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Most of the eruptions we hear about are eruptions that have impacted large communities, and the active volcanoes that tend to be the most monitored are those that pose imminent danger to communities living in the surrounding regions of the volcano. Quite a number of active volcanoes are located in relatively remote areas, but their activity is being reported more often now because of satellite imagery. One such active volcano is Bagana.
Figure above: Location of Bagana on Bouganville Island (Image from Bultitude, 1976)
Bagana is actually one of world’s most active volcanoes, and definitely one of the most active in Papua New Guinea, where it is located. It is located on Bouganville Island, one of the Papua New Guinea islands, far from near by cities or large towns. Its most recent eruption was in 2015, but it is continuously active, emitting volcanic gases and frequent thick lava flows, which are clearly visible from satellite imagery. During its eruptive phases, ash plumes from Bagana can be tracked, travelling as far as 70 km.
Figures above: Satellite imagery from NASA showing Bagana volcano and its lava flows as well as ash plume from space.
Quite often, when a volcanologists talks about hazards from a volcanic eruption, the most dangerous hazard they are concerned with are pyroclastic flows. The exceptions to this include Kīlauea (in Hawai`i, USA) and similar volcanoes where fluid lavas can travel far. Another exception is Bagana.
Figures above: Bagana volcano (left: Photo by Wally Johnson, 1988; right: Photo by George Steinmetz)
Bagana is only around 300 years old, but is part of a larger, older volcanic chain through the Buoganville island, which is 10 000 years old. One of the immediate notable features of Bagana is its steep sided cone. In volcanology, we know that the reason it is steep sided is because the lava flows (that have created this cone) are not fluid. If they were fluid, they would form gentle, long slopes (as seen at Hawaiian volcanoes).
Figure above: Shape of volcano is influenced by the fluidity and viscosity of the lava flow. The more viscous, the steeper the sides of the volcano. (Diagram by Chiara Cingottini, DensityDesign Research Lab)
The lava flows from Bagana are andesitic in composition (intermediate composition) and are considered the biggest volcanic hazard that Bagana produces. These lava flows are thick, and although they may not travel as fall as fluid lava flows, they can travel far enough, completely covering everything in its path. In addition to these thick lava flows, Bagana also produces pyroclastic flows, however, in comparison, the volume of pyroclastic material is minimum to the amount of lava produced.
Figures above: Thick lava flows on Bagana volcano (Photos by Wally Johnson, 1988, and from the Global Volcanism Program )
The reason Bagana is interesting, and can be used to better understand the volcanics in Papua New Guinea, is that eruptions at Bagana have been monitored for some time. The first recorded eruption of Bagana was in 1842, and eruptions since then have been recorded, even during the Pacific War (1940s). It is especially unique since loud, violent eruptions have been recorded at Bagana, yet this is not its primary eruption style. In 1937, an eruption from Bagana was heard in Kieta, around 50 km away.
Figure above: Devastated area from another Papua New Guinea volcano, Goropu. Several Papuan volcanoes were monitored during the Pacific War (Image by D.R. Marsh, from here)
Most recently, on the 3rd of March, 2016, another eruption at Bagana produced an ash column that rose up to 2 km, and then drifted over 110 km NE. Although remote, Bagana continues to be an interesting volcano to watch, especially because of its continuous activity that is repeatedly captured by satellites in space.
Figures above: Bagana eruptions from space (Images from NASA)