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 mass movement caused by gravity and environmental cycles, leading to gradual landscape changes.

Step-by-step solution

Understanding Creep as a Mass Movement

Creep is a type of mass movement characterized by the very slow and gradual downhill movement of soil and rock. It is different from most other mass movements, such as landslides or avalanches, which happen rapidly and are often noticeable immediately. In contrast, creep occurs so slowly that it is usually only detected by observing changes in the landscape over a long period of time.

Identifying the Forces Causing Creep

The primary forces causing creep include gravity, which constantly exerts a downward pull on soil and loose material, and processes like freeze-thaw cycles and soil moisture changes. These processes cause soil particles to move slightly further downslope each time they are dislodged or expanded. Repeated cycles of expansion and contraction due to temperature changes or moisture fluctuations contribute significantly to the creep process.

Recognizing the Effects of Creep

Creep results in subtle landscape changes such as tilted trees, bent fences, leaning utility poles, and the slow deformation of roads and buildings. It is often recognized by these cumulative effects rather than by observing the movement itself. Over time, these changes can have significant impacts, potentially requiring structural adjustments or reinforcements.

Key concepts

Mass Movement

Mass movement refers to the movement of soil, rock, and debris down a slope under the influence of gravity. This natural process can range from rapid events like landslides and avalanches to slow and imperceptible movements such as soil creep.
These movements are part of the Earth's dynamic nature and can alter landscapes significantly.
Mass movements are fundamentally driven by the force of gravity, but their occurrence and speed are influenced by several factors.

• Slope angle: Steeper slopes can trigger faster mass movements.
• Water content: Moisture can add weight and reduce friction, facilitating movement.
• Vegetation: Roots can stabilize soil, reducing the risk of movement.

Understanding different types of mass movements helps in predicting potential geological hazards and planning preventive measures to protect infrastructure.

Gravity

Gravity is the driving force behind all types of mass movements, including soil creep. It is a natural force that pulls objects towards the center of the Earth.
For mass movement, gravity acts to move soil, rock, and other materials downhill once other stabilizing factors are overcome.

• Steepness: The steeper the slope, the more effectively gravity can act on the material.
• Material weight: Heavier materials are more susceptible to gravitational pull.

In the case of soil creep, gravity works slowly and continuously, causing materials to gradually shift. Over time, even the smallest movement can accumulate, leading to noticeable changes in the landscape. This constant pull by gravity is what makes soil creep a persistent yet subtle force in reshaping terrain.

Freeze-Thaw Cycles

Freeze-thaw cycles are critical in the process of soil creep. These cycles occur when temperature fluctuations cause water within the soil to freeze and thaw repeatedly.
When water freezes, it expands, pushing soil particles apart. Upon thawing, the soil particles settle slightly further downslope.
This process repeats over many cycles, each time moving the soil fractionally. Key aspects of freeze-thaw cycles include:

• Temperature variation: Areas with frequent temperature shifts around the freezing point are most affected.
• Soil moisture: Presence of water is crucial for ice formation and subsequent soil particle movement.

Each cycle contributes a small, incremental movement of soil, playing a significant role in the gradual progression of soil creep.

Soil Moisture Changes

Changes in soil moisture are another important factor influencing soil creep. As soil moisture content fluctuates due to precipitation, drying, or other environmental conditions, the individual particles within the soil can undergo movement.
Moisture changes affect soil creep through:

• Water absorption: When soil absorbs water, it becomes heavier and more mobile.
• Drying and contraction: Dry conditions can cause soil to shrink, rearranging particles downslope.

These moisture-driven movements, though minor on their own, compile over time to create significant changes. Understanding how soil moisture variations contribute to soil creep is essential for assessing long-term ground stability and managing the effects on built structures.