:01 3700 1.9 209 going over mud bottom with gravels
13:03 3691 2.6 211 outcrops showing relative rounded surface, cross section of pillow? sample#13 in box6 13
13:10 3677 1.6 208 leave from the outcrop, mud bottom with rock chips and gravels
13:12 3650 3.7 211 outcrop of talus blocks, passing over, go over the small ridge
13:15 3624 1.8 208 mud bottom with rock chips
13:18 3612 3.3 213 swarm of debris blocks
13:19 3609 2 237 soft talus deposits
13:21 3598 2.1 213 outcrop then mud with gravels
13:23 3590 1.3 210 soft talus sediment
13:24 3574 2.9 211 outcrop of broken pillow? Forming small domes
12:27 sample#14 in box3 14
13:30 3555 1.3 208 ridges of bottom going down left-hand side
13:33 3547 2.2 212 blocks of sand
13:35 3544 1.6 211 bedding is observed in the blocks
13:38 3538 1.5 192 block of volcaniclasitic conglomerate, sample a breccia #15 in box4 15
13:41 3535 2.1 209 field of block of sedimentary rocks
13:43 3512 3.6 210 canyon going down right hand side, then steep outcrop appears
13:45 3511 2.7 202 outcrop of volcaniclastics, pushcore (yellow) PC 2
13:49 3466 2.5 209 continue very steep outcrop, alternating of volcaniclastic and pillow breccia
13:52 3443 1.4 205 end of outcrop, dome of pillow, sample #16 in box5 16
13:54 3431 3.1 209 bench of sedimentary rock, pushcore (green) PC 3
13:58 3425 2.6 214 going on mud bottom
14:00 3399 3 189 thin sheet of old sediments
14:02 3391 0.8 214 going over mud with ripple marks
14:04 3390 2.7 221 high reflection straight ahead on sonar
14:06 3391 2.7 220 going over mud with ripple marks
14:08 3390 0.8 220 large block on mud bottom
14:11 3377 1.8 211 shin sheet structure on bottom
14:16 3367 2.2 209 shin bench on bottom
14:20 3346 1.4 190 going over mud bottom
14:22 3340 1.2 194 ridges on bottom, behind them rocks blocks appear
Sampling attempt, sample #17 in box 9 17
14:32 3330 1.1 222 going on mud bottom
14:34 3320 0.5 212 pushcore (blue) PC 4
14:35 3315 leave the bottom

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