Exploding Lakes As An Energy Source?

In 1986, approximately 1,800 people were killed when Lake Nyos in Cameroon 'exploded' without warning, producing a tsunami and a huge cloud of CO2 which asphyxiated people up to 25km away. Many other lakes around the world face a similar threat, and I've been thinking of ways to turn this problem into an opportunity.

Exploding lakes are deep bodies of water in which the lower levels are saturated with CO2. The gas is dissolved just like it is in can of coke, and held in place by pressure from the water above. If the water is disturbed, eg by volcanic activity, and pushed upwards then the reduced pressure causes the gas to form bubbles which rush to the surface. But as they move upwards they suck in more water beneath them, releasing more bubbles in an uncontrollable chain reaction which 'overturns' the entire lake and brings all the water from the bottom to the top.

The CO2 is usually the result of organic matter decomposing at the bottom of the lake, so it increases with time.

For the lake to be at risk of exploding, the CO2 concentration must be very high and in most places this never happens due to the normal flow of water out of the lake or movement within the lake that stirs the water and prevents dangerous build-ups of gas. But the CO2 still causes problems in, for instance, hydro-electric schemes. As the water flows out through a turbine to generate electricity, there is a reduction in pressure which causes the bubbles to 'erupt' violently and this cause damage to the turbines over time. It's called cavitation and is a big engineering problem which affects hydro-electic schemes with very deep reservoirs.

One solution is degassing, and this is where it gets really interesting.

By lowering a long tube vertically into a lake with a lot of gas dissolved into it, one can limit the spread of any activity. Drawing some water upwards releases bubbles which rise upwards, drawing more water into the pipe and creating a self-sustaining flow of water and gas which can result in a spectacular fountain. This has already been demonstrated successfully at Lake Nyos. The water and gas are seperated in a controlled manner and the concentration of CO2 can be reduced to safe levels. But the cool thing is that you don't need any ongoing energy input (ie a pump) to move water from bottom of the lake to high in the air. You have a free source of kinetic energy.

I don't have any information about whether the degassing plants that are currenly in trials just use a tube and rely on massive energy being available, or whether there are any special tricks involved. I do know from reading Richard Nakka's Rocketry website that shaping a nozzle correctly wi... according to principles that are well understood. So I'm guessing that in theory any body of water with gas dissolved in it can be induced to keep moving by using the power of the emerging bubbles.

There are only a few known exploding lakes, but there are many bodies of water with lots of CO2 dissolved in them - hence the damage to hydro-electric schemes on the Amazon River. The biggest of them all covers 70% of this planet's surface - the ocean, and I remember being given a demonstration of the power of dissolved gas in seawater a few years ago.

We were on a diving trip, and someone took a plastic soda bottle down with them. At 30m depth, he filled the bottle with seawater and closed the lid tightly. When he opened it at the surface, it was like a can of Pepsi after being used as a football - it sprayed everywhere! Imagine how much energy is stored in seawater at a depth of thousands of meters!

Strangely enough, scientists working on OTEC projects - which address issues of energy security and water supply - complain that 20-40% of the energy they produce is used to pump water up from the deep ocean to the surface. If sea-water contains dissolved gas, and dissolved gas can be liberated to create kinetic energy, then why are people pumping water? I don't understand this, so I have written to one of the major research centres to ask if they have thought of this.

I'll let you know the response.