Case of Ambrym Volcano, Vanuatu Archipelago

Impacts of troposheric volcanic gas plumes on terrestrial ecosystems: case of Ambrym volcano, Vanuatu archipelago

Philipson Bani1, Patrick Allard2, Douglas Charley3, Esline Garaebiti3

1- Institut de Recherche pour le Développement, B.P.A5, 98848 Nouméa Cedex, Nouvelle Calédonie. [email protected] 2- Groupe des Sciences de la Terre, Laboratoire Pierre Sue, CNRS-CEA, Saclay, France, 3- Department of Geology Mines and Water Resources, Port Vila Vanuatu, [email protected], [email protected]

ABSTRACT causing lost of life (1894, 1913, 1929, and 1951) and forcing the Gases released non-eruptively into the troposphere by population to move to other islands (e.g., [4]). degassing volcanoes have been the subject of numerous The present day activity is limited to the main active craters in the investigations, since volcanic emissions may convey valuable caldera, namely Benbow and Marum (Fig.2) and varies from lava information about subsurface magma activity and magma lakes to sporadic explosions. The most remarkable feature of this hydrothermal interactions, which can be used in conjunction volcano is its continuous high degassing. In 1774, during his with other geophysical techniques for eruption monitoring. second voyage to the Pacific Cook described “on the part nearest The release of volcanic gases and aerosols may significantly to us which is of a considerable height, we observed two very influence the chemistry of the troposphere at the local, large columns of smoak, which I judge ascended from Volcanoes regional and global scale. [5]. This description fits remarkably well to the present day Because the physico-chemical environment of troposphere activity (Fig.3), and emphasizes the long term volcanic high volcanic plumes can be quite different from anthropogenic degassing that leads to volcanic impacts on Ambrym terrestrial emissions, distinct chemical transformation pathways in the ecosystem. atmosphere may results. In a similar manner, volcanogenic air contaminants may affect exposed ecosystems through distinct reactions. Long ignored in the global volcanic emission budget, Ambrym volcano (Vanuatu archipelago) was revealed through recent measurements as one of the largest known contemporary point sources of volcanic emissions on Earth. Temporary and continuous detrimental effects on natural and cultivated vegetation have been observed in relation to its passive volcanic degassing. Deposition of halogen acids, combined with SO2 and sulphuric acid aerosols has caused significant defoliation of vegetation on the island, and a very high fluorine flux results in long-term exposure to high fluoride levels. This paper highlights evidences of volcanic emissions high impacts on Ambrym Island.

Keywords Ambrym volcano, high volcanic degassing, impacts on ecosystems.

1. INTRODUCTION Ambrym Island is a 40 x 30 km triangle shape like volcano (Fig.1) – it rises up to 1800 m from sea bed [1] and it's one of the most active volcanos in Vanuatu archipelago. The morphology of Ambrym resembles that of a shield volcano on top of which lies a voluminous tuff cone. The collapse of this later cone, 2000 years ago [2], formed a large caldera of 12 km in diameter [3]. Figure 1. Vanuatu archipelago – Ambrym (in grey) in the According to Ambrym historical records (e.g., [4]), the volcanic centre of this Melanesian arc. activity has been active since the first description of Capt. Cook in 1774 [5]. Major eruptions are reported to occur on Ambrym 2. AMBRYM VOLCANIC GAS EMISSIONS scavenged out of the gas-particle plume and dilutes in the atmosphere. The sedimentation of tephra thereby carries AND THEIR IMPACTS significant quantities of fluorine into earth surface. Much of the The first measurements of Ambrym gas emission was made in fluorine is contained in bioavailable compounds and can rapidly 2005 by Bani et al. [6], thanks to the new miniature UV lead to skeletal deformity, bone lesions, and deformation of teeth. spectrometer (DOAS). These authors highlighted the extreme Epidemiological study is also required on this as symptoms exist degassing of this volcano which varied between 2500 and 35000 (Fig.4). Acidic compounds in the volcanic plume (HCl, HF, and tonnes of SO2 per day. Very few volcanoes on earth are capable of SO2) regularly induce vegetation and crops damages on Ambrym releasing such quantity of sulphur into the atmosphere during which often lead to food shortage. passive degassing. Such degassing indicates the Ambrym is among the biggest source of volcanic degassing on earth. Drinking water samples collected in January 2005 on Ambrym typically contained between 3 to10 ppm F, knowing that WHO High amounts of BrO (2 – 8 t/d), F (2000 – 4000 t/d) and Cl (700 recommends < 1.0 ppm F in drinking water for tropical – 1200 t/d) were also recorded on Ambrym. environments. A survey undertaken with 250 children on west Ambrym indicates that 53 % are moderately affected by the With this high degassing, SO2 levels exceed background levels and have led to a continuous detrimental effects on 170 km2 area excess of fluoride while 8 % are severely affected. [7] north-west of the active craters (Fig.2). At time depending on the volcanic activity and on the meteorological conditions the affected area may increase to 330 km2 including inhabitant zones of this island (Fig.3).

Figure 4. Symptoms of high fluoride on Ambrym Island – young with teeth affected by excess of fluoride. Photo courtesy-Crimp 2005.

3. CONCLUSION Figure 2. Continuous detrimental affected area north-west of Long and sustained high degassing of Ambrym has led to the craters. continuous detrimental effects on Ambrym environment and health. Some 330 km2 areas are regularly exposed to volcanic high emissions. Ambrym regularly suffer from food shortage due to crop damages by the volcano acidic emissions. Epidemiological and environmental studies on volcanic emissions impacts are required as symptoms are evidenced.

4. ACKNOWLEDGMENTS We acknowledge the French Embassy in Port Vila, the Institut de Recherche pour le Développement and the Pacific Science Inter- Congress for their assistance to present this overview on Ambrym volcanic impacts.

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