Little Blue Lake is a water-filled doline in the Australian state of

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

located in the state's south-east in the locality of

Mount Schank Mount Schank is a high dormant volcano in the southeast corner of South Australia, near Mount Gambier. It was sighted by James Grant on 3 December 1800 and named after Admiral John Schank, designer of Grant's ship, HMS '' Lady Nelson''. Moun ...

about south of the municipal seat of

Mount Gambier Mount Gambier is the second most populated city in South Australia, with an estimated urban population of 33,233 . The city is located on the slopes of Mount Gambier, a volcano in the south east of the state, about south-east of the capital Ad ...

. It is notable locally as a

swimming hole A swimming hole is a place in a river, stream, creek, spring, or similar natural body of water, which is large enough and deep enough for a person to swim in. Common usage usually refers to fresh, moving water and thus not to oceans or lakes. ...

and nationally as a

cave diving Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other ...

site. It is managed by the

District Council of Grant The District Council of Grant is a local government area located in the Limestone Coast region of South Australia, and is the southernmost council in the state. The council was formed on 1 July 1996 after the amalgamation of the District Counci ...

and has been developed as a recreational and tourism venue.

Naming

The sinkhole's name is attributed to the property of its water to turn

blue Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when obs ...

in colour on an annual basis in a similar manner to the Blue Lake. However in more recent times the sinkhole generally remains

green Green is the color between cyan and yellow on the visible spectrum. It is evoked by light which has a dominant wavelength of roughly 495570 Nanometre, nm. In subtractive color systems, used in painting and color printing, it is created by ...

in colour throughout most of the year. This is believed by some to be due to

groundwater pollution Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwanted ...

from

agricultural Agriculture or farming is the practice of cultivating Plant, plants and livestock. Agriculture was the key development in the rise of Sedentism, sedentary human civilization, whereby farming of Domestication, domesticated species created food ...

fertilizer A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...

s increasing the nutrient levels. The lake is also known as Baby Blue and is referenced in caving literature by its Cave Exploration Group of South Australia (CEGSA) Inc. identification number, 5L9.

Description

The lake is located on the north side of Mount Salt Road, Mount Schank about west of the

Riddoch Highway Riddoch Highway is a rural highway in south-eastern South Australia, designated as route A66 between Keith and Mount Gambier, with the remainder between Mount Gambier and Port MacDonnell designated as route B66. It is named after John Riddoch, t ...

, the main road between Mount Gambier and Port MacDonnell and about south of the municipal seat of Mount Gambier. The lake is located on

crown land Crown land (sometimes spelled crownland), also known as royal domain, is a territorial area belonging to the monarch, who personifies the Crown. It is the equivalent of an entailed estate and passes with the monarchy, being inseparable from it. ...

in section 963 in the cadastral unit of the

Hundred of MacDonnell 100 or one hundred (Roman numeral: C) is the natural number following 99 and preceding 101. In medieval contexts, it may be described as the short hundred or five score in order to differentiate the English and Germanic use of "hundred" to des ...

. The lake has a diameter of about , cliffs approaching a height of about above water level and a maximum depth of about . Access to the water’s edge is via an artificial

cutting Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force. Implements commonly used for wikt:cut, cutting are the knife and saw, or in medicine and science the scal ...

in the south side of the sinkhole. The bottom of the lake is at an average depth of about with the shallowest point at a depth of about , being the top of the rubble pile resulting from the excavation of the cutting. An undercut ledge reaches a maximum depth of approximately along the full extent of both the south (i.e. under Mount Salt Road) and the west sides of the sinkhole’s bottom. The underwater visibility is normally poor, but can at times improve below a depth of about . A notable feature of the lake is the accumulation of rubbish dumped in the lake over a period of several decades including a 1966 Morris 1100, a

bowser , or King Koopa, is a fictional character, the primary antagonist in Nintendo's Mario (franchise), ''Mario'' franchise, and the arch-nemesis of Mario. In Japan, the character bears the title of . Bowser is the leader of the turtle-like Koopa ...

traffic sign Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduce ...

s and ’witches hats’.

Geological origins

The Little Blue Lake is one of a number of similar landforms occurring in the area to the south of the dormant volcano in Mount Gambier including the area around the dormant volcano at Mount Schank. These cenotes are similar in form as they all have collapse dolines with circular plans, cliffs, lakes filled to the water table, large rubble cones on their floors and clustered together in several groups along in the flat coastal plain composed of a

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

limestone known as Gambier Limestone. These cenotes differ from other

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

landforms in the south east of South Australia by their relative depth (i.e. as deep as in one cenote), the absence of any underwater

phreatic ''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "well" ...

passages and a different water chemistry. It is theorised that these cenotes were formed by the collapse of large underground water-filled chambers following the lowering of sea levels at the most recent Glacial Maximum about 20,000 years ago. The chambers themselves are likely to have been formed by groundwater acidified by gaseous

Carbon Dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

(CO₂) rising up through fractures from the magma chambers during the volcanic eruptions occurring during the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

and the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

rather than by the usual acidification process involving the absorption of atmospheric CO₂ by water prior to entering the water table. The cenotes then filled with freshwater as the sea level started to rise at about 8,000 years ago. The presence of

stromatolites Stromatolites () or stromatoliths () are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). The ...

in at least eight cenotes including the Little Blue Lake is suggested as being an indicator of the recent formation of these landforms.

Exploration

Exploration of the lake's underwater environment commenced in the 1950s. The lake’s submerged extent was surveyed by Lewis and Stace in 1980 and by the

Cave Divers Association of Australia The Cave Divers Association of Australia (CDAA) is a cave diving organisation which was formed in September 1973 to represent the interests of Recreational diving, recreational scuba divers who dive in water‐filled caves and sinkholes princip ...

(CDAA) during the 1990s.

Present day

The lake is a popular venue for swimming and cave diving. The land which includes the sinkhole was dedicated as a reserve "for the purposes of a Public Pleasure Resort" under the ''Crown Lands Act 1929'' on 19 March 1986 and placed under "the Care, Control and Management" of the former

District Council of Port MacDonnell The District Council of Grant is a local government area located in the Limestone Coast region of South Australia, and is the southernmost council in the state. The council was formed on 1 July 1996 after the amalgamation of the District Coun ...

. The District Council of Grant installed stairs and a floating pontoon in 2002 to improve the lake’s amenity for both residents and visitors after a review of public safety. A parking area also exists on the lake's east side. Access for cave diving is limited to holders of the CDAA Deep Cavern grade.

References

External links

Little Blue Lake Cliff Jumping
{{DEFAULTSORT:Little Blue Lake Sinkholes of Australia Limestone Coast Underwater diving sites in Australia Lakes of South Australia Swimming venues in Australia