"Moderate Strombolian activity continued in July. Explosive activity at Southern crater showed little change throughout the month, with ejections at a rate of 1-2 per minute. The ejections continued to be rich in incandescent material and formed pale grey-brown ash clouds rising 200-300 m above the crater. Observers at 4-5 km distance noted rumbling and roaring sounds from the Southern crater on most days, but sharp detonations were heard on 24-25 June. Debris avalanches in the SW valley were semi-continuous. Main crater usually released dense white vapours or very pale, lightly ash-laden emissions. Blue vapour emissions were noted on several days at the end of the month, and no Main crater incandescence or eruption sounds were observed.

"Seismic activity was relatively steady compared with previous months, although mild fluctuations occurred. Seismic amplitudes were up to about 10 times normal. Daily totals of earthquakes averaged about 1,500. No significant tilt changes were recorded."

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: C. McKee, RVO.