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Lake Nyos Science and a Killer Lake. 2 Background Lake Nyos lies in an old volcano crater (maar) in Cameroon, a country of Africa.Lake Nyos lies in an.

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Presentation on theme: "Lake Nyos Science and a Killer Lake. 2 Background Lake Nyos lies in an old volcano crater (maar) in Cameroon, a country of Africa.Lake Nyos lies in an."— Presentation transcript:

1 Lake Nyos Science and a Killer Lake

2 2 Background Lake Nyos lies in an old volcano crater (maar) in Cameroon, a country of Africa.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.Mt. Cameroon, an active volcano, is located 300 km away. What can you conclude about the climate in Cameroon?What can you conclude about the climate in Cameroon?

3 3 Lake Nyos, the Village The village of Lake Nyos is located at the base of the volcano that holds the lake.The village of Lake Nyos is located at the base of the volcano that holds the lake.

4 4 Lake Nyos, the Inhabitants The village was home to 1,800 people and some 3,000 cattle.The village was home to 1,800 people and some 3,000 cattle.

5 5 One summer night... On the night of August 21, 1986, Lake Nyos quietly killed all but a few of the inhabitants of the village.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.The last victim killed lived 27 km downstream from the lake.

6 6 The following day... The normally placid lake showed signs of a violent event.The normally placid lake showed signs of a violent event. The water turned brown.The water turned brown. Vegetation as far as 80 m from the shoreline sustained significant damage.Vegetation as far as 80 m from the shoreline sustained significant damage.

7 7 Aftermath Only a few individuals survived the night.Only a few individuals survived the night.

8 8 For several years, scientists puzzled over this catastrophe...

9 9 MISSION: Work in groups to come up with possible explanations for this event. RESOURCES: TIME: 10 minutes. Yer noggin. Be prepared to present your explanation to the class at the end of the 10 minutes.

10 10 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.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.It is also unlikely that the event involved a “phreatic eruption”--an eruption driven by the vaporization of groundwater without the ejection of magma.

11 11 A Limnic Eruption The eruption at Lake Nyos was powered by CO 2 gas bubbles, ascending and expanding within the lake water.The eruption at Lake Nyos was powered by CO 2 gas bubbles, ascending and expanding within the lake water. What “everyday experience” involves a similar phenomenon (on a smaller scale)?What “everyday experience” involves a similar phenomenon (on a smaller scale)? So what caused this catastrophic event to occur in a peaceful lake?

12 12 The Valley Below As the lake released clouds of CO 2, the gas spilled down the mountain- side and into the valleys.As the lake released clouds of CO 2, the gas spilled down the mountain- side and into the valleys. 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?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?

13 13 Spring Water, Naturally Carbonated... Since the lake is a maar, it is most probable that a cluster of warm springs, rich in CO 2, feed the lake through the bottom.Since the lake is a maar, it is most probable that a cluster of warm springs, rich in CO 2, feed the lake through the bottom. Where does the CO 2 come from?Where does the CO 2 come from?

14 14 How Much is Too Much? A lake can dissolve a volume of CO 2 more than 5 times its water volume. Are the layers saturated with CO 2 ?Are the layers saturated with CO 2 ? How many gallons of H 2 O and CO 2 are contained in each layer? (1 dm 3 = 1 L; 1 gal. = 3.79 L)How many gallons of H 2 O and CO 2 are contained in each layer? (1 dm 3 = 1 L; 1 gal. = 3.79 L) It is believed that the lake emitted 20,000,000,000 gal. of CO 2 during the event in Do you think the lake emptied itself of enough CO 2 in 1986 to be safe in 1992?It is believed that the lake emitted 20,000,000,000 gal. of CO 2 during the event in Do you think the lake emptied itself of enough CO 2 in 1986 to be safe in 1992? Compositional data for Lake Nyos, Do the two layers contain the same concentration of CO 2 ?Do the two layers contain the same concentration of CO 2 ?

15 15 All Things Being Unequal... What quality of the lake might explain why more CO 2 is dissolved in the lower layer?What quality of the lake might explain why more CO 2 is dissolved in the lower layer? What is the significance of the above diagram?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?What is a thermocline, and how does it relate to lake turnover? Would Lake Nyos undergo lake turnover?

16 16 A well-labeled axis says 1,000 words. Why do you think it is or isn’t stratified?Why do you think it is or isn’t stratified? What do you think causes the variation in temperature?What do you think causes the variation in temperature? Given the info in the graph, would you argue that Lake Nyos is thermally stratified?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.

17 17 A Landslide Victory? The current belief is that a landslide triggered a chain reaction... Since the lake is relatively thermally stable, it is unlikely that simple lake turnover caused the eruption.

18 18 Fountain soda, anyone? The chain reaction involved nucleation of CO 2 bubbles as they rose through the lake.The chain reaction involved nucleation of CO 2 bubbles as they rose through the lake. This could only occur if [CO 2 ] was greater at the bottom. Why?This could only occur if [CO 2 ] was greater at the bottom. Why? But we still haven’t answered why [CO 2 ] is greater at the bottom of the lake...But we still haven’t answered why [CO 2 ] is greater at the bottom of the lake...

19 19 NEW! Dannon Yogurt: [CO 2 ] on the... Based on the data presented in this graph, what do you think most influences the solubility of CO 2 in Lake Nyos?Based on the data presented in this graph, what do you think most influences the solubility of CO 2 in Lake Nyos? 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?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? CO 2 saturation CO 2 concentrationH 2 O Density

20 20 Actually, it’s safe…trust me. CO 2 saturation CO 2 concentrationH 2 O Density The graph below displays the relative safety of the lake water as it relates to depth.The graph below displays the relative safety of the lake water as it relates to depth. 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 [CO 2 ] of layer A exceeds the [CO 2 ] saturation point.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 [CO 2 ] of layer A exceeds the [CO 2 ] saturation point. Even though the bottom layer is the safest... This function estimates the amount of energy necessary to lift a parcel of water up to its eruption point.This function estimates the amount of energy necessary to lift a parcel of water up to its eruption point. In short, the further to the right the red line goes, the less likely that layer will spawn a limnic eruption.In short, the further to the right the red line goes, the less likely that layer will spawn a limnic eruption. This may seem counter-intuitive, given that the bottom of the lake has the highest CO 2 concentration.This may seem counter-intuitive, given that the bottom of the lake has the highest CO 2 concentration. However, keep in mind that the bottom layer of the lake has the highest density (more energy is needed to lift it).However, keep in mind that the bottom layer of the lake has the highest density (more energy is needed to lift it).

21 21 Safe Is a Relative Term …it’s dissolving more and more CO 2, and thus the increasing need to de-gas the lake.

22 22 Degassing Complexified One year after the event, the French Delegation aux Risques Majeurs proposed a degassing method based on off- shore oil production techniques.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 CO 2 ain’t no cash crop.The problem was that the proposal was expensive, and CO 2 ain’t no cash crop.

23 23 Degassing Simplified Enter: Michel Halbwachs, professor at the Centre de Recherches Volcanologiques, University of Savoie, France.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.”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.

24 24 “We have to intubate.” The current degassing strategy is no more complicated than taking a plastic (HDPE) pipe and extending it to the bottom of the lake.The current degassing strategy is no more complicated than taking a plastic (HDPE) pipe and extending it to the bottom of the lake. Once you prime the pipe with a pump... …it creates a self- siphon- ing system. If the water is most dense on the bottom of the lake, why does it move to the top of the pipe?If the water is most dense on the bottom of the lake, why does it move to the top of the pipe? Hmmm...

25 25 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.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?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?

26 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.Given the success of the 1990 self-siphon test, the research group received funding for a larger-scale test in The diagram above shows the surface component of the pipe assembly.The diagram above shows the surface component of the pipe assembly.

27 27 Steady! The pipe surface raft being hauled out to the middle of the lake...

28 28 “Don’t worry. I’ve got a 2 nd thumb.” Cutting and assembling the pipe...

29 29 “Man, I forgot my Gore-Tex boots.” Feeding the pipe into the water... Government workers?

30 30 McFly: “You are my density.” Scientists selected high-density polyethylene as the pipe material for many reasons. One reason was because HDPE almost floats in water.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.Let’s say you have sample of HDPE that occupies a volume of 10. mL. Predict what the mass of this sample will be. If HDPE “almost” floats in water, then why is the pipe floating in the picture below?If HDPE “almost” floats in water, then why is the pipe floating in the picture below?

31 31 Just in case... Even though the risk of an eruption was very low, scientists didn’t want to take chances. Oxygen tanks.

32 32 Easy does it... Once primed, the system took care of itself. Just one step back, and... Why is it safe to use a motor in the lake?

33 33 Success!

34 Expedition In 2001, the research team beefed up the apparatus.In 2001, the research team beefed up the apparatus. 120 ft. “geyser.”120 ft. “geyser.” 90% of geyser energy is lost to friction.90% of geyser energy is lost to friction. Assuming a “frictionless environment, how high would the geyser go?Assuming a “frictionless environment, how high would the geyser go? About as high at the Empire State Building.About as high at the Empire State Building.

35 35 Mo’ money. With more funding, the research team has been able to add more features to the degassing system.With more funding, the research team has been able to add more features to the degassing system. This includes automatice shut-off mechanisms, and...This includes automatice shut-off mechanisms, and...

36 36 Mo’ money, Mo’ money...a satellite link for remote monitoring and remote control.

37 37 Mo’ money, please. Scientists estimate that the current degassing rate (single pipe) is barely keeping up with the CO 2 input from the springs.Scientists estimate that the current degassing rate (single pipe) is barely keeping up with the CO 2 input from the springs. They hope to get more funding to de- gas the lake completely.They hope to get more funding to de- gas the lake completely.

38 38 Ecological Impact Not as bad you would think.Not as bad you would think. Biggest impact is from bringing anoxic water from the bottom of the lake to the surface.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 Mm 3 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 Mm 3 freshwater each year  more dilution. In addition, single pipe discharge of CO 2 is equivalent to the output of a 1.2 MW coal-fired plant without all the other acid-rain producing pollutants.In addition, single pipe discharge of CO 2 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 CO 2 impact on local ecosystem.

39 39 Clearly the water isn’t that bad!

40 40 Just when you thought it was safe... The top layer of Lake Nyos is held in place by a natural dam.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.Geologists have studied this dam, and found that it’s in bad shape. Business, or pleasure?

41 41 Dam it, Jim! The upper unit is eroding away.The upper unit is eroding away. What would happen, if the upper unit gave way?What would happen, if the upper unit gave way?

42 42 What the heck is that? There are many proposals on the table for how best to address this.There are many proposals on the table for how best to address this.

43 43

44 44 Water Chemistry

45 45 Sources Degassing the Killer Lakes: Lake Nyos and MonounDegassing the Killer Lakes: Lake Nyos and Monoun LAKE NYOS and LAKE MONOUN The Killer Lakes of Cameroon, West AfricaLAKE NYOS and LAKE MONOUN The Killer Lakes of Cameroon, West Africa Photo Gallery:Photo Gallery:


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