Monthly Archives: February 2012

My (Very Belated) Two Cents on Heartlandgate

There’s been reams of digital ink spilled about the leak of a large quantity of documents from the Heartland Institute, which is a think-tank devoted to to anti-environmentalism. The leaked documents are available here on DeSmogBlog, and the contents aren’t especially surprising: there’s lists of donors, including big tobacco companies and pharmaceutical companies, there’s the names of people on their payroll, including Anthony Watts, and there’s some strategy documents which don’t have anything startlingly unexpected in them that I’ve seen. The added wrinkle is that the documents were collected by Peter Gleick, an American environmental scientist who worked, among other things, in ethics. He contacted the Institute with a false identity and got a hold of the documents, which was a deeply stupid move that demolishes Gleick’s credibility as an ethical scientist. While it’s nice to have these documents, as they confirm a lot of the tactics and participants that climate and environmental scientists thought were a part of anti-environmental movement, it’s not like there’s much that earthshattering in them.

I don’t have very much to say about the documents themselves, though I encourage you to have a look at them — primary sources are optimal! I do have a few words to say about how the documents were obtained and what that means for the scientific community as a whole, and a few other words about the strategy to dissuade teachers from teaching science, which is the bit from the documents that’s caused the most hubbub in the media.

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File Under Things You Never Thought You’d Need To Worry About: Exploding Lakes!

Limnic explosions are really bizarre and not very well understood, since there’s only been two confirmed and documented events in recent history (Lake Monoun and Lake Nyos, both in Cameroon, in 1984 and 1986 respectively), and it’s difficult to study an exploding lake for what should be obvious reasons.

What happens is this: gas emitted from the lakebed dissolves into the lower depths of the lake water, creating a supersaturated solution. Solutions consist of who components: the solvent, or the liquid which forms the bulk of the solution, and the solute, which is the material dissolved in the solute. A solution is undersaturated when the quantity of solvent can dissolve more solute than is currently in solution, saturated when the critical amount of solute is dissolved in the solvent and no more can be added to the solution, and supersaturated if, under some circumstance, more solute than can normally be dissolved in the solvent is present in the solution. A supersaturated solution is generally unstable, and if the solution is jarred or disturbed, the compound dissolved in the water will suddenly precipitate out, releasing a lot of energy and heat. While this is commonly demonstrated in high school chemistry class by dropping a crystal of salt into a large flask of supersaturated salt water, the same basic principle can apply to a lake, too.

Three things are needed for a limnic eruption to be even remotely possible:

  • The lake must be tropical, so that it doesn’t overturn. Lakes in temperate regions (for example, the Great Lakes) overturn due to the seasonal fluctuation of the air temperature above the lake. As the air cools in winter, the surface water cools and sinks, pushing water from the depths up to replace it. This means that there is no consistent bottom layer of water that remains undisturbed for long periods of time.
  • The lake must be deep and very stably stratified, so that there is a bottom layer of water that is not disturbed for a long period of time and doesn’t interact with the surface or sunlight.
  • There must be a geophysical source of gas, usually CO2 or methane (CH4) at the bottom of the lake. This may be as a result of volcanic activity under the lake.
Four schematic lakes.

Top left: a tropical lake that does not over turn. Top right: a temperate lake overturns. Bottom left: a stratified lake Bottom right: a lake with a gas source in the lake bed.

Without all three of these ingredients, a limnic explosion is not possible, because there is no way to create a supersaturated bottom layer. If the first is lacking, the bottom layer of water interacts with the upper layers, and the dissolved gas will dissipate. If the fluid is not strongly stratified, the gas will easily diffuse upwards and out of the bottom layer. If there is no source of gas, there is nothing to explode. Lake Nyos is a very deep crater lake, which sits on top of a dormant volcano. It’s surrounded by tall hills, which shields it from strong winds (which can help stir lakes). It’s a perfect candidate for a limnic explosion.

What’s still very unclear is how a limnic explosion is set off. Some scientists suspect a small earthquake jiggled the lake and set it off, while others think that there was a change in the stability of the lake. If the stability of the lake changed, the stratification could weaken and an overturning circulation could form, bringing the bottom water to the surface where the sudden change in pressure could cause the gas to rapidly expand (and thus explode out of the water). Some scientists think that for some reason a plume of light water formed at the bottom of the lake and entrained the bottom layer water as it rose to the surface (ie, the light water dragged the denser water up to the surface with it) . There’s a theory that an unusually severe thunderstorm the night before the explosion deposited a layer of cold water at the surface, which then caused an overturning circulation to form and the gas, again, to reach the surface and expand rapidly. Another idea is that the inflow from rivers was colder than usual. The precise mechanism is still unclear, especially since it’s difficult to accurately analyze what cause the explosion after the fact, and before the fact it was an otherwise unremarkable lake in remote Cameroon.

What is clear is that the bottom water with the extremely high concentration of CO2 reached the surface, and the change in pressure caused the dissolved CO2 to explode out of the water and into the surrounding atmosphere. Carbon dioxide is heavier than air, so when all the gas exploded out of the lake, it sank and hugged the ground, and ran through the valleys in the hills surrounding the lake. The high concentration of CO2 in the cloud from the explosion asphyxiated nearly 1800 people, some as far away as 20 km from the lake, and countless animals. The victims appeared to die peacefully; eyewitness accounts from survivors tell a tale of people falling suddenly or quickly into a coma and never awakening, or people who were asleep (the explosion occurred at around 10 pm) never waking up.

In the wake of the explosion, scientists devised a way to degas the lake to prevent CO2 from building up in the lake again and thus decreasing the potential for another explosion. They have installed a pipe and a pump that vents the bottom layer of saturated water to the surface, allowing the CO2 to bubble off at a continuous rate that allows it to dissipate before it can form a lethal cloud. A similar structure is installed in Lake Monoun, though since the lake is smaller less pipes are needed. I’ve had a surprising amount of difficulty finding current information about the state of these degassing projects, unfortunately, and it’s unclear to me whether the projects were ever finished or if they’re still in operation.

A pipe to degas the lake.

The pipe connects the bottom fluid layers to the surface, allowing the gas to bubble off into the air. Initially the water must be pumped, but as the water becomes buoyant in the tube (due to the expanding gas), water from the bottom gets sucked up to replace the water in the pipe, and the pump is no longer needed.

Lake Kivu, which sits between the Democratic Republic of Congo and Rwanda, is the only other known lake that is at risk for a limnic explosion. Lake Kivu is about 2,000 times larger than Lake Nyos, and is not nearly as remote — about 2 million people live near its shores. Lake Kivu contains not only CO2, but also high concentrations of methane (CH4), which has lead to some engineering projects which attempt to retrieve the methane for use as fuel. This is doubly useful in that in the process of extracting the methane, some CO2 is also extracted. Fortunately, the gas concentrations in Lake Kivu are not nearly as high as those in Lake Nyos, and so it is probably less likely to explode, but the consequences (and death toll) from a limnic explosion at Lake Kivu are likely to be several orders of magnitude higher than from previous confirmed explosions. Considering that the effect of extracting the methane may not be enough to offset the natural build-up of gas, and also that the scientific community still knows very little about limnic explosions and what triggers them, Lake Kivu is possibly a ticking bomb.

Saponification, or Why Not to Buy The Discount Lutefisk

Soap is ubiquitous in modern life, in many forms, from hand soap to laundry detergent to shampoo. Chemically, soaps are alkali salts of fatty acids, and are formed by taking a fat or oil and combining it, either at room temperature or at or around the boiling point of the fat, with a strong alkali compound like sodium hydroxide. (Alkali compoounds are chemicals that have a high pH; please see the post on the pH scale for reference.) The alkali compound used is usually a hydroxide, either sodium, potassium, or occasionally lithium. All these hydroxides are very reactive, which is useful for forming soap, but they are also very corrosive, and so soapmaking must be done very carefully to avoid accidents.

A typical chemical reaction to create soap

A triglyceride is a fatty acid with three branches. It reacts with NaOH to produce soap molecules with a hydrophobic tail and a hydrophilic head and a molecule of glycerol.

At the heart of soap’s effectiveness is that soap molecules have two distinct parts. One part is hydrophobic (ie, does not mix will with water) and grabs on to dirt (which typically is oil based, ie, also hydrophobic) while the other part is hydrophilic (ie, mixes well with water).

A bit of dirt gets covered in soap molecules, all with the hydrophobic end attached to the dirt, with the hydrophilic end trailing like a string away from the dirt. This structure is sometimes called a micelle, though the term is not just used for soap.

A micelle is formed when soap molecules surround a bit of dirt.

Lutefisk is made in a similar manner to soap, and it’s one of those things, like soy sauce, that I wonder how on earth someone figured out how to make it (and thought to try eating it). It’s a Nordic dish made by taking salted fish like cod, treating it with lye (ie, a very strong alkaline compound) for a couple of days, and then soaking it in water for several days to rinse out the caustic lye. Traditionally, the fish is treated with ash, which is alkaline but not nearly as strong as lye, and then buried for several months. Either way, the chemical reaction between the fats and oil in the fish and the lye needs to be stopped before all the fats saponify; though the whole point of making lutefisk is that some of the fats saponify, rendering the entire fish soap seems even more unsavory than only a partial rendering. The end result is a fish concoction that is somewhat gelatinous and falls apart easily, is either baked or broiled, and looks about as appetizing as you’d expect given how it’s made. I’ve never eaten it myself, but it’s got a reputation for smelling and tasting awful with a very unpleasant texture, but apparently some people genuinely enjoy it. While on description alone I can’t say as I’d recommend it, if you’re going to eat it, it seems especially prudent, given the chemistry involved in making it, to avoid the dented can on the discount shelf at the grocery store.

The pH Scale

There’s a common line in soap commericals that goes something along the lines of “This soap is pH balanced, for soft, smooth skin.” The claim about the soft, smooth skin may or may not be accurate, but what does “pH balanced” mean?

The pH scale is a measurement of the acidity of an aqueous (ie, water-based) liquid compound. The capital H indicates that it’s a measurement of hydrogen ions (denoted H+ in chemical notation); the definitive meaning of the p is lost to the sands of time. A low pH value means that the solution is acidic, and has more H+ ions than OH- ions, while a high pH means the solution is basic (or alkaline — the two terms are interchangeable) and has more OH- ions than H+. The more extreme the inbalance (ie, the lower or higher the pH) the stronger the solution, and the more likely it is to eat through your skin if you spill it.

A flask and a beaker with and acid and basic fluid respectively.

The fluid in the flask on the left is more acidic than the fluid in the beaker on the right is basic.

The precise value of the pH of a solution is given by the negative logarithm of the concentration of hydrogen ions in the solution, though there are compounds that can act as catalysts in specific solutions that will alter the measured pH. Logarithms are a useful way of describing quantities that vary of a wide range of scales. Mathematically, if x = b^y, y = log_b (x).

Logarithmic equations.

Logarithms are typically either in base 10 (ie, b=10) or base e (ie, b = e = 2.718…; these are also called natural logarithms). The most commonly known logarithmic scale is the Richter scale, which measures the strength of earthquakes. The Richter scale is a base 10 scale, so an earthquake of magnitude 6.0 is 10 times stronger than an earthquake of magnitude 5.0, and 1000 times (ie, 10^3 times) stronger than an earthquake of magnitude 3.0.

Similarly, the pH scale is a base 10 logarithmic scale. A solution of pH 4.0 is ten times more acidic than a solution of pH 5.0, and 10 times less acidic (ie, more alkaline) than a solution of pH 3.0. The scale runs from 0.0 to 14.0, (explain why zero can be reached due to catalytic reactions and whatnot)

pH scale

Click to enlarge.

The pH of a solution can be tested using a variety of compounds called indicators that are known to change colour at specific pH values. Indicators do not generally interact with the solution, and so do not drastically alter the chemical mix in the solution. An indicator can be added to a solution, and then the solution can be titrated (ie, another solution is dripped slowly into the original solution to reach a desired pH) until the indicator changes colour. The colour change of the indicator indicates that the solution has reached a specific pH. Litmus paper is a crude indicator: it will indicate if a solution is acidic or basic, but does not determine exactly how acidic or basic the solution is.

In a general sense, then pH balanced, means that the solution in question has the same pH as its surroundings. Skin has a pH of around 5.5, so in the context of facial soap, the manufacturer may be using “pH balanced” to mean that the soap has a pH around 5.5, so the soap will not undergo an acid-base reaction with (and thus irritate) the user’s skin.