Julie Gaubatz

Merit Winner: TMA Excellence in Science Teaching Awards

Julie Gaubatz - W.H. Taft High School, San Antonio, Texas
The Mysterious Tragedy at Lake Nyos
Sample Lesson

Lesson Overview

This lesson was designed for students in the ninth through 12 ^th grades and requires four 50-minute class sessions. It provokes students to draw on knowledge and strategies from various scientific domains to answer questions they raise themselves as they attempt to solve the mystery surrounding the August 1986 tragedy that occurred in West Africa's Lake Nyos valley.

Scientists from across the world visited Lake Nyos after hearing rapidly spreading word of the mysterious deaths of 1,700 valley residents. They and other visitors were stunned to find entire populations of villagers, livestock, and wild animals dead. The precipitating events apparently had happened suddenly - hundreds of birds appeared even to have died in midflight. As students in the lesson attempt to answer their questions about what could have caused the Lake Nyos tragedy, they are given "confidential governmental briefings" based on actual eyewitness testimony and realistic, but elaborated, empirical data from which they must generate their hypotheses. They are then asked to use the most viable of their causal hypotheses to develop a feasible plan to prevent similar tragedies (of which the Lake Nyos incident was the second in a two-year span) from happening again. As they investigate further, students learn about the characteristics and behaviors of gases, a bit of geology, and how a variety of substances affect the pulmonary system, including cigarette smoke, commonly abused inhalants, and gaseous pollutants, one of the latter of which (although occurring naturally) was implicated in the Lake Nyos event.  To culminate the project, student present their findings to their classmates using posters, oral summaries, and/or PowerPoint software.  This lesson connects the biomedical/health sciences, forensic sciences, geology, and studies of the behavior of gases to heighten students' awareness of the dangers of exposing their lungs - either accidentally or intentionally - to dangerous substances.

Learning Objectives

• Describe some behaviors and characteristics of gases.
• Describe how gases interact with the pulmonary system.
• Apply knowledge of gases, the pulmonary system and geology to determine the cause of the tragedy at Lake Nyos.
• Connect demonstrations and laboratory activities to phenomena that can be applied to solving (assigned) problems.
• Use individual and disparate pieces of data to create coherent hypotheses.
• Present a convincing explanation of the Lake Nyos event and propose a solution to prevent future tragedies at central and western African lakes in poster, PowerPoint, and oral formats.
• Increase awareness of other cultures, countries and geological characteristics found outside the students' hometown.
• Connect the actions of gases and the pulmonary system to the dangers of smoking and psychoactive inhalants.

Materials Used

• Various Handouts
  • Laboratory station handouts; "confidential briefing information"; concluding information; and reference materials on geology, the pulmonary system, gases, and inhalents.
• Laboratory Materials
  • Lab station A: Various bottles of carbonated drinks.
  • Lab station B: Straws, bromophenol blue solution (pH indicator), paper cups.
  • Lab station C: Periodic table and EITHER balloons filled with various gases OR a video segment showing balloons filled with various gases to demonstrate the density of gases in comparison to air (suggested video clip from NNN).
  • Lab station D: Dry ice, cookie tray with water, three candles anchored to the cookie tray, matches, clear cake cover or large beaker.
• Presentation Materials

  • Computers with PowerPoint OR poster board, scissors, markers, glue, paper, etc.

Methods of Implementation

These lessons are written for four 50-minute sessions, but easily can be modified to fit 90-minute block sessions.

Students are introduced to the lesson with a brief overview of the observations made by visitors to the Lake Nyos valley on the morning after the tragedy. In brief, in August 1986 travelers entering the Lake Nyos region found whole populations of villagers dead, along with their livestock and wild animals. No noticeable smell was in the air, no disease was apparent, no violence seemed to have occurred. It looked as if everyone had dropped dead without warning or panic. The only odd observation was that Lake Nyos itself seemed different. Near the lake, a strong sulfurous smell was evident, and the lake had changed from beautifully clear to muddy and clouded. Perhaps the tragedy resulted from something in the lake?

Students then take their directives in the form of a handout that begins with the words, "Thank you, Doctors                   and                   for agreeing to help us solve this mysterious tragedy. …"  Students are given "confidential briefing materials" that include fictional data (e.g., gas chromatographs, pH readings) coupled with actual survivors' testimonies, pictures, and observations from the scientists who arrived first on the scene, as well as topographical maps of the Lake Nyos valley that help students use the knowledge they gain from various laboratory activities to solve the mysterious tragedy.  Students are given time to read their briefing materials and to discuss with a co-investigator their initial thoughts and feelings about the information they have received so far.  Typically, they are immediately drawn in by the strange, seemingly inexplicable tragedy.  Students are especially intrigued by the photographs and real-life testimonies, which enhance their recognition that this was a real event and a genuine tragedy.

Once students have had sufficient time to digest the briefing materials and discuss their initial hypotheses, they are encouraged to explore various laboratory stations and complete background research activities in a student-directed, teacher-facilitated fashion. Students move from one station to the next at their own pace, in any order with which they feel comfortable.  This exploratory phase requires the remainder of the first class session and most of the second class session.  At the guided laboratory stations, students observe that gases rise out of liquids when pressure is decreased, that carbon dioxide has acidic properties, and that although gases are less dense than water, some are lighter (less dense) than air, while some are heavier (more dense) than air. They also observe that the gaseous form of dry ice is heavier than air. From their background research activities, they learn about the partial pressures of various gases and how these affect the pulmonary system, including substances inhaled from smoking, psychoactive inhalants, and pollution. They also explore stations illustrating the role of oxygen in keeping organisms alive, the geological properties of the Lake Nyos area, and the cultural and political aspects of northwestern Cameroon, the country in which Lake Nyos is situated. All of these learning/lab station activities are very brief and students change activities often, which keeps their interests high. Students use the information gained from their laboratory explorations and background research to construct a hypothesis that might explain the Lake Nyos tragedy and to devise a culturally and politically sensitive method to prevent future similar tragedies from occurring in this area.

After their initial explorations, most students come to the hypothesis that carbon dioxide had accumulated in the depths of the lake, and that natural lake turnover caused the layers of water containing dissolved carbon dioxide to move upward, thereby decreasing the pressure exerted on the gas and resulting in a large and sudden release of carbon dioxide from the lake. The carbon dioxide, which is heavier than air, displaced oxygen at the ground level and suffocated all living things in the low-lying areas of the valley. Whereas villages at high altitudes were relatively unscathed, villages downhill from the lake (in the valley itself) suffered widespread deaths.

Students use the third class session of the lesson to prepare their oral presentations, keeping in mind the cultural perspectives of the people in the area. Students may use PowerPoint software or poster boards to illustrate their hypothesis, supporting evidence and proposals to prevent future tragedies. This allows students to express their logic as well as their creativity as they integrate their learning from the previous class sessions.

During the fourth session, students present their hypotheses, supporting evidence, and preventative recommendations to the class. Students' presentations are graded on a rubric system. Finally, they complete a short test that assesses their understanding of gas behaviors and characteristics, the connection between partial pressures of gases and the pulmonary system, and the dangers of cigarette smoking, psychoactive inhalants, and air pollution.

Evaluation Tools

Students are evaluated on laboratory technique, group dynamics, and their final presentation as shown:

Students also are given a brief multiple-choice, short-answer, and essay test to assess their understanding of gas behavior, geology and the effects of various substances (such as cigarette smoke, inhalants, and carbon dioxide) on pulmonary systems.

Description of What Makes the Lesson Effective

This lesson stimulates students' interests in the sciences by illustrating why scientific methods are essential for solving real-life mysteries.  The story of Lake Nyos intrigues nearly everyone who has heard it: a mysterious tragedy that killed many villagers, livestock, and wild animals, materializing suddenly and just as suddenly disappearing, leaving virtually no trace of its origins.  The use of survivors' testimonies coupled with the observations of scientists on the scene, photographs of the devastation, and maps of the Lake Nyos valley combine to give students a realistic awareness that these events actually happened to actual people. The presentation of this data in the form of a "confidential governmental briefing" hooks their interest and motivates them to use learning opportunities in the classroom lab stations to understand this unusual event.

The requirement that students develop culturally and politically sensitive preventative measures brings the parameters of real scientific work into the classroom: Scientists perform their work not in abstract isolation but in living, dynamic human societies in which their findings and ideas ultimately are accepted or denied. This reality also allows students to think about their own cultural backgrounds and to take seriously the cultural backgrounds of other people in the world.

Finally, culminating this lesson with creative presentations gives students the opportunity to showcase their creative sides, either in their visual or oral presentations.  It's a time to have fun with what they've learned; on that day (the final day of the lesson), they are the experts. It's their opportunity to acknowledge and celebrate their successes, sometimes only partial, in solving the Lake Nyos mystery.

In the final analysis, however, this lesson focuses not only on the human populations around Lake Nyos but also on the students themselves by having them think about their own bodies, how their lungs work, and the medical reasons behind why introducing unhealthy substances into their lungs, such as cigarette smoke, air pollution, or psychoactive inhalants, is so potentially dangerous.

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