Mound Springs

Australia: The Land Where Time Began

Mound Springs

These occur where the water in the aquifers of the Great Artesian Basin finds it way to the surface. In some it results from the aquifer beds deep underground that are narrow, some of the water being forced to the surface where it seeps, and in the past, wetter times, probably ran out with more force. The mounds at the far end of the basin, where the beds carrying the aquifers slopes up to the surface, the water remaining in the aquifer comes to the surface in a number of mound springs that form an arc to the west of Lake Eyre. The mounds form from the minerals and associated debris and mud that comes up with the water,

The largest concentration of springs occurs in part of the arc to the southwest and northwest of Lake Eyre. Dalhousie Springs lies 250 km northwest of Lake Eyre. In an area of 70 km² there are 80 active springs.

New type of mound-spring found on the Liverpool Plains

In a field cleared for cotton growing in the Lake Goran catchment, in the centre of the of the Liverpool Plains, 2 clay mounds formed and began oozing water. The Goran Basin, of Quaternary age, has unconsolidated alluvial deposits of Jurassic and Tertiary basalts. At the site of the new mound-springs, the Garrawill Volcanics are overlain by recent clays in the Jurassic Oxley Basin. At the top of the basalt a weathered layer forms a confined aquifer.

The formation of the mound springs is believed to have been a result of the thinning of the confining clay layer over a high point of the underlying basalt that allowed the artesian pressure to push groundwater to the surface. The actual mounds, began to be visible in 1990, as a result of the swelling of the clays as they became saturated. The whole process appears to be an unintended consequence of removing the native deep-rooted vegetation for cropping, altering the hydrology of the entire region, which, together with increased recharge area, allowed the water table to rise. The mound springs emerged after a increasingly wet period in the 1980s, and wet year in 1990, during which Lake Goran flooded extensively. Evidence has been found that mound springs were present in the area during the Pleistocene. During the wet phase before the drying of the Pleistocene ice age there is evidence in the form of the distribution of stone tools and flakes that the Aboriginal People were concentrated in the area of mound springs.

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