The Observatoire Volcanologique de Goma has raised concerns about the possibility of a major eruptive episode on Mount Nyiragongo in the Virungu Mountiains of the North Kivu Province in eastern Democratic Republic of Congo. Local people in the area began to report loud and continuous rumblings from the volcano early in February 2016, and an expedition to the volcano by staff at the observatory at the beginning of March found that a new vent had opened at the northeastern end of the lower crater terrace, with lava issuing from this and forming a second lava lake (such a lake has been present at the volcano's main vent since 2002). A second visit to the volcano on 10-11 March found that lava had begun to flow from the new lake into the original one, though overall activity did seem to have subsided slightly.
The new lava lake on Mount Nyiragongo on 11 March 2016. Note lava flowing from the lake on the right side of the image. Observatoire Volcanologique de Goma.
This vent is considered to be particularly dangerous as it lies on one of two major fracture zones which run through the volcano. Eruptions on these fracture zones can cause the main edifice of the volcano to split, allowing lava that has built up in lakes within the central caldera over years or decades to drain rapidly, leading to rapidly flowing lava flows that spread over the surrounding countryside. The most recent two such episodes, in 1977 and 2002, both killed over a thousand people each, with a lava flow from the 2002 eruption destroying a large part of the town of Goma.
The new lava lake on 28 February 2016.
Nyiragongo and neighbouring volcano Nyamuragira account for 40% of all volcanic activity on the African continent. They produce a low silicone basalt. This tends to have a very low viscosity, i.e. it flows very freely, rapidly covering a wide area. Because of this few people choose to live near the mountains, so they are seldom a threat to human life, though it has in the past caused problems for vulnerable wildlife populations, such as the human-familiarised chimpanzees and gorillas of Virungu National Park.
Nyamuragira and Nyiragongo lie on the Eastern Branch of the East African Rift; most volcanoes in this area produce more typical siliclastic lavas, but there are several other basaltic volcanoes in the area, such as the less active Visoke, which last erupted in 1957, and the inactive Karasimbi, Mikeno and Muhavura volcanoes. The Western Branch of the Rift Valley also has basaltic volcanoes, most notably Ol Doinyo Lengi, to the south of Lake Natron in Tazania, the worlds only active carbonitic volcano (i.e a volcano that produces lavas containing carbonate compounds), and the nearby extinct, but dramatic, Mount Shombole.
The locations of Nyamuragira (purple) and Nyiragongo (red). Google Maps.
The East African Rift is slowly splitting the African Plate in two along a line from the Red Sea through Ethiopia, and which includes the great lakes and volcanoes of east-central Africa. This has the potential to open into a new ocean over the next few tens of millions of years, splitting Africa into two new, smaller, continents; Nubia to the west and Somalia to the east.
Movement on the African Rift Valley, with associated volcanoes. Rob Gamesby/Cool Geography.
Eruptions from Nyamuragira and Nyiragongo also tend to be unusually rich in Sulphur Dioxide (SO₂), with the volcano producing a large proportion of all the volcanic SO₂ that enters our atmosphere. To give this a sense of proportion, about 75% of all the SO₂ entering our atmosphere originates from the burning of fossil fuels. The effects of SO₂ in the atmosphere are a little complicated. Firstly it is poisonous, though this is only a danger close to the source where it is concentrated. Since most people avoid going close to active volcanoes, this usually only presents a hazard to professional volcanologists. Secondly it mixes with water to form sulphuric acid, i.e. acid rain, which can be a major problem downwind of volcanic eruptions and large industrial centres, with the rain causing severe damage to vegetation and aquatic life. Thirdly SO₂ droplets act as coolant. Since both volcanic and industrial SO₂ is usually produced alongside larger quantities of Carbon Dioxide (CO₂), which is a greenhouse gas, this is usually a negligible effect, but cooler weather can be produced downwind of major eruptions, as the CO₂ disperses more rapidly than the SO₂.
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