CRUISE REPORT

Japan Agency for Marine-Earth Science and Technology

(JAMSTEC)

R/V Natsushima

Cruise NT14-22

Structural development of volcanic caldera in

Kume-jima western offshore

December 25 to 30, 2014

(Naha to Naha)

CRUISE INFORMATION

Cruise ID: NT14-22 Name of vessel: R/V NATSUSHIMA(JAMSTEC) Title of the cruise: Structural development of volcanic caldera in Kume-jima western offshore Title of proposal: Structural development of volcanic caldera in Kume-jima western offshore Cruise period: December 25 to 30, 2014 Ports of call: Naha to Naha Research area: Kume-jima western offshore Research Map is shown in Figure 3-1.

TABLE OF CONTENTS: List of cruise personnel Acknowledgements Cruise narrative and schedule of operations NT14-22 Navigation Tracks 1. Cruise objectives ·························································· 1 2. Operations and data processing information ························ 3 3. Dive results ································································· 4 4. Heat Flow meter measurements ········································ 14 5. Surface geophysical survey ·············································· 16 6. Seismic survey: processing and result of seismic reflection data 19 7. Shore-based studies ····················································· 22 8. Summary ···································································· 23 9. References ·································································· 24

LIST OF CRUISE PERSONNEL: SCIENTIFIC PERSONNEL: Yumiko Harigane

nstitute of Geology and Geoinformation, Geological Survey of Japan/AIST

Gen Shimoda Institute of Geology and Geoinformation, Geological Survey of Japan/AIST

Taichi Sato Institute of Geology and Geoinformation, Geological Survey of Japan/AIST

Hidenori Kumagai Research and Development (R&D) Center for Submarine Resources/JAMSTEC

Yuka Masaki Research and Development (R&D) Center for Submarine Resources/JAMSTEC

Toshimasa Nasu Marine TechnicianNippon Marine Enterprises, LTD.

Mitsuteru Kuno Marine TechnicianNippon Marine Enterprises, LTD.

Kyoko Tanaka Marine TechnicianNippon Marine Enterprises, LTD.

Takuya Onodera Marine TechnicianNippon Marine Enterprises, LTD.

Shore-based Scientist Osamu Ishizuka

Institute of Geology and Geoinformation, Geological Survey of Japan/AIST

Tomoyuki Sato Institute of Geology and Geoinformation, Geological Survey of Japan/AIST

Hyper Dolphin 3000 OPERATION TEAM: Tomoe Kondo, Submersible Operation Manager Katsushi Chiba, 2nd submersible Technical Officer Yosuke Chida, 2nd Submersible Technical Officer Atsushi Takenouchi, 2nd Submersible Technical Officer Takuma Onishi, 2nd Submersible Technical Officer Ryo Saigo, 2nd Submersible Technical Officer

CREW: Hiroaki Masujima, Captain Takaaki Shishikura, Chief Officer Takeshi Egashira, 2nd Officer Toshiyo Ohara, Jr. 2nd Officer Tomoaki Yukawa, 3rd Officer Tadashi Abe, Chief Engineer Naohito Tadooka, 1st Engineer Ryuzo Mikami, 2nd Engineer Takamasa Ochiai, 3rd Engineer Fukuo Suda, C/R, Chief Electronic Operator Michiyasu Katagiri, 2nd Electronic Operator Takayuki Mabara, 3rd Electronic Operator

Seiji Hosokawa, Boat Swain Hatsuo Oda, Quarter Master Yoshiaki Matsuo, Quarter Master Takuya Miyashita, Quarter Master Hideo Ito, Quarter Master Yasunobu Kawabe, Sailor Kenta Nasu, Sailor Kozo Miura, No 1. Oiler Shinya Sugi, Oiler Keita Funawatari, Oiler Shotaro Sumitomo, Assistant Oiler Daiki Satoi, Assistant Oiler Toyonori Shiraishi, Chief Steward Shinsuke Tanaka, Steward Hiroyuki Ohba, Steward Akio Suzuki, Steward Ryu Kubota, Steward

ACKNOWLEDGEMENTS

We are grateful to Captain Hiroaki Masujima and the excellent crew of the Natsushima, the Hyper Dolphin 3000 operation team manager Tomoe Kondo and the Hyper Dolphin 3000 team for their outstanding efforts to make this scientific program successful. We also thank JAMSTEC for their support of this project.

CRUISE NARRATIVE AND SCHEDULE OF OPERATIONS

2014/12/25Weather: overcast/ Wind direction: SW/ Wind force: 2/ Wave: 1 / Swell: 1 /Visibility: 8 nautical mile (12:00 JST)09:00 Let go all shore line & Left NAHA for research area. 09:30-10:10 shipboard education & training for scientists. 16:30 Arrived at research area.

XCTD. 16:41 XBT. 17:11-18:08 Towed cesium magnet meter. 17:21-17:45 Carried out eight figure running. 18:18 XBT. 18:30-18:35 Towed cesium magnet meter. 19:03-19:22 Towed cesium magnet meter. 19:37 Com’ced MBES mapping survey.

2014/12/26Weather: cloudy/ Wind direction: NNE/ Wind force: 4/ Wave: 3 / Swell: 2/Visibility: 8 nautical mile (12:00 JST)

-06:19 Finished MBES mapping survey. 08:13 Hoisted up “H.P.D.3000”.08:17 Launched “H.P.D.3000”.08:31 “H.P.D.3000” dove & com’ced her operation #1761.09:15 “H.P.D.3000” landed on the sea bottom (D=1097m).15:37 “H.P.D.3000” left the sea bottom (D=894m).16:05 Refloated “H.P.D.3000”.16:14 Hoisted up “H.P.D.3000”.16:18 Recovered “H.P.D.3000” & finished her operation.17:29-17:37 Launched cesium magnet meter.17:49-17:53 Launched GI-gun.18:01-18:11 Launched streamer cable.18:34- Com’ced SCS survey.

2014/12/27

Weather: cloudy/ Wind direction: ENE/ Wind force: 3/ Wave: 3 / Swell: 2/ Visibility: 8 nautical mile (12:00 JST)

-06:30 Finished SCS survey 06:30-06:39 Recovered GI-gun. 06:42-06:50 Recovered streamer cable. 06:46 Recovered cesium magnet meter. 08:10 Hoisted up “H.P.D.3000”. 08:14 Launched “H.P.D.3000”. 08:26 “H.P.D.3000” dove & com’ced her operation #1762. 09:31 “H.P.D.3000” landed on the sea bottom (D=1965m). 15:33 “H.P.D.3000” left the sea bottom (D=1525m). 16:14 Refloated “H.P.D.3000”. 16:26 Hoisted up “H.P.D.3000”. 16:30 Recovered “H.P.D.3000” & finished her operation. 17:31 XCTD. 17:42-17:45 Launched cesium magnet meter. 18:01­ Com’ced MBES mapping survey. 20:32-20:52 Carried out eight figure running.

2014/12/28Weather: rain/ Wind direction: West/ Wind force: 2/ Wave: 3 / Swell: 1/Visibility: 8 nautical mile (12:00 JST)

-06:31 Finished MBES mapping survey. 06:36 Recovered cesium magnet meter. 07:13-07:20 Carried out MBES mapping survey. 08:14 Hoisted up “H.P.D.3000”. 08:17 Launched “H.P.D.3000”. 08:29 “H.P.D.3000” dove & com’ced her operation #1763. 09:06 “H.P.D.3000” landed on the sea bottom (D=972m). 11:31 “H.P.D.3000” left the sea bottom (D=593m). 11:49 Refloated “H.P.D.3000”. 11:58 Hoisted up “H.P.D.3000”. 12:02 Recovered “H.P.D.3000” & finished her operation.

2014/12/29

Weather: fine but cloudy/ Wind direction: NW/ Wind force: 6/ Wave: 4 / Swell: 3/ Visibility: 8 nautical mile (12:00 JST) 13:05-13:09 Launched GI-gun. 13:12-13:17 Launched streamer cable. 13:32-18:00 SCS survey 18:00-18:05 Recovered cesium magnet meter. 18:00-18:06 Recovered streamer cable. 18:08-18:10 Recovered GI-gun.

2014/12/30 Weather: fine but cloudy/ Wind direction: NW/ Wind force: 6/ Wave: 4 / Swell: 3/ Visibility: 8 nautical mile (12:00 JST) 0:00 Left research area for NAHA

09:00 Sent out 1st shore line, arrived at NAHA,conpleted NT14-22.

1

1. Cruise objectives

The Ryukyu Arc is situated between the islands of Kyushu and Taiwan (~1200 km in the full length).

This volcanic arc is by subduction of the Philippine Sea plate beneath the Eurasia Plate along the

Ryukyu trench, and is composed of forearc islands, chains of arc volcanoes, and a back-arc rift

called Okinawa Trough. Ryukyu Arc is commonly divided into three segments (northern, central and

southern) that bounded by the Tokara Strait and the Kerama Gap, respectively (Figure 1-1; e.g.,

Konishi, 1965; Kato et al., 1982).

Sato et al. (2014) mentioned that there is no active subaerial volcano in the southwest of Iotori-shima

in the Central Ryukyu Arc, whereas the Northern Ryukyu Arc (i.e., the Tokara Islands) has active

frontal arc volcanoes (Figure 1-1). Therefore, the existence of volcanoes and volcanotectonic history

of active volcanic front in the southwestern part of the Central Ryukyu Arc are still ambiguous.

Figure 1-1. Bathymetry map of North and Central Ryukyu Arc modified from Sato et al. (2014).

This may showing the present-day volcanic front (black line), Holocene volcanoes (open triangles),

Pleistocene volcanoes (open circles), and Pliocene volcanoes (solid triangles) [Sato et al., 2014].

Contour interval is 500 m. This figure was drawn using JTOPO30 (Japan Hydrographic

Association).

2

Wide area geophysical and geological survey around the west off of Kume-Jima Island was mainly

conducted using R/V Kaiyou-maru No.7 during GK12 cruise operated by the Geological Survey of

Japan/National Institute of Advanced Industrial Science and Technology, Japan. As a result, we have

found a new submarine volcanoes and calderas on the west off of Kume-Jima Island, where located

the southwestern part of Central Ryukyu Arc. Total 36 dredge sites in this area collected the dacite

and andesite samples with pumice, hydrothermally altered rocks in each volcano.

The major objectives of the NT14-22 cruise are:

1) To define the nature of these volcanoes in the west off of Kume-Jima Island and to test our

hypotheses for what kinds of magma generation occurs during the development of these volcanoes.

2) To establish the spatial distribution of all igneous rocks on the submarine volcanoes.

3) To precisely determine the chronology of eruptive events.

4) To better understand the relationship between back-arc rifting and arc volcanism.

3

2. Operations and data processing information

Hyper Dolphin 3000 usually dove with payloads that included six rock sampling boxes

(Morinaga-box), with two thermometer (analog and digital), one Stand-Alone Heat Flow (SAHF)

probe, one vacuum water bottle and one push core (MBARI).

Data and samples from the dives were archived as customary. Half of all samples will be archived at

JAMSTEC. Brief sample descriptions and photographs are included in Chapter 4. Samples

distributed to the scientific party are also listed in Chapter 4. All of standard data products were

provided to the shipboard scientific party.

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3. Dive results

Summaries of the results of each dive with representative pictures, track maps, and dive logs are

included in the sections below. All dive locations are also shown in Figures 3-1. A comprehensive

list of sample descriptions is included in Chapter 4.

Figure 3-1. Hyper Dolphin 3000K diving four locations in the west off of Kume-jima Island during

NT14-22 cruise.

5

Table 3-1. NT14-22 Dive list.

6

Dive HPD#1761 Report

Observer: Yumiko Harigane (per.pro. Hidenori Kumagai)

Pilots: Y. Chida, T. Onishi

Technical Information:

Location: Within a caldera of Daisan-Kume Knoll, western off Kume-jima Island (Figure 3-1)

Objective: Geological observation and rock sampling of the bottom of depression and the western

slope in western off Kume-jima Island. Measurement of temperature on the surface by SAHF.

On Bottom: Off Bottom:

Time (local): 09:15 15:37

Latitude: 26°17.259’N 26°17.572’N

Longitude: 126°28.140’E 126°28.805’E

Depth (m): 1097 894

17 samples collected (16 rocks and 1 push core). 5 SAHF stations.

Purpose:

The main purpose of the dive HPD#1761 was to observe outcrop of the bottom of caldera in

Daisan-Kume Knoll at the west off of Kume-jima Island and collect the constituted rocks from these

outcrops. In GK12 cruise, pumice, hydrothermally altered rocks and sediments were recovered by

K-grab and dredge during GK12 cruise. However, there is no detail information about outcrop and

basement rock. In this dive, we expect to observe the bottom of caldera in Daisan-Kume Knoll and

obtain other kinds of volcanic rock in order to understand the variation of volcanic rocks.

Observations:

The dive began at 09:15 and 1097 mbsl (meter below seafloor level) on a flat seabed covered by

sand with gravels. During approach the bottom, visibility was very low around 20 m altitude and

below, due to suspended matters possibly from hydrothermal activity. Fistly SAHF measurement

was performed without sampling. At the retrieval of SAHF, fine white sediments spread, which

seems to be hydrothermal clay or minerals. Approx. 40 m travel, bare rocks found several

white-yellow spots scattered on top; four rocks were sampled (R01, R02, R03 and R04) and SAHF

measurement was performed again.

7

After an eight-min travel, a deed shell was found; likely to Calyptogena. Then, Vehicle headed to

waypoint #3. Less than 5min, almost at the center of the caldera, white-colored area appeared, and

then, huge chimney complex was appeared. This chimney complex seems to be developed on cracks

of seafloor or cracked mound; however, no significant emanation of fluid was recognized. Then,

vehicle resumed traveling eastward to waypoint#3. Passing a seafloor step, white shrimps were

observed (may be Shinkaia). Then, a porous white rock was sampled. One more sampling of a rock

with woody skin was failed); thin-layered platy rock and one more fragment were sampled, then.

The seafloor of the vicinity was flat and muddy. Immediately after the rock sampling, dead clam

shell found again on partly rippled seabed. At the point, SAHF measurement and push coring were

performed. A zone passing for 15 min from 12:05 (JST), white to yellow colored patch were

frequently observed on bare rocks. At 12:23, a colony of Shinkaia shrimps was found on a mound

composed of red-colored mound associating with weak shimmering and slight gas bubbling. Red

chimney fragment and one more were sampled there (R09 and R10). At 12:40, the vehicle arrived at

the foot of the small hill covered by debris, which seems to be formed later activity of post caldera

formation. On the slope, white and gray colored rocks were sampled. During up-slope of the hill,

collapsed chimneys were also found. Near the top of the hill, starfish, sponges and barnacles (?)

increased. The vehicle went down to the sandy seafloor of the bottom of caldera again. Weak ripples

were observed and visibility became worse. Within 150 m from the previous sampling point, a dead

chimney appeared again and dead white clam shells were also found near the dead chimney. At

13:40, the vehicle arrived at waypoint #8, almost the foot of the caldera wall, where the seafloor was

covered by brown colored mud. At the point SAHF measurement and sampling were performed.

Approaching to the caldera wall, abundant sponges were observed on the rocky seabed. During

caldera wall climbing, twice sampling were performed. The top of the caldera wall was covered by

dark colored sediment, occasional exposure of rounded possibly vesiculated blocks, possibly

pumices. The last SAHF measurement in this dive was performed there, and head to north to observe

seafloor. Large block having clear foliation on the surface were frequently found; they may be highly

vesicurated woody pumices

The dive ended at 15:37, in 894 mbsl after a 130 m observation of top of caldera rim.

Summary:

Dive #1761 surveyed the caldera floor and its wall of the Daisan-Kume Knoll, western off Kume

Island.

8

Dive HPD#1762 Report

Observer: Yumiko Harigane (per.pro. Hidenori Kumagai)

Pilots: T. Onishi, A. Takenouchi

Technical Information:

Location: Within a deep hole, the deepest part of these Kume-jima submarine volcanoes in the west

off of Kume-jima island (Figure 3-1)

Objective: Geological observation and rock sampling of the bottom of depression and the western

slope in western off Kume-jima Island. Measurement of temperature on the surface by SAHF.

On Bottom: Off Bottom:

Time (local): 09:31 15:33

Latitude: 26°22.022’N 26°22.434’N

Longitude: 126°14.189’E 126°14.997’E

Depth (m): 1965 1525

15 samples collected (14 rocks and 1 push core, but 2 rock lost). 3 SAHF stations.

Purpose:

The main purpose of HPD#1762 dive was to observe outcrop of the deepest part of these Kume-jima

submarine volcanoes and collect the rocks from these exposures. This area located from Daini-Kume

Knoll to ~13 km if the west. The dacite and pumice were recovered by gravity core and dredge

during GH11 and GK12 cruise (Ishizuka et al., 2012, Harigane et al., 2014). In this dive, we expect

to observe the volcanic stratigraphy in the deepest part of these Kume-jima submarine volcanoes,

while we would like to obtain other kinds of volcanic rock in order to understand the variation of

volcanic rocks.

Observations:

The dive began at 09:31 and 1965 mbsl on a foot of cliff scattered collapsed boulders on muddy

seabed. After the two rocks (pumice) sampled, the 1st SAHF measurement performed.

Then, vehicle headed toward waypoint#2. During the travel, angular to sub-angular, boulders and

gravels were scattered. After a 300 m travel, the vehicle seated again and sampled from the slope. On

the top of the dome, angular block of a few tens cm in size were piled. From such a pile, an angular

9

block was sampled. Occasionally jointed blocks were observed until the top of the domy topographic

high and downward slope. Just a tower like shape of the pile of fragments was composed of well

vesiculated consolidated volcaniclastics.

During the flying down to waypoint #4, thinly sedimented talus of rather smaller sub-angular blocks

were observed until the bottom of the crater in eastern side of the central high. On the bottom of the

crater, of 2916 mbsl, weakly rippled sandy sediment was sampled by M-BARI-type push-corer and

heat flow measurement was performed. Then resume the travel to #4. Passing through of the

midpoint to waypoint #4, seabed was changed from muddy flat one to abundant gravel scattered one.

Just after passing waypoint #4, vehicle faced to the steep cliff composed by massive flow with

several well-jointed dykes.

Some alternation of massive units and well-jointed units were continued up to 1900 mbsl. Within a

cliff, rather fresh white colored pumices were found on the slope shallower than 1800 mbsl. Around

the point of 1750 mbsl, well layered of light colored outcrop covered by dark angular fragment was

observed; both black and white fragment were sampled there. Around the depth of 1625 mbsl of the

cliff, very massive thick white tufficeous appearance layer topped by black fragments were observed.

The white layer was poorly consolidated, say fragile. The up-ward slope was ended at 14:17 at 1489

mbsl; then, the slope was changed to downward, which should be a rim of the crater/hole. On the rim

of the hole, sediment cover was rather thin, which occasionally prohibit the SAHF measurement.

The dive ended at 15:33 on the flat seabed of the hole wall during the course to waypoint #6 (water

depth: 1525 mbsl).

Summary:

Dive #1762 surveyed the hole floor and its wall of western off Kume Island, collected 15 samples

(14 rocks and 1 push core, but 2 rock lost) and measured 3 SAHF stations.

10

Dive HPD#1763 Report

Observer: Yumiko Harigane (per.pro. Hidenori Kumagai)

Pilots: A. Takenouchi, R. Saigo

Technical Information:

Location: On an eastern flank of Daini-Ryukyu Knoll, western off Kume-Jima Island (Figure 3-1)

Objective: Geological observation and rock sampling of an eastern flank of Daini-Ryukyu Knoll,

western off Kume-Jima Island.

On Bottom: Off Bottom:

Time (local): 09:06 11:31

Latitude: 26°12.960’N 26°13.308’N

Longitude: 126°13.894’E 126°13.310’E

Depth (m): 973 593

6 samples collected (6 rocks: pumices).

Purpose:

The main purpose of this dive was to observe outcrop of an eastern flank of Daini-Ryukyu Knoll,

western off Kume-Jima Island and collect the rocks from these exposures. In the Daini-Ryukyu

Knoll, dacite and pumice were recovered by dredge during GK12 cruise (Harigane et al., 2014).

Here, we expect to obtain other kinds of volcanic rock in order to understand the variation of

volcanic rocks.

Observations:

The dive began at 09:06 and 973 mbsl on a foot of eastern flank of a volcanic edifice western-off

Kume-Jima Island. In the vicinity of the landing area, large boulders showing clear cooling joint

structure were abundantly scattered of 40m in length. The landing area was a terrace of the contour

and widely covered by blocks of jointed angular ones. Ascending the slope covered by such jointed

blocks until approximately 900 mbsl. Around the slope of 900 mbsl, the shape of blocks dominated

by rounded one that maybe a top surface of the flow: lava or pyrocrastics. A short zone of a flat

surface of a flow, seafloor changed back into a zone scattered by angular jointed boulders. Then,

similar seafloor continuum of scattering of jointed blocks. A sub-rounded block sampled there was

11

pumice that was broken into two pieces at the sampling. Until the top of the crater rim, the

appearance of the seafloor was not so changed; continuously covered by thin sediment and scattering

angular to sub-angular blocks. At the top of the crater rim, a columnar jointed block was sampled

that highly vesiculated as woody pumice.

The vehicle flied down to the bottom of the crater where the seafloor was thinly sedimented talus. A

piece of the radial-jointed domy-body was sampled but highly vesicurated pumice, which may be a

part of inflated lava dome. Then the vehicle searched any sign of hydrothermal activity in the crater

floor, and directed northeastern peak of crater rim (waypoint #5) During the travel, well-jointed

dyke-like obejects were frequently found in talus.

The dive ended at 11:30 on the outer slope of the local summit of the crater rim after the sampling of

two pumices: one was sub-angular, like a piece of columnar joint, and the other was rounded:

approximately 100 m away from waypoint #5 (water depth: 593 m).

Summary:

Dive #1763 surveyed the eastern slope and hole floor of this volcano and collected six pumice

samples.

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Dive HPD#1764 Report

Observer: Yumiko Harigane (per.pro. Hidenori Kumagai)

Pilots: A. Takenouchi, R Saigo

Technical Information:

Location: A deep crater of northern volcano of Daini-Ryukyu Knoll in western off Kume-Jima Island

(Figure 3-1)

Objective: Geological observation and rock sampling from a deeper crater to an southeastern slope

of northern volcano of Daini-Ryukyu Knoll, western off Kume-Jima Island. Measurement of

temperature on the surface by SAHF.

On Bottom: Off Bottom:

Time (local): 14:18 15:52

Latitude: 26°16.895’N 26°17.080’N

Longitude: 126°15.911’E 126°15.723’E

Depth (m): 1419 1237

9 samples collected (8 rocks and 1 push core). 1 SAHF station.

Purpose:

The main purpose of HPD#1764 dive was to observe outcrop of a deeper deep and a southeastern

slope of northern volcano of Daini-Ryukyu Knoll, western off of Kume-Jima Island and collect the

rocks from these exposures. Pumice was mainly recovered by dredge in this volcano during GK12

cruise (Harigane et al., 2014). In this dive, we expect to obtain other kinds of volcanic rock in order

to understand the variation of volcanic rocks.

Observations:

The dive began at 14:18 and 1419 mbsl on sedimented seabed in the bottom of a crater associated

with several local peaks on its rim. In the vicinity of the landing area, sparse floats, rather large ones

(up to 1m) with sags, were observed; they were possibly pumice but showing clear cooling joint

structures. At the check of SAHF probe, reddish clay adhered on the probe retrieved, which

suggested hydrothermal input beneath the seabed. At the same point, push coring succeeded;

13

however, the bottom of the corer was broken possibly hit on a hard fragment beneath the seabed.

Shortly after the start of travel, slight depression likely to small pockmarks were also found. After a

one-hundred meter travel on seafloor, two rocks were sampled; one was well laminated

volcanicrastic material, possibly welded tuff.

Resuming travel to the inner wall of crater, elongated low ridge with red colored top was suddenly

appeared. Sampled fragment from the ridge was mineralized volcanicrastic material including small

yellow and white grains: possibly pyrites. Many floats showing similar appearance were also found

until the foot of crater wall.

The foot of crater wall was slightly sedimented mounds and occasional exposure of wrinkled rock.

One much oxidized fragile block was sampled from such wrinkled rock. The crater wall was gently

changed into rocky seabed of which surface occasionally shows flow-line like pattern. At 1305 mbsl,

approximately 100 m up from the bottom of the wall, one of exposed rock that aligning 300°, was

sampled. The lineation of the exposure was parallel to the steepest line of descent from the peak. 50

m shallower from the sampled point, mostly sedimented slope of rather dark color, big boulder with

Mn-coating appeared, then, a debris avalanche-like block with gig-saw pattern was also appeared.

From the surface, a platy block was detached and sampled. Above that point talus continued and

partly jointed outcrop appeared. Two rocks were sampled from the outcrop. It was the almost.

The dive ended at 15:52 almost on the midpoint to waypoint #3 as the shallowest point of targeted

area (water depth is 830 m).

Summary:

Dive #1764 surveyed the southeastern slope of volcanic edifice western off Kume Island, collected

nine samples (8 rocks and 1 push core) and measured 1 SAHF station.

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4. Heat flow meter measurements

During the NT14-22 cruise, heat flow survey was held at the west of Kumejima area using with two

Stand-Alone Heat Flow (SAHF) probes. The objective of this measurement is to know the

distribution of heat flow data near the rock sampling site.

Figure 4-1. Stand-Alone Heat Flow (SAHF).

The specification of SAHF is as follows:

Material Alloy of titanium

Weight 3.1kg in air

Length of probe 600 mm

Number of thermistors 5

External Interface RS232C (9600BAUD, 8bit, Non-Parity, 2 Stop Bit)

Method

SAHF meter (Figure 4-1) is designed to measure heat flow by manned submersibles or ROVs. Five

thermistors situated within this probe at 11 cm intervals that were marked by yellow label (Figure

4-1). The two heat flow probes (#7 and #9) equipped with ROV Hyper Dolphin 3000 (HD) during

the NT14-22 cruise.

After HD lands on the seafloor, SAHF is grabbed by HD’s manipulator and takes the reference

temperature for 5 minutes. Then, SAHF is put vertically into sediment and measure temperature

gradient for at 15 minutes. While HD try to collect sediment sample using M-BARI core in order to

measure the thermal conductivity. Thermal conductivity was measured at the laboratory in the ship

with M-BARI core samples.

Results

Table 4-1 shown below is the details of all the SAHF measurements and M-BARI core.

15

Ta b l e 4 -1. The list of all the SAHF measurements anf MBARI core.

Longitude Latitude Depth Calibration time P enetration time P ull out time M-BARI SHF-1 26-17.262 126-28.136 1097.3 Dec. 26, 2014 9:21 Dec. 26, 2014 09:30 Dec. 26, 2014 09:35 －

Dec. 26, 2014 09:36 Dec. 26, 2014 09:54 －

SHF-2 26-17.267 126-28.166 1097.3 Dec. 26, 2014 10:08:56 Dec. 26, 2014 10:13:31 Dec. 26, 2014 10:31:30 －

SHF-3 26-17.307 126-28.353 1102 Dec. 26, 2014 11:40:00 Dec. 26, 2014 11:45:02 Dec. 26, 2014 12:01:30 ○

SHF-4 26-17.459 126-28.611 1075.2 Dec. 26, 2014 13:46:04 Dec. 26, 2014 13:52:37 Dec. 26, 2014 14:09:13 －

SHF-5 26-17.504 126-28.811 904.9 Dec. 26, 2014 14:58:15 Dec. 26, 2014 15:06:29 Dec. 26, 2014 15:22:00 －

SHF-6 26-22.010 126-14.187 1964.3 Dec. 27, 2014 09:53:20 Dec. 27, 2014 10:00:00 Dec. 27, 2014 10:17:19 －

SHF-7 26-22.099 126-14.395 2017 Dec. 27, 2014 11:26:40 Dec. 27, 2014 11:33:27 Dec. 27, 2014 11:49:11 ○

SHF-8 26-22.372 126-15.003 1526 Dec. 27, 2014 15:04:50 Dec. 27, 2014 15:11:54 Dec. 27, 2014 15:28:38 －

SHF-9 26-16.894 126-15.907 1419 Dec. 28, 2014 14:21:10 Dec. 28, 2014 14:28:33 Dec. 28, 2014 14:44:13 ○

16

5. Surface geophysical survey

We conducted a surface geophysical survey to collect multi-narrow beam bathymetry, magnetic field

data. The ship tracks of the research area are shown in Figure 5-1. Multi-narrow beam bathymetric

data on the NT14-22 cruise were obtained using a SEABAT 8160 (Swath width 150°; 126 beams

with its width and interval of 1.5° and 1.5°, respectively), which also provides a backscatter image

that will be processed after the cruise. An example of the bathymetric data is shown in Figure 5-1.

Sound velocity profiles were obtained by XCTD and the descriptions are listed in Table 5-1. The

D-GPS (Differential Global Positioning System) was used to derive the ship’s location.

Magnetic field data were also collected with two instruments: a shipboard three component

magnetometer (Tierra Tecnica Ltd, SFG1211) that can measure the vector geomagnetic field using

deck-mounted fluxgate magnetometers and gyros, and a ship-towed cesium magnetometer

(Geometrics Inc, G-882) that can measure the intensity of the geomagnetic field. The STCM data

contain the effects of the ship’s magnetic field that must be corrected in order to derive the real

geomagnetic field. Twelve constants related to the ship’s permanent and induced magnetic field will

be estimated using data from “Figure 8 turns”. “Figure 8 turns” is made by steering the ship in a tight

circle, both clockwise and counter clockwise. During the cruise, “Figure 8 turns” were conducted

twice and it is listed in Table 5-2. Ship-towed cesium magnetometer was towed 247.6 m (200 m of

cable length and 47.6 m of vessel reference point form aft) behind Vessel Reference Point.

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Figure 5-1. Bathymetric data obtained in the research area.

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Table 5-1. List XCTD survey”

No. Date Time(UT) Latitude Longitude Depth

1 25/Dec 09:18 26-39.19 N 126-18.21 E 1892 m

2 27/Dec 08:31 26-22.49 N 126-11.07 E 1642 m

Table 5-2. List of “Figure 8 turns”

No. Date Time(UT) Latitude Longitude

1 25/Dec 08:22-08:44 26-37.35 N 126-18.64 E

2 27/Dec 11:32-11:52 26-00.08 N 126:10.45 E

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6. Seismic survey: processing and result of seismic reflection data

Single channel seismic reflection data were acquired along 2 lines (SCS1-NT14-22 and

SCS2-NT14-22)(Table 6-1) with total length of approximately 125 km (90 km in SCS1-NT14-22

and 35 km in SCS2-NT14-22)(Figure 6-1).

We employed the G.I.Gun (Sercel Inc.) for seismic source. Source volume was 150 cubic inch (G:45,

I:105). Towing length was 30 m from aft peak, air pressure was 14.5 MPa. The receiver was the

single-channel streamer cable (S.I.G. Inc.). Length of active section is 65 m and lead in cable is 135

m. Shooting interval was 12 sec (approximately 25 m in distance with ship speed of 4 kn).

Recording time-length was 10 sec and sampling rate was 1 msec.

Acquired reflection data were processed using Seismic Unix (Open source software supported by the

Center for Wave Phenomena at the Colorado School of Mines). Data processing flow includes trace

header editing, linear move out correction (to remove trigger delay: 0.1 sec), early mute (0.4 sec),

band-pass filtering (the corner frequencies are 5, 40, 200 and 400 Hz), amplitude compensation and

predictive deconvolution. Acoustic basement crops out in most area and few reflectors are observed.

Sediments with horizontal reflectors are distributed in the adjacent area to Okinawa Trough and

between the sub-marine volcanoes (Figure 6-2). The thickness of the sediment is up to 0.4 sec (Two

Way travel Time, 300 m with acoustic velocity of 1,500 m/sec).

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Figure 6-1. Line map of the seismic reflection survey.

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Figure 6-2. Processed seismic sections. (a) Line SCS1-NT14-22. (b) Line SCS2-NT14-22.

22

7. Shore-based studies

A comprehensive work plan for the collected rock samples was developed by the shipboard

scientific party. This work will include major element analyses, trace element analyses,

geochronology studies, mineral analyses, petrographic characterization, and radiogenic isotope

characterization. The work will be completed at the Geological Survey of Japan/AIST, JAMSTEC,

and other possible collaborators. Analytical responsibilities include as below.

•Microstructural observation (microscope, SEM): GSJ

•Whole rock chemical composition (XRF, ICP-MS): GSJ

•Mineral chemistry (major elements: EPMA, trace elements: LA-ICP-MS): GSJ

•Ar/Ar dating and some radiogenic isotopes (Sr, Nd, Pb): GSJ

•Bathymetric, magnetic and seismic data will be merged with existing data and synthesized at GSJ.

•Volcanic and geologic synthesis will be done at GSJ, JAMSTEC, etc.

•Links between volcanic structure, the thermal conductivity and characteristics of magma be merged

with existing data and synthesized at JAMSTEC and GSJ.

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8. Summary

We investigated 3 volcanoes and 1 depression in the west off of Kume-jima island. In the west off of

Kume-jima Island, we used 4 dives (Dive HPD#1761, HPD#1762, HPD#1763, HPD#1764) to

observe at the volcanic section formed in the submarine volcanoes of the west off of Kume-jima

island. Dive HPD#1761 surveyed the bottom of volcanic caldera in Daisan-Kume Knoll and

observed a hydrothermal chimney and mound with a colony of shrimps and shells. The west of this

dive area seems to be higher thermal activity than the east of this dive area based on the

measurement by SAHF. We mainly collected hydrothermally altered rocks from these hydrothermal

chimney and mounds in the Dive HPD#1761. The deepest dive of Dive HPD#1762 located from

Daini-Kume Knoll to ~13 km if the west. This dive observed dacite from domy structure at the

bottom of depression, and pumice and (volcanic?) mudstone from the steep cliff composed by

layering. Dives HPD#1763 surveyed an eastern flank of Daini-Ryukyu Knoll. This area widely

covered by the jointed angular blocks that mainly consist of pumices. Dive HPD#1764 was

conducted at northern volcano of the Daini-Ryukyu Knoll. This dive surveyed from the bottom of

crater to eastern slope. On the bottom of crater, we found an outcrop of elongated low ridge with red

colored top. On the eastern slope of this volcano, mostly sedimented slope of rather dark color, big

boulder with Mn-coating and a debris avalanche-like block with gig-saw pattern were appeared.

Dive HPD#1764 recovered hydrothermally altered rock, tufficeous rock and andesite.

We also conducted surface geophysical (multi-narrow beam bathymetric data and magnetic field

data) and seismic survey around submarine volcanoes in the west off of Kume-jima island.

Multi-narrow beam bathymetric data on the NT14-22 cruise were obtained using a SEABAT 8160.

Magnetic field data were also collected with two instruments (a shipboard three component

magnetometer and a ship-towed cesium magnetometer) in order to measure the vector and the

intensity of the geomagnetic field, respectively. The bathymetric and geomagnetic data covered the

Daigo-Kume Knoll area and Daini-Kume Knoll area. Single channel seismic reflection data were

acquired along 2 lines (SCS1-NT14-22 and SCS2-NT14-22) with total length of approximately 125

km (90 km in SCS1-NT14-22 and 35 km in SCS2-NT14-22). The observed subsurface structures of

the some sub-marine volcanoes from seismic reflection data can be subdivided into several units,

whereas the reflectors are obscure due to the acoustic scattering in the volcanoes.

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9. References

Harigane, Y., Ishizuka, O., Shimoda, G., Sato, T., 2014. The preliminary results of new submarine

caldera on the west of Kume-jima island, Central Ryukyu Arc, Japan. Eos Trans. AGU Fall Meet.

Suppl., Abstract T53A-4659, San Francisco, California, Dec. 15-19.

Ishizuka, O., Harigane, Y., Amano, A., Katayama, H., Lee, S., Nishida, N., Sato, T., Inoue, T., Arai,

K., 2012. Rock samples recovered during GH11 cruise. GSJ Interim Report, 58, 73-86 (in

Japanese with English abstract).

Konishi, K., 1965. Geotectonic framework of the Ryukyu Islands (Nansei-Shoto). J. Geol. Soc. Jpn.,

71, 437–457 (in Japanese with English abstract).

Kato, S., Katsura, T., Hirano, K., 1982. Submarine geology off Okinawa Island. Rep. Hydrogr. Res.,

17, 31–70 (in Japanese with English abstract).

Sato, T., Oda, H., Ishizuka, O., Arai, K., 2014. Detailed bathymetry and magnetic anomaly in the

Central Ryukyu Arc, Japan: implications for a westward shift of the volcanic front after

approximately 2.1 Ma. Earth, Planets and Space, 66:68, doi:10.1186/1880-5981-66-68.