Mound springs are natural outlets for the waters of the Great Artesian Basin (GAB), where artesian pressure forces water to the surface. Most springs occur on the margins of the Basin in the Far North of South Australia, north-western NSW and south-western Queensland.

Most of the springs have only small flows or seepages, but one at Dalhousie in the Far North of South Australia has a daily output of around fourteen million litres per day.

The term mound springs reflects the characteristic mounds that have developed at many (but not all) of the springs. In some areas the mounds have been building for thousands of years. Spring flows were stronger in the geological past.

The precipitation of salts and minerals, along with the erosion of the sands and clays of the surrounding country, has created the mounds.

Characteristic features of the landscape around many springs are the gibbers, deeply coloured and highly polished stones and boulders that are the broken up fragments of an old plateau. Wind and water have eroded the soil away, leaving the stones as a surface layer. Closely packed in many places, they are often referred to as desert pavement. The red and brown colouration, aptly called desert varnish, comes from a surface coating of iron and manganese oxides and the high polish is a result of thousands of years of sand blasting.

The Great Artesian Basin underlies 22% of Australia and is one of the largest groundwater basins in the world. Natural discharge from the Basin occurs around its margins where the aquifers (water-bearing sediments) meet impervious surrounding rocks.

Elsewhere in the Basin, such as at Dalhousie Springs, water rises to the surface through geological fractures. The aquifers can be up to 3,000 metres deep. With water moving laterally through the Basin at only one to three metres per annum, the waters are up to two million years old.

Replenishment (recharge) of the GAB occurs mainly along the western slopes of the Great Dividing Range. There is also some minor recharge around the Basin’s south western margins in South Australia.

The recharge areas are elevated well above the Basin and the result is a pressurised system where the only natural outlet for the waters is via the mound springs and a more diffuse process known as vertical leakage.

The mound springs of Far North South Australia are part of the artesian springs of the Great Artesian Basin (GAB). The GAB underlies 22% of Australia and is one of the largest groundwater basins in the world. Natural discharge from the GAB occurs around its margins where confining beds are thin and through fractures from faulting and folding elsewhere in the Basin.

It is estimated that there are approximately 5000 individual mound springs in Far North SA. These are of international importance because of their outstanding natural and cultural features. As virtual oases in the desert, the springs were, and still are, of vital importance to Indigenous people. The springs also support a range of endemic plant and animal species of enormous conservation significance. They provided essential water supplies for early European explorers and settlers and were instrumental in guiding the routes of the Overland Telegraph line and Ghan railway in the late nineteenth century.

Since bores were first sunk into the GAB over one hundred years ago it is estimated that natural flows from these springs have declined by 30%. There have also been impacts from stock and pest plants and animals. A number of programs are now in place to address such impacts, and the Friends of Mound Springs group is playing its part in this process.

The isolated nature of the GAB springs has produced many plants and small animals of great ecological, evolutionary and biogeographical significance. A large number of the invertebrate animals are endemic, being found only at these locations, and endemic fish and plants also occur.

The vegetation of the springs consists of both dryland and wetland species. Aquatic species such as reeds, sedges and rushes are common. Of particular significance is the salt pipewort (Eriocaulon carsonii), an endangered plant that is found only at a few mound springs.

Research has been undertaken in recent years to provide more information about the location, ecology and hydrology of mound springs. This information is essential in guiding conservation and management programs.