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Christopher R. Kimberly Science and a Killer Lake

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1 Christopher R. Kimberly Science and a Killer Lake
4/15/2017 9:07:32 AM Lake Nyos Science and a Killer Lake At the bottom of each slide (when necessary), I will type notes that explain how the slide will work in the classroom. Unless specified otherwise, all questions that appear on the slides will be posed to the class, as a whole. This lesson is designed for students in their first year of high school chemistry. I think it would be most appropriate to have students engage in this lesson after they have been introduced to gas solubility. I envision this lesson taking at least two 40-minute periods. NOTE: If you are reading these notes printed on a hardcopy of the presentation, you should know that many of the slides contain animations that cannot do not appear on the paper. Conseqently, some images and text will not be displayed on the printout. Lake Nyos Presentation

2 Christopher R. Kimberly
4/15/2017 9:07:32 AM Background Lake Nyos lies in an old volcano crater (maar) in Cameroon, a country of Africa. Mt. Cameroon, an active volcano, is located 300 km away. What can you conclude about the climate in Cameroon? Hopefully, students will notice that Cameroon lies near the equator, and they can draw conclusions based on this. I want them to talk about climate now, so they will be prepared to think about lake turnover later in the presentation. Lake Nyos Presentation

3 Christopher R. Kimberly
4/15/2017 9:07:32 AM Lake Nyos, the Village My hope is that the next several slides will pique the students’ curiosity, and motivate them to answer subsequent questions. These slides are the “hook.” The village of Lake Nyos is located at the base of the volcano that holds the lake. Lake Nyos Presentation

4 Lake Nyos, the Inhabitants
Christopher R. Kimberly 4/15/2017 9:07:32 AM Lake Nyos, the Inhabitants The village was home to 1,800 people and some 3,000 cattle. Lake Nyos Presentation

5 Christopher R. Kimberly
4/15/2017 9:07:32 AM One summer night... On the night of August 21, 1986, Lake Nyos quietly killed all but a few of the inhabitants of the village. The last victim killed lived 27 km downstream from the lake. Lake Nyos Presentation

6 Christopher R. Kimberly
4/15/2017 9:07:32 AM The following day... The normally placid lake showed signs of a violent event. The water turned brown. Vegetation as far as 80 m from the shoreline sustained significant damage. Lake Nyos Presentation

7 Christopher R. Kimberly
4/15/2017 9:07:32 AM Aftermath Only a few individuals survived the night. Lake Nyos Presentation

8 For several years, scientists puzzled over this catastrophe...
Christopher R. Kimberly 4/15/2017 9:07:32 AM For several years, scientists puzzled over this catastrophe... Lake Nyos Presentation

9 Christopher R. Kimberly
4/15/2017 9:07:32 AM MISSION: Work in groups to come up with possible explanations for this event. TIME: 10 minutes. After each group presents their ideas, we will discuss all the proposed explanations as a class, and try to come to consensus about the best possible explanation before advancing to the next slide. Yer noggin. RESOURCES: Be prepared to present your explanation to the class at the end of the 10 minutes. Lake Nyos Presentation

10 Christopher R. Kimberly
4/15/2017 9:07:32 AM What Didn’t Happen Although a few witnesses claim to have observed flashes of light, loud noises, and some victims received what were tentatively classified as burns, the event at Lake Nyos did not involve a volcanic eruption. It is also unlikely that the event involved a “phreatic eruption”--an eruption driven by the vaporization of groundwater without the ejection of magma. Lake Nyos Presentation

11 Christopher R. Kimberly
4/15/2017 9:07:32 AM A Limnic Eruption So what caused this catastrophic event to occur in a peaceful lake? The eruption at Lake Nyos was powered by CO2 gas bubbles, ascending and expanding within the lake water. What “everyday experience” involves a similar phenomenon (on a smaller scale)? Perhaps students will recognize the similarity to the fiz and bubbles associated with opening a soda bottle. Lake Nyos Presentation

12 Christopher R. Kimberly
4/15/2017 9:07:32 AM The Valley Below As the lake released clouds of CO2, the gas spilled down the mountain- side and into the valleys. I am hoping that students will recognize that CO2 is a colorless, odorless gas. We will also discuss the physiology of CO2 poisoning (i.e., increased breathing rate). Imagine that you were in the village of Lake Nyos on the night of August 21, 1986 and that you woke up in the middle of the night. What would you have seen / felt? Lake Nyos Presentation

13 Spring Water, Naturally Carbonated...
Christopher R. Kimberly 4/15/2017 9:07:32 AM Spring Water, Naturally Carbonated... Since the lake is a maar, it is most probable that a cluster of warm springs, rich in CO2, feed the lake through the bottom. Where does the CO2 come from? The question above will lead to a discussion of volcanic gases. Lake Nyos Presentation

14 Christopher R. Kimberly
4/15/2017 9:07:32 AM How Much is Too Much? A lake can dissolve a volume of CO2 more than 5 times its water volume. Do the two layers contain the same concentration of CO2? Compositional data for Lake Nyos, 1992. Are the layers saturated with CO2? How many gallons of H2O and CO2 are contained in each layer? (1 dm3 = 1 L; 1 gal. = 3.79 L) It is believed that the lake emitted 20,000,000,000 gal. of CO2 during the event in Do you think the lake emptied itself of enough CO2 in 1986 to be safe in 1992? I would have students address these questions in small groups, so they can check each others calculations. “Do the two layers contain the same concentration of CO2?” With the first question, I hope to reinforce the notion that although Layer #1 has more total CO2 dissolved, it is less concentrated. One cannot make conclusions about concentration based on solute quantity alone. “Are te layers saturated with CO2?” Students will need to comment on saturation based on the first sentence of the page. My guess is that some groups will initially overlook the first sentence and claim that they do not know enough information to answer the question--I think I’ll let them wrestle with that for awhile. “How many gallons of H2O and CO2 are contained in each layer? (1 dm3 = 1 L; 1 gal. = 3.79 L)” Students cannot fully appreciate the volume of the lake when measured in cubic meters, and they can always use more practice with unit conversions! “It is believed that the lake emitted 20,000,000,000 gal. of CO2 during the event in Do you think the lake emptied itself of enough CO2 in 1986 to be safe in 1992?” Based on the fact that the lake had dissolved in it more than 3 times the volume of CO2 released, I am hoping that students will conclude that the lake was not safe in 1992. Lake Nyos Presentation

15 All Things Being Unequal...
Christopher R. Kimberly 4/15/2017 9:07:32 AM All Things Being Unequal... What quality of the lake might explain why more CO2 is dissolved in the lower layer? Given that we will have just learned that the solubility of gases is indirectly related to the temperature of the water, I am guessing that the majority of students will suggest that the variation in [CO2] is due to thermal stratification. This slide will be a good opportunity to review lake turnover, a concept that students would have learned in biology the previous year. Based on student discussion of climate at the beginning of the presentation, I am hoping that students will recognize that Lake Nyos does not undergo seasonal turnover. What is the significance of the above diagram? What is a thermocline, and how does it relate to lake turnover? Would Lake Nyos undergo lake turnover? Lake Nyos Presentation

16 A well-labeled axis says 1,000 words.
Christopher R. Kimberly 4/15/2017 9:07:32 AM A well-labeled axis says 1,000 words. Given the info in the graph, would you argue that Lake Nyos is thermally stratified? Warm springs feed the bottom of the lake. The sun warms the surface of the lake. This graph is a great reinforcement of the need to look carefully at numerical values and to label axes. Even though there is evidence of slight thermal stratification, I hope that students will notice (from the graph on the previous page--I may flip back to that graph as we discuss this) that a temperature range of a couple degrees is far from the typical 16-degree range in a (summer) stratified lake. I am curious to hear what creative response emerge to answer the last question. Why do you think it is or isn’t stratified? What do you think causes the variation in temperature? Lake Nyos Presentation

17 Christopher R. Kimberly
4/15/2017 9:07:32 AM A Landslide Victory? Since the lake is relatively thermally stable, it is unlikely that simple lake turnover caused the eruption. I will ask students if they see anything in the picture that might indicate the occurrence of landslide. The current belief is that a landslide triggered a chain reaction... Lake Nyos Presentation

18 Christopher R. Kimberly
4/15/2017 9:07:32 AM Fountain soda, anyone? The chain reaction involved nucleation of CO2 bubbles as they rose through the lake. This could only occur if [CO2] was greater at the bottom. Why? But we still haven’t answered why [CO2] is greater at the bottom of the lake... “This could only occur if [CO2] was greater at the bottom. Why?” I wouldn’t expect them to recognize that there will be a [CO2] saturation gradient, causing deeper water with high [CO2] to bubble out when it rises and crosses the saturation point. However, it will be interesting to hear their thinking on this question. Lake Nyos Presentation

19 NEW! Dannon Yogurt: [CO2] on the...
Christopher R. Kimberly 4/15/2017 9:07:32 AM NEW! Dannon Yogurt: [CO2] on the... CO2 saturation CO2 concentration H2O Density Based on the data presented in this graph, what do you think most influences the solubility of CO2 in Lake Nyos? The goal with this slide is to have students recognize that pressure is primary factor influencing CO2 solubility. Introductory chemistry students do not typically learn about Henry’s law, but we can draw connections to the influences of atmospheric pressure on boiling point. HINT: If you dove to the bottom of the lake (not recommended), and you brought a balloon from the surface, what would the balloon look like at the bottom? Lake Nyos Presentation

20 Actually, it’s safe…trust me.
Christopher R. Kimberly 4/15/2017 9:07:32 AM Actually, it’s safe…trust me. This function estimates the amount of energy necessary to lift a parcel of water up to its eruption point. However, keep in mind that the bottom layer of the lake has the highest density (more energy is needed to lift it). In short, the further to the right the red line goes, the less likely that layer will spawn a limnic eruption. Given water at depth A, the safety coefficient is calculated by integrating the difference in density from depth A to the depth at which the [CO2] of layer A exceeds the [CO2] saturation point. The graph below displays the relative safety of the lake water as it relates to depth. This may seem counter-intuitive, given that the bottom of the lake has the highest CO2 concentration. CO2 saturation CO2 concentration H2O Density Even though the bottom layer is the safest... Since students will not be familiar with integration, I will discuss the safety coefficient in qualitative terms. Lake Nyos Presentation

21 Christopher R. Kimberly
4/15/2017 9:07:32 AM Safe Is a Relative Term Before displaying the text below this graph, I will ask students to explain the significance of the graph. …it’s dissolving more and more CO2, and thus the increasing need to de-gas the lake. Lake Nyos Presentation

22 Degassing Complexified
Christopher R. Kimberly 4/15/2017 9:07:32 AM Degassing Complexified One year after the event, the French Delegation aux Risques Majeurs proposed a degassing method based on off-shore oil production techniques. The problem was that the proposal was expensive, and CO2 ain’t no cash crop. Lake Nyos Presentation

23 Christopher R. Kimberly
4/15/2017 9:07:32 AM Degassing Simplified Enter: Michel Halbwachs, professor at the Centre de Recherches Volcanologiques, University of Savoie, France. I think he said something like, “Hey man, it’s ‘facile.’ Just take some plastic pipes and stick ‘em in the water.” In 1990, he did just that. Lake Nyos Presentation

24 Christopher R. Kimberly
4/15/2017 9:07:32 AM “We have to intubate.” If the water is most dense on the bottom of the lake, why does it move to the top of the pipe? The current degassing strategy is no more complicated than taking a plastic (HDPE) pipe and extending it to the bottom of the lake. …it creates a self-siphon- ing system. Once you prime the pipe with a pump... Since we begin the year with a unit on organic chemistry, we will talk a little about the molecular structure HDPE. Hmmm... Lake Nyos Presentation

25 Christopher R. Kimberly
4/15/2017 9:07:32 AM You the boss. Although Michel Halbwachs orchestrated the first degassing “field” test, the lake research was conducted by a multi-national team from the start, including scientists from France, Japan, the U.S., and Cameroon. Given that you are an internationally renowned gas expert (not the gastrointestinal kind), the team of Lake Nyos scientists is seeking your advice on an important question: To best avoid catalyzing a limnic eruption, how deep should the self-siphoning pipes be placed? I will have students work in small groups to come up with a plan for this. Lake Nyos Presentation

26 Christopher R. Kimberly
4/15/2017 9:07:32 AM 101 Ways to Use a 55-gal. Drum Given the success of the 1990 self-siphon test, the research group received funding for a larger-scale test in 1995. The diagram above shows the surface component of the pipe assembly. Lake Nyos Presentation

27 Christopher R. Kimberly
4/15/2017 9:07:32 AM Steady! The pipe surface raft being hauled out to the middle of the lake... Lake Nyos Presentation

28 “Don’t worry. I’ve got a 2nd thumb.”
Christopher R. Kimberly 4/15/2017 9:07:32 AM “Don’t worry. I’ve got a 2nd thumb.” Cutting and assembling the pipe... Lake Nyos Presentation

29 “Man, I forgot my Gore-Tex boots.”
Christopher R. Kimberly 4/15/2017 9:07:32 AM “Man, I forgot my Gore-Tex boots.” Government workers? Feeding the pipe into the water... Lake Nyos Presentation

30 McFly: “You are my density.”
Christopher R. Kimberly 4/15/2017 9:07:32 AM McFly: “You are my density.” If HDPE “almost” floats in water, then why is the pipe floating in the picture below? Scientists selected high-density polyethylene as the pipe material for many reasons. One reason was because HDPE almost floats in water. Let’s say you have sample of HDPE that occupies a volume of 10. mL. Predict what the mass of this sample will be. I hope to obtain samples of HDPE for students to measure and calculate its density. Lake Nyos Presentation

31 Christopher R. Kimberly
4/15/2017 9:07:32 AM Just in case... Oxygen tanks. Even though the risk of an eruption was very low, scientists didn’t want to take chances. Lake Nyos Presentation

32 Christopher R. Kimberly
4/15/2017 9:07:32 AM Easy does it... Why is it safe to use a motor in the lake? Just one step back, and... We may refer back to the safety coefficient graph to discuss the relativve safety of the upper layer of the lake (thus the motor boat). Once primed, the system took care of itself. Lake Nyos Presentation

33 Christopher R. Kimberly
4/15/2017 9:07:32 AM Success! Lake Nyos Presentation

34 Christopher R. Kimberly
4/15/2017 9:07:32 AM 2001 Expedition In 2001, the research team beefed up the apparatus. 120 ft. “geyser.” 90% of geyser energy is lost to friction. Assuming a “frictionless environment, how high would the geyser go? Before making reference to the Empire State Building, I will have students do the “frictionless environment” calculation at their seats. They will need to agree with at least one neighbor before I will look at their work. About as high at the Empire State Building. Lake Nyos Presentation

35 Christopher R. Kimberly
4/15/2017 9:07:32 AM Mo’ money. With more funding, the research team has been able to add more features to the degassing system. This includes automatice shut-off mechanisms, and... Lake Nyos Presentation

36 Christopher R. Kimberly
4/15/2017 9:07:32 AM Mo’ money, Mo’ money ...a satellite link for remote monitoring and remote control. Lake Nyos Presentation

37 Christopher R. Kimberly
4/15/2017 9:07:32 AM Mo’ money, please. Scientists estimate that the current degassing rate (single pipe) is barely keeping up with the CO2 input from the springs. They hope to get more funding to de-gas the lake completely. Lake Nyos Presentation

38 Christopher R. Kimberly
4/15/2017 9:07:32 AM Ecological Impact Not as bad you would think. Biggest impact is from bringing anoxic water from the bottom of the lake to the surface. However, the single pipe only brings about 1.2 Mm3 to the surface per year. This gets diluted more than 50-fold in the upper 45 m of the lake due to mild mixing. Run-off brings in about 24 Mm3 freshwater each year  more dilution. In addition, single pipe discharge of CO2 is equivalent to the output of a 1.2 MW coal-fired plant without all the other acid-rain producing pollutants. There has been talk of studying CO2 impact on local ecosystem. Lake Nyos Presentation

39 Clearly the water isn’t that bad!
Christopher R. Kimberly 4/15/2017 9:07:32 AM Clearly the water isn’t that bad! Lake Nyos Presentation

40 Just when you thought it was safe...
Christopher R. Kimberly 4/15/2017 9:07:32 AM Just when you thought it was safe... The top layer of Lake Nyos is held in place by a natural dam. Geologists have studied this dam, and found that it’s in bad shape. Business, or pleasure? Lake Nyos Presentation

41 Christopher R. Kimberly
4/15/2017 9:07:32 AM Dam it, Jim! The upper unit is eroding away. The village below would obviously be flooded. In addition, if the dam gave way, it would remove the top layer of the lake. This would be akin to removing the cap from a soda bottle: limnic eruption! What would happen, if the upper unit gave way? Lake Nyos Presentation

42 Christopher R. Kimberly
4/15/2017 9:07:32 AM What the heck is that? There are many proposals on the table for how best to address this. Lake Nyos Presentation

43 Christopher R. Kimberly
4/15/2017 9:07:32 AM Lake Nyos Presentation

44 Christopher R. Kimberly
4/15/2017 9:07:32 AM Water Chemistry Depending on how the lesson goes, I may come back to this data later in the year to discuss acid-base equilibria and pH calculations as it relates to the lake. Lake Nyos Presentation

45 Christopher R. Kimberly
4/15/2017 9:07:32 AM Sources Degassing the Killer Lakes: Lake Nyos and Monoun LAKE NYOS and LAKE MONOUN The Killer Lakes of Cameroon, West Africa Photo Gallery: Give each pair of students a sample of baking soda and vinegar. Given these materials, and anything the students would like to supplement it with, they must prove that the CO2 would flow down the mountain and into the valley. Lake Nyos Presentation


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