Possible eruption on Tinakula.

Tinakula is a volcanic island in the Santa Cruz Islands, part of the Solomons, roughly 500 km east of San Cristobel, or 500 km north of Vanuatu. The island forms the peak of a massive stratovolcano (cone shaped volcano) rising 3-4 km from the sea floor to form an island 3.5 km across and 851 m high. The summit crater of Tinakula was breached by a landslide in 1965, forming an open scarp on the west side of the island that runs down to the sea.

Due to its remote location Tinakula is not visited very often, and so is not monitored from the ground. However it is visible to satellites, allowing a level of surveillance. On 13-14 February 2012 NASAs MODIS Instrument detected increased heat coming from Tinakula, and on 14 February the Earth Observing-1 satellite imaged a plume of ash and smoke issuing from the summit of the volcano.

Image of Tinakula captured by the Earth Observing-1 satellite on 14 February. Scale bar is 500 m. Earth Observatory.

Eruptions of this kind do not seem to be unusual on Tinakula. Satellites detected similar activity in 2004, 2006, 2007, 2009, 2010 and 2011. Eruptions were observed by boat in 1984 and 1985, and an eruption in 1971 was observed by airplane and seen from Trevanion Island, 20 km to the south; this eruption caused a small tsunami, though no-one was hurt. Numerous other explosions have been recorded on the island since its discovery by the Spanish in 1595. The island was inhabited till about 1840, when the entire population was wiped out in a particularly violent episode. Since then there have been sporadic attempts to colonize Tinakula by people from neighboring islands, but all have been abandoned.

The Santa Cruz Islands are a volcanic island arc on the boundary between the Pacific and Australian Plates. The Australian Plate is being subducted beneath the Pacific Plate. As it sinks into the Earth's interior it is heated, and partially melts. Some of the melted material rises through the overlying Pacific Plate as magma, forming the volcanoes of the Santa Cruiz Islands, including Tinkula.

See also Ash cloud reported over Karkar Island, Series of Earthquakes shakes Vanuatu, Earthquake in Vanuatu, Magnitude 6.8 Earthquake hits Bam Island and Volcanoes on Sciency Thoughts YouTube.

Eruption on Mount Kanaga.

On Saturday 18 February 2012 a network of seismic sensors on Mount Kanaga, on Kanaga Island in the Aleutian Island Chain, Alaska, detected an outburst of Earthquake activity that lasted about an hour, according to the Alaska Volcano Observatory. Subsequently a small plume was detected drifting northeast of the island by the NOAA-15 weather satellite.

Satellite image of Mount Katanga, taken in 2002. Taken from the International Space Station with the E4 Kodak DCS760C Electronic Still Camera. NASA/Earth Observatory.

Mount Kanaga is a 1307 m high stratovolcano (cone shaped volcano) located at the northern tip of Kanaga Island in the Central Aleutians. It sits inside the older Kanaton Caldera, and has erupted a number of times since it was discovered by Europeans in 1763, the most recent significant eruptive cycle having lasted from December 1993 to August 1995, and produced a number of volcanic plumes, some of which reached 4500 m in height. Much of northern Kanaga Island is covered by layers of ash and pumice up to 7 m thick, with soil layers trapped in between, but it is not certain if all this material was produced by Mount Kanaga or whether volcanoes in neighboring islands contributed.

The Aleutian Islands are located on the boundary between the Pacific and North American Plates. The Pacific Plate is being subducted beneath the North American Plate in the Aleutiam Trench to the south of the Islands. As it sinks into the Earth's interior it is partially melted by the heat from the planet's core, the some of the melted material then rises up through the overlying North American Plate as magma, forming the volcanoes of the Aleutian Island Arc.

See also Is Mount Cleveland, Alaska, about to erupt? and Volcanoes on Sciency Thoughts YouTube

Eruptions from the Tompaluan Crater, Lokon-Empung, Sulawesi. December 2011.

Lokon-Empung is a double volcano located near the eastern tip of the northern arm of Sulawesi, Indonesia. It has two cone-shaped peaks, Lokon to the southwest and Empung 2.2 km to the northeast, with a saddle of volcanic rock separating the two. Of these Lokon is the larger, though it has not erupted in recorded history, whereas the slightly smaller Empung last erupted in the late eighteenth century. Situated on the saddle between the two summits is Tompaluan, a double crater that remains active to the current day.

Smoke rising from Tompaluan Crater. The Lokon summit is to the right, Empung to the left.

On 27 December 2011 the Pusat Vulkanologi Dan Mitigasi Becani Geologi (Indonesian Centre for Volcanology and Geological Hazard Mitigation) detected a series of seismic tremors beneath the mountain and imposed ban on traveling within 2.5 km of the crater. The following day the Jakarta Post reported a series of explosions from the crater.

Tompaluan is a very active volcano. In June-August 2011 a series of explosive eruptions and lava flows lead to over six thousand people being evacuated from around the mountain, with one fatality due to a heart attack during the evacuation process. Since then there have been smaller eruptions in October and November. There was also a small eruption in February this year. Prior to this year Tompaluan erupted in 2008, 2007, 2003, 2002, 2001, 2000, 1999, 1998, 1996, 1994, 1991, 1988, 1987, 1986, 1984, 1975, 1973, 1971, 1969, 1966, 1965, 1963, 1962, 196, 1958, 1951, 1949, 1942, 1930, 1893, and 1829. All eruptions prior to this appear to have been from the Empung crater.

The Lokon-Empung volcanic complex is located at the southern end of the Sangihe Volcanic arc, where an extension Molucca Sea Plate is being subducted beneath an extension of the Eurasian Plate, sometimes called the Sangihe Plate. As this happens part of the subducting plate is melted by the heat of the Earth's interior, and rises up through the overlying plate as liquid magma, forming volcanoes at the surface. 320(ish) km to the east the Molucca Plate is also being subducted beneath an extension of the Philippine Sea Plate, sometimes called the Halmahera Plate, producing a second chain of volcanoes in the Halmahera Islands. At some point in the future the Molucca Plate will vanish and the two volcanic arcs will meet.

The Molucca Sea, five million years ago (above) and today (bellow).

See also Volcanic activity in the Halmahera Islands, Fresh eruption on Mount Karagetang and Volcanoes on Sciency Thoughts YouTube.

What happens when a volcano meets a subduction zone?

This week a reader in New Zealand asked me what happens when a volcano meets a subduction zone? This is a slightly complex question, as there are different answers for different types of volcano, so I've written a full article to answer the question in full.

The question was asked with reference to the Kermadec Islands, which are an island arc created as one section of ocean plate is subducted beneath another. As the underlying Pacific Plate disappears beneath the overlying Australian Plate it is partially melted. The lighter minerals from the underlying plate then rise up through the overlying plate, forming a row of volcanoes, the island arc at the surface.

How volcanoes are formed in the Kermadec Islands.

Eventually all of the underlying plate will be consumed, and the subduction zone will encounter the far side of the plate, which may have another subduction zone with an island arc, or possibly a continent. Neither of these can be easily consumed, so the subduction zone closes, forming a suture. This starves the volcanoes of new material and they cease activity. Where two ocean subduction zones meet then one of the subduction zones may survive, with the two sutured island arcs sitting on top of the remaining subduction zone. Some scientists think that the Earth's earliest continents formed in this way, by the accretion of large numbers of suture zones. Suture zones tend to be mineral rich, and are often exploited by mining companies for their natural wealth.

The formation of a suture zone, in what is now part of the Himalayas.

The next common source of volcanic activity are mid-ocean ridges, where new crust is being created by convection currents within the Earth's mantle. Mid Ocean ridges underly the volcanoes of Iceland and St. Helena; the East African Rift volcanoes are thought to occur where a new ocean ridge is forming, breaking the continent apart.

New ocean crust forming at a mid-ocean ridge.

These structures can be subducted if they are overrun by a subduction zone. This disrupts the convection currents that from the ridge, stopping the volcanic activity, but does not form a suture, so that there is a break in the subducting material, between what are effectively two plates. The San Andreas Fault in California is formed this way. The overlying surface that people build cities upon is all part of the North American Plate, but beneath the surface the ancient Farallon Spreading Ridge is being subducted, forming a deep fault that occasionally causes spectacular and devastating earthquakes.

At the San Andreas Fault the subduction of a spreading ridge has lead to spectacular faulting at the surface, but volcanic activity has stopped.

The third type of volcanoes found on Earth are hotspot volcanoes. These occur away from plate margins, and drift across the surface of the Earth apparently independently of the movement of the continents. The volcanoes of Hawaii, the Canaries and the Seychelles are hotspot volcanoes. Many scientists believe that these volcanoes sit on top of mantle plumes that originate deep within the Earth; deeper than the convection currents that cause the movement of the continents, and therefore independent of them.

The Hawaiian Islands depicted sitting on top of a mantle plume.

Under this model a mantle plume is largely independent of the movement of the plates. It's origin is deep bellow the forces that cause ocean spreading and subduction zones, and it ought to be able to pass under these structures without major effect. It is thought that the Hawaiian Hotspot may have crossed Siberia during the Mesozoic, and that the Seychelles Hotspot once lay beneath India.

The movement of volcanic hotspots across the Pacific Ocean.

However not all scientists agree with this interpretation of volcanic hotspots. Some scientists believe in a shallow origin for these structures. Under this model a volcanic hotspot is a spreading ridge that has failed to expand into a new area of ocean creation. Such hotspots would have origins with shallow convection currents in the Earth's mantle, and would be disrupted by an encounter with a subduction zone, with the volcanoes dying and being sutured to the overlying plate. The hotspot might then persist for a while as a localized centre of earthquake activity.

See also Eruptions on Mount Nyamuragira in the Virunga National Park, Eruptions on Mount Nabro, The End of the Cretaceous and Volcanoes on Sciency Thoughts YouTube.

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Fresh eruption on Mount Karangetang, Indonesia.

Mount Karangetang (sometimes known as Api Siau) is a stratovolcano (a cone shaped volcano formed from successive layers of ash and lava) located on Siau Island, roughly 130 km to the north of Sulawesi, or a third of the way to the Philippine Island of Mindanao. It is one of the most active volcanoes in Indonesia and frequently erupts several times a year.

The location of Mount Karangetang.

The volcano started to spit gas and lava 600 m into the air towards the end of last week, then this morning (8 August 2011) a large explosion was followed by an ashfall on the volcano's slopes causing people to flee in panic. Early reports suggested that one person had been injured by the ashfall, and several more were missing, although local search and rescue authorities have now found the missing people and confirm the injured man only fell while fleeing, receiving cuts and bruises.

Local people were right to be concerned about the eruption, Mount Karangetang has a vicious reputation, having killed three people as recently as June 1997, when a pyroclastic flow entered a village. Another pyroclastic flow killed six people in May 1992. Siau Island is only 10 km × 5 km at its widest and is dominated by the Mount Karangetang, yet it is home to 22 000 people, 600 of whom live on the upper slopes of the volcano.

Mount Karangetang.

Siau Island is part of the Sangihe Islands, a group of volcanic islands running north from the northernmost point on Sulawesi to the southernmost point on Mindanao. Conventional geology places this in the eastern Sunda Plate, but geologist Colin Macpherson of the Department of Earth Sciences, University of Durham, has developed a new model of geology in the region. Under Macpherson's model the Sanghi Islands lie on the western margin of a northward extension of the Molucca Plate, which is being subducted beneath the Sangihe microplate to the west. To the east of this the Molucca Plate extension is being subducted beneath the Halmahera Plate. This is not yet universally accepted.

Macpherson's Model of the Sangihe Islands.

See also Magnitude 6.8 earthquake hits Bam Island, Papua New Guinea, Sumatra shaken by a series of earthquakes and Volcanoes on Sciency Thoughts YouTube.