Uncovering the Geological Marvels of the Hormuz Formations

As the US-Israel war on Iran extends into its third week, all eyes are on the Strait of Hormuz, the critical chokepoint through which a fifth of the world’s energy supply passes. Iran’s effective closure of the narrow strait has disrupted these flows and driven up the price of oil. What has attracted less attention is the more alluring — and geologically more interesting — part of the Persian Gulf region: the anomalously colourful Hormuz formations and mountainous ranges. These surreal, painted formations, salt caves and ochre-stained shores have catalyzed a burgeoning geotourism industry. Here’s a deeper dive into how these geological marvels were formed, why they look so colourful, and what it tells us about the Earth’s past. While conventional mountain ranges are generally forged through the collision of tectonic plates, the mountains in the Hormuz range are, in fact, vast deposits of salts and minerals. So how did that happen? The process of their formation began roughly 500-600 million years ago, during the Late Precambrian to Early Cambrian period. During this time, shallow and mineral-rich seas repeatedly flooded the region. As these waters repeatedly evaporated, they left behind thick layers of salt over the course of millenia. Over time, these salt beds were buried under innumerable layers of marine sediment and volcanic rock. Their emergence into mountains was driven by three distinct geological mechanisms: Tectonic movement: The Arabian and Eurasian tectonic plates collided with each other, compressing the crust and creating deep structural fractures. These fractures acted as “elevators”, forcing the highly pressurised salt deposits towards the surface. Salt flows: As these low-viscosity, high-buoyancy salt deposits flowed towards the surface, they acquired a putty-like consistency. This process is called halokinesis in geology. Eventually, these punched through the crust to form massive domes as well as mountainous islands — such as the island of Hormuz. Chemical weathering: The ascension of these salt pillars also dredged up a mixture of volcanic rock, clay and metal-rich minerals. The continuous exposure of this cocktail of materials to surface water, oxygen and unblocked sunlight catalyzed the process of chemical weathering. This is what gives these formations their kaleidoscopic colours. The iron oxide rusted into a deep shade of hematite red (the same material on the surface of Mars), the limonite (a mixture of hydrated iron and goethite) yellowed and copper compounds turned a striking green due to intensive oxidation, forming a striking contrast against the white of the unreactive halite deposits. This multi-coloured interaction is what we know today as the mountains of Hormuz. The rainbow colours Depicted in the picture attached, the resulting landscapes observed in the Hormuz formation comprise a concentration of over seventy distinct minerals, each of which boasts its own hue. This, in turn has birthed a terrain which differs from all other mountainous ranges in the world and serves as a laboratory for studying salt flow and deep-crustal processes usually hidden kilometres below ground. The evaporitic phenomenon observed in the Persian Gulf region is not an isolated event. The structures of the Hormuz formation are part of a much larger paleogeographic (study of earth’s surface in the past) system. Regions where evaporite deposition and halokinesis occur simultaneously result in what are known as coeval salt basins. These basins extend eastward across tectonic boundaries, continuing through the heavily mined Salt Range in Pakistan and reaching deep into the subsurface geology of northwestern India. Today, the Hormuz formation stands as a masterpiece of planetary chemistry and geological evolution. But the continuing tensions in the Strait of Hormuz threatens both the formation’s geotourism economy and obscures their scientific heritage.