During 6-10 December, small-scale volcanic activity that began at Aoba (also locally called Mt. Manaro) on 27 November continued from active vents within Lake Vui, the summit crater lake. Molten material entered the crater lake and reacted with water, producing small explosive eruptions and a plume of steam and gas that rose to a height of 3.9-4.5 km (12,800-14,800 ft) a.s.l. The eruption built a cone around the active vents, enclosing them on three sides and forming an island ~200 m wide and 50-60 m high in the lake. There were two active vents; one emitted water, rocks, and mud, and the other emitted steam and gas. As of 10 December, the eruption had little effect outside of the crater lake (minor ashfall occurred only during the first 3 days after the eruption). During the report period, volcanic tremor was recorded at the volcano and a moderate sulfur-dioxide flux was measured (~2,000 tons per day). There was no evidence of ground uplift or cracking near the lake, suggesting that there was no large volume of magma close to the surface.

Geological Summary. The island of Ambae, also known as Aoba, is a massive 2,500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Sources: GeoNet, Vanuatu Meteorology and Geo-Hazards Department (VMGD)