![]() The chances of such a sequence of events may go up as the planet warms, MacIntyre says. They could flush enough built-up sediment from the many streams feeding into the lake to cause the layers to mix, MacIntyre says. Lowered water levels during dry periods could also leave Kivu more vulnerable to disruption from particularly heavy rain. Climate is also a potential culprit.Īt least one past eruption discovered in the sediment record appears to have been caused by drought that evaporated enough water from the top of the lake to reduce the pressure at the lower levels and release the dissolved gases. Kivu is in a seismically active area, so an earthquake could generate waves in the lake that would mix the layers enough to release the trapped gases. While a landslide of the scale suspected in the Nyos eruption might not cause enough mixing at Kivu, due to the lake’s size and depth, there are several other possible triggers. Eruptions can also be caused when something forces the deep water with its dissolved gases to mix with the layers above, reducing the pressure on the gases and allowing them to quickly come out of solution and escape, similar to the effect of shaking a can of soda and then opening it. If the water becomes completely saturated with dissolved gases, any additional CO2 or methane injected into the lake will be forced to bubble out of solution, rise and be released into the air. ![]() Limnic eruptions can occur for two reasons. These sediment bands are “very unusual, organic-rich layers”, Katsev says, that may be the result of eruptions. ![]() Sediment cores taken from the bottom of the lake have revealed features known as brown layers that are unlike the surrounding sediments. Scientists have found what may be evidence of at least one previous limnic eruption at Kivu that likely occurred between 3,500 and 5,000 years ago, and possibly several more recent ones. “Just think of the entire water mass sitting there for thousands of years and doing nothing,” says Wüest, who has studied convection in various lakes of the world, including weird outliers like Lake Kivu. There is mixing within each layer, but they don’t interact with each other. The layers can be separated roughly into two regions: one of less-dense surface water above a depth of about 60m (200ft) and, below that, a region of dense saline water that is itself further stratified, says Alfred Wüest, an aquatic physicist at the Swiss Federal Institute of Technology in Lausanne. The Indian megacity digging a million wells.How a tropical island recovered from black rats.Russia’s grand plan to clean its Arctic nuclear waste.The result, says limnologist Sergei Katsev of the University of Minnesota Duluth, is a lake with several distinct layers of water of sharply different densities, with only thin transition layers between. The deeper water is also saltier due to sediment raining down from the upper layers of the lake and from minerals in the hot springs, which further increases the density. This mixture of water and dissolved gases is denser than water alone, which discourages it from rising.
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