January 23, 2023

Professor of Earth and Environmental Sciences Uses the Tools of His Trade at Moroccan Ruins

As a geophysicist, Ahmed Lachhab never imagined he would be applying the same tools he uses to study lakes in Pennsylvania to help archeologists in Morocco.

Yet in an article published in the academic journal Archeological Prospection, Lachhab, associate professor of earth and environmental sciences at Susquehanna University, lays out how he used ground-penetrating radar to help archeologists preserve ancient Roman mosaics at Volubilis, a UNESCO World Heritage Site in northwestern Morocco.

“Volubilis is an ancient Roman city that dates to about the third century B.C.,” Lachhab explained. “It was a prosperous city marked by attractive villas with large mosaic floors that illustrate ancient Roman mythology.”

Lachhab first encountered Volubilis in 2018 when he began taking students there through Susquehanna University’s Global Opportunities study-abroad program. During the GO Morocco experience, Students engaged in a daylong workshop where they explore Volubilis, its history and learn how to restore sections of the damaged Roman mosaics.

The Romans built the mosaics in a prescribed way, layering mortar atop a foundation of soil and boulders. Over the ensuing years, the foundations of the mosaics have shifted, leading to the mosaics becoming unleveled, fractured and separated from their surrounding walls.

“When the site first underwent restoration between 1940 and 1950, archaeologists lifted the mosaic and re-laid it over rebar-enforced concrete slabs,” Lachhab said. “This is a very labor-intensive process that is nearing the end of its lifespan, meaning the mosaics are again in need of restoration.”

Instead, Lachhab proposed using the tools of his trade – laser level survey, drone photogrammetry and ground-penetrating radar — at Volubilis’ House of Venus and the House of Dionysos. As a geophysicist, Lachhab normally uses these techniques to determine the volume of water and sediment deposits in lakes and man-made reservoirs. At Volubilis, he surveyed three mosaics: Dionysos and the Four Seasons, Diana’s Bath and Bacchus and the Four Seasons.

He first used a self-leveling laser to survey the surface of the mosaic, noting where the rippling and sinking is. He then used a drone to take a series of detailed photographs of these mosaics and created 3D photogrammetry models and orthomosaics maps (a series of photos pieced together to create a larger detailed images) to inspect surface features and accurately measure their spatial dimensions. Finally, Lachhab surveyed the mosaics using ground-penetrating radar to collect 2D profiles and create 3D diagrams of the mosaic layer down to 50 cm depth. ​

“The integration of the three techniques was proven to be necessary to assess the actual state of these mosaics,” Lachhab said. “Most importantly, the GPR shows the presence of void spaces — places where the land has settled — sometimes on both sides of the concrete slab, as well as the presence of fissures that are both restricted internally beneath the mosaic and/or crossing the entire mosaic layer all the way to the surface.”​

Lachhab’s Methods of Interest to Other Archeologists 

Diana's Bath, an ancient Roman mosaic at Volubilis Diana's Bath, an ancient Roman mosaic at VolubilisNow, instead of lifting the entire mosaic, the archaeologists used Lachhab’s maps to locate any areas of void beneath the mosaic and fill only that space with binding material, using a syringe inserted into the mosaic.

“It’s a much more noninvasive method when beginning the restoration process on these ancient works of art,” Lachhab explained.

Lachhab presented his findings at a recent meeting of the International Committee for the Conservation of Mosaics in Bulgaria. Likely the only geophysicist in the room, he was approached by other archaeologists eager to have him survey their sites elsewhere in Bulgaria and Greece.

“This is a breakthrough in the field of archaeology,” Lachhab said. “It gives a good feeling to be preserving these precious mosaics that have been there for over 2,000 years. I’m enjoying this learning process as well, and it is Susquehanna’s GO program that brought this about.”