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Submarine volcanism--a call for help from geophysicists, satellite remote sensors, aviatiors, etc.
From: Rick Wunderman
NOTE NEW Email!!! wunderma@xxxxxx
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This is a call from the Smithsonian’s Global Volcanism Program for geophysicists, pilots, and satellite remote-sensors to help illuminate submarine eruptions in the North and South Pacific. The former case is quite local; the latter has spawned pumice rafts drifting over large areas.
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1. The North Pacific eruption is the least known. Here’s all currently available information on this seemingly local event (forwarded to us from Olivier Hyvernaud (Laboratoire de Géophysique Papeete French Polynesia - FRANCE)). It is a Notice to Mariners:
1921/06(97). NORTH PACIFIC.
CHART 97521 (6TH ED).
DISCOLORED WATER WITH SUBMARINE VOLCANIC ACTIVITY REPORTED WITHIN 1700 METERS OF 24-17.5N 141-29.4E AT 040400Z OCT.
(041009Z OCT 2006)
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2. PUMICE RAFTS
Pumice rafts presumably generated in the Tonga region are currently drifting through the Fiji islands. A series of mariner’s reports have now emerged on this South-Pacific pumice raft, which may have come from Metis Shoal or another submarine volcano in North Tonga generated in perhaps mid-September 2006.
We have pieced together the following PRELIMINARY report on the raft. In addition, we have a map plotting where the key mariner’s observation occurred, as well as several photographs documenting the raft. The figure captions are included, but for brevity we have left the graphics files out of this report (see the links below for some of the photos).
WHAT IS STILL BADLY NEEDED ARE OBSERVATIONS OF THE RAFT(S) EARLY STAGES. Those might shed light on the source vent location, the eruptive style, and the birth and dispersal of the now-drifting pumice.
Metis Shoal
Tonga Islands, SW Pacific
19.18̊S, 174.87̊W; summit elev. 43 m
All times are local (= UTC + 13 hours)
Although no direct observations of an eruption from Metis Shoal have been reported, it appears that recent pumice rafts drifting from Tonga to Fiji originated at that volcano. A compilation of reports plotted using Google Earth shows the timing and distribution of reports posted through mid-October 2006 (figure 1) that are discussed in this report.
The earliest report found to this point comes from a boat with callsign KB1LSY, noting that "thick pumice" slowed them to 2 knots for 30 minutes during the early morning hours of 28 August as they were approaching the northern islands of the Lau Group in Fiji, about 500 km NW of Metis Shoal.
The Soren Larsen sailed through "a sea of floating pumice" one evening that "sounded like we were sailing through ice" just before reaching Fiji. This encounter was probably on 30 August when their online tracker located them just W of the central Lau islands after departing Neiafu, Vava'u Island, Tonga on the 28th. No eruptive activity or pumice was not noted in their online logs for 14-15 and 23-24 August when they transited along the island chain east of Metis Shoal.
Between 23 August and 7 September the Encore II was at Neiafu. While listening to the “Rag of the Air” net broadcast out of Fiji during this period the crew learned of pumice rafts along their expected path to Fiji. The operator of this broadcast, which provides weather reports for boats going between Tonga and Fiji, apparently informed mariners that an underwater volcano corresponding to the location of Metis Shoal (though not identified by name), described as "continuously erupting, and from time to time creates a small island that later disappears," had been producing pumice that later floated into the Vava’u area. One report was of a mass of pumice about 11 km long and at least a meter ("many feet") thick. The crew later described seeing pumice pieces that had been collected in Vava’u which were the size of grapefruits
The Encore II departed from Neiafu on 8 September on a course taking them around a set of Fijian islands and reefs called the Lau Group. The crew believed that this route, going NW around the Lau Group, helped them avoid most of the pumice. As they approached their turning point about two thirds of the way to Fiji, they encountered "rivers of pumice" floating roughly parallel to their NW course due to the SE winds (figure 2). Some rocks that they collected were about 5-10 cm in diameter, although most was about the size of pea gravel. The parallel streams of pumice, only a single layer thick, were sometimes up to 90 m wide and 400 m long. The crew of the Encore II later heard reports from several boats that took a more westerly route through the Lau Group to Fiji that they encountered much larger areas of pumice. Crew on the Norwegian sailboat Stormsvalen went through larger and thicker areas of pumice, leaving a track in the pumice as they went through (figures 3 and 4). They noted that for boats traveling through the pumice during higher winds and seas encountered a problem of airborne pumice pelting the crews and their boats. One crew reported pumice covering their deck. Later in their voyage the Encore II saw pumice streams and small floating rocks while cruising around the southeastern end of Vanua Levu.
Figure 1. Photograph showing small areas of floating pumice just NE of the Lau Group if islands, Fiji, around 10 September 2006. Courtesy of the Encore II crew.
Figure 2. Photograph showing a large pumice raft near the Lau Group of islands, Fiji, on an unknown date in early to mid-September 2006. Courtesy of the Stormsvalen crew via the Encore II.
Figure 3. View of a large pumice raft after the passage of a sailing vessel near the Lau Group of islands, Fiji, on an unknown date in early to mid-September 2006. Courtesy of the Stormsvalen crew via the Encore II.
A biologist aboard the M/V National Geographic Endeavour reported that on the morning of 16 September they observed an extensive region of floating pumice "... in long, wind-driven rows, approximately 1-5 m wide and up to several hundred meters long." Pieces of pumice averaged 0.5-8 cm in longest dimension. The largest piece observed was approximately 15 cm in longest dimension. The observations continued for 3.5 hours, with little interuption, until they made landfall at Vatoa Island in the Lau Group. Moderate windrows of pumice, up to several inches deep, were observed on the beaches of Vatoa.
On 19 September David Forsythe reported that large rafts of pumice were passing through the northern Lau group in Fiji (figure 5). Gooseneck barnacles up to 10 mm length on the largest pieces "indicate some weeks/months at sea."
Figure 5. Panorama view of Indigo Swan Beach, Naitauba Island, Fiji, September 2006. Courtesy of David Forsythe.
The Fiji Times Online reported on 20 September that villagers living along the coastal areas of Saqani in Cakaudrove were battling to clear their pumice-covered seashores and rivers. Villagers saw the pumice floating in the sea near their homes on 18 September, and by the next day the pumice covered the river and villagers could not fish or travel by boats and bamboo rafts to their plantations.
On 30 September the Windbird log noted that "There was a volcanic eruption in northern Tonga a couple of months ago and cruisers are still having to avoid the huge pumice field that is floating about between Tonga and Fiji."
Roger Matthews arrived in Kandavu, Fiji, on 30 September and reported that pumice had been coming ashore for about a week. At that time the goose barnacles on the bigger clasts were about 2-3 mm, by 7 October barnacle size on arriving pumice had increased to around 4-6 mm. He was also in contact with an Australian volcanologist who was fishing in Koro (Lomaiviti Group) and who also observed the pumice.
Bob McDavitt's "Weathergram" for 15 October noted that reports from yachts sailing between Tonga and Fiji indicated that pumice was no longer present.
As of 16 October the French Polynesian hydroacoustic network had not recorded any recent volcanic activity from Tonga, but data was still being retreived from remote islands.
Geologic Summary. Metis Shoal, a submarine volcano midway between the islands of Kao and Late, has produced a series of ephemeral islands since the first reported activity in the mid-19th century. During periods of inactivity, waves have been observed to break on rocky reefs or sandy banks with depths of 10 m or less. Dacitic tuff cones formed during the first 20th-century eruptions in 1967 and 1979 were soon eroded beneath the sea surface. Its latest eruption in 1995 produced an island with a diameter of 280 m and a height of 43 m following growth of a lava dome above the surface.
Information Contacts: Encore II Crew (URL: http://www.encorevoyages.com/); KB1LSY Crew (URL: http://www.pangolin.co.nz/yotreps/tracker.php?ident=KB1LSY); Bob McDavitt's Weathergram (URL: http://www.pangolin.co.nz/yotreps/list_manager.php#Bob McDavitt's Pacific Weathergrams); Nick Sambrook, Tall Ship Soren Larsen (URL: http://www.sorenlarsen.co.nz/2006/V237_Tonga-Fiji/V237_Tonga-Fiji_Nick.htm; http://www.sorenlarsen.co.nz/Voylog_Track.htm); Roger Matthews, Private Bag 93500, Takapuna, North Shore City 1332, New Zealand; Olivier Hyvernaud (Email: hyvernaud@xxxxxxxxxx); Windbird Crew (URL: http://handleysail.com/logs/?cat=1&paged=2); David Forsythe, Naitauba Island, Fiji (Email: Da-vid_Forsythe@xxxxxxxxxx); David Cothran, 1211 Colestin Rd., Ashland, OR 97520, USA (Email: david@xxxxxxxxx). <mailto:david@xxxxxxxxx).>
Encore II Crew http://www.encorevoyages.com/ <http://www.encorevoyages.com/> ,
KB1LSY Crew http://www.pangolin.co.nz/yotreps/tracker.php?ident=KB1LSY <http://www.pangolin.co.nz/yotreps/tracker.php?ident=KB1LSY> ,
Bob McDavitt's Weathergram, McDavitt's Pacific Weathergrams http://www.pangolin.co.nz/yotreps/list_manager.php#Bob <http://www.pangolin.co.nz/yotreps/list_manager.php#Bob>
Metis Shoal information from the Global Volcanism Program
http://www.volcano.si.edu/world/volcano.cfm?vnum=0403-07= <http://www.volcano.si.edu/world/volcano.cfm?vnum=0403-07=>
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Rick Wunderman
NOTE NEW Email!!! wunderma@xxxxxx
(My previous address still accepts incoming mail)
Editor
Bulletin of the Global Volcanism Network
Smithsonian Institution
National Museum of Natural History
10th & Constitution Ave., NW
Washington, DC 20560-0119
Web: www.volcano.si.edu
Phone (202) 633 1827
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