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Over The Horizon
A new island in Tonga has recently been the object of study by the Institute of Geological and Nuclear Sciences (GNS).
Somewhere around June 6, underwater volcanic activity at Metis Shoal in Tonga broke through to the sea surface. By June 14 the eruptive activity had started to create an island above sea level and by June 20 the island covered an area of 280 x 240 metres and reached 54m above sea level. Volcanic eruptions were also reported from two other locations. This rapid onset of volcanic activity caused concern in Tonga, which requested assistance from New Zealand.
As New Zealand's national authority on earthquake and volcanic hazard risk assessment, GNS was asked to assess the risk posed by the new volcano, and volcanologist Brad Scott visited Tonga to assess the on-going activity.
A detailed aerial inspection from an RNZAF Orion quickly established there was only a single eruption source at Metis Shoal. Volcanic eruptions there have previously produced islands in 1858, 1878, 1886, 1894, 1967, and 1979.
The highest recorded island reached about 122 metres above sea level and may have survived for up to three years. Both the 1967 and 1979 eruptions produced low-angle pumice cones about the active vents, and large rafts of pumice. The pumice cones were quickly eroded away once eruptive activity stopped.
Observations by Scott during his visit and by local observers allow the course of the present eruption to be recorded. It is forming a lava dome at the summit of the volcano, which rises over 1500m from the sea floor. The 1995 eruption may differ in duration and style of activity from previous events.
During Scott's visit, meetings were held with the Government of Tonga to outline the volcanic history, present eruption status, volcano hazards and future activity. Presently, the most significant hazards are acid rain and fume clouds, explosive outbursts from the lava dome, and the possibilities of dome collapse and the formation of further shoals. GNS has recommended that access be restricted to no less than 1.5km from the island.
Several submarine volcanoes exist in the Tongan area and are locally known as Fonwafo'ow, which translates as "jack-in-the-box" islands. Following the 1979 eruption the island formed was named Late-iki, and this name may be reused for the new island. Another suggestion is that it be named after rugby hero Jonah Lomu.
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