olelog

Between the Sahara and the Atlas Mountains lye a string of salt lakes. On a field trip to the Tunisian salt lakes I once again realised that not only do we speak different languages, like Arabic, French and English, but the same words have different meanings for, say, geomorphologists, sedimentologists, geographers etc. Let us have a brief look at a few words of Arabic origin.



In Morocco, Algeria, and Tunisia these “lakes” are traditionally called Chotts - or are they? The French term "chott" is a transliteration of the Arabic shat, a term for a broad canal, an estuary or lake. These shats are not really lakes, but smooth depressed areas. The largest North African “salt lake” is the Shat el Jerid.

Originally the term chott was in Tunisia used for the part of the flats with halophyte (salt tolerant) vegetation - the vegetation free part of the (muddy) salt flat being the sabkha.



In this case the halophyte is Salicornia arabica. Salicornia is edible and can a.o. be used in salads (don’t add any salt!).

Sabkha (Sabka, Sabkhah, Sabkhat, Sebkha, Sebkhet) is also a transliteration from Arabic. Strictly speaking the Arabic term Sabka refers to the broad, salt-encrusted, supratidal surfaces or coastal flats bordering lagoonal or inner shelf regions. The geologic ‘type area’ is on the Trucial Coast of Arabia (Abu Dhabi). An essential feature of a sabkha is that it is only flooded occasionally.

Sorry for deviating, but the Trucial Coast was known as the Pirate Coast in the late eighteenth and early nineteenth centuries until Britain through a Treaty of Peace, imposed a truce that condemned piracy, hence the name Trucial Coast.

Modern Sabkhas are important analogues for sedimentation environments in the past.

Now if you compare it with the definition of “playa” (another geologic term used by sedimentologists and derived from Spanish: shore or beach), that is a flat-bottom depression found in interior desert basins and adjacent to coasts within arid and semiarid regions, periodically covered by water that slowly filtrates into the ground water system or evaporates into the atmosphere, causing the deposition of salt, sand, and mud along the bottom and around the edges of the depression - and if we stress that it is a “saline playa“ - well then playas are in fact also known as sabkhas, alkali flats, dry lakes or mud flats. If the surface is primarily salt then they are called salt pans, salt lakes or salt flats (not that I expect everybody to agree on that).

When I visited Chott El Jerid 4 years ago, I saw practically no water, but instead a blinding whitish sun-reflecting flat hurting the eyes and making it impossible to take good photographs, but this time most of the depression was on the contrary filled with water with a muddy flat around it, where gypsum and rock salt. was beginning to condensate on some of the surface.

And now further south to the Sahara, or to the so-called Great Erg Oriental (meaning Great Eastern Sand Sea). Erg takes its name from the Arabic word erg, meaning "dune field". Also known as sand seas or dune seas these accumulations of dunes cover about 20 percent of the Sahara. An erg is thus a large, relatively flat area of desert covered with wind-swept sand with little or no vegetative cover. Strictly speaking, an erg is defined as a desert area that contains more than 125 km² wind-blown (”aeolian“) sand and where sand covers more than 20% of the surface.

Seen on Twitter:
If science knew all the answers, it would stop.
How beautiful it is to do nothing, and then rest afterward. - Spanish proverb.

My tweeted links:
SEED allows Chris Rowan (of Highly Allochthonous ) to opine on geoengineering http://seedmagazine.com/content/article/business_as_abnormal/

Love links:
Ol Doinyo Lengai at the NASA Earth Observatory at the Volcanism Blog: http://volcanism.wordpress.com/2009/09/17/ol-doinyo-lengai-at-the-nasa-earth-observatory/

One of the reasons that China is “interested” in Tibet is (most probably) Lithium. Chabyer salt lake, in the Tibet Autonomous Region, at an elevation of 4,400 m is the largest lithium mine in China. I have of course a few problems with the name as it is transcribed from either Tibetan (or should I say Tibeto-Burman) or one of the Chinese languages. Another way of spelling it is “Zabuye”. This has lent its name to the mineral Zabuyelite, with the formula Li₂CO₃. Zabuyelite was discovered in 1987 at Zabuye/Chabyer Salt lake. It forms colourless vitreous monoclinic crystals. Such is the solubility of Lithium carbonate that it is unlikely to occur naturally anywhere except in evaporites and arid conditions. Chabyer salt lake is also known as Chabyer Caka. Caka is just the Tibetan word for salt lake, and actually there are more salt lakes than fresh water lakes in Tibet.

Chabyer Caka is a large bittern-salt lake (the main compounds of the salt are Lithiumcarbonate and Borax) in the Gangdisi Mountains (or is it the Lunggar Mountains?) in the interior of the Tibetan Plateau. The lake consists of two sub-basins, a southern and a northern one, joined by a narrow channel. The lake has a total area of 243 km², a mean depth of 70 cm, and a maximum depth of less than 2 m. The salt content of the lake water is 360-410 g per litre. The basin originated through faulted structures. The underlying bedrock is Cretaceous-Eogene acidic igneous, mudstones and sandstones. A large area of playa is being exposed around the lake, and mirabilite (also known as Glauber's salt, a hydrous sodium sulfate mineral) is currently being deposited in the lake. The location of the calabash-shaped lake is 31° 20' N 84° 05' E, which I have tried to pin-point on my map of Tibet - 1050 km from Lhasa.

The lithium exploration began in 1982. By the end of 2004 it had reached a production capacity of 7500 tons of solid lithium carbonate per year. China may emerge as a significant producer of brine-source lithiumcarbonate around 2010. There is potential production of up to 55,000 tons per year if projects in Qinghai province and Tibet proceed.

The total amount of lithium recoverable from global reserves has been estimated at 35 million tonnes, which includes 15 million tons of the known global lithium reserve base.

Here follows an overview of lithium production from the U.S. Geological Survey, Mineral Commodity Summaries, January 2009.


Lithium salts are indeed found in evaporites and salt lakes. Subsurface brines have become the dominant raw material for lithium carbonate production worldwide because of lower production costs as compared with the mining and processing costs for hard-rock ores.

The market for lithium compounds with the largest potential for growth is batteries, especially rechargeable batteries. Non-rechargeable lithium batteries are used in calculators, cameras, computers, electronic games, watches, and other devices. Demand for rechargeable lithium batteries continues to grow for use in cordless tools, portable computers, mobile telephones, and video cameras. Future generations of electric vehicles may use lithium batteries (so-called lithium-ion batteries). Mitsubishi, which plans to release its own electric car soon, estimates that the demand for lithium will outstrip supply in less than 10 years unless new sources are found.

A misunderstanding seems to have crept into some of the articles. Chabyer Caka is certainly NOT one of the three largest salt lakes in the world. It may well be one of the three most important lithiumcarbonate-containing lakes ???.

• http://www.zabuye.com.cn/main.php?sLAN=en
  
• http://www.green-energy-news.com/arch/nrgs2008/20080024.html
  
• http://solveclimate.com/blog/20080415/tibet-land-lithium
  
• http://zabuye.en.alibaba.com/
  
• http://www.andhranews.net/Technology/2008/March/26-Tibet-lithium-producer-38867.asp
  
• http://my.opera.com/nielsol/blog/2009/02/10/lithium-bonanza
  

In a post two years ago I featured methane in Lake Kivu.

Lake Kivu contains approximately 55 km³ of dissolved methane gas at a depth of 300 m. Previously, the methane concentration was assumed to be in steady state. However, recent analysis indicates that the methane concentration has increased significantly by 15 to 20% since the 1970s’ measurements. For carbon dioxide, the observed concentration increase was on the order of 10%, but was not statistically significant. The main hypothesis for this increased production of methane is a rise of the nutrient inputs caused by the fast-growing population in the catchment of Lake Kivu. Until 2004, extraction of the gas was done on a small scale, with the extracted gas being used to run boilers at a brewery. As far as large-scale exploitation of this resource is concerned, the Rwandan government is in negotiations with a number of parties to produce methane from the lake. Extraction is said to be cost effective and simple because once the gas rich water is pumped up the dissolved gases (primarily carbon dioxide, hydrogen sulphide and methane) begin to bubble out as the water pressure gets lower. This project is expected to increase Rwanda's energy generation capability by as much as 20 times and will enable Rwanda to sell electricity to neighboring African countries.

So far so well.

Extracting valuable methane from the lake's depths might, however, trigger an outburst of gas that could wash a deadly, suffocating blanket over the 2 million people who live around Kivu's shores.

A group of biochemists warns that if unregulated extraction continues unabated, it could trigger a catastrophic outgassing of carbon dioxide - another dissolved gas abundant in the lake's depths. Such a disaster occurred at Lake Nyos in Cameroon in 1986, killing 1700 people. Kivu contains 300 times more CO₂ than Nyos did.

Like Nyos, Lake Kivu is permanently stratified: a deep layer of dense water laden with CO₂, methane, salt and nutrients is locked away beneath a surface layer of fresh water. Methane is generated by lake-bed bacteria that feed on a stream of dead algae sinking from the surface. The CO₂ enters through volcanic seeps.

The most dangerous practice is pumping waste water into the lake's shallows. If degassed water is dumped at the surface, it sinks, mixing water and salts between the lake's layers. Enough mixing would disrupt the density stratification of the lake, and could bring huge volumes of CO₂-rich water to the surface. The pressure reduction would cause the CO₂ to bubble out of solution.

Another question is of course “what could happen if the methane is NOT exploited?". Indeed the Government of Rwanda is working with experts to mitigate an imminent explosion of the gases trapped under the surface of Lake Kivu that could cause a serious human catastrophe. Recent reports suggest that the huge amounts of carbon dioxide and highly combustible methane gas trapped under the surface of Lake Kivu could explode soon if not exploited, leading to disastrous effects on the surrounding population. In an interview with the Rwandan newspaper The New Times, Charles Nyirahuku, the Head of Oil and Gas Unit in the Ministry of Infrastructure and Energy, confirmed that indeed the alarm is there but the Ministry is working round the clock with experts to ensure that the fears are mitigated. "Indeed much has been said about the danger and all this time we have been discussing possible mitigating measures. We carried out a comprehensive study and found out that one way to mitigate the danger is to extract the gas. For the moment that is what we are focusing on." (He may be biased of course?)

It is in any case evident that a strict set of rules and regulations has to be followed to ensure that the whole process of extraction is secure so that no explosion is triggered - and the possibility of one is completely eliminated.

• http://www.newscientist.com/article/mg20327254.500-methane-mining-could-trigger-killer-gas-cloud.html?DCMP=OTC-rss&nsref=online-news
  
• http://allafrica.com/stories/200908280047.html
  
• http://allafrica.com/stories/200811210816.html
  

So far nobody, but a few nations are doing their utmost to claim it - on geological grounds, of course, which gives rise to a lot of great science.

Joint U.S.-Canada exploration of the Arctic sea floor discovered an unusual underwater mountain and evidence that could boost the two countries' claims that their boundaries extend farther north. For the past two months ships from the countries have ventured north in icy areas of the Arctic where almost no surface ships have been, in an effort to find out how far the continental shelf extends.

The Danish Continental Shelf Project in collaboration with the Swedish Polar Research Secretariat made a cruise with the Swedish Polar icebreaker Oden in 2009 in the Arctic Ocean north of Greenland. The aim of the expedition was to collect scientific data for the Danish and Canadian Continental Shelf projects in order to document claims for an extended continental shelf to the north of Greenland and Canada beyond the present 200 nautical mile zone. Field reports are available on line at http://a76.dk/expeditions_uk/lomrog2009_uk/ . In the 5th Field Report of 22 August they reported that they had reached the geographical North Pole. This report contains a map of their route until then.

The cruise ended in Longyearbyen on Svalbard, and according to the last (9th) Field report the expedition has been very successful and several researchers have acquired more and better data than they hoped for.

• http://news.yahoo.com/s/ap/20090910/ap_on_sc/us_sci_deep_arctic_2
  
• http://a76.dk/expeditions_uk/lomrog2009_uk/
  

In Danish:

• http://www.dr.dk/Nyheder/Indland/2009/09/11/113804.htm?rss=true