Strange Places on Earth | Alnaslaa Rock and Ausungate Mountains

Laser or erosion?

Deep in the Tayma Oasis in Saudi Arabia’s Tabuk province lies a 4,000-year-old rock formation with an unusual feature: It is split down the middle by a straight cut with the precision of a laser beam.

The Al Naslaa rock is made up of two sandstones supported by a naturally-formed pedestal with a perfect slit down the middle.

While the exact cause of the split has yet to be determined, windblown sand and periodic rain could have created the unusual shape.

Most likely the ground shifted slightly underneath one of the two supports and the rock split. Or, it could be an old pressure crack that has been pushed/pulled apart . Or, it could be an old fault line, since fault motion often creates a zone of weakened rock that erodes relatively easier than the surrounding rock.

However, that has not stopped a few social media users from speculating that the desert’s ancient inhabitants could have used laser beams to cut the rock in half.

Rainbow on Earth?

One of the most magnificent geologic features in the world is the Ausangate Mountain of the Peruvian Andes. The mountain is striped with colors ranging from turquoise to lavender to maroon and gold. However, this "painted mountain" is notoriously difficult to find and get to, requiring several days of hiking to reach its peak deep within the Andes by way of Cusco.

The painted Ausangate mountain is also considered to be holy and believed to be the deity of Cusco by local Peruvians. It is a site of daily worship and offerings by local citizens. Every year thousands of Quechua pilgrims visit the Ausangate Mountain for the Star Snow festival which takes place a week before the Corpus Christi feast.

The mountain sits at an elevation of 6,384 meters. The reason we see the rainbow coloration in the stratigraphic layers of the Ausangate mountain is largely due to weathering and mineralogy. Red color indicates iron oxide or rust as a trace mineral. Sediments that are iron rich will change when exposed to oxygen and water, like iron nail which gets rusted.

The different coloration is due to different environmental conditions and mineralogy when the sediment was originally deposited and subsequently diagenetically altered. Introduction of goethite or oxidized limonite will introduce a brownish coloration to sandstones. The bright yellow coloration could be due to iron sulphide as trace minerals within the pore cement. In addition, chlorite will often color sediments varying shades of green dependent on diagenetic history and concentration.