The Dead Sea, Jordan

I wonder just how many times has the Treasury building at Petra in Jordan featured in Hollywood movies.  Certainly the sight of if appearing as glimpses of rock hewn burnt sandstone from the dark shades of the cooling canyon walls is evocative of a lost past and secrets hidden in the desert.  To get the chance to survey in Jordan was therefore not something I was going to say no to.  Back when I was surveying in Sudan for the director of ACOR (American Center of Research in Jordan), Pearce Paul Creasman asked if I could suggest geophysical methods that might help out with a project he had going at the Dead Sea and what might help to survey sites at Petra.  From his descriptions of both sites and the targets, buried wall features in both, then a combination of electromagnetic, magnetic and GPR were likely candidates.

The first trip was scheduled to investigate the Dead Sea site and to make a recognisance at Petra. The site at Callirrhoe on the Dead Sea has a history of occupation from at least early Roman through Byzantine to periodic Bedouin use in more recent times. 

During Roman occupation it was used as a harbour serving a small village that nestles in the steep hillside to the east.  The village is supplied by a series of fresh water springs outflowing from palaeo-shorelines that extend up the hillside in a series of steps for at least 300m higher than the village.  The port site is now located at -400m elevation, that is approximately 50m above the present level of the Dead Sea.  Previous investigations suggest that the Dead Sea could almost have completely dried out during the last interglacial and with palaeo-shorelines extending some hundreds of meters above present levels then this makes our sea level records up in Scotland look positively pedestrian!

Geophysics

The geophysical investigation objectives included mapping the site for buried wall structures, defining the boundaries of the site and in particular the habour front and mapping spring sites associated with the site.  Previous investigations had uncovered parts of the inshore buildings at the site and shown that these were covered by different types of sediment accumulation.  In the field I was once again joined by my brother, Prof Martin Bates who was to investigate the sedimentation history of the site with respect to the periods of occupation and use and sealevel heights.  The investigation was conducted in conjunction with the Jordanian Department of Antiquities and run as a training program for their staff in geophysics and geo-archaeology.

Ground Conductivity from CMD Explorer, (1mS/m - 2000mS/m)

The main geophysical investigation tool was the CMD explorer.  The results from this are shown below draped on the topographic landscape.  We mapped from the site down the steep slope to the shore of the Dead Sea.  Ground conductivity showed a large variation in values with a rapid increase in conductivity close to the shoreline.  Across the site conductivity varied between 6-20mS/m with consistency in patterns between all three coil separations/penetration depths.  The magnetic susceptibility showed similar trends to the conductivity with variations in value indicating linear anomalies interpreted as the buried and extant wall structures. The geo-archaeological investigations showed a complex history of flooding and water retreat across the site that matched to historical records of sealevel change during the early Roman era.   

Sealevel projected to -400m at approximate height during early Roman occupation

A projection of the ancient sealevel is shown below with a close correlation to the outline of the harbour front as mapped by the geophysics.

The visit to Petra showed the difficulty that it would be in running geophysics in the narrow canyon and expecting any kind of satellite-based positioning. The arid conditions also suggested that the use of GPR might be possible with penetration to significant depths with 250-500MHtz antenna.  A proposal was made to visit the site and run test surveys early in 2024.  We did return and I will write on this later.