Smithsonian Institution
Global Volcanism Network Bulletin v. 20, no. 6, June 1995

Metis Shoal (Tonga)  Eruption builds new island

Tonga, SW Pacific Ocean
19.18S, 174.87W; summit elev. -4 m (prior to this activity)

On 6 June the Hydrographic Office in Tonga notified the New
Zealand Hydrographic Office that an eruption was in progress at
Metis Shoal (figure 3). The NZ Hydrographic Office then issued a
Long Range Navigation Warning to all shipping. The ship
Obtfriesland reported the shoal in eruption while passing on 9
June at 1050. At least five volcanic ash aircraft advisories were
issued by the Wellington Volcanic Ash Advisory Center on 12-13
June. The notices stated that the eruption began early on 12
June, apparently the time of the first plume report by an
aircraft. Ash was reported up to 18-24 km. Drift directions of
the plume changed in each notice, with estimated speeds of 28-46

An island breached the surface ~12 June, but the growth of a lava
dome above sea level was first observed on 14 June. A video taken
on 14 June by a local tour operator (Allan Bowe), ~400-500 m away
from the new island, was widely distributed by television news
organizations. The video narrator noted that the water around the
boat was discolored green. Based on the video and photographs,
Brad Scott estimated that the dome was ~30 m high with a diameter
of 150-180 m. The volume of tha lava dome was estimated at ~1 x
10^6 m^3, giving a daily extrusion rate of ~1 x 10^5 m^3.

Ash-laden eruptions seen on the video discharged from two
sources. The first was directed NW, apparently from the dome
wall. The second generated stronger explosions vertically from
the dome center to heights of 300-500 m. The NNE face of the dome
was steaming vigorously from what appeared to be parallel
vertical sources, probably fractures in the advancing flow front.
The steam plume, originating from the N and S sides of the dome,
was rising 500-800 m before being blown downwind for several

By 20 June the lava dome was 240 x 280 m in size (67,200 m^2) and
~54 m above sea level; the next day it was an estimated 200-500 m
across and 50-80 m high. The volume of the dome was estimated at
~2.8 x 10^6 m^3, three times that on 14 June. The daily extrusion
rate during 14-21 June was ~4 x 10^6 m^3, a 4-fold increase over
the 6-14 June period.

During 20-21 June a white steam plume rose as high as 1-2 km, and
occasional small explosions produced ash columns to ~500 m. The
active vent was in the SE corner of the island. On the evening of
20 June, the growing NE front of the dome was incandescent, and
some observers reported that the summit was pulsing 3-5 m
vertically. A small lobe was extruded onto the top of the dome
and the NE front of the dome was active. Phreatic explosions
occurred at the flow front. The dome changed overnight on 20-21
June, moving downward and NE. The steep-sided lava dome split and
subsided between 21 and 25 June. Another aviation volcanic ash
advisory on 21 June noted a report of ash below 24 km in the
vicinity of the volcano drifting SE at ~18-19 km/hour.

On 23 June the Tongan government asked the New Zealand government
for advice on the eruption. As a result, Brad Scott (IGNS) joined
a Royal New Zealand Air Force maritime patrol flight on 25 June.
He reported that by 25 June the elliptical dome, ~300 x 250 m,
elongate NNE, and ~50 m high, had stopped growing.Trending NW was
a raised platform ~150 x 80 m, and 2-3 m above sea level. The
lobe formerly on top of the dome had been displaced ~40-50 m NE
and was lower than the highest point, which then stood on the S
side. Blue fume emissions from a depression in the central part
of the dome indicated a high SO2 content. A circular lobe of lava
to the NE overlay a strongly ribbed flow front. Zones of
discolored water (yellow-brown) extending outward from the
volcano apparently represented submarine fumarolic discharge.

Scott travelled on a tugboat near the island on 28 June. Steam
emissions had decreased appreciably since 21 June, but the dome
profile appeared unchanged since the 25th, indicating a
significant decline in the eruption rate. Assuming a diameter of
280 m and a height of 43 m on 28 June, the erupted volume was
calculated to be ~3 x 10^6 m^3. No pumice has been observed, in
contrast with past eruptions. The 1967 and 1979 events erupted
dacitic pumice and formed low-angle tuff cones, which were soon
eroded away. The current lava dome appeared solid in late June,
and may resist erosion for some time.

Two other eruption locations reported by aircraft were
investigated, but nothing was found; those sites were apparently
the aircraft locations at the time of the observations. The
Tongan government was advised to place a restricted access zone
around the island, and was briefed about acid rain/fume,
explosive outbursts, dome collapse, and the formation of further

Metis Shoal is located in the Tonga Islands about halfway between
Kao and Late, ~50 km NNE of Kao (figure 3). Eight previous
episodes of activity are known since 1851; new islands were
created on at least three (1858, 1967, and 1979), and possibly
five, of those occasions. The 1967-68 island appeared around 11
December 1967, and had submerged again by 19 February 1968
(Melson and others, 1970). In 1979, large pumice rafts were first
seen in May between Tonga and Fiji. Metis was seen in strong
eruption in June, with ash emission in July, and fumarolic
activity in August. The island, named Late Iki by the Tongan
government, disappeared in October 1979 (Bulletin v. 4, nos. 5-8,
10, & 12; see Woodhall, 1979, for more details).

References: Melson, W.G., Jarosewich, E., and Lundquist, C.A.,
1970, Volcanic eruption at Metis Shoal, Tonga, 1967-1968:
description and petrology: Smithsonian Institution Press,
Smithsonian Contributions to the Earth Sciences, no. 4, 18 p.

Woodhall, D., 1979, Cruise of the R.V. Balikula to investigate
recent volcanic activity in Tonga, July 11-18, 1979:  Fiji
Ministry of Lands & Mineral Resources, Mineral Resources Division
Report 14, 13 p.

Information Contacts: Brad Scott, Volcano Surveillance Manager,
Institute of Geological & Nuclear Sciences, New Zealand (Email:; Bureau of Meteorology, Northern Territory
Regional Office, POB 735, Darwin NT 0801, Australia.

Figure 3. Map of the Tonga Islands, showing the island groups and
location of Metis Shoal, which re-emerged as an island in June