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Report on Fonualei (Tonga) — November 2001


Bulletin of the Global Volcanism Network, vol. 26, no. 11 (November 2001)
Managing Editor: Richard Wunderman.

Fonualei (Tonga) Typical steam emissions observed in August 2000

Please cite this report as:

Global Volcanism Program, 2001. Report on Fonualei (Tonga) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 26:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200111-243100



18.023°S, 174.317°W; summit elev. 188 m

All times are local (unless otherwise noted)

In February 1974 a ship's captain reported that Fonualei was "emitting small quantities of steam, foam, and rocks all around the crater" (CSLP Card 1802). Large fluctuations in fumarolic activity were observed by geologists in July 1979 (SEAN 04:12).

On 19 August 2000, Jeff and Raine Williams, aboard the S/Y Gryphon, passed Fonualei enroute from Tonga to Wallis Island. They noted that the lower part of the island was covered with lush tropical vegetation, but the upper parts were scarred brown and gray, and steam was venting from the top of the island. Along the coast were rugged volcanic cliffs and black sand beaches.

[Sections about seismicity and pumice rafts have been moved. Later investigations showed that they probably originated from an unnamed submarine volcano in the Tonga Islands.]

Geological Summary. The small island of Fonualei (~2 km diameter) contains a fumarolically active crater breached to the SE with a fresh lava flow extending to the sea and forming a rugged shoreline. Steep, inward-facing scarps mark the rim of a partially exposed caldera. Blocky lava flows fill much of the northern caldera moat and reach the sea to the north and east. In contrast to the andesitic and basaltic rocks of other islands of the Tonga arc, Fonualei lavas are of dominantly dacitic composition. Eruptions have been recorded since 1791, with the largest taking place in June 1846, when explosive eruptions produced large pumice rafts, ashfall damaged crops on the island of Vava'u (70 km SSE), and ash was reported by vessels up to 950 km distant. In 1939 explosive and effusive activity occurred from summit and flank vents, and water spouts were reported 1.6 km SE of the island.

Information Contacts: Jeff and Raine Williams, P.O. Box 729, Funkstown, MD 21734, USA.