Weathering is the natural process through which rocks, soils, and minerals break down at or near the Earth’s surface. This breakdown can occur through physical, chemical, or biological means. Biological weathering involves the actions of living organisms. Small mammals play a significant role in altering landscapes and contributing to both the physical and chemical breakdown of Earth’s materials.
Physical Weathering from Direct Actions
Small mammals directly contribute to physical weathering through burrowing and digging. Animals like moles, gophers, prairie dogs, and marmots excavate tunnels and chambers for shelter, foraging, and raising young. As they dig, their claws and teeth exert mechanical force on soil particles and rock fragments, loosening and displacing them. Prairie dogs, for instance, create extensive burrow systems that can be several meters long and a few meters deep, with entrance holes 10-30 cm in diameter. This tunneling exposes underlying rocks and soil to the surface, making them more susceptible to further weathering by wind and water.
The volume of material moved by these animals can be substantial; studies have estimated that prairie dogs and badgers can excavate tens of tons of soil per acre. This constant disturbance breaks down larger aggregates of soil and rock into smaller pieces, increasing their surface area. Gophers, with their large, visible front teeth, can effectively loosen dirt, rocks, and roots. Even smaller rodents like mice and voles create extensive burrow systems just a few centimeters below ground, fragmenting soil and minor rock structures.
Indirect Contributions to Weathering
Small mammal activities indirectly accelerate other weathering processes by modifying the environment. The burrows and tunnels they create act as conduits, increasing the penetration of water and air into the subsurface. When water seeps deeper into the ground through these pathways, it can lead to enhanced freeze-thaw cycles. As water freezes within cracks and expands, it exerts pressure, further widening these fissures and breaking apart rocks. This process, known as frost wedging, is more effective when water can access deeper layers, which mammal burrows facilitate.
Increased air circulation within burrow systems promotes oxidation, a chemical weathering process where oxygen reacts with minerals in rocks, causing them to weaken and rust. These underground networks create favorable conditions for plant roots to penetrate deeper into the soil and rock. As roots grow and expand within these pre-existing cracks, they exert pressure, leading to root wedging. The disturbance also brings fresh material to the surface, where it becomes more exposed to various weathering agents.
Chemical Weathering from Biological Processes
Small mammals contribute to chemical weathering through biological processes. Their waste products, such as urine and feces, introduce acidic compounds into the soil and rock environment. These acidic substances can react with and dissolve certain minerals present in rocks, leading to their chemical alteration and breakdown.
Respiration from small mammals within their burrows releases carbon dioxide (CO2) into underground spaces. This elevated CO2 then reacts with soil moisture to form carbonic acid, a weak acid that can dissolve carbonate minerals like limestone. The decomposition of organic matter, including dead plant material and the remains of the animals themselves, within these burrows produces humic acids and other organic acids. These acids can chelate metal ions in minerals, effectively removing them from the rock structure and accelerating chemical decay.