Question

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. Explain the process of creep and discuss how it differs from solifluction. (A)

Short answer

Creep is the slow, downward movement of soil or rock caused by the expansion and contraction of particles due to elements such as freeze-thaw cycles and wetting-drying cycles. Solifluction, on the other hand, occurs specifically in periglacial environments and involves the downslope flow of water-saturated soil over a frozen subsurface layer. While both processes result in the gradual movement of soil and sediment due to gravity, they have distinct causes and mechanisms, with creep being attributed to factors like temperature and moisture changes, and solifluction being attributed to the melting of ice and ground frost in periglacial environments.

Step-by-step solution

Define Creep

Creep is a geomorphic process that involves the slow, downward progression of rock or soil due to gravity. It occurs when the layers of sedimentary rock and soil on a slope gradually move downward over time. This motion is caused by the expansion and contraction of the soil particles due to various factors such as freeze-thaw cycles, wetting and drying cycles and other thermal changes.

Explain the Mechanism of Creep

The process of creep usually occurs due to the expansion and contraction of soil particles or rock fragments. When the soil moisture content increases, it causes the soil particles to expand. In cold climates, the freezing of water in the soil pores generates the expansion. As the soil particles expand, they push against each other and slowly move apart. When the moisture content decreases, or the water in the soil freezes, the particles contract. But, due to gravity, they do not return to their previous positions, and thus, a net downward movement happens over time.

Define Solifluction

Solifluction is a type of slower mass movement that occurs specifically in periglacial environments (areas located at the fringes of ice sheets and glaciers). This process involves the slow downslope flow of soil and sediment saturated with water. The water often comes from the melting of ice or ground frost. Solifluction is most common in areas where the ground is affected by permafrost, as the surface soil layer tends to thaw during warmer periods, resulting in a more slippery surface.

Explain the Mechanism of Solifluction

Solifluction occurs when the surface layer of soil, which is saturated with water, flows downslope over a frozen and impermeable subsurface layer. As the excess water cannot drain downward through the frozen layers, it leads to an increased water content in the upper soil layers. This wet, fluid layer then moves downslope due to gravity, causing a slow mass movement of the soil.

Compare Creep and Solifluction

While both creep and solifluction involve the slow downhill movement of soil and sediment due to gravity, they have some key differences. Creep mainly occurs due to the expansion and contraction of soil particles as a result of factors such as freeze-thaw cycles, wetting and drying cycles, and other changes in temperature and moisture, whereas solifluction occurs specifically in periglacial environments due to the downslope flow of saturated soil over a frozen subsurface layer. Additionally, solifluction is mainly caused by the presence of excess water in the soil resulting from the melting of ice and ground frost, while creep can occur due to various factors leading to expansion and contraction of soil particles.

Key concepts

Creep in Geology

Creep refers to the very slow movement of soil or rock down a gentle slope. It is a quiet, almost imperceptible process that continues to reshape landscapes over time. The main cause of creep is the alternate expansion and contraction of soil particles due to changes in moisture and temperature.

For example, when soil gets wet, it expands; as it dries, it contracts. During freezing conditions, water within the soil expands as it turns to ice. Each cycle of freezing and thawing can lift soil particles upward, and then, due to gravity, they settle slightly off to the side from their original positions. Over years, this results in a gradual 'creep' of the land downhill.

This movement is often so slow it can be difficult to detect without careful measurement, but the effects can become visible over time, seen in bent tree trunks, tilted fences or poles, and cracked roads.

Solifluction

Solifluction is a specific type of earthflow that occurs in cold climates, particularly within periglacial environments where the ground undergoes repeated freeze and thaw cycles. Solifluction is distinctive because it involves a layer of thawed soil and sediment flowing over an impermeable layer of frozen ground or permafrost.

During warmer seasons, the active layer above the permafrost thaws, becoming saturated with water from melted ice and snow. Since the water cannot percolate through the still-frozen ground beneath, the soil becomes oversaturated, and gravity pulls this slurry of soil and water downhill.

Visual Evidence of Solifluction

One can often identify solifluction by lobe-shaped formations on hillsides or terracettes, which are like small steps or terraces formed by the movement of the soil. These features highlight solifluction's role in landscape development in cold regions.

Mass Wasting

Mass wasting encompasses all processes by which soil, sand, regolith, and rock move downslope under the force of gravity. While mass wasting can occur as sudden events, like landslides or rockfalls, many forms of mass wasting, such as creep and solifluction, proceed slowly.

• Landslides and rockfalls are rapid and often dangerous forms of mass wasting.
• Creep and solifluction represent slow-moving types that gradually alter the landscape.

Water is a critical factor in mass wasting; it adds weight to the soil, reduces friction between particles, and, in the case of solifluction, creates a lubricating layer that precipitates movement. Mass wasting continuously shapes the terrain by moving vast amounts of earthen material, contributing to the ongoing evolution of our planet's topography.

Periglacial Environments

Periglacial environments are regions where the climate is not cold enough to support a year-round ice cover, but still cold enough to deeply affect soil processes and geomorphology. These areas are found on the edges of glaciers and ice sheets and include tundra landscapes and parts of the high mountains.

Freeze and thaw cycles dominate these landscapes, causing phenomena such as frost heaving, solifluction, and patterned ground. Permafrost—a layer of permanently frozen ground—exists beneath the surface layer.

Adaptations to the Environment

In periglacial zones, vegetation and animal life have adapted to the harsh conditions. Human structures in these areas also require special engineering solutions to prevent damage from the movement of the ground caused by freeze and thaw cycles.