Mild eruptive activity occurred at Manam's two summit craters during the first week of November. Main Crater released occasional pale gray ash clouds accompanied by weak roaring noises during 2-4 November; no glow was visible at night. The summit was covered on the 5th and 6th. When it became clear on the 7th, it was seen emitting only weak-to-moderate volumes of white vapor. This level of emissions continued until the end of the month and throughout December.

Southern Crater released thin white vapor during the first few days of November. However, activity shifted from Main Crater on the 7th and Southern Crater released pale gray ash emissions at irregular intervals. An explosion at 1140 produced an ash cloud that rose several hundred meters above the summit, resulting in fine ashfall on the NW part of the island. Although both craters were covered by atmospheric clouds on 9th, weak roaring noises were evident. Southern Crater released small-to-moderate volumes of white vapor after 10 November through December.

Seismic activity was low during November. However, there was a slight increase in seismic amplitudes during the first week of the month. This increase coincided with the mild increase in activity observed from the two summit craters. Seismic amplitudes dropped for a while after mid-November 1999. It reached a trough in the second week of December, then began to increase again. The level was still rising at the end of the December. These observations took place within the range of normal background level.

The steady fluctuating inflation measured by the water-tube tiltmeter since July levelled off in late October. No changes were observed in November or December. There was an accumulated inflationary tilt of about 20 µrad between July and late October.

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: I. Itikarai, H.Patia, and F. Taranu, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.