Eruption on Manam Motu.

Manam Motu is a volcanic island 13 km off the north coast of Papua New Guinea; it is essentially a submarine stratovolcano (cone-shaped volcano) with its tip sticking above the sea, forming a 10 km diameter circular island with the summit of the volcano at the centre. The island is remarkably symmetrical, with four valleys at 90° angles leading from the summit to the sea, which carry ejecta from the frequent eruptions.

Satellite image of water vapor emerging from Manam Motu, taken by NASA's Earth Observing-1 Satellite on 28 June 2009. Earth Observatory. 

The Rabaul Volcano Observatory in Papua New Guinea reported the appearance of a vapor cloud above Manam Motu on 5-6 May 2012, followed by an ash cloud on 6-7 May, combined with incandescence (glowing) over the summit. On the 10-11 another ash cloud was observed, accompanied by further incandescence. Incandescence resumed on 13-14 May, with further ash eruptions on the 13th. On 16 May a darker grey/black ash cloud was produced, accompanied by an increase in ejected incandescent tephra (tephra is any material ejected from a volcano, it can be ash, rock fragments or lava; this is a particularly useful term when volcanologists don't want to get close enough to inspect the ejected material). Another ash cloud was produced on 26 May, followed by a Strombolian eruption (eruption of incandescent tephra and lava bombs) on the 27th. This was followed by more further ash clouds on the 28th and 29th, and another Strombolian eruption on the 30th.

Manam Motu is one of Papua New Guinea's most active volcanoes; it underwent four eruptive cycles in 2011. The island was inhabited until 2004, when the island's population of ~9000 was evacuated after an eruption killed five people. The Papuan government allowed re-settlement to begin in March 2007, but three people were killed on the island within a month; the island's inhabitance status is currently unclear. Prior to 2004 the most recent fatalities had been in 1996, when a pyroclastic flow (avalanche of hot ash and poisonous gas) hit the village of Budua, killing 13.

Despite its small size and inhospitable nature Manam Motu was apparently settled for a long time, having developed its own distinctive language (Manam). 

Manam Motu is located on the southern margin of the South Bismarck Plate, close to its boundary with the Australian Plate, which underlies the Papuan mainland. The Australian Plate is being subducted beneath the South Bismarck, and as it does so it is partially melted by the friction and the heat of the planet's interior. Some of the melted material then rises up through the overlying South Bismarck Plate as magma, fueling the volcanoes of the north Papuan margin.

See also Earthquake in the Loyalty Islands, Eruption on Mount Sirung, Eruption on Mount Pago, Eruptions on Batu Tara and Volcanoes on Sciency Thoughts YouTube.

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Magnitude 6.8 Earthquake hits Bam Island, Papua New Guinea. 1 August 2011.

Just before 9.40 am local time on the 1st of August 2011 an earthquake with a magnitude of 6.8 hit Bam Island of the northeast coast of Papua New Guinea. The earthquake was very shallow, at about 17 km, which means it probably caused severe shaking at the surface. It was preceded by a smaller, magnitude 5 earthquake at about 4.10 am local time. There are no reports of any casualties, however given the remote location of the island this means little. There is little official contact between the Papuan Government in Port Moresby and the island. What little information is available is provided by missionary societies (the island officially converted to Christianity in 2008), who estimate the population to be between 2000 and 3000. No tsunami warning has been issued.

The location of Bam Island.

Bam Island is the easternmost of the Schouten Islands, a group of small volcanic islands off the northeast coast of Papua New Guinea (not to be confused with the Shouten Islands of Indonesian West Papua). Bam has a 685 m high, double-coned stratovolcano (cone shaped volcano formed by successive layers of ash and lava). This volcano was more-or-less constantly active from its discovery in 1872 until 1960, when eruptions abruptly stopped. It is possible that the earthquakes may herald the start of a new volcanic cycle (though it is hard to judge how probable this is).

Bam Island

The Schouten Islands contains two other volcanoes.

Kadovar is 18 km to the east of Bam. It is another stratovolcano, with a summit 365 m above sea level. The volcano may have erupted in 1700, though this is uncertain. There has been some more recent activity. In 1977 a fumarole (gas emission) briefly caused the island to be evacuated, and in 1981 the sea to the northeast of the island was stained an orange colour for several weeks.

Blup Blup is 23 km northeast of Bam and 11 km north of Kadovar. There have been no recorded eruptions on Blup Blup, though there is an area of hydrothermal activity off the west coast (i.e. submerged hot springs). There are stories of eruptions in 1830 and 1616 but Smithsonian Global Volcanism Program dismisses both of these.

Satellite Image of Blup Blup Island.

Papua New Guinea forms part of the Pacific Rim of Fire. It has a complicated geological structure, essentially lying on a transform plate margin, where the Pacific and Australian Plates are rubbing past one-another. However the situation is more complex, as there are a number of small plates caught between the two, possibly the result of fragmentation on the plate margin. The Schouten Islands lie on the margin between the South Bismark Plate and the Australian Plate.

The geological setting of the Shouten Islands.

The southern margin of the South Bismark Plate is being subducted beneath the Australian plate. As the plate is drawn into the earth's interior, the rocks are melted by the heat of the Earth's interior, and the lighter portion rises up through the overlying Australian Plate forming the volcanoes of the Shouten Islands and New Britain.

See also New Submarine Islands Discovered in the South Sandwich Islands, Earthquake in the Kermadec Islands triggers tsunami alert and Volcanoes and Earthquakes on Sciency Thoughts YouTube.