Petra, Jordan - The Lost City of Stone, one of the wonders of world

Introduction

Petra was founded in the 4th century BC by the Nabataean Arabs and was known in Arabic as Sila'a, Ar Rakeem, or biblically as 'Rqm,' all of which imply 'carved in the rock.' The Romans captured the site in AD 106, and it was dubbed Petra in Greek, or Al Betra in Arabic, both of which mean "carved in the rock." Several earthquakes are thought to have wreaked havoc on Petra, leading to its total ruin and eventual exodus in the 6th century AD.

Figure 1 The Kasneh (Treasury) shining in the sun at the end of the long dark canyon known as the Siq – surely one of the most impressive and iconic sights in the world. Source: Anne Whaley Sousou.

Locality

Petra is situated in the middle of southern Jordan's rugged desert, halfway between the Red Sea and the Dead Sea, but it was also next to an ancient highway leading eastwards from the high plateau to Wadi Araba. The site is also accessible from Ma'an, which is located to the east. Abu Mousa is the name of the settlement that surrounds Petra, as well as the valley (wadi) that leads to Petra.

Figure 2 Simplified map of Petra showing different types of localities.

Topography

Topographically the area is a harsh mountainous territory with an altitude of 1443 meters above sea level at Wadi Musa town, descending to 1100 meters at the Visitor's Center, 1000 meters at the Siq's entrance, and around 900 meters near Qasr al-Bint in the western reaches of ancient Petra with many numbers of gorges.

Figure 3 Google Earth map showing type locality of  Petra, along with Wadi-e-Musa to right.

Stratigraphy

Petra is made up of two geological sandstone formations: the Umm Ishrin formation, which accounts for the majority of the monuments, and the Disi formation, which accounts for a smaller percentage of the structures. The formation is 300-350 meters thick and comes from the Late Cambrian Period (500 million years old).

Figure 4 Simplified stratigraphy of Petra.

Geology of Petra

The Precambrian igneous rocks of the Aqaba Granite Complex make up the highlands to the south of Petra, which is broken through by a succession of intrusive dikes. The huge quartzose sandstones of the Middle Cambrian to Lower Ordovician age that makeup Petra's rocks and monuments are unconformably overlain. The rock's qualities may have influenced the Nabataeans' decision to build their city here, as it was clearly suitable for rock carving and digging, as well as appealing to the eye. However, most of them worked and excavated stone is showing symptoms of degradation after 2,000 years, not least due to the footprints of numerous tourists. The gorges were produced thousands of years ago when the force of desert flash floods exploited lines of weakness in the rocks such as faults, joints, and fractures, a process that is still ongoing today.

Figure 5 Simplified geological map of Jordan (modified after NRA, 2006, in Naylor et al., 2013).

Figure 6 Simplified geological map of Petra at 1:5.000 scale, Jordan National Resources Authority (1991), (from Heinrichs, 2008, modified).