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Centre for Earth and Environmental Science Research

Pumice rafting and biota dispersal across the Southwest Pacific following the 8-11 August 2006 Home Reef submarine volcanic eruption, Tonga.

Executive Summary
ResearchersDr Scott Bryan (Kingston University, Principal Investigator)
Dr Jason Evans (Yale University, Co-Investigator)
Associate Professor John Jell (University of Queensland, Co-Investigator)
Dr Alex Cook (Queensland Museum, Co-Investigator)
Funding Body/SourceNERC
Duration2007-2008
Project SummaryThe research in this Urgency Grant is taking the opportunity to study pumice raft(s) that were recently generated by a shallow marine explosive eruption at the Home Reef volcano in the Tongan Islands.

Dr Scott Bryan has been awarded a Natural Environment Research Council (NERC) Urgency Grant with co-investigators Dr Jason Evans (Yale University), Associate Professor John Jell (University of Queensland) and Dr Alex Cook (Queensland Museum) to track and study pumice rafts originating from the August 8-11 explosive eruption of the Home Reef volcano in Tonga, as they travel across the Southwest Pacific to eastern Australia over the next year. The project was awarded in January 2007, and funding is for one year.

Birth and Death of a Volcanic Island

A wave-modified pumice mound ~75 m in diameter is all that remained of the Home Reef volcanic island 6 months after the eruption. Photo taken on February 18, 2007.

The research in this Urgency Grant was prompted by the brief opportunity to study pumice raft(s) that were recently generated by a shallow marine explosive eruption at the Home Reef volcano in the Tongan Islands. The eruption began on August 8 2006, and produced a small island up to 1.5 km diameter that was first observed by the crew of the yacht Maiken on August 12, 2006. The island has been rapidly reducing in size in response to wave erosion, being only 450 m in diameter by December 2006. We visited Home Reef on February 18, 2007 to find the island all but disappeared, with only a small (50-75 m diameter), <5 m high wave-reworked mound remaining of the new volcanic island.

Pumice Rafts

Approximately one year old colonial coral Pocillopora damicornis attached to an algal covered pumice clast, collected from Mackay harbour in April 2003. Coin is 2.3 cm diameter. This pumice was formed by the September 2001 eruption of Volcano 0403-091 (very similar to the 2006 Home Reef eruption), an unnamed seamount in Tonga.

Approximately one year old colonial coral Pocillopora damicornis attached to an algal covered pumice clast, collected from Mackay harbour in April 2003. Coin is 2.3 cm diameter. This pumice was formed by the September 2001 eruption of Volcano 0403-091 (very similar to the 2006 Home Reef eruption), an unnamed seamount in Tonga.

Floating rafts of pumice are an important, but poorly understood natural phenomena, from their generation by silicic explosive eruptions and dispersal by wind and ocean currents, to their recruitment and long-range transport of biota. Pumice rafts provide an important natural vector for the long-range dispersal of many marine species, overcoming physiological limitations on their dispersal range, and allow intermittent contact and exchange between shallow marine ecosystems that otherwise remain extremely isolated by vast stretches of deep ocean. Pumice rafting will have been an important process in the geological past, and in the future, it may serve as a natural mechanism for ecosystems damaged by human activity to recover species and biodiversity. In many cases, pumice rafts also represent the only record with which to understand the petrogenetic origins and eruptive processes of shallow marine explosive eruptions of silicic magma in island arc settings.

An initially very large pumice raft was produced by the eruption, estimated to be 8 km in diameter (55 km2). Floating pumice material from the eruption was directed by wind and ocean currents to the North and West of Home Reef, arriving in Fiji in September, and then Vanuatu in November 2006. Pumice raft(s) have now passed New Caledonia and are progressing westward, following a similar trajectory of previous rafts to eastern Australia. The rafts will reach eastern Australia by the middle of this year where a significant proportion of the floating pumice will be stranded along the coastline, and the rafting event will largely be completed.

The Southwest Pacific is a key area to study these phenomena with pumice rafts being generated once every five to fifteen years from relatively small-volume explosive eruptions from volcanoes in the Tonga-Kermadec islands. The pumice rafts, generated from the submarine explosive eruption at the Home Reef volcano beginning August 8, have passed through important areas of tropical reefs, the timing of which corresponded to the late Spring coral spawning, as well as the summer cyclone season. These pumice rafts therefore provide a brief window of opportunity to understand in much greater detail, the mechanisms of pumice rafting, how this vector is exploited by a range of biota, and how successful it is for the long-range dispersal of biota to the Great Barrier Reef, an important area of global biodiversity.

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