Discolored seawater plume 6 km long

On 12 January, an aviator from the JMSA observed seawater discolored to yellowish green in an area 500 m wide and 6 km long, flowing from Minami-Hiyoshi seamount to the S. Discolored water was last observed in February 1992 (BGVN 17:02).

Periodic water discoloration and water-spouting has been reported over this submarine volcano since 1975, when detonations and an explosion were also reported. Located 90 km SE of Minami-Iwo-Jima, Minami-Hiyoshi lies near the SE end of a coalescing chain of youthful seamounts, and is the only historically active vent. The morphologically youthful seamounts Kita-Hiyoshi and Naka-Hiyoshi lie to the NW, and Ko-Hiyoshi to the SE.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

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

January 1977 (NSEB 02:01) Cite this Report

Bubbling water and discoloration

The crew of a JMSA aircraft recently observed that bubbling water near Minami Iwo-Jima had changed to an ashen brown color. Orange and yellow flotsam was seen in the area. [The location given for this observation was 23.48°N, 141.67°E, or 90 km SSE of Fukutoku-okanoba, in the vicinity of Minami-Hiyoshi seamount.] Activity was reported nearby (23.50°N, 141.92°E) in August 1975.

Information Contacts: AFP; U.S. Defense Mapping Agency.

February 1977 (NSEB 02:02) Cite this Report

Two zones of discolored water observed from the air

On 10 January, a JMSA aircraft noted two adjacent zones of discolored water. One zone was 5.5 x l km, colored gray and milky white at the center. Each color was thought to have been generated by a separate vent. The second zone, 6.5 km long, was pale green to yellowish-brown. No volcanic ejecta were observed. By 24 January, activity had decreased markedly. Depth at the site is reported to be 130 m.

Information Contacts: JMA, Tokyo; Japanese Press.

April 1977 (NSEB 02:04) Cite this Report

Zone of discolored water seen on 27-28 March

A discolored belt was observed on the sea surface at this site on 27 and 28 March. Similar activity had been reported at Minami-Hiyoshi beginning 10 January, but had declined by 24 January.

[The JMA provided additional chronological information on the 1977 discolorations. They were observed by the crew of JMSA aircraft on 10-14, 17-18, 21, 26, and 28-29 January, and 3-4, 11, 18, and 24-25 February. JMSDF crews continued to see them on 10, 11, and 17 March, but saw no discolorations on 18, 19, 21, 23, and 25 March. Discolorations were again visible on the next 3 days (26-28 March) during JMSDF flights, but were not seen on 6 April by a JMSA flight nor by any subsequent flights that year.]

Information Contacts: JMA, Tokyo.

May 1978 (SEAN 03:05) Cite this Report

Green discolored water seen on 10 January

Four areas of pale green discolored water were observed on 10 January. [JMA has added the information that JMSA flight crews on 10 and 24 January saw no discoloration, but it was seen on 26 January and again on both 23 February and 24 March by JMSDF aircraft personnel. As noted in the long tables above under Fukutoku-okanoba, discoloration was not seen on 13 April or on any subsequent flights.]

Information Contacts: JMA, Tokyo.

July 1979 (SEAN 04:07) Cite this Report

Discolored water seen during January-March 1978

Minami-hiyoshi, formerly named Hiyoshi-oki-no-ba, was active January-March 1977 and January-March 1978. [Discolored water was specifically noted, in an included table of observations during January 1978-July 1979, on 26 January, 23 February, and 24 March 1978.]

Information Contacts: JMA, Tokyo.

April 1980 (SEAN 05:04) Cite this Report

No water discoloration seen since March 1978

The Japan Maritime Safety Agency continues frequent monitoring flights over three known submarine volcanoes. [Discolored water at Minami-hiyoshi was not seen during August 1979-March 1980 (see table 1 below).]

Information Contacts: JMSA, Tokyo; JMA, Tokyo.

November 1980 (SEAN 05:11) Cite this Report

No observed activity since March 1978

The Japan Maritime Safety Agency (JMSA) continues frequent monitoring flights over several known submarine volcanoes. [Discolored water at Minami-hiyoshi was not seen during April-October 1980 (see table 1 below).]

Information Contacts: JMSA, Tokyo; JMA, Tokyo.

December 1980 (SEAN 05:12) Cite this Report

No seawater discoloration seen in November-December 1980

The Japanese Maritime Safety Agency (JMSA) continues frequent aerial monitoring of several known submarine volcanoes. [Discolored water was not seen at Minami-hiyoshi during November-December 1980 (see table 1 below).]

Information Contacts: JMSA, Tokyo; JMA, Tokyo.

October 1981 (SEAN 06:10) Cite this Report

No discolored water seen during January-October 1981

The Japan Maritime Safety Agency (JMSA) continues frequent monitoring flights over several known submarine volcanoes. [No discolored water was specifically noted, in an included table of observations, during January-October 1981 (see table 1 below).]

Information Contacts: JMSA, Tokyo; JMA, Tokyo.

September 1982 (SEAN 07:09) Cite this Report

No water discoloration seen since March 1978

JMSA [and JMSDF have] continued frequent monitoring flights over several known submarine volcanoes (table 1). No discolored sea water has been observed near Minami-Hiyoshi since March 1978.

Table 1. Volcanic activity at three sites in the Volcano Islands, January 1978-December 1982, detected by JMSA and JMSDF monitoring flights. Activity indicated as D = Discolored water; N = No discolored water, - = No overflight, ? = not reported. This table combines data from 4:7, 5:4, 5:11, 5:12, 6:10, and 7:9, plus additional 1982 data not published in the Bulletin.

Date	Fukutoku-Okanoba	Minami-Hiyoshi	Fukujin
10 Jan 1978	D	N	D
24 Jan 1978	D	N	D
25 Jan 1978	D	-	D
26 Jan 1978	-	D	D
23 Feb 1978	D	D	N
24 Mar 1978	D	D	D
13 Apr 1978	D	N	N
25 May 1978	D	N	N
28 Jun 1978	D	-	-
29 Jun 1978	D	N	N
25 Aug 1978	D	N	D
24 Oct 1978	N	N	N
15 Nov 1978	D	-	-
16 Nov 1978	D	N	N
14 Dec 1978	D	N	N
11 Jan 1979	D	-	-
24 Jan 1979	D	N	N
08 Feb 1979	D	N	N
27 Mar 1979	D	[N]	-
26 Apr 1979	D	N	D
15 Jun 1979	N	N	N
11 Jul 1979	N	-	-
12 Jul 1979	D	N	D
24 Aug 1979	N	N	-
09 Sep 1979	D	-	-
13 Sep 1979	D	N	N
25 Oct 1979	D	N	D
08 Nov 1979	D	N	D
12 Dec 1979	D	N	D
29 Jan 1980	-	-	D
15 Feb 1980	D	N	D
19 Mar 1980	D	N	D
24 Apr 1980	D	N	N
12 May 1980	D	-	D
16 Jun 1980	D	N	N
07 Jul 1980	D	-	-
08 Jul 1980	D	N	N
14 Jul 1980	D	N	N
18 Aug 1980	N	N	N
04 Sep 1980	N	N	N
21 Oct 1980	N	N	N
14 Nov 1980	D	N	N
18 Dec 1980	D	N	N
07 Jan 1981	-	-	D
08 Jan 1981	-	-	D
09 Jan 1981	D	N	N
29 Jan 1981	D	-	-
12 Feb 1981	D	[-]	-
20 Feb 1981	D	[N]	N
12 Mar 1981	D	[-]	-
13 Mar 1981	D	N	N
16 Mar 1981	D	N	N
20 Apr 1981	D	N	N
17 Jun 1981	N	N	N
16 Jul 1981	D	-	-
17 Jul 1981	D	[N]	[N]
22 Jul 1981	D	N	N
17 Aug 1981	D	N	N
17 Sep 1981	D	N	N
19 Oct 1981	N	N	N
11 Nov 1981	N	N	[-]
21 Dec 1981	D	N	N
12 Jan 1982	-	-	D
19 Jan 1982	D	N	D
09 Feb 1982	D	N	N
28 Feb 1982	D	-	-
16 Mar 1982	D	N	D
01 Apr 1982	D	-	N
02 Apr 1982	D	N	N
16 Apr 1982	D	N	N
14 May 1982	D	N	N
16 Jun 1982	D	N	N
22 Jun 1982	D	-	-
13 Jul 1982	D	?	N
20 Aug 1982	D	?	N
27 Sep 1982	D	?	N
13 Oct 1982	D	?	N
17 Nov 1982	D	?	N
15 Dec 1982	D	?	D

Information Contacts: JMSA, Tokyo; JMA, Tokyo.

March 1984 (SEAN 09:03) Cite this Report

No water discoloration seen since March 1978

Frequent monitoring of several known submarine volcanoes has continued. . . . Minami-Hiyoshi produced discolored sea water January-March 1977 and January-March 1978 but no further activity has been observed.

Information Contacts: JMA, Tokyo.

December 1990 (BGVN 15:12) Cite this Report

No water discoloration seen in 1990

No discolorations were observed at . . . Minami-Hiyoshi . . . during 1990.

Information Contacts: Hydrographic Department, JMSA.

February 1992 (BGVN 17:02) Cite this Report

Discolored water

An area of green discolored water, 3-5 km long, was observed over the volcano during an overflight on 12 February. Subsequent overflights revealed additional water discolorations on 28 February, and 2, 3, and 4 March, although no discoloration was seen on 21 February. The 4 March discoloration appeared to have a source area 100 m across. Overflights have been conducted almost every month in the Izu and Volcano Islands by the JMSA. This was the first observed incidence of water discoloration since the mid-to-late 1970's, when bubbling, spouting, and discolored water were occasionally sighted.

Information Contacts: JMSA.

January 1996 (BGVN 21:01) Cite this Report

Discolored seawater plume 6 km long

On 12 January, an aviator from the JMSA observed seawater discolored to yellowish green in an area 500 m wide and 6 km long, flowing from Minami-Hiyoshi seamount to the S. Discolored water was last observed in February 1992 (BGVN 17:02).

Periodic water discoloration and water-spouting has been reported over this submarine volcano since 1975, when detonations and an explosion were also reported. Located 90 km SE of Minami-Iwo-Jima, Minami-Hiyoshi lies near the SE end of a coalescing chain of youthful seamounts, and is the only historically active vent. The morphologically youthful seamounts Kita-Hiyoshi and Naka-Hiyoshi lie to the NW, and Ko-Hiyoshi to the SE.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.