Discolored water

Light green discolored water, centered over the vent in a fan-shaped zone ~8 km long, was seen from the air on 18 March. The next day, a circle of light green discolored water ~1.8 km in diameter was visible.

Information Contacts: JMA.

Information is preliminary and subject to change. All times are local (unless otherwise noted)

February 1970 (CSLP 10-70)

Explosions and discolored water on 29 January; larger eruption on 3 February

Card 0859 (04 February 1970) Numerous explosions and discolored water on 29 January

The submarine volcano Myojin-sho exploded on 29 January between 1400 and 1600 hours. Located at 31°N, 139°59.5' E, the volcano shot a 200-300-m-wide water spout 100 m into the air at 1420, 1435, and 1443 hours. The explosions were accompanied by sulfur-colored smoke, as reported by the fishing boat Shintokumaru ##2. Another boat, the Shintokumaru ##12, reported five or six similar explosions, each of 3-4 minutes duration, at 1540 hours.

Card 0866 (13 February 1970) Larger eruption on 3 February

The Myojin-sho Reef in the Pacific erupted again at around 1040 [on 7 February], the 3rd Regional Maritime Safety Agency Headquarters in Yokohama revealed. The eruption was reported by the fishing boat No. 2 Shintoku Maru, which was sailing near the volcanic reef, located 150 km S of Hachijojima Island. According to the report, the eruption was greater in scale than the previous one which had occurred 29 January. Crew members of the fishing vessel witnessed great clouds of spray and seawater of dark-red color around the reef.

Information Contacts:
Card 0859 (04 February 1970) Tokiko Tiba, National Science Museum, Tokyo, Japan.
Card 0866 (13 February 1970) S. Motoda, Hokkaido University, Hakodate, Japan; W.H. Littlewood, American Embassy, Tokyo, Japan.

March 1970 (CSLP 10-70)

Explosions in January and February detected by hydrophones

Card 0880 (09 March 1970)

"The submarine eruption of Myojin-sho on 29 January was detected by sofar hydrophones of the Pacific Missile Range at Wake and Midway Islands. The origin time for the first explosion was 0330 GMT; for the last 1153 GMT. Eight large explosions occurred between 0330 and 0639, five between 0925 and 1012, and continuous high level activity between 1020 and 1110 GMT.

"Nine strong explosions from Myojin-sho originating between 0245 and 0511 GMT, 13 February, were recorded by the sofar hydrophones of the Pacific Missile Range at Wake and Midway. The hydrophones also recorded strong signals from the direction of Myojinsho on 14, 16 and 17 February with the strongest activity at 1044 GMT 17 February. One explosion was recorded on 25 February originating at 1914 GMT."

Information Contacts: Rockne H. Johnson, Hawaii Institute of Geophysics, University of Hawaii, USA.

April 1970 (CSLP 10-70)

Eruption on 23 April sends water and smoke 200 m high

Card 0927 (30 April 1970) Eruption on 23 April sends water and smoke 200 m high

The following information was passed to the Center via the American Embassy. Myojin-sho erupted again 23 April according to a report reaching Shizuoka from the Japanese fishing boat Kaigyo Maru of Izu, Shizuoka, Prefecture. The crew of the Kaigyo Maru witnessed the eruption at a point 50 km SE of the reef. It sent a column of water and smoke 200 m high.

Information Contacts: Japanese Fishing Fleet, Izu, Kyodo, Japan.

May 1970 (CSLP 10-70)

Detailed observations of activity from fishing boats and observation flights

Card 0938 (14 May 1970) Detailed observations of activity from fishing boats and observation flights

"The submarine volcano Myojin-sho exploded on 23 April 1970. Fishing boats, the Kairyu-maru and the 7th Kinosya-maru, reported as follows: 23 April, 0620 JST: explosion; water spout was given out 200-500 km high and about 100 m wide. 0630 -0637 JST: explosion. 0710 JST: explosion; volcanic smoke was observed to be 20-30 m high. After this, there were three to four explosions until 0800 hours on the same day. Water spout seemed to be higher than 200 m. The JMSA (Japan Maritime Safety Agency) observed the states of the submarine volcano from the air at 1125-1200 JST on 23 April and reported as follows: Sea water, about 100 m across, above the submarine volcano, was discolored by sulfur. A yellow belt of water discolored with sulfur, 1,000 m wide and 2,000 m long, moved in the SW direction from the discolored zone. At the front of this belt was a floating pumice zone 50-100 m wide and 1,000 m long, seemingly emitted on the occasion of the observed explosions. At 1100-1140 JST on 1 May, the members of JMA and JMSA observed this volcano from the air. No volcanic island above sea-level was seen, but light green sea water above the volcano suspended with sulfur or ejecta from the submarine-crater was observed (across 50-60 m). A discolored belt of water from this suspended zone was observed to move in the SE direction and to be 50-60 m wide, several hundred meters long. The sea temperature near this submarine volcano was measured with an infrared thermometer from the airplane but an extraordinary temperature was not detected."

Information Contacts: Yosihiro Sawada, Japan Meteorological Agency, Tokyo, Japan.

July 1970 (CSLP 10-70)

Explosion bubbles and floating pumice on 18 June

Card 0972 (15 July 1970) Explosion bubbles and floating pumice on 18 June

"In the morning of 18 June 1970, members of the fishing boat the 3rd Zinkokumaru observed the bubbles of a submarine volcanic explosion under sea-level about 50 m deep. Much pumice (max. 40 cm across) was floating near the sea surface above the submarine crater."

Information Contacts: Yosihiro Sawada, Japan Meteorological Agency, Tokyo, Japan.

July 1979 (SEAN 04:07) Cite this Report

Water discoloration observed on 13 July 1979

After 10 years of inactivity, discolored water was observed on 13 July 1979 at Myojin-sho.

Information Contacts: JMSA, Tokyo; JMA, Tokyo.

November 1980 (SEAN 05:11) Cite this Report

Discolored water

The crew of the fishing boat Suitenmaru 11 saw discolored water over Myojin-sho on 15 November at around 1530. They reported that no discoloration had been seen there that morning. JMSA personnel flew over the site on 18 November and observed three circular areas of pale green water, each 50-80 m across, aligned within a 300-m zone. [Discolored water was] also seen the following day by the crew of the fishing boat Shinkomaru 26 and again by JMSA personnel on 26 November. No floating ejecta or upwelling of water were noted, however.

Information Contacts: JMSA, Tokyo; JMA, Tokyo.

December 1980 (SEAN 05:12) Cite this Report

Discolored water seen on 23 December

The Japanese Maritime Safety Agency (JMSA) continues frequent aerial monitoring of several known submarine volcanoes. Renewed activity at Myojin-sho was first observed from a fishing boat on 15 November. [Overflights on 14 November and 18 December did not cover Myojin-sho, but that on 23 December observed discolored water at the site.]

Further Reference. Smoot, N.C., The growth rate of submarine volcanoes on the South Honshu and East Mariana Ridges: JGVR. [Bathymetric data on this and following seamounts throughout the Mariana arc.]

Information Contacts: JMA, Tokyo.

October 1987 (SEAN 12:10) Cite this Report

Discolored water within 100 km

Discolored water within a 100-m radius of Myojin-sho, the central cone of the submarine volcano, was recognized by observers on a fishing boat at 1040 on 21 October. No discolored water had been seen at 0603 that day and none was seen the next day during a JMSA overflight.

Information Contacts: JMA.

March 1988 (SEAN 13:03) Cite this Report

Discolored water

Light green discolored water, centered over the vent in a fan-shaped zone ~8 km long, was seen from the air on 18 March. The next day, a circle of light green discolored water ~1.8 km in diameter was visible.

Information Contacts: JMA.