Soil Creep: Is It Really Mass Movement? You Won’t Believe!
The gradual downslope movement of soil, often observed in areas influenced by freeze-thaw cycles, is known as soil creep. Understanding whether is soil creep a type of mass movement requires analyzing its characteristics compared to other processes like landslides. The debate is frequently discussed among experts within the Geological Society of America, as these movements reshape landscapes over long periods. Soil creep’s subtle impact differentiates it from more dramatic forms of mass wasting, prompting continued scrutiny of its categorization.
Image taken from the YouTube channel Pres Currylea Geography Pres Currylea Geography , from the video titled Evidence of a soil creep .
Soil Creep: A Surprising Form of Mass Movement?
The question "is soil creep a type of mass movement?" sparks a lot of debate, and understanding it requires a deep dive into both definitions. The answer, in short, is yes, but the nuances are what make it interesting. Let’s break down why.
Defining Mass Movement
Mass movement, also known as mass wasting, refers to the down-slope movement of soil and rock under the influence of gravity. Crucially, mass movement doesn’t typically require a transporting medium like water, wind, or ice, although water can certainly play a role in lubrication and saturation.
Key Characteristics of Mass Movement:
- Driven by Gravity: Gravity is the primary force.
- Downslope Movement: Material moves from higher to lower elevations.
- Absence of a Transporting Medium (Usually): While water may contribute, it’s not the primary driver.
Different Types of Mass Movement:
To understand where soil creep fits, consider the spectrum of mass movement types. These are often categorized by speed and material type:
- Rockfalls: Rapid, free-falling rocks.
- Landslides: Sudden slides of soil and rock.
- Mudflows: Flows of water-saturated debris.
- Debris Flows: Similar to mudflows but with larger, coarser material.
- Slumps: Rotational slides of a mass of soil or rock.
- Soil Creep: Extremely slow, almost imperceptible movement of soil.
Defining Soil Creep
Soil creep is the slow, gradual, and continuous downslope movement of soil and regolith (unconsolidated rock and soil material). It’s the tortoise of the mass movement world. While a landslide might occur in seconds, soil creep takes years, decades, or even centuries to significantly alter a landscape.
What Causes Soil Creep?
Several factors contribute to this slow but relentless process:
- Freeze-Thaw Cycles: Water expands when it freezes, pushing soil particles upward (perpendicular to the slope). When it thaws, the particles settle back down, but gravity pulls them slightly downslope.
- Wetting and Drying Cycles: Similar to freeze-thaw, soil expansion with wetting and contraction with drying causes incremental downslope movement.
- Burrowing Animals: The activity of burrowing animals like earthworms, gophers, and moles disturbs the soil and loosens it, making it more susceptible to gravitational forces.
- Root Growth: Tree roots can wedge apart soil and rock, making them more susceptible to movement. Conversely, the removal of vegetation can increase creep rates by reducing soil stability.
- Gravity: The fundamental force pulling everything downward.
Recognizing the Signs of Soil Creep:
Because it’s so slow, soil creep is difficult to observe directly. However, there are several telltale signs:
- Tilted Trees: Trees on a slope may grow curved trunks to compensate for the tilting of the ground.
- Curved Fence Posts: Fence posts embedded in the ground may gradually lean downslope.
- Terracettes: Small, step-like formations on hillsides caused by soil accumulation behind obstacles.
- Exposed Tree Roots: Roots can become exposed as soil is slowly pulled away from around them.
- Debris Accumulation: An accumulation of soil or debris at the base of a slope.
- Displaced Retaining Walls: Small retaining walls may buckle or shift downslope over time.
Why Soil Creep Is Considered Mass Movement
Despite its glacial pace, soil creep fulfills the key criteria for being classified as mass movement:
- Driven by Gravity: Gravity is the underlying force causing the movement.
- Downslope Movement: Soil particles are unequivocally moving downwards.
- No Transporting Medium Required: While factors like water and burrowing animals can accelerate the process, they are not fundamentally required for creep to occur. The movement happens due to gravity acting on the soil itself.
Think of it like this: mass movement is a broad category. Some types are fast and dramatic, while others, like soil creep, are slow and subtle. Both are still the result of gravity acting on earth materials and causing them to move downslope.
Soil Creep vs. Other Mass Movement Types: A Comparison
| Feature | Soil Creep | Landslide | Mudflow |
|---|---|---|---|
| Speed | Extremely slow (millimeters or centimeters per year) | Very fast (meters per second or minute) | Fast to moderate (meters per hour or day) |
| Water Content | Can be influenced, but not necessarily saturated | Can range from dry to saturated | High, essentially a slurry |
| Material | Primarily soil and regolith | Soil, rock, debris | Water-saturated soil, debris, and vegetation |
| Triggering Event | Gradual processes (freeze-thaw, wetting-drying) | Heavy rainfall, earthquakes, slope instability | Heavy rainfall, volcanic activity, dam failure |
| Observability | Difficult to observe directly | Obvious and immediate | Readily apparent |
FAQs About Soil Creep
This section addresses common questions about soil creep and its classification as a form of mass movement. Hopefully, these FAQs can clarify understanding of this slow geological process.
How is soil creep different from other types of landslides?
Soil creep is the slowest type of mass movement, often imperceptible without careful observation over extended periods. Unlike landslides, mudflows, or debris flows, soil creep involves a gradual, continuous downhill movement of soil and regolith. Other types of landslides tend to be more sudden and dramatic.
What are some common signs that soil creep is occurring?
Observable signs of soil creep include tilted fences and utility poles, curved tree trunks growing uphill to compensate for the shifting ground, and terracettes (small, step-like formations) on slopes. These features indicate the slow but persistent downslope movement of the soil.
Is soil creep a type of mass movement?
Yes, soil creep is a type of mass movement, although a very slow one. Mass movement, in general, refers to the downslope movement of soil and rock under the force of gravity. Because soil creep involves the gradual downslope movement of soil due to gravity, it fits the definition of mass movement.
What factors contribute to soil creep?
Several factors can contribute to soil creep. These include gravity, freeze-thaw cycles (which expand and contract the soil), wetting and drying cycles (which cause soil to swell and shrink), burrowing animals, and root growth. These processes weaken the soil structure and facilitate its slow movement downhill.
So, what’s the verdict? Figuring out if is soil creep a type of mass movement can be tricky, but hopefully, this article cleared things up! Keep an eye out for those tell-tale signs next time you’re hiking. See you around!
