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Surtseyan Style Eruption in the Ambae (Vanuatu, New Hebrides) Caldera Lake in 2005 December and Its Implication to Volcanic Haza

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Surtseyan Style Eruption in the Ambae (Vanuatu, New Hebrides) Caldera Lake in 2005 December and Its Implication to Volcanic Haza SurtSurtseyanseyan stylestyle eruptioneruption inin thethe AmbaeAmbae (V(Vanuatu,anuatu, NewNew Hebrides)Hebrides) calderacaldera lakelake inin 20052005 DecemberDecember andand ititss implicationimplication toto volcanicvolcanic hazardshazards andand emergencyemergency managementmanagement onon anan oceanocean islandisland Karoly Nemeth and Shane J. Cronin Volcanic Risk Solutions, Institute of Natural Resources, Massey University, 300th Anniversary Volcano International PO Box 11 222, Palmerston North, New Zealand Conference Commemorating the 1706 Arenas Negras Eruption ([email protected]; [email protected]) Garachico, Tenerife, Canary Islands, SPAIN tuff rings/maars After a long silence, Lake Vui on Ambae Island erupted on the 28th of November 2005, Lake Vui disrupting the lives of 10 000 inhabitants. Surtseyan- style explosions burst through the Islands summit lake waters forming a new tuff-cone and threatening to form lahars. The island has an NE-SW elongated shape. Along its axis scoria cones and fissure-fed lava fields July 2005 occur. The island rises to 1496 m. At the summit, two craters occur, surrounded by crescentic caldera wall. Inside the caldera complex a large phreatomagmatic tephra ring forms a broad outward-sloping volcanic edifice ~ 150 m above the caldera floor. This tephra ring encloses scoria cones the 2.1 km diameter, acidic Lake Vui. This water mass is the major concern in any volcanic hazard assessment on Ambae, due to its potential as a lahar source. Since the early 1990s, Lake Vui activity has occurred in Lake Vui through a single vent area, with a series of heating-cooling cycles that culminated in a small one-day phreatic eruption in 1995. Historic eruptions on Ambae have been documented in 1575, 1670 and 1870. The latest of these events is believed to have built a small cone inside Lake Vui. A new eruption on Ambae volcano in 2005 late November to early January demonstrates characteristic features of Surseyan style eruptions. scoria cones These events were characterised by a rapidly changing explosion styles and magnitude. A July 2005 new 120-140 m high tephra cone was formed within Lake Vui in less than 8 days. A lateral Ambae migration of the vent, a low magma-supply rate, and the predominance of mud-rich waters appear to have kept the coolant ratios high throughout this event, dampening the magnitude of explosions produced. The explosions built to a maximum intensity around 9-10 days after tuff rings/maars the first breaching of the lake surface by Surtseyan jets. The largest of these explosions may have been intensified by choking induced by the collapsing wet wall of the conduit. Many workers have pointed out that eruptions through crater lakes are too complex, and unpredictable to apply existing theoretical physical models for the potential evolution of such volcanoes. Considering the limited size of an island, creating a useful volcanic hazard map is challenging due to the largely multivariable processes may be involved in the evolution of the intra-caldera lake Surtseyan tephra ring. The 2005 December eruption in Ambae is generated logistic trouble in relocating the island inhabitant. On the basis of the available volcanological data it is now confirmed that the 2005 eruption was similar to those occurred in 1870, and it maybe used as an event scenario for future eruptions in Ambae. 05 12 2005 05 12 2005 continuous uprush of tephra continuous uprush of tephra steam cloud old island cock's tail jets new island Existing volcanic hazard map of Ambae island. 50 m 50 m Initial Surtseyan style emergent volcanic eruptions just 7 days after the first eruptions 05 12 2005 08 12 2005 08 12 2005 tephra charged cock's tail jets cock's tail jets with ballistic steam cloud mud bombs steam cloud 50m new island grow over old island low rim emergent 50 m open vent 50 m tephra ring tsunami waves on lake surface nearly completed tephra ring/cone Fast growing tephra cone in Lake Vui Less frequent but more energetic eruptions in the final stage of the activity The 2005 December eruption can be Fully developed tephra cone in Lake Vui Initial erosional stage of the new tephra cone viewed as a likely eruption scenario in a summit eruption through Lake Vui. This eruption didnt generated cock's tail jets closed vent, no free lake water accessto vent lahars through caldera lake displacement. Deposits that assigned old island completely covered to be deposited by lahars need to be by new tephra ring reevaluated and the hazard map needs significant revision. completed tephra ring/cone 50 m 50 m 100 m 100 m 08 01 2006 MASSEY UNIVERSITY MASSEY RESEARCH ONLINE http://mro.massey.ac.nz/ Massey Documents by Type Journal Articles Surtseyan style eruption in the Ambae (Vanuatu,New Hebrides) caldera lake in 2005 December and its implication to volcanic hazards and emergency management on an ocean island. Nemeth, Karoly 2006-01-01 http://hdl.handle.net/10179/9661 29/09/2021 - Downloaded from MASSEY RESEARCH ONLINE.
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