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Unnamed

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  • Tonga
  • New Zealand to Fiji
  • Submarine
  • 2001 CE
  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 18.325°S
  • 174.365°W

  • -40 m
    -131 ft

  • 243091
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number
Most Recent Weekly Report: 14 August-20 August 2019 Citation IconCite this Report

A submarine eruption in early August from an unnamed seamount about 50 km NW of Vava’u in Tonga created extensive areas of pumice rafts. Sailing crews encountered the pumice starting on 9 August about 40 km NNW of Late Island. Rachel Mackie described a pronounced odor of sulfur, and eventually being surrounded as far as she could see, with the surface pumice layer being 30 cm deep and containing pieces up to 80 cm in diameter. Sentinel-2 satellite imagery from 11 August showed the raft, averaging about 2.5 km across but strung out for 35 km NE-SW, located 70 km WNW of Late Island; another band of scattered rafts extended directly back from the main mass towards Late for 50 km. The raft continued drifting, and was at least another 60 km SW from its previous location as of 16 August. Eruptive activity at this location was previously reported in September-October 2001.

Sources: Sentinel Hub, Martin Jutzeler, Rachel Mackie


Most Recent Bulletin Report: November 2019 (BGVN 44:11) Citation IconCite this Report

Submarine eruption in early August creates pumice rafts that drifted west to Fiji

Large areas of floating pumice, termed rafts, were encountered by sailors in the northern Tonga region approximately 80 km NW of Vava'u starting around 9 August 2019; the pumice reached the western islands of Fiji by 9 October (figure 7). Pumice rafts are floating masses of individual clasts ranging from millimeters to meters in diameter. The pumice clasts form when silicic magma is degassing, forming bubbles as it rises to the surface, which then rapidly cools to form solid rock. The isolated vesicles formed by the bubbles provide buoyancy to the rock and in turn, the entire pumice raft. These rafts are spread and carried by currents across the ocean; rafts originating in the Tonga area can eventually reach Australia. This report summarizes the pumice raft eruption from early August 2019 using witness accounts and satellite images (acquisition dates are given in UTC). Pending further research, the presumed source is the unnamed Tongan seamount (volcano number 243091) about 45 km NW of Vava'u, the origin of an earlier pumice raft produced during an eruption in 2001.

Figure (see Caption) Figure 7. The path of the pumice from the unnamed Tongan seamount from 9 August to 9 October 2019 based on eye-witness accounts and satellite data discussed below, as well as additional Aqua/MODIS satellite images from NASA Worldview. Blue Marble MODIS/NASA Earth Observatory base map courtesy of NASA Worldview.

The first sighting of pumice was around 1430 on 9 August NW of Vava'u in Tonga (18° 22.068' S, 174° 50.800' W), when Shannon Lenz and Tom Whitehead on board SV Finely Finished initially encountered isolated rocks and smaller streaks of pumice clasts. The area covered by rock increasing to a raft with an estimated thickness of at least 15 cm that extended to the horizon in different directions, and which took 6-8 hours to cross (figure 8). There was no sulfur smell and the sound was described as a "cement mixer, especially below deck." There was also no plume or incandescence observed. Their video, posted to YouTube on 17 August, showed a thin surface layer of cohesive interconnected irregular streaks of pumice with the ocean surface still visible between them. Later footage showed a continuous, undulating mass of pumice entirely covering the ocean surface. Larger clasts are visible scattered throughout the raft. The pumice raft was visible in satellite imagery on this day NW of Late Island (figure 9). By 11 August the raft had evolved into a largely linear feature with smaller rafts to the SW (figure 10). Approximately four hours later, about 15 km to the WSW, Rachel Mackie encountered the pumice. Initially the pumice was "ribbons several hundred meters long and up to 20m wide. It was quite fine and like a slick across the surface of the water." By 2130 they were surrounded by the pumice, and around 25 km away the smell of sulfur was noted.

Figure (see Caption) Figure 8. The pumice raft from the unnamed Tongan seamount on 9 August 2019 taken by Shannon Lenz and Tom Whitehead on board SV Finely Finished. The photos show the pumice raft extending to the horizon in different directions. Scattered larger clasts protrude from the relatively smooth surface that entirely obscures the ocean surface. Courtesy of Shannon Lenz and Tom Whitehead via noonsite.
Figure (see Caption) Figure 9. The pumice raft from the unnamed Tongan seamount on 9 August 2019 (UTC) can be seen NW of Late Island of Tonga in this Aqua/MODIS satellite image. The dashed white line encompasses the visible pumice. The location of the pumice in this image is shown in figure 7. Courtesy of NASA WorldView.
Figure (see Caption) Figure 10. The Sentinel-2 satellite first imaged the pumice from the unnamed Tongan seamount on 11 August 2019 (UTC). This image indicates the pumice distribution with the main raft towards the W and the easternmost area of pumice approximately 45 km away. The eastern tip of the pumice area is located approximately 30 km WNW of Lake islands in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Michael and Larissa Hoult aboard the catamaran ROAM encountered the raft on 15 August (figure 11). They initially saw isolated clasts ranging from marble to tennis ball size (15-70 mm) at 18° 46′S, 174° 55'W. At around 0700 UTC (1900 local time) they noted the smell of sulfur at 18° 55′S, 175° 21′W, and by 0800 UTC they were immersed in the raft with visible clasts ranging from marble to basketball (25 cm) sizes. At this point the raft was entirely obscuring the ocean surface. On 16 and 21 August the pumice continued to disperse and drift NW (figures 12 and 13). On 20 August Scott Bryan calculated an average drift rate of around 13 km/day, with the pumice on this date about 164 km W of the unnamed seamount.

Figure (see Caption) Figure 11. Images of pumice from the unnamed Tongan seamount encountered by Michael and Larissa Hoult aboard the catamaran Roam on 15 August. Left: Larissa takes photographs with scale of pumice clasts; top right: a closeup of a pumice clast showing the vesicle network preserving the degassing structures of the magma; bottom left: Michael holding several larger pumice clasts. The location of their encounter with the pumice is shown in figure 7. Courtesy of SailSurfROAM.
Figure (see Caption) Figure 12. The pumice from the unnamed Tongan seamount (volcano number 243091) on 16 August 2019 UTC. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 13. On 21 August 2019 (UTC) the pumice from the unnamed Tongan seamount (volcano number 243091) had drifted at least 120 km WNW of Late Island in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

An online article published by Brad Scott at GeoNet on 9 September reported the preliminary size of the raft to be 60 km2, significantly smaller than the 2012 Havre seamount pumice raft that was 400 km2. Satellite identification of pumice-covered areas by GNS scientists showed the material moving SSW through 14 August (figure 14).

Figure (see Caption) Figure 14. A compilation of mapped pumice raft extents from 9 August (red line) through to 14 August (dark blue) from Suomi NPP, Terra, Aqua, and Sentinel-2 satellite images. The progression of the pumice raft is towards the SW. Courtesy of Salman Ashraf, GNS Science.

On 5 September the Maritime Safety Authority of Fiji (MSAF) issued a notice to mariners stating that the pumice was sighted in the vicinity of Lakeba, Oneata, and Aiwa Islands and was moving to the W. On 6 September a Planet Labs satellite image shows pumice encompassing the Fijian island of Lakeba over 450 km W of the Tongan islands (figure 15). The pumice entered the lagoon within the barrier reef and drifted around the island to continue towards the W. The pumice was imaged by the Landsat 8 satellite on 26 September as it moved through the Fijian islands, approximately 760 km away from its source (figure 16). The pumice is segmented into numerous smaller rafts of varying sizes that stretch over at least 140 km. On 12 September the Fiji Sun reported that the pumice had reached some of the Lau islands and was thick enough near the shore for people to stand on it.

Figure (see Caption) Figure 15. Planet Labs satellite images show Lakeba Island to the E of the larger Viti Levu Island in the Fiji archipelago. The top image shows the island on 7 July 2019 prior to the pumice raft from the unnamed Tongan seamount. The bottom image shows pumice on the sea surface almost entirely encompassing the island on 6 September. The location of the pumice in this image is shown in figure 7. Courtesy of Planet Labs.
Figure (see Caption) Figure 16. Landsat 8 satellite images show the visible extent of the unnamed seamount pumice on 26 September 2019 (UTC), up to approximately 760 km from the Tongan islands. The pumice seen here extends over a distance of 140 km. The top image shows the locations of the other three images in the white boxes, with a, b, and c indicating the locations. White arrows point to examples of the light brown pumice rafts in these images, seen through light cloud cover. The island in the lower right is Koro Island, the island to the lower left is Viti Levu, and the island to the top right is Vanua Levu. The location of the pumice in this image is shown in figure 7. Landsat 8 true color-pansharpened satellite images courtesy of Sentinel Hub.

Pumice had reached the Yasawa islands in western Fiji by 29 September and was beginning to fill the eastern bays (figure 17). By 9 October bays had been filled out to 500-600 m from the shore, and pumice had also passed through the islands to continue towards the W (figure 18). At this point the pumice beyond the islands had broken up into linear segments that continued towards the NW.

Figure (see Caption) Figure 17. These Sentinel-2 satellite images show the pumice from the unnamed Tongan seamount drifting towards the Yasawa islands of Fiji. The 24 September 2019 (UTC) image shows the beaches without the pumice, the 29 September image shows pumice drifting westward towards the islands, and the 9 October image shows the bays partly filled with pumice out to a maximum of 500-600 m from the shore. These islands are approximately 850 km from the Tongan islands. The Yasawa islands coastline impacted by the pumice shown in these images stretches approximately 48 km. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.
Figure (see Caption) Figure 18. This Sentinel-2 satellite image acquired on 9 October 2019 (UTC) shows expanses of pumice from the unnamed Tongan seamount that passed through the Yasawa islands of Fiji and was continuing NWW, seen in the center of the image. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Information Contacts: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Salman Ashraf, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Scott Bryan, School of Earth, Environmental & Biological Sciences, Science and Engineering Faculty, Queensland University of Technology, R Block Level 2, 204, Gardens Point (URL: https://staff.qut.edu.au/staff/scott.bryan); Shannon Lenz and Tom Whitehead, SV Finely Finished (URL: https://www.noonsite.com/news/south-pacific-tonga-to-fiji-navigation-alert-dangerous-slick-of-volcanic-rubble/, YouTube: https://www.youtube.com/watch?v=PEsHLSFFQhQ); Michael and Larissa Hoult, Sail Surf ROAM (URL: https://www.facebook.com/sailsurfroam/); Rachel Mackie, OLIVE (URL: http://www.oliveocean.com/, https://www.facebook.com/rachel.mackie.718); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Fiji Sun (URL: https://fijisun.com.fj/2019/09/12/pumice-menace-hits-parts-of-lau-group/).

Weekly Reports - Index


2019: August


14 August-20 August 2019 Citation IconCite this Report

A submarine eruption in early August from an unnamed seamount about 50 km NW of Vava’u in Tonga created extensive areas of pumice rafts. Sailing crews encountered the pumice starting on 9 August about 40 km NNW of Late Island. Rachel Mackie described a pronounced odor of sulfur, and eventually being surrounded as far as she could see, with the surface pumice layer being 30 cm deep and containing pieces up to 80 cm in diameter. Sentinel-2 satellite imagery from 11 August showed the raft, averaging about 2.5 km across but strung out for 35 km NE-SW, located 70 km WNW of Late Island; another band of scattered rafts extended directly back from the main mass towards Late for 50 km. The raft continued drifting, and was at least another 60 km SW from its previous location as of 16 August. Eruptive activity at this location was previously reported in September-October 2001.

Sources: Sentinel Hub; Martin Jutzeler; Rachel Mackie


Bulletin Reports - Index

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

11/2019 (BGVN 44:11) Submarine eruption in early August creates pumice rafts that drifted west to Fiji




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


November 2001 (BGVN 26:11) Citation IconCite this Report

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 (see Caption) 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 (see Caption) 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 Contacts: Olivier Hyvernaud; Laboratoire de Géophysique; PO Box 640 Papeete; Tahiti; French Polynesia; Roman Leslie, Centre for Ore Deposit Research, University of Tasmania, GPO Box 252-79, Hobart, TAS 7001, Australia (URL: http://www.utas.edu.au/codes/).


January 2002 (BGVN 27:01) Citation IconCite this Report

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 (see Caption) 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 Activity
27-28 Sep 2001 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 Sep 2001 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, 174.365°W.
28 Sep 2001 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 Oct 2001 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 surface".
03 Oct 2001 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 Oct 2001 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 Oct 2001 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 Nov 2001 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.


October 2003 (BGVN 28:10) Citation IconCite this Report

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 (see Caption) 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 (see Caption) 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 in dicate 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. Samples HI1 and GC1: 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. Samples P1 and P2 (n=3 for both): 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 GC1 P1 P2
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 Contacts: Scott Bryan, Department of Geology & Geophysics, Yale University, PO Box 208109, New Haven CT 06520 8109 USA; Alex Cook, Queensland Museum, PO Box 3300, South Brisbane, Queensland 4101 Australia.


May 2007 (BGVN 32:05) Citation IconCite this Report

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 (see Caption) 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; Peter Colls, School of Physical Sciences, Univ. of Queensland, St Lucia, Queensland 4072, Australia.


November 2019 (BGVN 44:11) Citation IconCite this Report

Submarine eruption in early August creates pumice rafts that drifted west to Fiji

Large areas of floating pumice, termed rafts, were encountered by sailors in the northern Tonga region approximately 80 km NW of Vava'u starting around 9 August 2019; the pumice reached the western islands of Fiji by 9 October (figure 7). Pumice rafts are floating masses of individual clasts ranging from millimeters to meters in diameter. The pumice clasts form when silicic magma is degassing, forming bubbles as it rises to the surface, which then rapidly cools to form solid rock. The isolated vesicles formed by the bubbles provide buoyancy to the rock and in turn, the entire pumice raft. These rafts are spread and carried by currents across the ocean; rafts originating in the Tonga area can eventually reach Australia. This report summarizes the pumice raft eruption from early August 2019 using witness accounts and satellite images (acquisition dates are given in UTC). Pending further research, the presumed source is the unnamed Tongan seamount (volcano number 243091) about 45 km NW of Vava'u, the origin of an earlier pumice raft produced during an eruption in 2001.

Figure (see Caption) Figure 7. The path of the pumice from the unnamed Tongan seamount from 9 August to 9 October 2019 based on eye-witness accounts and satellite data discussed below, as well as additional Aqua/MODIS satellite images from NASA Worldview. Blue Marble MODIS/NASA Earth Observatory base map courtesy of NASA Worldview.

The first sighting of pumice was around 1430 on 9 August NW of Vava'u in Tonga (18° 22.068' S, 174° 50.800' W), when Shannon Lenz and Tom Whitehead on board SV Finely Finished initially encountered isolated rocks and smaller streaks of pumice clasts. The area covered by rock increasing to a raft with an estimated thickness of at least 15 cm that extended to the horizon in different directions, and which took 6-8 hours to cross (figure 8). There was no sulfur smell and the sound was described as a "cement mixer, especially below deck." There was also no plume or incandescence observed. Their video, posted to YouTube on 17 August, showed a thin surface layer of cohesive interconnected irregular streaks of pumice with the ocean surface still visible between them. Later footage showed a continuous, undulating mass of pumice entirely covering the ocean surface. Larger clasts are visible scattered throughout the raft. The pumice raft was visible in satellite imagery on this day NW of Late Island (figure 9). By 11 August the raft had evolved into a largely linear feature with smaller rafts to the SW (figure 10). Approximately four hours later, about 15 km to the WSW, Rachel Mackie encountered the pumice. Initially the pumice was "ribbons several hundred meters long and up to 20m wide. It was quite fine and like a slick across the surface of the water." By 2130 they were surrounded by the pumice, and around 25 km away the smell of sulfur was noted.

Figure (see Caption) Figure 8. The pumice raft from the unnamed Tongan seamount on 9 August 2019 taken by Shannon Lenz and Tom Whitehead on board SV Finely Finished. The photos show the pumice raft extending to the horizon in different directions. Scattered larger clasts protrude from the relatively smooth surface that entirely obscures the ocean surface. Courtesy of Shannon Lenz and Tom Whitehead via noonsite.
Figure (see Caption) Figure 9. The pumice raft from the unnamed Tongan seamount on 9 August 2019 (UTC) can be seen NW of Late Island of Tonga in this Aqua/MODIS satellite image. The dashed white line encompasses the visible pumice. The location of the pumice in this image is shown in figure 7. Courtesy of NASA WorldView.
Figure (see Caption) Figure 10. The Sentinel-2 satellite first imaged the pumice from the unnamed Tongan seamount on 11 August 2019 (UTC). This image indicates the pumice distribution with the main raft towards the W and the easternmost area of pumice approximately 45 km away. The eastern tip of the pumice area is located approximately 30 km WNW of Lake islands in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Michael and Larissa Hoult aboard the catamaran ROAM encountered the raft on 15 August (figure 11). They initially saw isolated clasts ranging from marble to tennis ball size (15-70 mm) at 18° 46′S, 174° 55'W. At around 0700 UTC (1900 local time) they noted the smell of sulfur at 18° 55′S, 175° 21′W, and by 0800 UTC they were immersed in the raft with visible clasts ranging from marble to basketball (25 cm) sizes. At this point the raft was entirely obscuring the ocean surface. On 16 and 21 August the pumice continued to disperse and drift NW (figures 12 and 13). On 20 August Scott Bryan calculated an average drift rate of around 13 km/day, with the pumice on this date about 164 km W of the unnamed seamount.

Figure (see Caption) Figure 11. Images of pumice from the unnamed Tongan seamount encountered by Michael and Larissa Hoult aboard the catamaran Roam on 15 August. Left: Larissa takes photographs with scale of pumice clasts; top right: a closeup of a pumice clast showing the vesicle network preserving the degassing structures of the magma; bottom left: Michael holding several larger pumice clasts. The location of their encounter with the pumice is shown in figure 7. Courtesy of SailSurfROAM.
Figure (see Caption) Figure 12. The pumice from the unnamed Tongan seamount (volcano number 243091) on 16 August 2019 UTC. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 13. On 21 August 2019 (UTC) the pumice from the unnamed Tongan seamount (volcano number 243091) had drifted at least 120 km WNW of Late Island in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

An online article published by Brad Scott at GeoNet on 9 September reported the preliminary size of the raft to be 60 km2, significantly smaller than the 2012 Havre seamount pumice raft that was 400 km2. Satellite identification of pumice-covered areas by GNS scientists showed the material moving SSW through 14 August (figure 14).

Figure (see Caption) Figure 14. A compilation of mapped pumice raft extents from 9 August (red line) through to 14 August (dark blue) from Suomi NPP, Terra, Aqua, and Sentinel-2 satellite images. The progression of the pumice raft is towards the SW. Courtesy of Salman Ashraf, GNS Science.

On 5 September the Maritime Safety Authority of Fiji (MSAF) issued a notice to mariners stating that the pumice was sighted in the vicinity of Lakeba, Oneata, and Aiwa Islands and was moving to the W. On 6 September a Planet Labs satellite image shows pumice encompassing the Fijian island of Lakeba over 450 km W of the Tongan islands (figure 15). The pumice entered the lagoon within the barrier reef and drifted around the island to continue towards the W. The pumice was imaged by the Landsat 8 satellite on 26 September as it moved through the Fijian islands, approximately 760 km away from its source (figure 16). The pumice is segmented into numerous smaller rafts of varying sizes that stretch over at least 140 km. On 12 September the Fiji Sun reported that the pumice had reached some of the Lau islands and was thick enough near the shore for people to stand on it.

Figure (see Caption) Figure 15. Planet Labs satellite images show Lakeba Island to the E of the larger Viti Levu Island in the Fiji archipelago. The top image shows the island on 7 July 2019 prior to the pumice raft from the unnamed Tongan seamount. The bottom image shows pumice on the sea surface almost entirely encompassing the island on 6 September. The location of the pumice in this image is shown in figure 7. Courtesy of Planet Labs.
Figure (see Caption) Figure 16. Landsat 8 satellite images show the visible extent of the unnamed seamount pumice on 26 September 2019 (UTC), up to approximately 760 km from the Tongan islands. The pumice seen here extends over a distance of 140 km. The top image shows the locations of the other three images in the white boxes, with a, b, and c indicating the locations. White arrows point to examples of the light brown pumice rafts in these images, seen through light cloud cover. The island in the lower right is Koro Island, the island to the lower left is Viti Levu, and the island to the top right is Vanua Levu. The location of the pumice in this image is shown in figure 7. Landsat 8 true color-pansharpened satellite images courtesy of Sentinel Hub.

Pumice had reached the Yasawa islands in western Fiji by 29 September and was beginning to fill the eastern bays (figure 17). By 9 October bays had been filled out to 500-600 m from the shore, and pumice had also passed through the islands to continue towards the W (figure 18). At this point the pumice beyond the islands had broken up into linear segments that continued towards the NW.

Figure (see Caption) Figure 17. These Sentinel-2 satellite images show the pumice from the unnamed Tongan seamount drifting towards the Yasawa islands of Fiji. The 24 September 2019 (UTC) image shows the beaches without the pumice, the 29 September image shows pumice drifting westward towards the islands, and the 9 October image shows the bays partly filled with pumice out to a maximum of 500-600 m from the shore. These islands are approximately 850 km from the Tongan islands. The Yasawa islands coastline impacted by the pumice shown in these images stretches approximately 48 km. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.
Figure (see Caption) Figure 18. This Sentinel-2 satellite image acquired on 9 October 2019 (UTC) shows expanses of pumice from the unnamed Tongan seamount that passed through the Yasawa islands of Fiji and was continuing NWW, seen in the center of the image. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Information Contacts: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Salman Ashraf, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Scott Bryan, School of Earth, Environmental & Biological Sciences, Science and Engineering Faculty, Queensland University of Technology, R Block Level 2, 204, Gardens Point (URL: https://staff.qut.edu.au/staff/scott.bryan); Shannon Lenz and Tom Whitehead, SV Finely Finished (URL: https://www.noonsite.com/news/south-pacific-tonga-to-fiji-navigation-alert-dangerous-slick-of-volcanic-rubble/, YouTube: https://www.youtube.com/watch?v=PEsHLSFFQhQ); Michael and Larissa Hoult, Sail Surf ROAM (URL: https://www.facebook.com/sailsurfroam/); Rachel Mackie, OLIVE (URL: http://www.oliveocean.com/, https://www.facebook.com/rachel.mackie.718); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Fiji Sun (URL: https://fijisun.com.fj/2019/09/12/pumice-menace-hits-parts-of-lau-group/).

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

Eruptive History

There is data available for 1 Holocene eruptive periods.

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

There is no Deformation History data available for Unnamed.

Emission History

There is no Emissions History data available for Unnamed.

Photo Gallery

The Global Volcanism Program has no photographs available for Unnamed.

GVP Map Holdings

The maps shown below have been scanned from the GVP map archives and include the volcano on this page. Clicking on the small images will load the full 300 dpi map. Very small-scale maps (such as world maps) are not included. The maps database originated over 30 years ago, but was only recently updated and connected to our main database. We welcome users to tell us if they see incorrect information or other problems with the maps; please use the Contact GVP link at the bottom of the page to send us email.


Title: Fiji, New Caledonia, Tonga
Publisher: DMA Aerospace Center
Country: Fiji
Year: 1986
Series: ONC
Map Type: Topographic
Scale: 1:1,000,000
Map of Fiji, New Caledonia, Tonga

Title: Tonga Region, Topo of
Publisher: USGS-CCOP/SOPAC S. Pacific Project
Country: Tonga
Year: 1982
Map Type: Bathymetric
Scale: 1:1,800,000
Map of Tonga Region, Topo of
Smithsonian Sample Collections Database

The following 1 samples associated with this volcano can be found in the Smithsonian's NMNH Department of Mineral Sciences collections, and may be availble for research (contact the Rock and Ore Collections Manager). Catalog number links will open a window with more information.

Catalog Number Sample Description Lava Source Collection Date
NMNH 117278 Drift Pumice -- --
External Sites