Lake Nyos . It is a lake that gives its name to the volcano on which it is located, at a height of 3,011 meters above sea level. It occupies its entire crater, one of the 29 maars that it occupies, which is known as the Oku Vocanic Field, located northwest of Cameroon . This is part of a zone of crustal fragility, called the Cameroon volcanic line, which encompasses the Mount Cameroon stratovolcano, and extends about 1,600 km, with half of its length submerged in the Atlantic.
Summary
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- 1 Features
- 2 Formation and Geological History
- 3 The 1986 Catastrophe
- 4 Medical problems
- 5 Degassing
- 6 The weakening of the dam
- 7 Sources
characteristics
The lake is more than 200 m deep. During the rainy season, the water overflows the shore and floods the neighboring valleys. The Lake Nyos crater may have been formed by an explosive phreatic eruption some 500 years ago. Its edge, which reaches 1.8 km wide, is formed by fragments of basaltic materials that contain large fractured blocks of granite. A pocket of magma found underneath the lake and CO2 carbon dioxide leaks into the water, transforming it into carbonic acid. Nyos is one of three known lakes exploding as it is saturated with carbon dioxide.
There are other lakes of this type such as:
Lake Monoun, 100 kilometers (62 miles) away SSE. Lake Kivu in Rwanda .
The 21 of August of 1986 , possibly caused by a landslide, Lake Nyos suddenly emitted a large cloud of CO2, which asphyxiated 1,700 people and 3,500 livestock in nearby villages. Although not totally unprecedented, it was the first large-scale suffocation caused by a natural event.
To avoid a repetition , a degassing tube from the lower layers to the upper part was installed in 2001 , allowing the carbon dioxide to escape in large quantities.
Formation and Geological History
The maars is believed to have formed in an eruption approximately 400 years ago, and is 1,800m (5,900 ft) wide and 208 m (682 ft) deep. The area has been volcanically active millions of years-after America’s South and Africa were separated by plate tectonics about 110 million years ago, West Africa also experienced rifting, although to a lesser degree. The gap that is known as the Mebere Rift Valley and extent of the magma crust has allowed it to reach the surface along a line that runs through Cameroon. Mount Cameroon is also on this fault line. Lake Nyos is surrounded by ancient lava flows and pyroclastic deposits. Although Nyos is inside an extinct volcano, magma still exists under it.
Approximately 50 miles (80 km) directly below the lake resides a pool of magma, which allows to expel carbon dioxide and other gases, the gases then travel up through the land, they are then trapped by the natural springs that surround the lake, ultimately, the increase in the surface of the water and the leader in the lake. The waters of the lake are held in place by a natural dam formed from volcanic rock. At its narrowest point, the wall is 40 meters (130 feet) high and 45 meters (148 feet) wide. Lake Nyos is one of only three lakes in the world of this type, known to be saturated with carbon dioxide – the others are Lake Monoun, also in Cameroon , and Lake Kivu in Rwanda. A magma chamber beneath the region is an abundant source of carbon dioxide, which seeps through the lake bed, loading the waters of Lake Nyos with an estimated 90 million tons of CO2. Most of the time the lake is stable and the CO2 remains in solution in the lower layers. However, over time the water becomes supersaturated, and if an event such as an earthquake or landslide occurs, large amounts of CO2 can suddenly come out of solution.
The 1986 Catastrophe
In 1986, a cloud of carbon dioxide that escaped from Lake Nyos killed about 1,800 people and 6,000 head of cattle. Up to 1 km of gas, traveling at almost 50 km / h, it descended the surrounding valleys, expanding about 23 km in all directions. As it advanced, the heavy gas clung to the ground, dislodging the air and suffocating men and animals. Causes of the catastrophe: the emanation of a large cloud of toxic gas was caused by the lake water being saturated with carbon dioxide that leaked from the underground springs. The gas is believed to have been dislodged from the bottom of the lake due to a landslide or earthquake. Since 1990, a team of French scientists has worked to degas the lake, and a series of pipes have been installed to prevent carbon dioxide build-up. It is the most serious limnic eruption in history.
Medical problems
In the aftermath of the eruption, many survivors were treated at the main hospital in Yaoundé, the country’s capital. Many of the victims were believed to have been poisoned by a mixture of gases such as hydrogen and sulfur gases . Poisoning from these gases could lead to pain, burning in the eyes and nose, coughing and other signs of suffocation. Following the disaster, the lake was known as the “deadly lake” by Guinness World Records in 2008 .
Degassing
The magnitude of the disaster led to much study on how recurrence could be prevented. Estimates of the rate of carbon dioxide entering the lake suggested that it could occur every 10-30 years, although a recent study shows that the release of water from the lake, caused by erosion of the natural barrier that maintains in the Lake water could, in turn, reduce the pressure on the lake’s carbon dioxide and cause a gas leak much earlier.
Several researchers independently proposed the installation of degassing the raft columns in the lake. The principle is simple: a pump that drives the water from the bottom of the lake, highly saturated with CO2, until the loss of pressure begins to release the gas from the two-phase liquid. In 1992 at Monoun, and in 1995 at Nyos, a French team demonstrated the feasibility of this approach. In 2001 , the U.S. Office of Overseas Disaster Assistance funded a permanent installation in Nyos of a degassing tube siphoning water from the lower layers to the top allowing carbon dioxide to leak. in great quantities.
More pipes are expected to be needed to make the lake safe: the original French estimates called for a total of five, and the current OFDA project calls for another two pipes, each with ten times the capacity of the current single pipeline. In the wake of the Lake Nyos tragedy, scientists investigated other African lakes to see if a similar phenomenon could occur elsewhere. Lake Kivu in Rwanda, 2,000 times larger than Lake Nyos, was also found to be supersaturated, and geologists found evidence of outgassing and events around the lake over every thousand years. The eruption of nearby Mount Nyiragongo In 2002 it sent lava flowing into the lake, causing fears that a gas eruption could be activated, but fortunately it was not, as the lava flow stopped and before it reached near the bottom layers of the lake where the gas is kept in solution by the pressure of the water.
The weakening of the dam
On August 18, 2005, Dr. Isaac Njilah, a geologist at the University of Yaoundé, suggested that the natural volcanic rock dike that holds the waters of the lake could collapse in the near future. Erosion has worn down the dam, causing holes and pockets to develop in the upper layer of the dam, the water already passing through the lower section. Meanwhile, landslides have reduced the strength of the dam outside. Seismic activity caused by the volcanic foundation of the lake could cause the lake wall to give way to this water, resulting in up to 50 million cubic meters (1.8 billion cubic feet) of water flooding downhill in the areas of the Northwest Province and the Nigerian states of Taraba and Benue. Dr. Njilah estimates that the area is home to more than 10.
The Cameroonian government, speaking through Dr. Gregory Tanyi-Leke of the Geological and Mining Research Institute, acknowledges the weakening of the wall, but denies that it presents an immediate threat. A United Nations team led by Olaf Van Duin and Nisa Nurmohamed from the Dutch Ministry of Transport and Public Works inspected the dam for three days in September 2005 and confirmed that the natural of the lips had weakened.
One possible means of avoiding such a catastrophe would be to strengthen the lake wall, although this would take a lot of time and money. Engineers could also introduce a channel to allow excess water to drain, if the water level were lowered by about 20 meters (66ft), the pressure on the wall would be significantly reduced.
