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CASE TEACHING NOTES for “A KILLER LAKE” Thomas Horvath, Biology Department, SUNY College at Oneonta

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• Human Health and Vulnerability in the Nyiragongo Volcano Crisis Democratic Republic of Congo 2002 Human Health and Vulnerability in the Nyiragongo Volcano Crisis Democratic Republic of Congo 2002 Final Report to the World Health Organisation Dr Peter J Baxter University of Cambridge Addenbrooke’s Hospital Cambridge, UK Dr Anne Ancia Emergency Co-ordinator World Health Organisation Goma Nyiragongo Volcano with Goma on the shore of Lake Kivu Cover : The main lava flow which shattered Goma and flowed into Lake Kivu Lava flows from the two active volcanoes CONGO RWANDA Sake Munigi Goma Lake Kivu Gisenyi Fig.1. Goma setting and map of area and lava flows HUMAN HEALTH AND VULNERABILITY IN THE NYIRAGONGO VOLCANO CRISIS DEMOCRATIC REPUBLIC OF CONGO, 2002 FINAL REPORT TO THE WORLD HEALTH ORGANISATION Dr Peter J Baxter University of Cambridge Addenbrooke’s Hospital Cambridge, UK Dr Anne Ancia Emergency Co-ordinator World Health Organisation Goma June 2002 1 EXECUTIVE SUMMARY We have undertaken a vulnerability assessment of the Nyiragongo volcano crisis at Goma for the World Health Organisation (WHO), based on an analysis of the impact of the eruption on January 17/18, 2002. According to volcanologists, this eruption was triggered by tectonic spreading of the Kivu rift causing the ground to fracture and allow lava to flow from ground fissures out of the crater lava lake and possibly from a deeper conduit nearer Goma. At the time of writing, scientists are concerned that the continuing high level of seismic activity indi- cates that the tectonic rifting may be gradually continuing. Scientists agree that volcano monitoring and contingency planning are essential for forecasting and responding to fu- ture trends. The relatively small loss of life in the January 2002 eruption (less than 100 deaths in a population of 500,000) was remarkable, and psychological stress was reportedly the main health consequence in the aftermath of the eruption. [Show full text]
• Lake Nyos Dam Assessment Lake Nyos Dam Assessment Cameroon, September 2005 Joint UNEP/OCHA Environment Unit United Nations Office for the United Nations Coordination of Humanitarian Affairs Environment Programme (OCHA) (UNEP) Published in Switzerland, October 2005 by the Joint UNEP/OCHA Environment Unit Copyright © 2005 Joint UNEP/OCHA Environment Unit This publication may be reproduced in whole or in part and in any form for educational or not-for-profit purposes without special permission from the copyright holder, provided acknowledgement is made of the source. Joint UNEP/OCHA Environment Unit Palais des Nations CH-1211 Geneva 10 Switzerland Tel. +41 (0) 22 917 3484 - Fax +41 (0) 22 917 0257 http://ochaonline.un.org/ochaunep The assessment was made possible through the kind assistance of the Ministry of Foreign Affairs and the Ministry of Transport, Public Works and Water Management of The Netherlands. Mission team: Ms. Nisa Nurmohamed Mr. Olaf van Duin Road and Hydraulic Engineering Institute Ministry of Transport, Public Works and Water Management The Netherlands Report Coordinator: René Nijenhuis, Joint UNEP/OCHA Environment Unit Photos: Nisa Nurmohamed, Olaf van Duin. Cover: Overview of Lake Nyos, Cameroon 2 Table of Contents 1. Executive summary 4 2. Introduction 5 3. Current situation of the dam 6 4. Carbon dioxide in Lake Nyos 7 5. Displacement of affected people 8 6. Suggested approaches 8 7. Lake Nyos Mitigation Project 9 8. Timeframe and costs 11 References and acknowledgements 13 Annex 1: Mission logbook 14 Annex 2: Carbon dioxide in Lake Nyos 16 3 Executive summary Upon request from the Ministry of Territorial Administration and Decentralization of Cameroon, the Joint UNEP/OCHA Environment Unit deployed of an assessment mission to assess the stability of he natural dam in Lake Nyos, Cameroon. [Show full text]
• Africa Lakes (31-May-06).Indd Fires Near Lake Malawi, Africa This image of southeastern Africa, ac- quired on 25 September 2004, shows scores of fi res burning in Mozambique south of Lake Malawi, whose southern tip is at the top center of the image. Active fi re detec- tions are marked in red. The fi res created a layer of smoke that darkened the surface of the land beneath it. At upper left in the im- age, the turquoise-colored body of water is the Lake Cahora Basa, created by a dam on the Zambezi River just inside Mozambique after the river leaves its course along the border of Zambia and Zimbabwe (NASA 2004). 3.2 Images of Change: surfaces, which spans the past 30 years and and forests, croplands, grasslands and ur- continues today. ban areas around the lakes. Africa’s Lakes By comparing two images of the same Changes seen in pairs of satellite images Various types of ground-based instruments, area taken 10, 20 or even 30 years apart, it should serve as a call to action. While some together with in situ surveys and analyses, is often easy to see human and naturally-in- are positive changes, many more are nega- can be used to measure the changes be- duced changes in a specifi c location. There tive. They are warning signs, which should ing brought about on the Earth through are very few places remaining on the planet prompt us to ask some serious questions human activities and global changes. But that do not show at least some impact from about our impact on these vital freshwater such changes can also be observed in more people’s activities. [Show full text]
• Goma Reached by Lava of Mount Nyiragongo, Decade Volcano Sentinel Vision EVT-875 Goma reached by lava of Mount Nyiragongo, decade 27 May 2021 volcano, DRC Sentinel-2 MSI acquired on 01 June 2020 at 08:06:11 UTC Sentinel-1 CSAR IW acquired on 13 May 2021 at 16:21:09 UTC Sentinel-5P TROPOMI SO2 acquired on 23 May 2021 at 11:10:2 3 UTC Sentinel-1 CSAR IW acquired on 25 May 2021 at 16:21:10 UTC Sentinel-2 MSI acquired on 27 May 2021 at 08:06:11 UTC 3D Layerstack Author(s): Sentinel Vision team, VisioTerra, France - [email protected] Keyword(s): Emergency, natural disaster, volcano, lava flow, atmosphere, urban planning, Democratic Republic of Congo, East African Rift, Great Rift Valley Fig. 1 - S5P TROPOMI (23.05.2021) - SO2 total column - Sulfur dioxyde emissions one day after the eruption started. 2D view Listed among the decade volcanoes, The Nyiragongo volcano is considered one of the most dangerous in the World. It lies 10 km from Goma and its two millions inhabitants and very close to Lake Kivu and its dissolved gasses. On 22 May 2021, it was reported that the volcano was erupting again. The Smithsonian Institution details: "At around 18:15 on 22 May seismicity at Nyiragongo spiked, around the same time observers reported at least two fissures opening on the lower Southern flanks, North-West of Kibati (8 km South-South-East) and Rukoko (10 km South). Lava from the first fissure, originating near the Shaheru crater, flowed East over a major road (N2) and then South. The second fissure produced lava flows that traveled South, overtaking and setting fire to many houses and structures in communities north of Goma, just West of Monigi (12 km South). [Show full text]
• Gas Buildup in Lake Nyos, Cameroon: the Recharge Process and Its Consequences Applied Geochemistry,Vol. 8, pp. 207-221, 1993 Pergamon Press Ltd Printed in Great Britain Gas buildup in Lake Nyos, Cameroon: The recharge process and its consequences W. C. EVANS U.S. Geological Survey, Menlo Park, CA 94025, U.S.A. G. W. KLING Department of Biology, University of Michigan, Ann Arbor, MI 48109, U.S.A. M. L. TUTTLE U.S. Geological Survey, Denver, CO 80225, U.S.A. G. TANYILEKE Institute for Geological and Mining Research, Yaounde B.P. 4110, Cameroon and L. D. WHITE U.S. Geological Survey, Menlo Park, CA 94025, U.S.A. (Received 31 December 1991; accepted in revised form 12 August 1992) Abstract--The gases dissolved in Lake Nyos, Cameroon, were quantified recently (December 1989 and September 1990) by two independent techniques: in-situ measurements using a newly designed probe and laboratory analyses of samples collected in pre-evacuated stainless steel cylinders. The highest concen- trations of CO2 and CH4 were 0.30 mol/kg and 1.7 mmol/kg, respectively, measured in cylinders collected 1 m above lake bottom. Probe measurements of in-situ gas pressure at three different stations showed that horizontal variations in total dissolved gas were negligible. Total dissolved-gas pressure near the lake bottom is 1.06 MPa (10.5 atm), 50% as high as the hydrostatic pressure of 2.1 MPa (21 atm). Comparing the CO 2 profile constructed from the 1990 data to one obtained in May 1987 shows that CO2 concentrations have increased at depths below 150 m. Based on these profiles, the average rate of COz input to bottom waters was 2.6 x 10~ mol/a. [Show full text]
• MIDDLES BMJ: First Published As 10.1136/Bmj.298.6685.1437 on 27 May 1989 MIDDLES BMJ: first published as 10.1136/bmj.298.6685.1437 on 27 May 1989. Downloaded from Lake Nyos disaster, Cameroon, 1986: the medical effects of large scale emission of carbon dioxide? Peter J Baxter, M Kapila, D Mfonfu Abstract loss oflife in the settlements ofNyos, Cha, and Subum, Carbon dioxide was blamed for the deaths of around and along valleys in a sparsely populated farming area 1700 people in Cameroon, west Africa, in 1986 when some 20 km long by 15 km wide6 (fig 1). Most of the a massive release ofgas occurred from Lake Nyos, a native population were either subsistence farmers or volcanic crater lake. The clinical findings in 845 Fulani cattle raisers; many cattle as well as other survivors seen at or admitted to hospital were animals were killed. Survivors near the lake recalled compatible with exposure to an asphyxiant gas. hearing wind or animals being disturbed and some Rescuers noted cutaneous erythema and bullae on reported a smell of gunpowder or rotten eggs before an unknown proportion of corpses and 161 (19%) suddenly losing consciousness. News of the event was survivors treated in hospital; though these lesions slow to emerge, and when a rescue team entered the were initially believed to be burns from acidic gases, area 36 hours later it came upon an awesome scene. further investigation suggested that they were One of us (DM) was a member of the team. associated with coma states caused by exposure to carbon dioxide in air. The disaster at Lake Nyos and a similar event at Lake Monoun, Cameroon, two years previously provide new information on the possible medical effects of large scale emissions of carbon dioxide, though the presence of other toxic factors in these gas releases cannot be excluded. [Show full text]
• Lakes Nyos and Monoun Gas Disasters (Cameroon)—Limnic Eruptions Caused By GEochemistry Monograph Series, Vol. 1, No. 1, pp. 1–50 (2017) www.terrapub.co.jp/onlinemonographs/gems/ Lakes Nyos and Monoun Gas Disasters (Cameroon)—Limnic Eruptions Caused by Excessive Accumulation of Magmatic CO2 in Crater Lakes Minoru Kusakabe Department of Environmental Biology and Chemistry University of Toyama 3190 Gofuku, Toyama 930-8555, Japan e-mail: [email protected] Citation: Kusakabe, M. (2017) Lakes Nyos and Monoun gas disasters (Cameroon)—Limnic erup- tions caused by excessive accumulation of magmatic CO2 in crater lakes. GEochem. Monogr. Ser. 1, 1–50, doi:10.5047/gems.2017.00101.0001. Abstract Received on December 5, 2015 This is a review paper on the Lakes Nyos and Monoun gas disasters that took place in the Accepted on May 11, 2016 mid-1980s in Cameroon, and on their related geochemistry. The paper describes: (i) the Online published on April 7, 2017 gas disasters (the event and testimonies); (ii) the unusual geochemical characters of the lakes, i.e., strong stratification with high concentrations of dissolved CO2; (iii) the evolu- Keywords tion of the CO2 content in the lakes during pre- and syn-degassing; (iv) the noble gas • Cameroon signatures and their implications; (v) a review of models of a limnic eruption; (vi) a • Lakes Nyos and Monoun revision of a spontaneous eruption hypothesis that explains the cyclic nature of a limnic • gas disaster eruption (Kusakabe 2015); (vii) a brief review of the origin of the Cameroon Volcanic • crater lakes Line (CVL) and the geochemistry of CVL magmas; (viii) a brief review of other CO - • magmatic CO2 2 • limnic eruption rich lakes in the world; and (ix) concluding remarks. [Show full text]
• A Volcanic Issue 1111 2 A volcanic issue – lessons 3 4 learned in Goma 5 6 7 Aranka Anema and Jean-François Fesselet 8 9 10 1 When Mount Nyiragongo erupted in 2002 it sent lava 2 through the town of Goma and into Lake Kivu. Relief 3 operations focused on how to treat biological pollution 4 in water from Lake Kivu and to manage the water’s 5 chemical contamination from lava flows. Either form of 6 contamination would have been less of a problem if 7 lessons learned from earlier eruptions had been more 8 readily available. 9 20111 ount Nyiragongo in the water sources and unhygienic living that lava flow into the lake would 1 Democratic Republic of conditions. destabilize the gases and cause either a 2 M Congo is one of Africa’s fatal explosion resulting from methane 3 most active volcanoes. On 17 January Chemical and biological or the spread of lethal low-lying carbon 4 2002 Nyiragongo erupted, sending lava contamination dioxide, as happened by Lake Nyos 5 across the town of Goma 10km away in Cameroon in 1986. In addition to 6 into Lake Kivu. Goma has a population Lake Kivu is the only source of water disquiet over the destabilization of 7 of approximately 400 000. Years of for drinking, cooking and hygiene in carbon dioxide and methane in the 8 conflict, displacement and poverty have Goma and the surrounding areas. lake, specialists were concerned about 9 rendered Goma’s population particu- During the crisis, humanitarian agen- two other key water supply issues: the 30 larly vulnerable to disease and mal- cies became concerned that the water lake’s fluoride pollution and the threat 1 nutrition. [Show full text]
• Solving the Mystery of Lake Nyos a Case-Based Unit for Photosynthesis and Cellular Respiration Solving the Mystery of Lake Nyos A Case-based Unit for Photosynthesis and Cellular Respiration Becky Ann Bartlett Isabel Resende Garth Gower Table of Contents – Teaching Notes Introduction to Teachers page How to Implement this Unit page National Standards Addressed page Project 2061 Standards Addressed page Guided Questions for the Story page Science Content for the Unit History of Lake Nyos page Photosynthesis Pathway page Respiration Pathway page Lesson Plan Outline page #1 Graphing Lake Data page #2 Stratification of Lakes page #3 Solubility of gas in a liquid page #4 Density of liquids page #5 Density of gases page #6 Respiration Experiment Part I page Part II page #7 C02 produced by respiration page #8 Photosynthesis Experiments Part I page Part II page Part III page Part IV page Glossary page Assessment Questions page Websites page Introduction to Teachers This unit uses a fictionalized story based on a real incident in Cameroon, West Africa as a means of instruction for photosynthesis and cellular respiration. Eight sequential, inquiry-based, hands-on experiments are provided to build student knowledge of photosynthesis and cellular respiration through discovery. A bank of assessment questions, from which the educator may choose, accompanies the unit as well. Photosynthesis and cellular respiration are traditionally covered in all High School Biology courses. These are difficult concept for most students to comprehend. The difficulty encountered by students lies in their inability to relate the importance of the chemical reactions of photosynthesis and cellular respiration to living systems. This case “Solving the Mystery of the Killer Lake” uses a fictionalized story, about a real incident in Cameroon, West Africa in 1986 as a vehicle for instruction in these two biochemical pathways. [Show full text]
• The 21 August 1986 Lake Nyos Gas Disaster, Cameroon Final Report of the United States Scientific Team to the Office of U.S. Fore DEPARTMENT OF THE INTERIOR U.S.GEOLOGICAL SURVEY The 21 August 1986 Lake Nyos Gas Disaster, Cameroon Final Report of the United States Scientific Team to the Office of U.S. Foreign Disaster Assistance of the Agency for International Development by Michele L. Tuttle U.S Geological Survey Michael A. Clark, M.D. Armed Forces Institute of Pathology Harry R. Compton U.S. Environmental Protection Agency Joseph D. Devine Brown University William C. Evans U.S. Geological Survey Alan M. Humphrey U.S. Environmental Protection Agency George W. Kling Duke University Edward J. Koenigsberg, M.D. Office of U.S. Foreign Disaster Assistance John P. Lockwood U.S. Geological Survey Glenn N. Wagner, D.O. Armed Forces Institute of Pathology Open-File Report 87-97 1987 Lake Nyos, Cameroon: Post-disaster, looking south, 29 August 1986 CONTENTS Page Executive Summary 1 Introduction 2 Geology 4 Gas Origin 7 Release of Gas from the Lake 12 Pathology 15 Conclusions 21 Remaining Hazards 22 Recommendations 23 Acknowledgements 25 Tables 1-5 26-30 Figures 1-13 31-44 Appendix I - Methods 45 Appendix II - Proposed Remediation of Lake Nyos Gas Problem 49 Appendix III - Additional Gas Analyses 50 References Cited 54 III EXECUTIVE SUMMARY The sudden catastrophic release of gas from Lake Nyos on 21 August 1986 caused the deaths of at least 1700 people in the northwest area of Cameroon. An eleven-person multidisciplinary team was sent for three weeks to investigate the cause and to recommend steps to mitigate future hazards of this nature. The results of the field and laboratory investigations are: * Lake Nyos occupies a volcanic crater that was formed by a violent explosion only a few hundred years ago. [Show full text]
• 56 Natural Hazards Natural Hazards CALL it a potential peril or a hidden hazard but the fact remains that Limnic eruption is a rare natural hazard, which is no less deadly because of its rarity. Although Limnic eruptions sometimes walk hand in hand with tsunami, there are no fiery explosions involved, no lahars, no lava flows, no avalanches, no cyclones or typhoons…yet the danger to life is no less real. Limnic eruptions are killers in their own right, albeit silent ones and it is a killer despite the fact that only two cases have been documented in recent times. Cattle killed during gas leak there were little or no signs of trauma to droplets. Carbon dioxide normally makes the bodies. Vegetation was flattened for up ~0.03% of air and concentrations of Limnic eruption (aka Lake overturn/ 100 meters around the eastern end of the more than 10 per cent can be fatal. Being A rollover) is the sudden eruption of lake but otherwise plant-life remained heavier than air, it settles like a blanket carbon dioxide from deep lake water. The unaffected. Apparently, the damage was cutting off access to regular air. In carbon dioxide smothers and kills. It is caused by a 5-meter tsunami-like wave that desperation a person gasps, and the more sudden, it is silent and it is a sinister killer. was triggered when the ‘something’ erupted a person gasps for air, the more carbon violently from the water. dioxide enters the system. The question that then arose was: From where did this carbon Liquidating Life Listing Cause dioxide cloud surface? Of course, the How On 15 August 1984, 37 people were Scientists soon realized that the ‘something’ and the Why behind the eruption also mysteriously suffocated to death near Lake was a mixture of carbon dioxide and water engaged scientific attention. [Show full text]
• Volcanic Lakes: the More You Know, the Less You Need IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan Forecasting Volcanic Activity - Reading and translating the messages of nature for society 4A1_3I-O1 Room A4 Date/Time: July 24 8:45-9:00 Volcanic lakes: the more you know, the less you need Dmitri Rouwet Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, Italy E-mail: [email protected] Volcanic lake research boosted after the 1986 Lake Nyos (Cameroon) lethal gas burst, a limnic rather than a volcanic event. This led to the foundation of the IAVCEI–Commission on Volcanic Lakes, which grew out into a multi–disciplinary scientific community since the 1990s. I here introduce the first data base of volcanic lakes, containing over 300 lakes. In my opinion, this number is surprisingly high, which implies that many of the lakes were mostly unknown, or at least unstudied to date. Some acidic crater lakes topping active magmatic–hydrothermal systems are monitored continuously or discontinuously. Such detailed studies have shown their usefulness in volcanic surveillance (e.g., Ruapehu, Yugama, Poás). Others are Nyos–type lakes, with possible gas accumulation in bottom waters, and thus potentially hazardous. Nyos–type lakes tend to remain stably stratified in tropical and sub-tropical climates (meromictic), leading to long-term build–up of gas, which can be released after a trigger. Many of the unstudied lakes are in the latter situation. In temperate climates, such lakes tend to turn over in winter (monomictic), liberating its gas charge yearly. Acidic crater lakes are easily recognized as active, whereas Nyos–type lakes can only be recognized as potentially hazardous if bottom waters are investigated, a less obvious operation. [Show full text]

Case Study of Lake Nyos

While it is a devastating story to learn about, it is good in the sense that it can be applied to so many science concepts. Biology teachers can bring it up when learning about the carbon cycle. Earth science teachers can discuss the story during their volcanoes unit. Physical science teachers can use it to introduce density of gases. It’s a phenomena that is so versatile!

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How did Lake Nyos suddenly kill 1,700 people?

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Key Takeaways

• On August 21, 1986, Lake Nyos in Cameroon released a large cloud of CO 2 , suffocating over 1,700 people and countless animals by displacing the oxygen around them.
• Scientists determined that CO 2 had been gradually leaking into the lake, eventually erupting in a deadly release triggered by a rockslide.
• To prevent future disasters, engineers installed pipes to continuously degas the lake, significantly reducing the risk of another CO 2 burst but leaving the area still potentially hazardous.

­Lake Nyos had long been quiet before it happened. Farmers and migratory herders in the West African country of Cameroon knew the lake as large, still and blue.

But on the evening of Aug. 21, 1986, farmers living near the lake heard rumbling. At the same time, a frothy spray shot hundreds of feet out of the lake, and a white cloud collected over the water. From the gro­und, the cloud grew to 328 feet (100 meters) tall and flowed across the land. When farmers near the lake left their houses to investigate the noise, they lost consciousness.

The heavy cloud sunk into a valley, which channeled it into settlements. People in the affected areas collapsed in their tracks -- at home, on roads or in the field -- losing consciousness or dying in a few breaths. In Nyos an­d Kam, the first villages hit by the cloud, everyone but four inhabitants on high ground died.

The valley split, and the cloud followed, killing people up to 15.5 miles (25 kilometers) away from the lake. Over the next two days, people from surrounding areas entered the valley to find the bodies of humans and cows lying on the ground.

By Aug. 23, the cloud had mostly blown away, and the silence had lifted. After being unconscious for up to 36 hours, some people revived to find, horrifically, that their family members, neighbors and livestock were dead.

The lake had changed, too. It was now shallower; plants and leaves floated in it; and its formerly picturesque blue hue had darkened into rust. What was the deadly force at Nyos? Find out next.

Investigating the Nyos Disaster

Lake monoun and other exploding lakes, recipe for a killer lake, degassing lakes with big straws.

­Scientists soon learned that the cloud contained carbon diox­ide (CO 2 ). That finding explained the cloud's heaviness, since CO 2 is denser than air. The cloud was actually CO 2 mixed with air. The CO 2 killed directly by shutting off people's consciousness and breathing. When the CO 2 concentration was 15 percent or less, people lost consciousness and later revived. Individuals who inhaled more than 15 percent CO 2 stopped breathing in minutes and died.

As for why the lake ejected CO 2 -- up to a third of a cubic mile of it -- scientists disagreed. One camp believed a volcanic eruption released CO 2 and blew up the lake. Another camp thought CO 2 was gradually leaking into and being stored in the lake. When the lake exploded, it released the gas in a gigantic, deadly burp.

"While the two camps of scientists were fighting, they agreed that CO 2 killed the people, and the people would be safer on higher ground," says William Evans, a geochemist with the U.S. Geological Survey who investigated the disaster. The Cameroonian government acted accordingly.

Evans' team installed CO 2 monitors on the lakeshore. The monitors were hooked to sirens that would sound if too much CO 2 entered the air. People knew the alarms meant they should go to high ground.

As years passed, scientists resolved the debate about the origin of the CO 2 . After measuring gas at the bottom of Lake Nyos, they found a CO 2 -rich layer, where levels of the gas were rising over time, suggesting gradual leakage into the bottom of the lake.

Scientists looked for markers of a volcanic eruption, such as sulfur and chloride in the lake. They also installed seismometers around the body of water to record tiny earthquakes that would follow a volcanic eruption. "It was the quietest area that the British Geological Survey had ever monitored," says Evans. The volcano hypothesis died. CO 2 was bubbling into the lake from below.

Scientists reasoned that CO 2 had been trapped in the bottom of Lake Nyos for a long time, held down by 682 feet (208 meters) of water. On the day of the eruption, however, something external triggered the release of gas. Most likely, it was a rockslide from one of the lake's walls. When the falling rocks sunk to the bottom of the lake, they pushed up some gas. Then most of the gas bubbled up.

­If this sounds like a freak occurrence to you, read on to learn about the lake that exploded in an eerily similar fashion just two years before.

­Almost two years earlier, on the evening of Aug. 15, 1984, Cameroonians about 62 miles (100 kilometers) southeast of Nyos had heard similar rumblings near a lake. The site of this prior explosion, however, was the smaller Lake Monoun. Around 11:30 p.m., CO 2 shot out of the lake and sunk into a valley, near a road. As people from the nearby village of Njindoun walked down the road on their way to work before dawn, they entered the cloud , collapsed and died.

By 10:30 a.m. or so, wind had swept the cloud away. A doctor and police officer arrived on the scene to find most of the 37 dead on a short stretch of road, including a man slumped over his motorcycle [source: Sigurdsson ].

The Cameroonian government suspected the explosion was an act of terrorism or the result of someone dumping chemicals into the lake. More traditional villagers in Njindoun believed legends that evil spirits periodically left the lake and killed neighboring people. "Probably these legends came about because of gas bursts in the past," says Evans.

Another lake in Africa may be building toward a burst. Lake Kivu, situated between Rwanda and the Congo in the African Rift Valley, is a legitimate worry. It's more than twice as deep as Nyos and can store more gas. Bacteria in the lake are chugging out methane, and CO 2 is leaking in from magma below. Sediment layers suggest the lake may have erupted 7,000 to 8,000 years ago, says Varekamp. Because 2 million people live near Kivu, the lake's gas pressure is being monitored. "If that ever were to go, that would be a natural disaster on a scale we haven't seen, except for the tsunamis in 2004," says Varekamp.

There's also Lake Quilotoa in Ecuador, which is rich in CO 2 , deep and in a tropical climate. "Some scientists consider it a potential analog of Nyos," says Varekamp.

­You may be wondering whether any lake can explode. Could it happen to the pond in your backyard? Let's return to our historic lakes to find out.

­Exploding lakes are rare, and the backstories of Lakes Nyos and Monoun explain why. In Cameroon, there are weak spots in the Earth's crust at which magma , or liquid rock, rises from the Earth's mantle . The magma shoots up quickly and vertically, cutting a tube toward the surface. If it reaches the surface, the magma may spurt out and rain a big pile of rock, depositing a cinder cone volcano .

If the magma hits wet rock as it rises, it explodes, blasting a crater in the ground. More than 18,000 years ago, such a blast formed the crater at Lake Monoun [source: Sigurdsson ]. A si­milar blast happened a few hundred years ago to form Nyos [source: ­Kling ]. Water filled the craters, and they became lakes.

At the bottom of each lake, the old tube where magma first rose to the surface remains. If you follow the tube some 3 to 6 miles (5 to 10 kilometers) down, you'll hit magma. The pressure down there forces out one of the most abundant gases in liquid rock: CO 2 . The gas rises up the tube into the lake. Researchers have identified more than 100 places in Cameroon where CO 2 leaks in large, but not dangerous quantities out of the ground, says Evans.

Several factors -- not just CO 2 -- have to align to create an exploding lake. First, the lake must be deep. When little water holds down the gaseous bottom water, the lake needs only a small disturbance -- wind -- to release the gas. In deep lakes, the overlaying water acts as a cork in a champagne bottle. Every 10 meters (33 feet) of water adds 1 atmosphere of pressure, so in a 100-meter (328-foot) lake, 10 atmospheres of pressure hold down the gas at the bottom, says Evans. Wind can't stir it up.

Second, the climate must be stable all year, which is why exploding lakes cluster in the tropics. Lake Superior in the United States, for instance, charges with gas from decaying matter until the season changes. Every fall, the lake's surface cools and gets denser, then sinks to the bottom. The gaseous bottom water rises. The lake turns over, or exhales -- most lakes do at least once a year, says Varekamp. In places where it's warm or cold year-round, lake layers hold their temperature and position. Third, it takes a trigger like a landslide , earthquake or too much gas to unsettle the gas layer.

Cameroon has all the right ingredients for exploding lakes: magma releasing CO 2 ­ into deep lakes, a tropical climate and a trigger.

­After Lake Nyos burst, an international team began discussing ways to degas bot­h lakes and avert future disasters. They talked about bombing the lakes to blow out the gas. But scientists worried a bomb would also blow out one of Lake Nyos's walls, causing an enormous flood . "That would be a disaster in its own right," says Evans. As early as November 1986, French scientists proposed a pipe.

"The pipe idea won out because it's simple, and there's not much risk associated with it," says Evans. "You could eliminate the gas in a controlled fashion."

Pipes were slow to be installed. Money and roads into Nyos weren't plentiful. "When we left Cameroon in 1986, we were certain that we had done good science, recommended how to fix the problem and said aid groups will come in next week and start piping the gas out. It was a wake-up call for all of us for how long this type of stuff takes," says Evans.

The first pipe went into Lake Nyos in 2001. A French engineering team sunk a 6-inch (15-centimeter) plastic tube 666 feet (203 meters) into the lake until it reached the gas layer [source: Halbwachs ]. Again, froth shot out like champagne from an uncorked bottle, but this time it wasn't a deadly surprise.

Today, Nyos is degassed to about 80 percent of the level after the 1986 explosion, says Evans. "The lake is safer today than it was in 2000, but it is still hazardous." A big enough input of energy, like a large earthquake or a landslide , could cause the lake to erupt, he says.

Another problem is Nyos' weak wall. "That natural dam could rupture any day," says Evans. "If the dam were to suddenly fail, the upper 40 meters [131 feet] of the lake would empty in a huge flood, and that would release the pressure on the gas remaining in the deep water. You could have a combination of a flood and a gas release." Evans says the gas should be piped out as soon as possible, and then the wall should be fixed. Two more pipes are planned, with the first possibly going in in spring 2009.

Lake Monoun has three pipes: one installed in 2003 and two in 2006. "Another eruption is probably not possible there, given that the lake is almost completely degassed," says Evans. "Monoun now would be a very nice place to live."

­So the next time ­you smell the sulfurous gas as your local lake turns over, think of it as a lake exhalation -- and be thankful that it's not a burp.

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• Will we ever run out of magma?
• How Volcanoes Work
• How is volcanic ash made?
• What would happen if Mount Vesuvius erupted today?
• Why could China's Three Gorges Dam cause an environmental disaster?
• Crater Lake National Park

More Great Links

• Degassing Lakes Nyos and Monoun
• San Diego State University description of the Nyos event
• NASA animation panning over the terrain at Nyos and Monoun
• How Lake Superior turns over
• USGS: Layers of the Earth
• Barberi et al. "The Gas Cloud at Lake Nyos (Cameroon, 1986): Results of the Italian Technical Mission." Journal of Volcanology and Geothermal Research. Vol. 39, no. 2-3, 1989.
• Evans, William. Personal interview. Conducted 2/27/2009.
• Halbwachs et al. "Lake Nyos Degassing Project: First Results Pertaining to the Degassing Under Way." European Geophysical Society XXVII General Assembly. April 2002. (3/19/2009)http://adsabs.harvard.edu/abs/2002EGSGA..27.6051H
• Kling, George W. et al. "The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa." Science. Vol. 236. no. 4798. April 10. 1987.
• Sigurdsson, H. et al. "Origin of the Lethal Gas Burst from Lake Monoun, Cameroun." Journal of Volcanology and Geothermal Research. Vol. 31. no. 1-2. 1987.
• Varekamp, Johan. Personal interview. Conducted 3/5/2009.

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A Killer Lake

By Thomas Horvath

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In 1986, Lake Nyos, a volcanic lake located in Cameroon, Africa, released a huge amount of carbon dioxide gas, killing over 1,700 people and countless livestock and other animals in the area. This case, intended for use in a limnology or an aquatic biology course, explores that event, introducing students to concepts related to lake formation, thermal stratification, and dissolved gases. Students interpret graphs containing temperature, dissolved oxygen, pH, and conductivity data for the lake, and then synthesize these different types of limnological data to understand what happened.

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• List the types of lakes that can be formed through volcanic activity and identify the characteristics of such lakes.
• Distinguish between holomictic and meromictic lakes.
• Describe the limnetic conditions necessary for meromixis to form in a lake.
• Identify the vertical zones of a meromictic lake.
• List the possible dissolved gases associated with lakes.
• List the sources of and factors affecting the quantity of dissolved gases in lakes.

Thermal stratification; meromictic lake; dissolved gas; meromixis; Lake Nyos; Lower Nyos; Cameroon; Africa

Subject Headings

EDUCATIONAL LEVEL

Undergraduate lower division, Undergraduate upper division

TOPICAL AREAS

TYPE/METHODS

Teaching Notes & Answer Key

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