In the past year Manam issued energetic eruptions. In contrast, Rabaul Volcanological Observatory (RVO) described milder behavior during March-July 2006.

Although steam emissions from Main and Southern craters dominated in early March, small eruptions occurred on 3 and 6 March 2006. A 7 March pyroclastic flow descended SE valley halting at 500 m elevation. Scoria and ashfall affected the E part of the island between the coastal settlements of Warisi and Bokure (see annotated image in BGVN 30:02). Fine ashfall was reported along the SW part of the island at night. On 22, 24-25, and 28-31 March, Main Crater emitted thick white vapor, while Southern Crater released white and blue vapor. Pale gray ash clouds were reported 30-31 March.

Glowing-lava fragments discharged from Southern Crater late on 31 March. During 4-20 March there was low-to-moderate seismicity. Audible noises, weak to roaring, were reported from Main Crater on 13 April, but no glow was seen at night. Clear weather on 14 April revealed both craters releasing diffuse white vapor.

During 26 April to 2 May, ash was observed on satellite imagery at ~ 3 km altitude On 24 and 25 May, an ash plume extended ~ 100 km WNW. Another ash plume was visible on 26 May, reaching an altitude of ~ 3 km altitude and drifting 48 km WNW.

According to Darwin VAAC, a pilot reported that an ash cloud from Manam reached altitudes of ~ 4.6 km on 17 July and drifted N. Ash was not visible on satellite imagery due to local cloud cover. The Darwin VAAC reported an ash cloud on 18 July moving N at an unknown altitude. On 29 July an ash cloud was visible on satellite imagery drifting WNW at an altitude of ~ 3 km.

Geological Summary. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical basaltic-andesitic stratovolcano to its lower flanks. These valleys channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most observed eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: Ima Itikarai and Herman Patia, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.