607 
Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 
Spring mound and aioun mapping from Landsat TM imagery 
in south-central Tunisia 
Arwyn Rhys Jones & Andrew Millington 
University of Reading, UK 
ABSTRACT: Groundwater upwellings on two playas in south-central Tunisia form rare geomorphological features 
known as spring mounds and aioun. They form clusters in certain playa facies. Lineament analysis of Landsat 
TM imagery of the playas was carried out on single bands, FCC's and convolved imagery, Lineament directions 
indicated strong underlying hydrogeological controls on these features related to Alpine folding and associated 
faulting and jointing. 
RESUME: Eaux de la terre montant lentement sur deux playas en Tunisie sud-centrale forme les phenomenes 
geomorpholgiques connus sous le nom de monticules aux sources et aioun. Ils forment des amas sur certines 
parties du playas. Traitement d'image lineament sur l'image de Landsat TM était entrepris utilisant les 
FCC's et les filtres directionals. Les directions des lineaments indiquaient la forte maitrise hydrogeologique 
sur les monticules aux sources et aioun ayant rapport a des plissment alpin associe a des faillies et des 
joints. 
1. INTRODUCTION 
Spring mounds and aioun are both geomorphological 
expressions of groundwater upwelling found on playas. 
Spring mounds are formed when deep groundwater 
escapes to the playa surface as a spring and there is 
either chemical deposition of groundwater salts or 
aeolian and lacustrine deposition of playa surface 
debris. The height of the mounds depends on the 
piezometric and discharge properties of the ground- 
water (Reeves, 1968). In Tunisia they commonly range 
from 10 to 15 m and cover areas of up to 7.5 Km2, 
although more commonly the maximum is about 2.5 Km . 
Figure 1. A spring mound found on the Chott el 
Fedjadj Tunisia, note its vegetated centre clearly 
visible on TM imagery 
They have been recorded in Australian, North American 
(Mabbutt, 1977) and North African (Cooke and Warren 
1973) playas. An ain (pi. aioun) may be a related 
feature, but their origins are far from clear. It 
Is thought that they may be related to solution 
subsidence in areas of rising groundwater (Cooke and 
Warren, 1973); however whether this is due to shallow 
or deep groundwater movements is unclear. If they 
are deep groundwater features they are undoubtedly 
related to spring mounds but if they are shallow 
groundwater features the factors controlling their 
distribution should be entirely different. Coque 
(1962) describes typical aioun on the Chott el Djerid 
as being about 4m deep and 5m in diameter. Over the 
last three years the same aioun have, however, shown 
very little surface relief (only up to about 10cm) ,• 
this may be due to infilling of the collapse 
structures with aeolian or lacustrine sediments. 
Their most striking features are the occurrence of 
concentric circular patterns of salts on playa 
surfaces. They have been recorded in North African 
and Iranian playas (Cooke and Warren, 1973; Coque, 
1962). 
Spring mounds and aioun occur in clusters which we 
have termed spring mound and aioun fields 
respectively. The former are more common in south- 
central Tunisia. Two major spring mound fields are 
found - the largest is on the Chott el Djerid to the 
south of the Djebel Tebaga and a second, smaller 
field is found in the south-west Chott el Fedjadj. 
One large aioun field is also found in the north 
east of the Chott el Djerid. These latter two fields 
are examined in this paper in more detail. 
2. HYDROGEOLOGY OF SOUTH-CENTRAL TUNISIA 
South of the North African Atlas Mountains, at the 
junction of the Saharan Platform and the folded 
Atlas Block are a series of playas occupying a zone 
of subsidence. Known locally as chotts they stretch 
from the Sebkhet el Hamma (about 20km west of Gabes 
in southern Tunisia) to Chott el Melhrir (in central 
Algeria) occupying a zone of subsidence. The 
largest of these playas is the Chott el Djerid which 
has an elongated north eastern arm in the core of an 
eroded anticline, known as the Chott el Fedjadj. 
The hydrological regimes of both chotts are 
dominated by groundwater seepage from the south in 
a surface quifer - the Continentale Terminate - and 
a deeper aquifer - the Continentale Intercalaire. 
In addition there is groundwater seepage from 
alluvial fans flanking the mountain ranges to the 
north of the chotts in the winter wet season. 
Although annually evaporation exceeds precipitation, 
for most of the year there is winter surface runoff