Large cracks in the ground are significant fissures or ruptures in the Earth’s surface, varying in width and depth. These openings are natural phenomena, often impacting human infrastructure and landscapes. They result from various geological and environmental processes, revealing dynamic interactions within the Earth’s crust and its surrounding conditions.
Cracks from Water Loss and Soil Shrinkage
Many noticeable ground cracks emerge from the loss of moisture in certain soil types, particularly those rich in clay. Clay soils possess a unique characteristic known as shrink-swell potential, meaning they expand when wet and contract significantly when they dry. During prolonged dry spells or drought conditions, water evaporates from the soil, causing its volume to decrease. This reduction in volume creates tensile stress within the soil, which it cannot withstand, leading to the formation of desiccation cracks.
These cracks vary in size and depth, depending on clay content, dryness, and soil structure. Such shrinkage can negatively impact plant roots by exposing them and reducing water absorption, and it can also exert pressure on building foundations, potentially causing structural issues. While these cracks may close when the soil rehydrates, the repeated cycle of shrinking and swelling contributes to ongoing ground instability.
Cracks from Geological Forces
Powerful forces deep within the Earth’s crust can also generate ground cracks. Tectonic plate movement is a primary driver, as the slow but continuous motion of these massive plates builds up immense stress in the Earth’s lithosphere. When this stress is released, often abruptly, it causes earthquakes, which can lead to visible surface ruptures along fault lines. These surface ruptures manifest as offsets in the ground, with one side of the fault moving vertically, horizontally, or both, relative to the other.
Another geological process forming large cracks is rifting, where the Earth’s crust pulls apart. This extension creates linear depressions and fissures that can span many kilometers. The East African Rift Valley provides a prominent example, where the African continent is slowly separating, resulting in extensive ground fissures. These cracks are often a manifestation of underlying tectonic tension, sometimes exacerbated by other factors like heavy rainfall.
Volcanic activity also contributes to ground cracking. As magma moves beneath the surface, it deforms the overlying ground, creating fissures. These fissures can serve as vents for lava eruptions, sometimes forming “curtains of fire.” They are common in rift zones and around shield volcanoes, where the crust is under tension and magma rises easily.
Cracks from Subsurface Voids
Ground cracks can also form due to the collapse of underground spaces, a phenomenon often associated with sinkholes. Sinkholes typically occur in regions with soluble bedrock, such as limestone, gypsum, or dolomite, which are susceptible to dissolution by groundwater. As rainwater percolates through the soil, it absorbs carbon dioxide and reacts with decaying vegetation, becoming slightly acidic. This acidic water then seeps into cracks and pores in the bedrock, gradually dissolving the rock and creating a network of underground caverns and voids over long periods.
When the roof of such a cavern weakens and can no longer support the overlying soil and rock, it collapses, leading to a sudden or gradual depression on the surface, or a visible crack. These natural processes create many large ground openings in karst landscapes. Human activities can also induce or accelerate such cracking; for instance, the collapse of old mining tunnels, abandoned underground infrastructure, or excessive groundwater pumping can remove subsurface support, causing subsidence and cracking.
Cracks from Ground Instability
Ground instability, often influenced by gravity and environmental changes, can also lead to the formation of significant cracks. Landslides, for example, frequently exhibit tension cracks at their upper edges or along their flanks. These cracks form as a mass of earth begins to pull away and move downslope, indicating incipient movement or areas of extension within the unstable ground. The appearance of tension cracks can serve as an early warning sign of potential slope failure, as they reduce ground stability.
Another cause of ground instability and cracking is the thawing of permafrost, which is ground that has remained frozen for at least two consecutive years. Much permafrost contains substantial amounts of ice. As global temperatures rise, this ice-rich permafrost thaws, leading to a loss of ground volume and structural integrity. This process, known as thermokarst, results in uneven ground subsidence and significant cracks. The thawing of permafrost poses considerable challenges to infrastructure in Arctic and sub-Arctic regions.