St. Andrew Strait is a

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

Papua New Guinea Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...

that has had eruptions in historical times. The volcano is not linked to any tectonic plates, the volcano is also in an area of very few earthquakes, suggesting that St. Andrew Strait is an Intraplate volcano. It consists of a group of

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

volcanic cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and ...

s that are mainly

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

in composition. The volcanism is curved, suggesting that the volcano has an ancient

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

. The centre of the volcano is

Lou Island Lou Island is an island of the Admiralty Islands, part of the Bismarck Archipelago, located in northern Papua New Guinea Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent Stat ...

. Lou island last erupted in 240 BC (give or take 100 years) and 340 AD, both eruptions came from the Bendal volcano. Lou island is the largest eruptive centre of the volcano, with 6 volcanic vents. Also the Pam islands (Pam Lin and Pam Mandian) also contain fresh deposits. Historic eruptions have come from the Tuluman Islands.

Eruptions

1880 eruption

A small submarine eruption came from the Tulaman islands on March 28, 1880. The vent that the eruption came from was probably one of the vents that formed Tuluman island in its 1953-1957 eruption. This was a small VEI 2 explosive eruption.

1953-1957 eruption

An eruption began June 27, 1953. The eruption began with submarine eruptions that formed a new island. The eruption came from 6 vents: *Vent 1. Located 1.3 km SSE of Lou Island. Emerged above the surface for two months, but was reduced to a submarine mound by wave action. *Vents 2,4,5. These three vents combined to form an island, 2 km south of Lou Island. The island reached a maximum length of 1 km. *Vent 3. Located 1.3 km south of Lou Island. The irregular shaped island reached a maximum length of 400 m. *Vent 6. Vent 6 is submerged and located 300 m south of vent 5. The eruptions were most intense in 1955 (and also near the end of the eruption) when lava effusion was dominant. The island was built 29 m above sea level. The eruption also produced

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

s. The eruption was one of only 3 major rhyolitic eruptions of the 20th Century.

References

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Volcano Live: Tuluman Volcano
Volcanoes of Papua New Guinea Complex volcanoes {{volcano-stub