Limnic Menace

By Coding Strategies on October 26th, 2018

Carbon dioxide (CO2) is used in the production of a wide variety of food and drink products, such as putting gas in beer, as a preservative that increases the shelf-life of packaged products, and the creation of dry ice. In June 2018, five CO2 producers across northern Europe went offline, creating a shortfall in this gas. Due to the lack of available CO2, there were shortages in beer, fizzy drinks and meat. Britain was particularly affected, because the shutdown of the plants meant that the UK had only one remaining plant producing this necessary gas. Distributors were concerned about continued production, and popular watering holes were worried about their ability to keep carbonated beverages on the menu. With an impending World Cup match and a scorching heat wave, some pubs were forced to source alternative beers rather than customer favorites. In addition, meat processors made changes to the “sell by” date because of lower levels of C02 in their packaged meats. This meant that grocers were required to sell the meat products more quickly, creating complications in the supply chain.

In addition to consumable supply problems, Scotland’s largest abattoir shut down temporarily because it ran out of the carbon dioxide used to stun pigs before they are processed. The facility generally processed 6000 animals a week, and was forced to send the pigs to other facilities for slaughter. And not just pork was at risk – nine of the UK’s largest poultry plants (supplying 60 percent of the market) were also at risk of an interruption in production. The trade journal Gas World described the shortage as the worst supply situation to hit the European carbon dioxide business in decades.

Lake Nyos is located in western Cameroon, near the Nigerian border in Africa. Nyos is a deep crater lake, a byproduct of an extinct volcano that last erupted about 400 years ago. This lake fills a roughly circular area in the Oku Volcanic Field, an explosion crater created when a lava flow interacted violently with groundwater. People have been settling on the shores of this picturesque and serene body of water since the time of the prior eruption. But, over a few hours in August of 1986, 1700 of those residents suddenly lost their lives; they had all suffocated because the lake had erupted.

It’s called limnic eruption, or a “lake overturn,” and was the result of a pocket of magma beneath the lake that leaked carbon dioxide. The science behind this event is similar to the result that occurs when a can of soda is shaken and then opened – it explodes when the carbon dioxide bubbles rapidly escape. In the case of lakes, though, it is much worse. Something on the bottom of the lake leaks carbon dioxide into the water; in this case volcanic gas was the likely culprit. CO2 dissolves into water more easily when the water is cold and under pressure. These conditions are present in the soda can, and also in the water at the bottom of some volcanic lakes (Lake Nyos was 682 feet deep at the time of the incident). The deep water areas of the lake becomes saturated with CO2, until there is an event that causes the trapped gas to suddenly escape upwards.

For lakes with a high amount of gas dissolved at lower, cooler depths the catalyst may be an earthquake or volcanic activity that creates a limnic eruption (limnic refers to bodies of water with low salt concentration, such as ponds or lakes). In the case of Lake Nyos, the massive release of carbon dioxide occurred on August 21, 1986 for unknown reasons. Most likely, the trigger was a rockslide from one of the lake’s walls; the falling rocks pushed up some of the trapped gas, then most of the gas was expelled in something similar to a giant burp. Farmers living near the lake heard a rumbling, and a frothy spray shot hundreds of feet into the air from the surface of the lake. A white cloud collected over the water, flowed across the nearby land and climbed to 328 feet tall. The gas cloud was moving at just over 60 mph, and those individuals who left their houses to investigate quickly lost consciousness. The released CO2 was heavier than the air and flooded the ground-level area surrounding the lake, crowding out the breathable, oxygen-rich air.

By August 23, the cloud had mostly blown away and the silence had lifted. Some of the residents had been unconscious for 36 hours, and revived to find that their livestock and neighbors did not survive the toxic cloud. And the lake changed, as well: it was now shallower, had plants and leaves floating on the surface, trees on the perimeter had been knocked down and the prior picturesque blue color had darkened to a rusty red-brown.

This was only the second time that a limnic eruption was recorded. The previous event occurred at Lake Monoun in Cameroon and claimed the lives of 37 nearby residents. But don’t lose sleep over exploding lakes – there are only three lakes in the world that currently meet the criteria for a potential limnic event: Lake Nyos, Lake Monoun and Lake Kivu on the border of the Democratic Republic of Congo and Rwanda. A limnic eruption of Lake Kivu could make the death toll from the Lake Nyos eruption look small – approximately 2 million people live on its shores. However, scientists have been working on “degassing” this lake, using a series of pipes to remove a lot of the gas. In addition, the gas in Lake Kivu appears to be methane. If this methane could be captured as it is removed, the Rwandan government could turn it into a power source.

There are ICD-10-CM codes for effects of external causes, which includes carbon dioxide exposure:

R55 - Syncope and collapse
T59.7X1A - Toxic effect of carbon dioxide, accidental (unintentional), initial encounter
Y92.828 - Other wilderness area as the place of occurrence of the external cause

So, the next time you are walking by a lake and notice an unpleasant smell, just be thankful that it’s not a belch of toxic gas. But as Rick Riordan writes in The Mark of Athena (Book 3 in the Heroes of Olympus series):

You can keep watch, in case – you know, the lake decides to attack us or something.