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  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 18.325°S
  • 174.365°W

  • -40 m
    -131 ft

  • 243091
  • Latitude
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The Global Volcanism Program has no activity reports for Unnamed.

The Global Volcanism Program has no Weekly Reports available for Unnamed.

Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

11/2001 (BGVN 26:11) Possible source for September T-waves and November pumice rafts

01/2002 (BGVN 27:01) Submarine center identified S of Fonualei may be the source of T-waves and pumice

10/2003 (BGVN 28:10) Pumice rafts from September-October 2001 eruption reach eastern Australia

05/2007 (BGVN 32:05) Bathymetric survey locates vent area and maps 2001 pumice deposits

Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

All times are local (= UTC + 13 hours)

11/2001 (BGVN 26:11) Possible source for September T-waves and November pumice rafts

[The following originally appeared as part of a report on Fonualei. Later investigations showed that the seismicity and pumice rafts in question most likely came from an unnamed submarine volcano in the Tonga Islands.]

Seismicity. During 28-29 September 2001 numerous short T-waves were registered by the French Polynesian Seismic Network. The preliminary location of the seismicity was determined to be near the Tonga archipelago at 18.18°S (well constrained) and 174°W (not as well constrained). This spot lies ~40 km W of Fonualei.

The swarm began at 0550 on 28 September and ended at 1113 on 29 September (figure 1). The strongest T-wave was registered at 1229 on 28 September at the PAE seismic station in Tahiti (figure 2). The hydro-acoustic activity was interpreted to be volcanic and explosive and not related to seismicity at the Tonga trench. According to the Laboratoire de Géophysique, the source could be near Fonualei.

Figure 1. A plot showing the overall character of the T-wave swarm inferred to have come from Fonualei during 28-29 September 2001. Basically, the cluster of T waves seen in the main part of the swarm (28 September) consisted of signals with short (15-second) periods. Some of these signals were comparatively strong. T waves seen later in the swarm (1100 on 29 September) had long (120-second) period. Courtesy of Laboratoire de Géophysique.
Figure 2. Seismic trace of the strongest of the T-wave signals attributed to Fonualei during the swarm of 28-29 September 2001. The trace was recorded at 1229 on 28 September at the PAE seismic station in Tahiti (the trace was labeled "PAE CPZ1 (Brut)"). Courtesy of Laboratoire de Géophysique.

Pumice rafts. Roman Leslie, a Ph.D. student at the University of Tasmania visited Fiji (hundreds of kilometers W of Tonga) during 9-25 November 2001. There he observed large (100-m diameter) pumice rafts of gray, aphyric pumice clasts ranging from sand-sized to ~20 cm in diameter. Local residents hadn't seen such large rafts before, but had noticed occasional clasts in recent history.

Leslie initially observed the pumice rafts while on Kadavu island of the Lomaiviti Group while diving on the southern Astrolabe Reef from the 10th-15th. He again saw pumice rafts in the Koro Sea during a flight from Suva to Koro on the 16th. Next, he found them on the coral coast (southern Viti Levu) on the 24th, where samples were collected ~5 km E of Sigatoka.

There he collected pumice samples from the beach at or near the high-tide mark, where they formed discontinuous wave-derived lag deposits of limited thickness, with ~5 m lateral extent. Beach pumice deposits and floating rafts (up to ~150 m in length) were poorly sorted and consisted of brown-grey clasts ranging from ~2 to 100 mm in diameter. Clasts were sub-angular to sub-rounded and appeared to contain small phenocrysts of clinopyroxene and plagioclase. Judging from the approximate color index and mineralogy it seemed that the samples were broadly andesitic.

Whether or not the pumice rafts seen in Fiji during November are related to the activity that registered as T-waves from Tonga during late September is uncertain. The rafts and T-waves may be entirely unrelated in terms of source location, or they may result from a common eruption, perhaps at Fonualei.

Information Contact: Olivier Hyvernaud; Laboratoire de Géophysique; PO Box 640 Papeete; Tahiti; French Polynesia (Email: hyvernaud@labogeo.pf); Roman Leslie, Centre for Ore Deposit Research, University of Tasmania, GPO Box 252-79, Hobart, TAS 7001, Australia (Email: rleslie@utas.edu.au, URL: http://www.geol.utas.edu.au/ codes/).

01/2002 (BGVN 27:01) Submarine center identified S of Fonualei may be the source of T-waves and pumice

The following was largely condensed from a report by Paul Taylor submitted to the Tongan government (Taylor, 2002). Our previous report on the topic appeared under the heading "Fonualei" (BGVN 26:11). The bulk of that report described T-wave signals on 28-29 September 2001 traced to near Fonualei and fresh pumice found along beaches in Fiji (hundreds of kilometers W of Tonga) during 9-25 November 2001. The T-wave signals and pumice sightings both relate to the activity discussed here.

During September through early November 2001, submarine volcanic activity was observed ~33 km S of Fonualei (figure 3). This same spot lies ~30 km NW of the Vava'u Group of the Tongan islands. This volcanic center lacked prior historical activity, although Taylor and Ewart (1997) indicated that a number of submarine structures were present between Late and Fonualei islands.

Figure 3. Map of the Vava'u region, with the Tonga Platform (to the E) and the active volcano belt (to the W), showing the site of the recent (September-October 2001) submarine volcanic activity. The symbols indicate active centers (white stars within black circles), i.e. those with recorded eruptions; inactive centers (solid black stars ), i.e. those with no recorded activity, and probable submarine centers (open stars). Bathymetric contours are in kilometers below sea level. Courtesy of Paul Taylor.

Form, structure, and depth. Although no details are available concerning the form and structure of this eruptive site, it is likely to be the summit of a submarine stratovolcano that rises from a NNE-SSW trending topographic high. A shoal has not been reported at the site during historical times. No surveys of this area have been conducted; however, its bathymetry suggests that several submarine structures rise from a depth of about 1 km to probably within 200-300 m of the surface. No shoal or island was observed when the site was visited by the Tonga Defense Services during early and mid-October 2001.

Volcanic activity. The activity appears to have been submarine and explosive in character. Known reports relating to this eruption are given in table 1. A plot of the seismic activity from stations in the Cook Islands and French Polynesia during 28-29 September 2001 were provided in Figure 1 of BGVN 26:11.

Table 1. A summary of observations relating to an unnamed submarine volcano (NW of Vava'u, Tonga). Latitudes and longitudes appear in degrees and decimal degrees; the original used degrees-minutes-seconds. Other significant revisions and substitutions to the original appear as text in brackets. Courtesy of Paul Taylor.

    Date (2001)       Activity

    27-28 September   T-phase seismic waves from a probable volcanic source
                      recorded in French Polynesia. Approximate coordinates of
                      18.39°S; 174.6°W, are located near the Vava'u Group.

    27 September      1800 - Reports of submarine activity were received from
                      near Vava'u. A local fisherman experienced "an abnormal
                      disturbance from the deep ocean." Shortly after an
                      ash-rich eruption column rose from the sea at 18.325°S,

    28 September      1300 - An "island" was reported to have formed during
                      the explosive activity with an ash-rich eruption column
                      still being produced. The "island" was estimated to be
                      about 2 miles [~ 3 km] long. The sea was "highly
                      disturbed and silky" at this time.

    01 October        0930 - Royal Tongan Airlines flights 801 and 802
                      reported that activity above the surface had ceased. A
                      huge underwater bank, about 1.5 miles [2.4 km] across,
                      was observed at 18.358°S, 174.346°W, [3.8 km SW] of the
                      initial location. The water was reported as "boiling
                      bubbles of seawater oozing out from the area to the sea

    03 October        A Tonga Defense Services patrol boat visited the area,
                      but due to heavy seas observations were restricted. The
                      surface of the sea in the region was discolored a "dark
                      whitish color". The discolored area was estimated to be
                      3 miles [~ 5 km] long (N-S direction) and 1.5-2
                      miles[2.4-3 km] wide. Near the reported location, the
                      sea appeared to contain a mixture of whitish and
                      yellow-brownish substances although no pumice was
                      observed floating on the surface. A local Notice to
                      Mariners (NTM 15/01) was issued, warning shipping to
                      stay away from the area.

    09 October        1600 - A Tonga Defense Services aircraft flew over the
                      site and reported that an area of discolored water was
                      present. No eruption column or pumice was observed and
                      the island reported earlier was not present.

    26 October        A Tonga Defense Services patrol boat visited the site
                      and observed an area of discolored water 300 m long
                      (NE-SW direction) centered on a position of 18.303°S,
                      174.377°W, [a spot 2.7 km NE of the initial position].
                      The discoloration was light-brownish in the center and
                      light greenish toward the outside. The charted depth of
                      the shoal at this location was 298 meters. No depth was
                      recorded by the boat's echo sounder and no attempt was
                      made to take a sounding over the discolored water.

    early November    Pumice strandings were reported along the coast of
                      Kadavu and on the S coast of Viti Levu, Fiji. Rafts
                      reported to be over 100 m in diameter with pumice
                      fragments ranging in size from under 1 cm to ~20 cm.

Comments. As noted above, the charted depth prior to the eruption was ~200-300 m and the syn-eruptive depth was not determined. Further, Taylor learned that post-eruptive depths had not been taken at the site. He goes on to state, "The initial activity was the result of submarine explosions, producing what was reported as 'an island' and an eruption column." In his report, Taylor concluded that the island was essentially a floating pumice raft and ". . . was more likely the effect of gases and pyroclastic material produced by the explosions breaking the surface, which appeared land-like. An eruption column of predominantly volcanic gas, steam, and pyroclastic material was then ejected above the surface."

Taylor (2002) goes on to discuss relevant volcanic hazards. Regarding approaching the volcano, he recommended that access be prohibited within 2 km, access restricted within the interval 2 to 4 km, and extreme care be taken when approaching or within the interval 4 to 5 km.

References. Taylor, P.W., 2002, Volcanic hazards assessment following the September-October 2001 eruption of a previously unrecognized submarine volcano W of Vava'u, kingdom of Tonga: Australian Volcanological Investigations, AVI Occasional Report No. 02/01

Taylor, P.W., 1999, A volcanic hazards assessment following the January 1999 eruption of Submarine Volcano III Tofua Volcanic Arc, Kingdom of Tonga: Australian Volcanological Investigations, AVI Occasional Report No. 99/01.

Taylor, P.W., and Ewart, A., 1997, The Tofua Volcanic Arc, Tonga, SW Pacific: A review of historic volcanic activity: Australian Volcanological Investigations, AVI Occasional Report No. 97/01.

Information Contacts: Paul Taylor, Australian Volcanological Investigations, PO Box 291, Pymble NSW 2073, Australia; Olivier Hyvernaud, Laboratoire de Geophysique, Papeete Tahiti, French Polynesia; Dan Shackelford, 3124 E. Yorba Linda Blvd., Apt. H-33, Fullerton, CA 92831-2324, USA.

10/2003 (BGVN 28:10) Pumice rafts from September-October 2001 eruption reach eastern Australia

A felsic shallow marine explosive eruption from a previously unknown volcano along the Tofua volcanic arc (Tonga) in September-October 2001 (BGVN 26:11 and 27:01) produced floating pumice rafts in Fiji in November 2001, approximately one month after it occurred. These sea-rafted pumice are the only recorded output of this subaqueous eruption at a remote location where direct observations are limited.

A new influx of sea-rafted pumice reached the eastern coast of Australia in October 2002 (figure 4), approximately one year after the eruption was first indicated by seismic activity and pumice stranding in Fiji. Pumice was stranded along at least two-thirds (>2,000 km) of the coastline of eastern Australia, extending from N of Townsville to Sydney. Typical amounts of pumice initially stranded on beaches were 500-4,000 individual clasts per m2; a minimum volume estimate of pumice deposited along the eastern Australian coastline is 1.25 x 105 m3. Most stranded pumice clasts are 1-5 cm diameter, although some outsized clasts are up to 10 cm. Many clasts were fouled by a variety of organisms, and dark algal coverings were common to all clasts that concealed the primary character of the pumice (figure 5). This is in contrast to pumice stranded on beaches in Fiji ~ 1 month after the eruption, which were clean of fouling organisms. Fouling organisms include algae, Bryozoa, serpulid worms, corals and, oysters with goose barnacles particularly abundant.

Figure 4. Map of the southwest Pacific Ocean showing the location of the unnamed volcano in the Tofua volcanic arc that erupted in September-October 2001 producing the pumice rafts. The general dispersal trajectory of the sea-rafted pumice is shown by the dashed line, and the pumice reached the eastern Australian coastline ~ 1 year after the eruption. Courtesy of Scott Bryan.
Figure 5. Closeup of beached pumice clasts from the unnamed volcano in the Tofua volcanic arc fouled by algae and goose barnacles (Lepas pectinata). Courtesy of Scott Bryan.

The pumice have a low phenocryst content (<5% modal) with the phenocryst assemblage consisting of calcic plagioclase (An88-74), pigeonite (En45 Fs46 Wo9), augite (En35 Fs29 Wo36), and titanomagnetite. Preliminary petrographic observations indicate that the pumice is compositionally homogenous, although there is considerable variation in vesicularity within and between clasts. Tubed pumice is a minor but distinctive clast type. The pumice, like previously stranded pumice on the Great Barrier Reef (Bryan, 1968, 1971), is low-K dacite in composition (table 2), characterized by low alkalis and high iron and silica. This composition is similar to other pumice-forming eruptions from the Tonga region (Bryan, 1968).

Table 2. Major element data on sea-rafted pumice clasts from eastern Australia, 2002. A, major element data for whole pumice clasts determined by the atomic absorption method of silicate rock analysis using Inductively-Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) at the University of Queensland. B, averaged pumice glass compositions analysed at the Centre for Microscopy & Microanalysis, University of Queensland, using a JEOL 8800-L (wavelength dispersive) electron microprobe. Analyses were performed with an accelerating voltage of 15 kV and with a probe current of 15 nA and a probe diameter of 10 microns to avoid volatilisation of alkali elements. Courtesy of Scott Bryan and Alex Cook.

    Element     HI1^A    GC1^A    P1^B     P2^B
                                  (n=3)    (n=3)

    SiO2        71.30    65.90    66.84    67.33
    TiO2         0.36     0.58     0.51     0.50
    Al2O3       12.80    12.31    12.29    12.16
    Fe2O3^T      5.50     9.88     --       --
    FeO^T        --       --       8.05     8.04
    MnO          0.10     0.18     0.16     0.15
    MgO          1.07     1.43     0.93     0.92
    CaO          4.34     5.77     5.40     5.23
    Na2O         3.45     3.20     2.71     2.80
    K2O          0.90     0.60     0.71     0.72
    P2O5         0.18     0.15     0.18     0.20
    BaO          --       --       0.03     0.05
    SrO          --       --       0.17     0.16
    LOI          0.92     1.87     --       --
    Raw Total   99.50    99.80    97.99    98.27

References. Bryan, W.B., 1968, Low-potash dacite drift pumice from the Coral Sea: Geological Magazine, v. 105, p. 431-439.

Bryan, W.B., 1971, Coral Sea drift pumice stranded on Eua Island, Tonga, in 1969: Geological Society of America Bulletin, v. 82, p. 2799-2812.

Information Contact: Scott Bryan, Department of Geology & Geophysics, Yale University, PO Box 208109, New Haven CT 06520 8109 USA (Email: scott.bryan@yale.edu ); Alex Cook, Queensland Museum, PO Box 3300, South Brisbane, Queensland 4101 AUSTRALIA (Email: alexC@qm.qld.gov.au).

05/2007 (BGVN 32:05) Bathymetric survey locates vent area and maps 2001 pumice deposits

An echo sounding depth survey of a recently active unnamed volcanic seamount (volcano number 0403-091) ~50 km NW of Vava'u was undertaken on 23 February 2007. The seamount is located within a roughly N-S segment of the submerged Tofua volcanic arc on a relatively broad plateau of less than 1,000 m depth, upon which five other seamounts rising to depths of 100 m are indicated on current bathymetric maps. One seamount indicated to shoal to depths of ~270 m, based on a reported spot depth recording in 1965, may correspond to this volcano.

No depth soundings were recorded at the previously described location of this volcano, with reported depths greater than 91 m. About 1.85 km (~1 nautical mile) to the NW, an area of shallow water (61-40 m) was mapped (figure 6). A relatively flat-topped seamount occurs with a maximum length of ~1.2 km (NW-SE) and 0.83 km width (NE-SW); much of the summit region is at or above 53 m below sea level. Two domal peaks cap the seamount and flank a depression on the E side. In profile, the seamount is steep-flanked, descending to water depths below 61 m over very short horizontal distances.

Figure 6. Bathymetric map and cross section of the unnamed Tongan seamount (volcano number 0403-091). NS: no depth sounding (ie. beyond depth-sounder range). Courtesy of Scott Bryan.

Two peaked areas on the seamount summit are inferred to represent pumice and other juvenile dacitic deposits from the 2001 eruption (BGVN 26:11 and 27:01). The broader domal area on the NW side would be consistent with maximum pumice deposition in response to NW-directed wind and ocean currents at the time of eruption and the dispersal of pumice rafts. Based on the summit profiles, at least 12 m of juvenile material erupted during the 2001 eruption may have accumulated on the summit. The prominent depression on the E side of the summit may therefore correspond to the vent area of the 2001 eruption, where crater floor depths are more than 61 m below sea level. The bathymetric survey indicates that the 2001 submarine dacitic explosive eruption occurred in shallow water depths (< 100 m).

General References. Bryan, S.E., 2007, Preliminary Report: Field investigation of Home Reef volcano and Unnamed Seamount 0403-091: Unpublished Report for Ministry of Lands, Survey, Natural Resources and Environment, Tonga, 9 p.

Bryan, S.E., Cook, A., Evans, J., Colls, P., Lawrence, M., Wells, M., Jell, J.S., Greig, A., and Leslie, R., 2004, Pumice rafting and faunal dispersion during 2001-2002 in the southwest Pacific: record of a dacitic submarine explosive eruption from Tonga: Earth and Planetary Science Letters, v. 227, p. 135-154.

Taylor, P.W., 2002, Volcanic hazards assessment following the September–October 2001 eruption of a previously unrecognised submarine volcano W of Vava'u, Kingdom of Tonga: Australian Volcanological Investigations, AVI Occasional Report No. 02/01, p. 1-7.

Information Contacts: Scott Bryan, School of Earth Sciences & Geography, Kingston Univ., Kingston Upon Thames, Surrey KT1 2EL, United Kingdom (Email: s.bryan@kingston.ac.uk); Peter Colls, School of Physical Sciences, Univ. of Queensland, St Lucia, Queensland 4072, Australia (Email: p.colls@mailbox.uq.edu.au).

A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about two-thirds of the way between Late and Fonualei volcanoes. The site of the eruption is along a NNE-SSW-trending submarine plateau south of Fonualei with an approximate bathymetric depth of 300 m. T-phase waves were recorded on September 27-28, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the east.

Summary of Holocene eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2001 Sep 27 2001 Sep 28 (?) Confirmed 2 Historical Observations

The Global Volcanism Program has no synonyms or subfeatures listed for Unnamed.

The Global Volcanism Program has no photographs available for Unnamed.

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title.

Bryan S E, Cook A, Evans J P, Colls P W, Wells M G, Lawrence M G, Jell J S, Greig A, Leslie R, 2004. Pumice rafting and faunal dispersion during 2001-2002 in the Southwest Pacific: record of a dacitic submarine explosive eruption from Tonga. Earth Planet Sci Lett, 227: 135-154.

Smithsonian Institution-GVN, 1990-. [Monthly event reports]. Bull Global Volc Network, v 15-33.

Taylor P, 2002. New submarine volcano (west of Vava'u). Aust Volc Invest Occ Rpt, 02/01: 1-7.

Volcano Types


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Oceanic crust (< 15 km)

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Affiliated Databases

Large Eruptions of Unnamed Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.