Alternative ventifacts

Iceland ventifact by Dr Tim Barrows on Sketchfab

Iceland isn’t the first place you would think has aeolian landforms. Aeolian landforms are those that are produced either by erosion or deposition by wind. The word derives from the name of the Greek god of wind, Aeolus. Erosive aeolian landforms are rare because there are few landscapes where water does not dominate erosive processes. The most common landscape where erosive landforms are preserved is a desert. The absence of water here preserves the landforms and severely restricts vegetation which increases sand supply for erosion and exposes bedrock.

In 2007 I visited the White Desert (El-Sahara el-Beyda) of Egypt. Part of the larger Sahara region, this desert receives no regular rainfall, with an annual average of just 2 mm, making it one of the driest places on Earth. With no vegetation to bind the surface or slow down surface winds, textbook examples of ventifacted surfaces have developed. The two examples below are developed on Late Cretaceous chalk. This fine-grained limestone was deposited in a warm sea about the same time the rocks of the white cliffs of Dover were formed.

Mushroom-shaped ventifacted outcrops, White Desert

Ventifacted chalk outcrops, White Desert

Earth is not the only planet with aeolian activity. This is one of the major geomorphic processes operating today on Mars. Without surface water, there is little erosion apart from slope processes taking place. Atmospheric pressure on Mars is only on average 0.6% of Earth’s, so it is somewhat surprisingly how much sediment gets blown around on the surface, sometimes into global-scale dust storms. Despite this, there are fields of yardangs (elongated erosional remnants of rock outcrops) and dunes. In a previous post I introduced the Mars Pathfinder mission. One of the rocks it photographed (Moe) has a striking resemblance to the ventifacted surface above, indicating similar processes operating on the Martian surface. The Spirit rover found an even better example, shown below. Despite the low atmospheric pressure, Mars has an advantage over Earth – time. Whereas the ventifacts shown above are thousands of years in the making, the ones on Mars are millions, if not hundreds of millions of years old.

Spirit Pancam composite color, Sol 584 (Laity and Bridges, 2009)

I found the ventifacted surface in the 3D model above in southeastern Iceland, a world away from hot dry Egypt. The ventifacted surfaces are developed on the landward side of  Ingólfshöfði. This is a small headland on the coast that is separated from the rest of Iceland by a sandur, or sand plain. Shallow sea water and shifting sands mean there is little vegetation around Ingólfshöfði, so the abundant sand supply and strong arctic winds can whip up considerable speed and the rock is literally sand blasted. The headland gains its name from Ingólfur Arnarson, who landed here in 874 CE. Together with his brother, they are recognised as the first permanent Norse settlers in Iceland.  They spent their first winter on the headland before going on to establish what became the capital at Reykjavík. After visiting the headland I suspect the winds played a significant role in moving camp.