๐ŸŒ‹VolcanoAtlas

Fonualei

Tonga's Remote Dacitic Island Volcano

Elevation

188 m

Last Eruption

1957

Type

Stratovolcano

Country

Tonga

Location

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Volcanic Hazards & Risk Assessment

Primary Hazards

  • Pyroclastic flows
  • Lava flows
  • Volcanic bombs and ballistics
  • Lahars and mudflows

Risk Level

Population at RiskLow
Infrastructure RiskHigh
Aviation RiskSignificant

Geological Composition & Structure

Rock Types

Primary
Unknown
Silica Content
Varied composition

Tectonic Setting

Unknown
Intraplate setting with hotspot or regional volcanic activity.

Age & Formation

Epoch
Unknown
Evidence
Unknown

Eruption Statistics & Analysis

MetricValueGlobal RankingSignificance
Total Recorded EruptionsUnknownLowModerately active volcano
Maximum VEIVEI UnknownMinorLocal impact potential
Recent Activity69 years agoHistoricalRecently active

Monitoring & Alert Status

Monitoring Networks

Global Volcanism Program
International eruption database

Current Status

Normal
No recent activity. Routine monitoring continues.

Authority Sources

Smithsonian GVP
Official volcano database

Related Volcanoes

All Tonga Volcanoes
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Stratovolcano Volcanoes
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Tonga-Kermadec Volcanic Regions
Regional volcanoes

Other Volcanoes in Tonga

Interesting Facts

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Fonualei is one of only a handful of dominantly dacitic volcanoes in the entire Tonga-Kermadec arc โ€” most neighboring volcanoes produce basaltic or andesitic lavas.

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The 1846 eruption deposited ash on ships sailing nearly 1,000 km from the island, making it one of the most far-reaching explosive events recorded in the 19th-century South Pacific.

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Although just 188 m above sea level, Fonualei rises approximately 1,000 m from the surrounding seafloor โ€” the visible island is merely the summit of a much larger submarine volcanic edifice.

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The Spanish name for the island, Amargura (meaning 'bitterness'), was given by navigator Don Francisco Mourelle in 1781 because the island appeared so barren and desolate from eruptions.

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In 1993, Fonualei became a critical refuge for the Tongan megapode (Megapodius pritchardii), one of the world's rarest birds, with a translocated population growing from 10 chicks to an estimated 300โ€“500 individuals by 2003.

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Fonualei's nearest neighbor, the island of Tokลซ (19.7 km SE), was once used as a base by people who maintained gardens on Fonualei during periods of volcanic quiescence in the 1830s.

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The waterspouts observed 1.6 km offshore during the 1939 eruption were likely phreatic explosions caused by submarine volcanic heating rather than meteorological phenomena.

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Pumice rafts from eruptions along the Tonga-Kermadec arc can drift thousands of kilometers โ€” a pumice raft from a 2019 submarine eruption near Fonualei eventually reached the Australian coast.

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Fonualei was designated an Important Bird Area by BirdLife International for its large sooty tern colony and other seabird populations.

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The Pacific Plate converges toward the Indo-Australian Plate beneath Tonga at up to 24 cm per year, making the Tonga-Kermadec Trench one of the fastest subduction zones on Earth.

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Despite sitting within one of the world's most active volcanic arcs, Fonualei has no dedicated monitoring instruments โ€” regional seismic detection relies on networks in French Polynesia over 2,000 km away.

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The American whaling ship Charles W. Morgan sailed through Fonualei's 1846 ash cloud for nine hours, with the logbook describing it as a 'Sand Mist' too thick to see through.

Frequently Asked Questions

Is Fonualei volcano still active?
Yes, Fonualei is classified as an active volcano. Its last confirmed magmatic eruption occurred in June 1957, and the volcano has maintained persistent fumarolic activity โ€” venting steam and sulfurous gases from its summit crater โ€” through at least the 2020s. In September 2022, scientists documented water discoloration and sulfuric gas emissions near the island, confirming ongoing hydrothermal activity. With six confirmed eruptions since 1791 and an average recurrence interval of roughly 25โ€“30 years, volcanologists consider Fonualei capable of future eruptions. Its position on the highly active Tonga-Kermadec subduction zone, one of the fastest converging plate boundaries on Earth, ensures a continued magma supply.
When did Fonualei last erupt?
Fonualei's most recent confirmed eruption began on June 16, 1957. Before that, eruptions occurred in 1951, 1939, 1906, 1846, and 1791. An uncertain eruption was reported in February 1974, when a ship's captain observed the island emitting steam, foam, and rocks, but this may have been heightened fumarolic activity rather than a true magmatic eruption. Hydro-acoustic signals detected near Fonualei in September 2001 were later attributed to an unnamed submarine volcano approximately 35 km to the south rather than Fonualei itself.
How big was the 1846 eruption of Fonualei?
The June 1846 eruption was rated VEI 4 on the Volcanic Explosivity Index, making it a 'cataclysmic' event and by far the most powerful eruption recorded at Fonualei. The eruption produced massive pumice rafts that spread across the ocean surface, deposited enough ash on the island of Vava'u (70 km away) to damage crops, and generated an ash cloud that was encountered by ships nearly 1,000 km from the source. The American whaler Charles W. Morgan sailed through the ash cloud for nine continuous hours. Contemporary reports suggest the atmospheric effects persisted in the northern Tonga region for at least a year.
Is Fonualei inhabited?
No, Fonualei is uninhabited and has been for all of recorded history. The island's small size (approximately 2 km in diameter), steep volcanic cliffs, active fumarolic emissions, and lack of a safe harbor make permanent settlement impractical. In the 1830s, residents of the nearby island of Tokลซ (19.7 km away) used Fonualei for gardens during periods of volcanic quiescence, but the island has never supported a permanent population. Today, Fonualei is primarily significant as a seabird nesting site and as a refuge for the critically endangered Tongan megapode.
Why does Fonualei produce dacite instead of basalt like other Tongan volcanoes?
Fonualei is geochemically unusual because it erupts predominantly dacitic lava (approximately 63โ€“68% silica), whereas most Tonga arc volcanoes produce basaltic or andesitic magma with lower silica content. The dacitic composition likely results from extensive fractional crystallization, a process in which basaltic magma evolves to more silica-rich compositions as it cools and minerals crystallize out within a shallow crustal magma chamber. This higher silica content makes Fonualei's magma more viscous and more prone to explosive eruption styles, which explains why its eruptions tend to be more violent relative to its small size.
Can you visit Fonualei?
Visiting Fonualei is possible but extremely difficult. There are no scheduled boat services, harbors, or infrastructure of any kind on the island. The only practical access is by private yacht or charter vessel from Neiafu, the capital of Tonga's Vava'u group, a journey of approximately 70 km across open ocean. Only two small beaches provide marginal landing spots through the otherwise cliff-bound coastline. Visitors should be aware that the summit area actively vents toxic volcanic gases, and the island hosts nesting populations of the critically endangered Tongan megapode that must not be disturbed.
What is the Tongan megapode and why is Fonualei important for it?
The Tongan megapode (Megapodius pritchardii) is a critically endangered bird endemic to Tonga that incubates its eggs in volcanically heated soil rather than sitting on a nest. In 1993, conservationists translocated 70 eggs and 10 chicks to Fonualei to establish a new breeding population, taking advantage of the island's geothermal heat and absence of introduced predators. By 2003, the population had grown to an estimated 300โ€“500 birds, making Fonualei one of the species' most important refuges. The bird's unique dependence on volcanic geothermal heat for egg incubation makes active volcanic islands like Fonualei irreplaceable habitat.
Could an eruption of Fonualei cause a tsunami?
While Fonualei's historical eruptions have not generated recorded tsunamis, the broader Tonga-Kermadec volcanic arc has demonstrated this capability dramatically. The January 2022 eruption of Hunga Tonga-Hunga Ha'apai, approximately 300 km south of Fonualei along the same arc, produced tsunamis that affected coastlines across the Pacific. A large explosive eruption or flank collapse at Fonualei could theoretically generate local tsunami waves, though the volcano's relatively small size makes a regionally significant tsunami less likely than from larger volcanic centers in the arc.