Iran's Hormuz coast turns blood-red overnight. Here's the science behind it

Located in the Persian Gulf near the Strait of Hormuz, this small island is already famous for its dramatic landscape and kaleidoscopic geology.

In Short

• Local residents and tourists frequently document this natural event
• Environmental experts, however, note that it is harmless to humans
• Hormuz Island sits atop layers of ancient salt domes and volcanic deposit

The shores of Iran’s Hormuz Island have once again stunned the world with an otherworldly transformation.

Following recent heavy rainfall, the island’s beaches and coastal waters have taken on a striking blood-red hue, a natural yet eerie spectacle that appears almost extraterrestrial.

Located in the Persian Gulf near the Strait of Hormuz, this small island is already famous for its dramatic landscape and kaleidoscopic geology. But when rainwater flows through Hormuz’s iron-rich hills and soil, the results are nothing short of mesmerising.

Scientists say the phenomenon is caused by the high concentration of iron oxide, particularly hematite, embedded in the island’s rocks. As rain dissolves and mobilises these minerals, the runoff stains the sand and shallow seawater shades of crimson and rust.

Hematite, a naturally occurring mineral form of iron oxide (FeO), is also responsible for the reddish colours seen on Mars, which explains why Hormuz is sometimes dubbed “the rainbow island of the Persian Gulf.” When exposed to moisture, hematite-rich soils oxidise more rapidly, intensifying their colour.

During and after rainfall, these fine mineral particles are carried down to the coast through erosion channels and surface runoff, transforming the beaches into a vast red palette.

Local residents and tourists frequently document this natural event, which has become both a scientific curiosity and a draw for photographers and geologists. Environmental experts, however, note that while harmless to humans, sustained erosion of surface sediments could gradually alter the island’s topography. The red colouration is entirely natural and temporary.

Hormuz Island sits atop layers of ancient salt domes and volcanic deposits, a geological mosaic rich in minerals such as ochre, gypsum, and iron ore. Its iron oxide deposits have long been mined by locals for use in traditional pigments, giving the island both economic and cultural importance.

Though fleeting, the blood-red glow of Hormuz shows how geology, climate, and chemistry can converge to paint nature in extraordinary hues, turning a post-storm landscape into a living canvas of planetary science.

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