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The Effects of Weathering on the Basaltic Mountains

Basaltic mountains are outcroppings of ancient lava rock, called basalt. Basalt is the most common bedrock mineral on Earth, however, it is rare on islands and continents. Its location on land is in areas that used to be underwater. The basalt outcroppings are from ancient lava flows that were subsequently covered by younger, softer rock. As the surrounding soft rock eroded or weathered, the hard basalt outcroppings are exposed. Once exposed, the basalt will begin to weather as well.

Effects of Fungal Weathering
- One of the first stages of weathering on basaltic rocks is its colonization by fungus. Varieties of fungus will begin to live and grow on the surface of the rock. Through their various chemical processes, they will eventually wear cracks and crevices in the surface of the rock.
Effects of Water Weathering
- The cracks and crevices created by the fungus will eventually fill up with rain water. As rain water flows in and out of the cracks, the erosion process is continued. Running water is a powerful erosion force that will continue to weather larger and larger crevices on the surface of the basalt. Basalt will eventually begin to be defined by thick ridges formed from continuous water erosion from both rain water and melting ice and snow.
Effects of Temperature Weathering
- In winter, freezing temperatures will freeze any water trapped in the cracks and crevices of the basaltic rock. As freezing water expands, it forces the crack to expand. This will cause the fractures in the basalt to widen. In summer, warmer weather will melt ice and snow, causing the water to run off. Year after year, as this process continues, the basalt outcroppings become more and more weathered.
Color Change
- Basalt is a dark black rock with very small, fine crystals embedded in its matrix. However, once basalt is continuously exposed to the effects of weathering, it will change to a yellow brown color. Some basalt may also turn gray to purple when exposed to the effects of sunlight and air.

Rocks & Minerals