During the first week of May, Main Crater gently emitted small to moderate ash clouds, similar to those in late April. On 9 May, activity increased slightly and ash clouds were ejected to 500-1,000 m above the summit resulting in light ashfall downwind. Forceful emissions and light ashfalls at Main Crater occurred on the 13th; there were also two loud explosions during 1500-1600. After that, there were weak-moderate ash emissions accompanied by roaring noises and infrequent rumblings. Rumblings on the 6th and 28th were attributed to rocks cascading into Southwest Valley. Activity increased again on the 29th. South Crater weakly emitted steam during May.

Seismicity showed an irregular rise during May (growing from 800 to 1,700 low-frequency events/day). Wave amplitudes, although low, doubled. Water-tube tiltmeters at Manam Volcano Observatory (4 km SW of the summit) showed a very small inflationary change (0.5 µrad), which may be significant because it continues the inflationary pattern evident since early March.

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: B. Talai, D. Lolok, P. de Saint-Ours, and C. McKee, RVO.