Abstract
Abstract. Volcanic eruptions through crater lakes often generate lahars, causing loss of life and property. On Ambae volcano, recent eruptive activities have rather tended to reduce the water volume in the crater lake (Lake Voui), in turn, reducing the chances for outburst floods. Lake Voui occupies a central position in the summit caldera and is well enclosed by the caldera relief. Eruptions with significantly higher magnitude than that of 1995 and 2005 are required for an outburst. A more probable scenario for lahar events is the overflow from Lake Manaro Lakua bounded on the eastern side by the caldera wall. Morphology and bathymetry analysis have been used to identify the weakest point of the caldera rim from which water from Lake Manaro Lakua may overflow to initiate lahars. The 1916 disaster described on south-east Ambae was possibly triggered by such an outburst from Lake Manaro Lakua. Taking into account the current level of Lake Manaro Lakua well below a critical overflow point, and the apparently low potential of Lake Voui eruptions to trigger lahars, the Ambae summit lakes may not be directly responsible for numerous lahar deposits identified around the Island.
Highlights
Ambae Island is the emerged part of the most voluminous volcano of the Vanuatu archipelago (Fig. 1), with 3900 m height from the seabed and a volume of 2500 km3
Bathymetry results obtained in this work (Fig. 2) indicate a generally shallower lake Manaro Lakua contrasting with the deep lake Voui
Volcanic eruptions through crater lakes are often accompanied by lahars, causing loss of life and properties
Summary
Ambae Island ( known as Aoba) is the emerged part of the most voluminous volcano of the Vanuatu archipelago (Fig. 1), with 3900 m height from the seabed and a volume of 2500 km. The recent Surtseyan eruption (Lardy et al, 2005; Garaebiti et al, 2005; Nemeth et al, 2006) – beginning on the 27 November 2005, lasted almost two months It was a minor event on a world scale, but one of the larger eruptions of the volcano in its short-record of volcanic activity. The scale of explosions during this event never reached the point where water was laterally ejected from the Lake Voui and no lahar was generated. This eruption has focussed attention on the island lahar hazard assessment, which has not taken full cognisance of the characteristics of the summit lakes and of potential lahar origins. New contributions of this work are the bathymetry of crater lakes, summit morphology, lake water volumes their potential for generating lahars
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