What Springs to mind EarthCache

Glorious Dalhousie Springs. Geothermal pools in the midst of a vast desert. A swim at dawn or dusk is a pleasure to be savoured and remembered. The spring stays at a constant 38 degrees the year round and due to its longevity is home to species found nowhere else on Earth.

Australia is home to the largest artesian system in the world. The Great Artesian Basin, which covers more than 20 per cent of the Australian continent, has around 600 artesian spring complexes in twelve major groups. Springs can range in size from only a few metres across to large clusters of freshwater pools known as 'supergroups'. Witjira-Dalhousie Springs is a supergroup that contains around 60 springs, extending over an area of more than 50,000 hectares.

Witjira-Dalhousie Springs was included in the National Heritage List on 4 August 2009.

Situated about 250 kilometres southeast of Alice Springs, Witjira-Dalhousie is the most northerly group of springs in South Australia. It is a complex of 'mound' springs, which means the groundwater flow deposits calcium and other salts from the mineral-rich waters. These deposits, combined with wind-blown sand, mud and accumulated plant debris, settle around the spring outflow forming mounds that resemble small volcanos.

Great Artesian Basin groundwater movement rates are slow, between one to five metres per year. As a result some water in the centre of the basin is more than one million years old. Dating techniques that measure groundwater flow reveal that the Witjira-Dalhousie Springs appears to be recharged by thousands of years old water that has percolated down through the beds of Finke River, and adjacent arid zone rivers, where they overlie outcrops of the Great Artesian Basin aquifer. As a geological feature the Witjira-Dalhousie Springs complex is unique in Australia. It illustrates on a huge scale an artesian spring's system, with faults, impermeable confining beds, aquifer outcrops, mound spring deposits, and the large pools and rivulets of artesian water.

Large complex of artesian springs developed in anticlinal structure of the Great Artesian Basin. The ground water is derived from deep aquifers and has travelled for long distances through the artesian basin. The waters emerge at the surface at temperatures of approximately 40 degrees. The groundwater discharge flows north and then east into the Simpson Desert as a braided stream channel complex. This is currently dry, but together with the evidence of large extinct mound springs points to large past discharges. The area is a mosaic of mound springs in varying stages of activity from extinct through to quiescient and actively flowing. Intervening areas are characterized by non-focussed ground water discharge.

Site descriptions

Area typical of surface between springs, patchily vegetated flat surface consisting of fawn gypsiferous silt colonized by grey pustular cryptobiotic crust and with puffy texture through crystallization of salts in the capillary fringe. The surface shows dessication cracks and patchy halite efflorescence. Sediment pedestals beneath some higher plants reveal deflation of surface. Excavations reveal that the subsurface is damp.

Cryptobiotic pustular mat, grey in colour on upper flanks of quiesent mound spring. Soil consists of puffy gypsiferous silt, with halite efflourence on the lower slopes. Top of mound spring covered by large trees with very dense understorey of tall grass.

Hot spring on side of active spring crest. Water discharges at approximately 40 degrees from spring approximately 1 metre deep and 1.5 metres in diameter. Water is clear and discharges at sufficient rate to feed a stream 50cm deep and approximately one metre deep. Several vents on the floor of spring discharge large bubbles at the rate of several per second. A distinctive, sulferous odour is noticeable. The spring is floored by an emerald green blistered microbial mat and locally has long filaments of green algae. Local films of ferrihydrite are present on the surface of the spring and there is an orange ferric hydroxide crust on the stream bed downstream.

Extinct mound spring consists of a hard cap made up of horizontal slabs of hard cap grey and white fenestral limestone surrounded by eroded cone of puffy gypsiferous silt. This is a small example, less than 20 metres in extent.

To log this cache as a find please send an email to the cache owner with the answers to the questions below and upload a picture of yourselves at the springs with your log on the cache page.

Q1. What is the source of the water that fills the spring.  

Q2. What is the water temperature when it emerges from underground.  

Q3. What is the area of the supergroup of springs in this region.  

Q4. Briefly describe the ground structure that leads to the formation of this type of spring complex.