Magic Lake @Wave Rock EarthCache

Yilgarn Craton

The Yilgarn Craton is an area of approximately 1.78 million km². Its bedrock is mostly granites and gneisses, and it is very stable.

The region has acid-saline ground water and has 100s of ephemoral lakes, of which 40% have a pH less than 4. These lakes are general shallow and surrounded by sand flats.

Acid-Saline Lakes

Acid-saline lakes are quite rare, with the Yilgarn Craton being only one of a few places in the world where they form naturally. They were more common in the past. The sustainability of these lakes is a characteristic of this region of West Australia. Although, climate change is predicted to continue the acidification of the ground waters, and hence lakes. The lakes themselves will have more extreme conditions and be less voluminous.

It has also been noted that the geological conditions of these lakes are not unlike the geological conditions that existed on Mars in the past. And studies have been undertaken, particularly at Lake Magic, to gain clues on what to look for on Mars when looking for evidence of past life.

These lakes usually have a high concentration of sulfur, aluminium and iron, and are chemically complex.

Several hypotheses for the high acidity of these lakes, which include:

• given high concentrations of sulphides in the host rocks, and consequential high sulfer content in the water, acidification is enabled through oxidisation of the sulfur
• given high iron content of the water, oxidation/hydrolysis of the iron may lead to higher acidity. Similarly the high aluminium content of Magic Lake in particular may be contributing to high acidity
• while the lakes conditions are not conducive to diverse life, there are acidophilic microorganisms found in the waters that promote the above two processes
• the weathered rocks provide little buffering capicity, and also contribute some acid
• some lakes also have a natural barrier beneath that prevents the ground water seeping into the lake, combined with a lack of high water input from rains, reduces dilution of the lake waters

Evapoconentration also leads to minerals and halites (aka crystalised salts) disolved in the water to precipitate out. When this occurs the minerals may trap acidic waters, aka "inclusions". When additional water eventually arrives, through rainfall for example, the minerals disolve again, releasing the contents of the inclusions and contributing in a small part to maintaining the acidity of the water despite the addition of water.

Many of the lakes in the region are shallow, with low water input. The heat of summer contributes to raising the acidity and salinity of the waters through evapo-concentration. The pH may be lowered by 1-2 units through the evaporation of water.

Early explores noted the diversity in colour of the lakes of the region. The colours vary based on several factors. The water chemistry differs between lakes. Those with higher iron or hematite content can have a reddish hue. Those with high sulphur content may appear yellow. Yellow may also be evidence in lakes with high aluminium and iron chlorides both present. The amount of water in the lake will also impact the intensity of the colour. When well hydrated, the lakes will often appear quite clear. During the later stages of evapoconcentration, the colours may be quite vivid. The presence of micro organisms also impacts the colours. The well known pink lakes in other areas are the result of microorganisms. Some bacteria lead to water high in iron and maganese and so also appear yellow.

The time of day will also have an impact as some lakes reflect the changing colours of the sky. One of the tourism draw cards noted for Lake Magic.

Lake Magic

Lake Magic is located only 1 kilometre north of the famous Wave Rock. 

The waters of Lake Magic in Western Australia are among the most geochemically extreme on Earth. This ephemeral acid-saline lake is characterized by pH as low as 1.6, salinity as high as 32% total dissolved solids, and unusually complex geochemistry, including extremely high concentrations of aluminum, silica, and iron.

Flooding, evapoconcentration, and desiccation of the lake are driven by local rain, hailstorms, and droughts and not simply by seasons. During intense rainstorms, and for weeks to months after, the lake is flooded to depths of 1–2 m. Arid periods promote evapoconcentration, which results in increasingly shallower, more acidic, and more saline waters, as well as precipitation of halite and gypsum. Eventually, Lake Magic sometimes undergoes total desiccation

Sources:

Benison, K. C. (2008). Life and Death Around Acid-Saline Lakes. Palaois, 23.

Benison, K. C. (2015). The Evolution of End-Member Continental Waters: The Origin of acidity in Southern Western Australia. GSA Today, 25(6)

Benison, K.C. et al. (2007). Sedimentology of Acid Saline Lakes in Southern Western Australia: Newly described processes and products of an extreme environment. Journal of Sedimentary Research, 77(5-6).

Benison, K. C. and Bown, B. B. (2013). Extreme Sulfur-Cycling in Acid Brine Lake Environments of Western Australia. Chemical Geology, 351.

Bowen, B. B. and Benison, K. C. (2009). Geocahmical Characteristics of Naturally Acid and Alkaline Saline Lakes in Southwern Western Australia. Applied Geochemistry, 24.

Conner, A. J. and Benison, K. C. (2013). Acidophilic Halpphilic Microorganisms in Fluid Inclusions in Halite from Lake Magic, Western Australia. Astrobiology, 13(9).

Jagnieki, E. A. and Benison, K. C. (2010). Criteria for the Recognition of Acid-precipitated halite. Sedimentaology, 57.

Stewart Johnson, S, et al. (2015). Insights from the Metagenome of an Acid Salt Lake: The role of biology in an exterme depositional environment. PLoS One, 10(4).

Zaikova, E, et al. (2018). Microbial Communities and their Predicted metabolic functions in a desiccating acid salt lake. Extramophiles, 22(3).

EarthCache Question

1. If the lake contains water, what colour is the water? What do you suppose causes that colour?
2. if the lake is dry, what colour is the lake bed (you may need to get up close? What do you suppose causes that colour? Also, compare the colour of the grounds surrounding the lake, is there a colour difference? Why might this be so?
3. (Optional) Take a photo with your gps with the lake in the background