Goma (RD Congo) (AFP)
Thursday’s orders to evacuate Goma, a town in the shadow of the Mount Nyiragongo volcano in DR Congo, highlighted a rare but potentially catastrophic risk – a “limnic eruption,” when volcanic activity combined with a deep lake can spit deadly, suffocating gas.
The phenomenon first gained worldwide attention in August 1984, when 37 people mysteriously died at Lake Monoun in western Cameroon.
Scientists found that carbon dioxide (CO2) dissolved in the depths of the lake had erupted, creating invisible clouds on the surface that were blown by winds into homes and fields, choking life.
Two years later, more than 1,700 people and thousands of cattle have died in Lake Nyos, also in Cameroon, reinforcing the belief that earthquakes and volcanic activity can trigger these unusual events.
Over 600,000 people live in Goma, although the region’s population is around 2 million, in addition to the more than 90,000 people living across the border in the Rwandan town of Gisenyi.
The two towns lie on the northeastern shore of Lake Kivu, which is dominated by the Nyiragongo, a nearly 3,500-meter-high stratovolcano that straddles the tectonic divide of the East African Rift.
The dreaded volcano came back to life on Saturday, spewing out two rivers of lava the next day, which claimed the lives of 32 people and left an estimated 20,000 homeless.
# photo1 This was followed by hundreds of aftershocks, some equivalent to small earthquakes, which collapsed or destroyed several buildings, tore cracks in the ground and terrified the population.
– Disaster scenario –
The evacuation order follows a warning from the Goma Volcano Observatory (OVG), which monitors the pulse of Nyiragongo and Nyamuragira Volcano, 13 kilometers (nine miles) away.
In a technical note seen by AFP, the OVG said it had seen worrying signs of Nyiragongo activity pointing to three potential outcomes.
In the first two scenarios, the Nyiragongo would erupt again, sending new lava flows south towards Goma and Gisenyi, destroying buildings in their path before reaching Lake Kivu.
Either way, the amount of lava that could enter the lake would not be enough to raise the temperature of its deep waters by at least one degree Celsius (1.8 degrees Fahrenheit) – a key condition for a limnic eruption.
But in the worst-case scenario, the Nyiragongo lava flows would combine with volcanic activity beneath the lake bottom.
This activity could take the form of a “fissure or phreato-magmatic eruption under the lake and / or a large earthquake of magnitude 6.5 or 7”, said the OVG.
In this scenario, “a limnic eruption would take place and the gas dissolved in the deep waters of the lake would rise to the surface, in particular the CO2, suffocating all living things around Lake Kivu on the Congolese and Rwandan side”.
# photo2 ″ There are reportedly thousands of deaths, ”the OVG said, noting the need for resources to conduct an“ urgent exploration ”of Lake Kivu.
– Volcanic region –
The OVG also warned against using rainwater to drink or wash food, given the ash fall from the volcano.
Six volcanoes dot the Goma region, dominated by Nyiragongo, which is 3,470 meters (11,400 feet) high, and Nyamuragira, 3,058 meters.
The Nyiragongo last erupted on January 17, 2002, killing over 100 people and covering almost the entire eastern part of Goma with lava, including half of the airport airstrip.
Its deadliest eruption dates back to 1977, when more than 600 people died.
Nyamuragira is also very active, having its last major eruption ten years ago.
© 2021 AFP