# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/DeHZri8gCwd
- **Gondola URL:** https://gondola.cc/posts/71427944-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/9b90ad4d3a.jpg
- **Posted:** 2026-10-05T14:19:09.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Two sandstone blocks in the Tayma oasis of north-western Saudi Arabia, split down the middle by a fracture so straight it looks laser-cut. Al Naslaa is roughly 6 metres tall, balanced on two narrow pedestals, and has become one of the most photographed geological curiosities on Earth. No laser required. Just stress, time, and wind.

The leading explanation is jointing. Sedimentary rock accumulates internal stress as it is buried, compacted, uplifted, and unloaded. When that stress exceeds the tensile strength of the rock, it relieves itself along planar fractures called joints. These form perpendicular to the direction of least principal stress, which is why joints are often strikingly flat and run in parallel sets across entire landscapes.

What turned an ordinary joint into Al Naslaa:

- A pre-existing plane of weakness, likely a tectonic joint or a softer seam within the sandstone, fixed the fracture geometry
- Wind-driven sand acted as an abrasive, scouring the gap and polishing the opposing faces into near-parallel walls
- Differential weathering removed weaker rock near ground level, where saltating sand grains strike hardest, carving the narrow pedestals
- Thermal cycling in the desert, with large swings between day and night, fatigued grain boundaries and accelerated granular disintegration

Saltation matters here. Wind-borne sand rarely rises more than a metre or so above the surface, concentrating erosion at the base. This is the same mechanism behind mushroom rocks and yardangs across the Sahara and the Arabian Peninsula.

The faces also carry petroglyphs of horses, ibex, and human figures, carved thousands of years ago by people living in one of Arabia’s oldest continuously inhabited oases.

Geology does not need precision tools. It has deep time.

#stemantics #geology #earthscience #erosion #rockformations

## Stats

- **Views:** 6,289
- **Likes:** 50
- **Shares:** 0
- **Comments:** 4

## Tags

geology, erosion, stemantics, rockformations, earthscience

---
Copyright (c) Gondola