Discover Egypt and Explore the Fossils and Geodiversity of the Blue Hole of Dahab on the Red Sea
- Wayne Munday
- Jul 1
- 4 min read
Updated: Sep 11
Sip back and discover Egypt and explore the fossils and geodiversity of the Blue Hole an ecotourism hotspot and striking circular karst doline or limestone sinkhole situated just a few kilometers north of the Bedouin village of Dahab on Egypt’s southeastern Sinai Peninsula on the Red Sea. Not only is this location geologically captivating as a collapsed cave system its deep cerulean waters are among the most perilous and iconic diving and freediving locations in the world. The surrounding the Eocene limestones are filled with fossils of corals, foraminifera especially Nummulites, molluscs and vertebrates. Today a thriving fringing coral reef crowns the Blue Hole as a haven for marine life.
The Sinai Peninsula is a geologically significant subplate nestled between the African and Arabian tectonic plates and is one of the world’s most active rift systems. This tectonic intersection plays a vital role in determining the region’s geodiversity and especially through the Dead Sea Transform Fault that has given rise to key geological features such as the Gulf of Aqaba. Tectonic movement has created several pull-apart basins including the Red Sea and Gulf of Suez. The Sinai Peninsula is a landscape forged by the powerful forces of tectonic rifting and crustal deformation.
Blue hole's or large, deep, circular marine sinkholes or karst doline's are not uncommon around the world and typically form on shallow carbonate platforms. Some include the Great Blue Hole in Belize, Dean’s Blue Hole in the Bahamas and the Dragon Hole in the South China Sea. The deepest known blue hole is the Taam Ja’ Blue Hole in Chetumal Bay off the coast of Mexico exceeding 420 meters in depth and thought to be the deepest blue hole in the world.
Blue Holes are similar but different to "cenotes" or natural sinkholes formed by the collapse of limestone bedrock revealing underground freshwater pools such as those found on Mexico’s Yucatán Peninsula as well as in Australia, Bahamas, Belize, Dominican Republic, Greece and Jamaica.
The geology of Sinai is as diverse as it is complex. In the north and central regions extensive limestone formations dominate the terrain. These sedimentary rocks including the notable Cenomanian Stage shallow water Halal Formation of the Upper Cretaceous.
The central portion of the peninsula is home to the Al-Tih Plateau a prominent feature composed primarily of Mesozoic to Tertiary sedimentary rocks from the Malha and Qiseib Formations that reflect a transition from fluvial or river to shallow marine environments. The plateau’s geology hosts a range of mineral resources, including limestone, kaolin, and manganese which have long been of industrial and commercial interest.
The Late Cretaceous to Eocene period sedimentary rock of nummulitic limestone and dolostone that make the Blue Hole was originally a natural cave system until its collapse after the last ice age forming a deep and circular chasm now linked to the Red Sea by a submerged tunnel called “The Arch”.
This formation likely began during the Pleistocene epoch when global sea levels were significantly lower due to glaciation. During this time, the area was above sea level, and rainwater infiltrated the limestone, expanding existing fractures and enlarging subterranean caverns.
As the Last Glacial Maximum roughly 20,000 years ago ended coastal cave systems began to flood. Eventually, the roof of the cavern collapsed under its own weight or due to seismic activity creating a vertical shaft we now call the Blue Hole. The rock tells a story of sea-level fluctuations from broader global climatic and oceanographic changes.
Within the local fossil record is found the Nummulites Gizehensis Group comprising closely related species within the Nummulites genus a large, disk-shaped foraminifera found in Eocene-aged rocks especially in Egypt. Named after Nummulites gizehensis these organisms thrived in warm and shallow marine environments.
Coral fossils including both solitary and colonial forms are also prominent and still remain today such as the small polyp stony coral Porites and arborescent (branching) species of Acropora. Very occasionally the remains of marine vertebrates such as fish and primitive cetaceans or whales called Archaeoceti ("ancient whales") are discovered in deeper inland rocks reflecting a long history of marine transgressions and regressions in the region.
The Blue Hole in Dahab plunges to a depth of around 130 meters and features a shallow seaward entrance called "the saddle" located just 6 meters below the surface. One of the Blue Hole's most distinctive features is "the arch" a 26-meter-long underwater tunnel that links the Blue Hole to the open Red Sea where the seafloor plummets to depths of up to 1,200 meters.
Celebrated for its rich marine life the Blue Hole is home to many colorful corals, tropical fish, and the occasional shark that inhabit its cave systems. This natural wonder makes it a sought-after location for divers from around the world though strong currents and over ambition have contributed to its reputation as one of the most dangerous dive sites globally.
