Assessment and Evolution of Surface-Subsurface Landform Connectivity of Jabal Al Qarah in Saudi Arabia: A Potential World-Class Geomorphological Heritage

The Earth's surface is rarely a static picture; it is a constantly changing canvas where wind, water, and time carve deep stories into the rock. Geologists study these stories to understand how landscapes evolve, but they often focus on two separate chapters: the world above ground and the world below it. Above, rivers cut valleys and wind scours cliffs. Below, water dissolves rock to form caves, or seeps through cracks to hollow out underground chambers. Usually, these two realms are studied in isolation. However, in some places, the surface and the underground are intimately connected, with the same forces shaping both the skyline and the hidden tunnels beneath it. Understanding this connection is crucial because it reveals the full history of a landscape, showing how a single geological event can ripple from the bedrock deep underground all the way to the peaks visible on the horizon. When these landscapes are unique and well-preserved, they become valuable records of Earth's history, offering lessons on climate change, rock behavior, and the slow, powerful work of erosion.

In the eastern province of Saudi Arabia, a place known as Jabal Al Qarah stands as a rare and striking example of this surface-subsurface connection. This hill is a mesa, a flat-topped mountain with steep sides that has been left standing after the surrounding land was worn away. What makes Jabal Al Qarah special is not just its shape, but the intricate network of features that link its top to its depths. A new study has mapped these features in detail, revealing a landscape where the ground above and the caves below are part of a single, continuous system. The researchers found that the hill is not just a solid block of stone, but a fractured puzzle where vertical cracks and faults guide water and wind to carve out a complex world of slots, pillars, and rectangular tunnels. This work highlights the site as a potential world-class treasure for geology, offering a clear view of how a mesa forms and how its internal structure dictates the shape of the land around it.

The story of Jabal Al Qarah begins millions of years ago, when the area was covered by a shallow sea. Over time, layers of sand, mud, and limestone settled on the ocean floor, creating a thick stack of sedimentary rock. Later, as the sea retreated and the land rose, this stack was lifted and tilted. The rock layers were not uniform; some were hard and resistant, while others were soft and easily worn down. As the surrounding landscape eroded, the harder rock of Jabal Al Qarah remained, detaching from a larger plateau to become an isolated hill. The surface of this hill is capped with a hard, cement-like layer called caliche, which acts as a protective roof. Beneath this roof, however, lie softer layers of mudstone and sandstone that are much more vulnerable to the elements.

The researchers walked the site to document every feature, from the broad shape of the hill to the smallest cracks in the rock. They found that the surface is a maze of deep, narrow grooves known as slots. These slots are not random; they follow a grid-like pattern of cracks and faults in the rock, creating a rectangular network that mirrors the underground structure. Water seeps into these cracks, and over time, it widens them, carving deep vertical incisions into the hillside. As the soft rock between the cracks washes away, it leaves behind tall, thin pillars of stone. Some of these pillars are topped with the hard caliche layer, which protects them from eroding as quickly as the rock below, giving them a mushroom-like shape. These formations, often called hoodoos, stand as silent sentinels at the edge of the mesa, marking the boundary between the solid rock and the eroded landscape.

Beneath the surface, the story continues in a series of caves and tunnels that are directly linked to the features above. The same grid of cracks that guides the water on the surface also guides it underground. As water flows through these fractures, it dissolves the softer rock, expanding the cracks into a network of rectangular tunnels. The study identified about twenty-eight of these linear tunnels, stretching for roughly 1.5 kilometers in total within a rectangular area. The shape of these caves is distinct; they are not the winding, organic tunnels often found in limestone caves formed by chemical dissolution. Instead, they are straight and angular, following the straight lines of the rock faults. One of the most famous caves, known as Ghar An Nashab I, serves as a gallery where visitors can walk through these geometric passages. Inside, the walls show alternating layers of red and grey rock, and in some places, the texture of the rock reveals the ancient roots of mangrove plants, a clue that this area was once a coastal environment.

The researchers also examined how the landscape is changing today. They noted that while the core features of the mesa remain intact, the edges are under threat. The soft rock at the base of the hill is constantly being worn away by weather, causing large slabs of rock to detach and fall. This process, known as mass wasting, fills the slots and canyons with boulders and creates new debris fields at the foot of the hill. While this is a natural part of the landscape's evolution, human activity is accelerating the damage. The hill is surrounded by a growing city and date farms, and new buildings are encroaching on the site. In some areas, construction has blocked the view of the landforms, and in others, it has damaged the fragile hoodoo rocks. The study points out that without a clear plan to protect the site, these unique features could be lost to urban development.

Despite these threats, the site holds immense value for science, culture, and tourism. The caves have been used by humans for centuries, serving as shelters and pathways, and they are now part of a UNESCO Cultural Heritage site. The cool, stable environment of the tunnels provides a home for bats and other wildlife, making the site ecologically important as well. For visitors, the landscape offers a dramatic display of geological processes, where one can see the direct link between the cracks on the surface and the tunnels below. The study suggests that with better management, such as guided tours that explain the geology and the protection of the fragile edges, the site could become a world-class destination for geotourism. This would not only help people understand the Earth's history but also support the local economy through sustainable tourism.

The findings of this research underscore the importance of Jabal Al Qarah as a global reference point for understanding how surface and subsurface landscapes are connected. It is a place where the history of the Earth is written in stone, from the ancient sea layers to the modern cracks and caves. The study concludes that this site is a rare example of a mesa that has evolved through a specific set of processes involving faulting, weathering, and erosion, creating a unique and complex landscape. By recognizing its value and taking steps to protect it, we can ensure that this natural wonder remains a source of knowledge and inspiration for future generations. The work done here does not just describe a hill; it tells the story of a dynamic Earth, where the forces that shape the ground beneath our feet are the same ones that sculpt the world above.