Iron-oxide runoff turns Hormuz Island waters crimson after heavy rains

Hormuz Island, off Iran's southern coast in the Persian Gulf, briefly turned crimson this week as iron-oxide–rich red soil flowed into the sea after heavy rain. The event drew attention not only for its striking color but for the basic geochemical process behind it: a mineral-rich soil called golak interacts with rainfall, producing water that takes on a deep red hue near the coast. While the sight has circulated online with references to biblical “blood rain,” scientists say the phenomenon is a natural rock-and-water interaction rather than any omen. Hormuz, also known as Rainbow Island for its multicolored mineral soils, has long been noted for color changes in its waters during intense rain events.

Videos captured the moment: crimson runoff cascaded over cliffs, pooled on beaches, and washed into the Persian Gulf as the rainstorm intensified. The color was most visible along shorelines and in small streams feeding the sea, with observers noting that the hue persisted along stretches where iron oxide-rich soil washed into deeper water. In this region, the phenomenon is tied to the island’s geology as well as the meteorological conditions that drive heavy rainfall.

The red coloring traces to hematite, the iron oxide that dominates Hormuz Island’s mineral suite. The island’s soils, formed over millions of years from shale, clay and volcanic deposits, contain more than 70 minerals, with hematite coloring the runoff when rainwater mobilizes soil particles and carries them toward the sea. The effect is reinforced by how hematite particles scatter light: they absorb shorter wavelengths of green and blue light and reflect longer red wavelengths, giving the water a crimson tint when the particles mix with rain and seawater. This runoff-driven coloration is a well-documented local phenomenon that can appear during heavy rainstorms and after volcanic activity that enriches soils with iron oxides.

Although the event has prompted comparisons to biblical scenes in social media posts and headlines, experts emphasize that there is no prophetic significance to the color change. Some readers connected the moment to Revelation 16:12, which describes the Euphrates drying up to prepare for future events; other biblical passages are cited in discussions about ancient Persia, a region that occupies a long historical and religious footprint. Scholars caution against drawing direct prophetic inferences from natural phenomena. Hormuz Island is not mentioned in biblical texts, and modern scientific explanations focus on geochemistry and geology rather than eschatology.

Beyond the Hormuz episode, the region has seen other red-water occurrences linked to different natural processes. In August, the biblical Sea of Galilee turned a vivid red, which officials attributed to a bloom of green algae called Botryococcus braunii. The pigment produced under strong sunlight can tint the lake, but officials stressed that the algae are harmless and that tests by the Kinneret Research Laboratory found the water safe for swimming. This contrast underscores how varying ecosystems can produce striking shared visuals—iron oxide in one case, algal pigment in another—yet hinge on distinct biological or chemical mechanisms.

For Hormuz Island, the color change is a reminder of how a landscape’s mineral makeup can influence local hydrology. The island’s practical geography—coastal cliffs, mineral-rich soils and runoff channels—means that heavy rain can temporarily transform coastal waters. Local researchers and visitors describe the effect as a vivid, if ephemeral, indicator of the island’s unique geology rather than a danger to marine life or people. In the broader context of climate and environment, the Hormuz episode highlights how intense rainfall events can translate into rapid, visible shifts in landscape color when mineral and geological factors intersect with hydrological processes.

As rainfall patterns in many parts of the world become more extreme in some seasons, researchers say such color-changing events could become more noticeable where mineral-rich soils meet active coastlines. Scientists continue to study Hormuz’s soils to understand how frequently color-changing runoff occurs and how long red-tinged water remains visible after a rain event. In the meantime, visitors to Rainbow Island can expect a spectacular, albeit temporary, display of Iran’s geological diversity and the powerful ways water interacts with earth’s mineral content.