The Coloured Earths of Chamarel: A Geological Wonder

Mauritius, an island known for its stunning landscapes and rich geological history, is home to one of nature’s most visually striking phenomena—the Coloured Earths of Chamarel. This natural wonder consists of rolling sand dunes with distinct bands of red, brown, violet, blue, green, and yellow soil, forming a breathtaking mosaic of colors.

Unlike typical geological formations where colors blend together, the hues in Chamarel remain distinct and unmixed despite natural forces such as rain and wind. This peculiarity, combined with the region’s volcanic origins, has intrigued geologists for decades. What forces shaped this colorful terrain? How do the minerals interact to produce such a striking effect? To answer these questions, we must examine the geological processes that have sculpted this remarkable landscape over millions of years.

Origins: A Landscape Forged by Fire and Time

The story of Chamarel’s Coloured Earths begins millions of years ago during a period of intense volcanic activity. Mauritius, like many islands in the Indian Ocean, was formed by hotspot volcanism, where magma from deep within the Earth’s mantle erupted through the ocean floor, eventually building up layers of solidified lava that became the island.

The Chamarel region specifically sits on basaltic lava flows that date back approximately 3 to 7 million years. These lava flows were rich in ferromagnesian minerals, which include iron and magnesium-rich compounds. Over time, these volcanic rocks underwent chemical weathering, breaking down into different types of clay minerals.

The key to Chamarel’s vibrant colors lies in the transformation of volcanic rock into lateritic soil—a type of soil rich in iron and aluminum oxides due to prolonged exposure to tropical weather conditions. But what exactly causes the different colors?

Geochemistry: Why Does the Soil Display So Many Colors?

The soil at Chamarel gets its colors from the different oxidation states of iron and aluminum oxides, two of the most abundant mineral components in the region.

Iron Oxides and Their Role in Red, Brown, and Yellow Colors

When iron-rich minerals in basaltic lava interact with oxygen and moisture, they undergo oxidation, forming different types of iron oxides.
The oxidation process is similar to how iron rusts when exposed to water and air.
Hematite (Fe₂O₃) produces shades of red and brown.
Goethite (FeO(OH)) is responsible for yellow and ochre tones.

Aluminum and the Formation of Blue and Violet Shades

In regions where iron has been leached out due to prolonged weathering, aluminum-rich minerals such as gibbsite (Al(OH)₃) dominate.
These minerals reflect light differently, leading to blue and violet hues in certain areas.

Silica and Clay Minerals: The Subtle Tints of Green and Grey
In areas with a higher silicon-to-iron ratio, the presence of silicate minerals and clay contributes to the formation of subtle green, grey, and even bluish shades.

Why Don’t the Colors Mix?

A fascinating aspect of the Coloured Earths is that the colors remain separated in distinct layers, rather than blending together over time. This phenomenon can be explained by two main factors:

Differential Settling of Particles

The particles that make up the different colors have varying densities, meaning that heavier iron-rich particles settle differently from lighter aluminum-rich ones.

Hydrophobic Nature of the Soil

Another surprising characteristic of the soil is its hydrophobic properties—it does not retain much moisture.
The low water retention prevents the different minerals from dissolving and mixing together, maintaining the distinct layers even after heavy rains.

This is why the colors persist year after year, despite exposure to natural elements.

Climate and Erosion: The Shaping of the Dunes

The Coloured Earths of Chamarel are not just a product of geochemistry—they are also shaped by climate-driven erosion.

Heavy Rainfall and Leaching

Mauritius experiences a tropical climate with heavy rainfall, which accelerates the leaching process. Over thousands of years, rainwater washed away silica and other soluble minerals, leaving behind iron and aluminum oxides that contribute to the coloration of the soil.

Wind Erosion and Dune Formation

The wind plays a crucial role in sculpting the rolling dunes that characterize Chamarel’s landscape. Over time, wind and gravity have caused fine particles to shift and settle, further accentuating the color patterns.

Interestingly, despite the shifting nature of the dunes, the color patterns remain intact due to the soil’s unique mineral properties.

Comparisons to Other Multi-Colored Geological Formations

While Chamarel’s Coloured Earths are unique in Mauritius, similar multi-colored landscapes exist around the world. Comparing them can provide valuable geological insights.

Danxia Landforms (China)

The Danxia landforms in China showcase red, orange, and yellow sedimentary rock layers shaped by millions of years of tectonic activity and erosion.
Unlike Chamarel, which is volcanic in origin, Danxia landscapes result from sandstone deposition and weathering.

Rainbow Mountain (Peru)

The Vinicunca (Rainbow Mountain) in Peru gets its vibrant colors from sedimentary rock layers rich in iron oxide, sulfur, and copper.
The hues are due to tectonic uplift and glacial erosion, exposing layers of mineral-rich rock.

Painted Desert (USA)

Located in Arizona, the Painted Desert features multicolored layers of sedimentary rock rich in iron and manganese oxides, similar to Chamarel’s soil composition.
However, its colors are due to river deposition and erosion over millions of years, not volcanic activity.

How Does Chamarel Compare?

Unlike the above formations, Chamarel’s colors come primarily from chemical weathering of volcanic basalt, making it a unique case of lateritic soil formation in a tropical environment.

The Role of Microorganisms in Soil Development

Recent research suggests that microbial activity may also play a role in the chemical composition of Chamarel’s soil. Microorganisms such as bacteria and fungi are known to influence the oxidation of iron and aluminum minerals in soils worldwide.

Iron-Oxidizing Bacteria
Certain bacteria can accelerate the oxidation of iron, influencing the formation of red and brown hues.

Fungal Activity in Lateritic Soils
Some fungi interact with mineral surfaces, facilitating the breakdown of basaltic rock into clay-rich soil.

Although the impact of microbial processes on Chamarel’s soil has not been widely studied, it presents a potential area of research to understand the full spectrum of factors contributing to the colors.