Question

How is creep different from most other types of mass movement? Explain the forces that cause creep, as well as the effect of creep.

Short answer

Creep is a slow, gradual mass movement caused by soil moisture cycles, impacting structures over time.

Step-by-step solution

Understanding Creep

Creep is a very slow and gradual type of mass movement, which involves the downhill movement of soil and regolith. Unlike rapid mass movements like landslides or rockfalls, creep occurs over long periods, often going unnoticed until significant effects accumulate.

Identifying the Forces of Creep

The primary force causing creep is the continuous cycle of freezing and thawing or wetting and drying of soil. When soil collects moisture and expands, it moves slightly outwards. As it dries or contracts, it moves slightly downwards due to the pull of gravity. This gradual cycle repeats, causing soil to move slowly downhill.

Effects of Creep

Over time, creep can cause fences, poles, and trees to lean and the ground to bulge slightly. It can damage structures, roads, and infrastructure as the soil shifts. Even though creep is slow, its effects are evident in areas with gradual slopes.

Key concepts

Mass Movement

Mass movement is the geomorphological process whereby soil, sand, regolith, and rock move down a slope under the force of gravity. This movement can occur rapidly, as in a landslide or rockfall, or take place slowly over long periods, like creep. Mass movements are categorized based on their speed, moisture content, and the material involved.

• Rapid Movements: These include landslides, rockfalls, and avalanches. They happen quickly and can cause significant destruction within a short time.
• Slow Movements: Creep is the most common example. Although its effects are subtle and slow to manifest, over time, it can lead to substantial changes in the landscape.

Mass movements play an essential role in shaping Earth's topography by transporting material from higher to lower areas, affecting ecosystems and human infrastructures alike.

Soil Erosion

Soil erosion involves the wearing away of the topsoil layer and is primarily caused by water, wind, or ice. While not identical to mass movement, soil erosion contributes to material being displaced and transported, often compounding the effects of mass movement phenomena like creep.

• Water Erosion: Occurs when flowing water dislodges soil particles and carries them away, forming channels or gullies.
• Wind Erosion: Happens in dry, barren environments where loose soil particles are blown away by the wind.
• Ice Erosion: Involves the movement of glaciers that scrape and carry away soil and rock.

Preventing or mitigating soil erosion often involves vegetation cover, terracing, and the installation of erosion control structures, which also help reduce the risk of mass movement by stabilizing the soil.

Frost Heave

Frost heave is a process that occurs when water in the soil freezes and expands, pushing the ground upwards. This process plays a significant role in facilitating creep by repeating the expansion and contraction cycle of soil.

• Freezing Phase: When temperatures drop, water in the soil freezes, causing ice lenses to form and push the soil upwards.
• Thawing Phase: As temperatures rise, the ice melts, and the soil settles slightly lower, influenced by gravity.

This cycle of freezing and thawing is especially prevalent in colder climates and can be destructive, affecting roads, sidewalks, and foundations over time. Measures to combat frost heave include insulating soil against cold temperatures and ensuring proper water drainage around structures.

Gravitational Forces

Gravitational forces are the unseen hand driving all types of mass movement, including creep. Gravity pulls materials down slopes, always acting downwards and perpendicular to the surface of the Earth. This force works persistently over time, causing any unattached material on a slope to move downhill.

• Direct Influence: Gravity directly pulls materials down slopes, as seen in landslides and rockfalls.
• Indirect Influence: It also indirectly influences processes like creep, where continuous cycles of soil expansion and contraction gradually allow gravity to exact its pull over time.

Understanding gravitational forces helps in assessing risks and planning effectively to reduce the impacts of mass movements. Engineering solutions often include slope reinforcement, drainage systems, and retaining walls to counteract or stabilize the gravitational pull on slopes.