Series 23 - Soil Erosion V - Erosion by Gravity

Summary

This lecture from Cornell University explores different types of erosion, focusing on gravity’s role in soil movement. The professor explains how gravity erosion, particularly soil creep and landslides, occurs when water reduces friction in soil layers. Using the Finger Lakes region as an example, the lecture demonstrates how sand and clay layers interact to cause catastrophic slides. It also discusses soil management techniques to prevent erosion, such as reducing compaction, limiting machine traffic, and using mulches to enhance soil structure and biological activity. Practical strategies for maintaining soil quality and reducing erosion are emphasized.

Takeaways

• 😀 Gravity erosion is a slow but constant process where soil and material move down a slope due to gravity.
• 🌱 Soil creep is the most common form of gravity erosion, often unnoticed, where soil gradually moves downslope.
• 🌧 Water plays a key role in accelerating gravity erosion by reducing friction and increasing soil weight.
• 🏞 Steep slopes and layered soils with varying water retention capacities are most vulnerable to gravity erosion.
• 🏠 A real-life example from the Finger Lakes region shows how alternating sand and clay layers can lead to catastrophic slides after heavy rainfall.
• 💧 Infiltration of water in soils, especially when there are sand lenses beneath clay, can trigger landslides due to water pressure.
• 🚗 A landslide event in Syracuse buried a house and a car, highlighting the destructive potential of gravity erosion during extreme weather.
• 🌿 Vegetative roots and reduced water movement can stabilize soils, preventing gravity erosion and landslides.
• 🚜 Compaction from heavy machinery can reduce soil infiltration and increase the risk of erosion, especially on wet soils.
• 🌾 Using mulches and reducing mechanical pressure on soils can improve water retention, enhance biological activity, and reduce erosion risk.

Q & A

What are the main types of erosion discussed in the transcript?

The transcript discusses three main types of erosion: wind erosion, water erosion, and gravity erosion.

How does gravity contribute to soil erosion?

Gravity causes soil erosion by moving material down slopes. This can occur gradually as 'soil creep' or more suddenly through landslides, often triggered by water reducing friction between soil particles.

What is 'soil creep' and how does it affect the landscape?

'Soil creep' is a slow and constant form of gravity-induced erosion where soil moves downward over time, gradually altering the landscape by shifting soil particles and causing long-term changes to the slope.

What factors make gravity erosion more likely to occur?

Gravity erosion is more likely to occur on steep slopes and in soils that are layered, such as those with varying water retention capacities, like sand and clay layers.

How does water affect gravity erosion?

Water reduces the friction between soil particles, making it easier for soil to slide downhill. When water infiltrates layered soils, it can saturate sand layers, increasing their weight and triggering landslides.

What example is given to illustrate the effects of gravity erosion?

The transcript references the Finger Lakes region, where the landscape's steep slopes and layered soils (sand and clay) have experienced gravity-induced landslides, including one that buried a van and caused significant damage.

What are some signs that gravity erosion may occur in an area?

Signs of potential gravity erosion include steep slopes, soil layering (e.g., sand and clay), and areas with high water retention where water may infiltrate and reduce friction, increasing the risk of landslides.

What management practices can help reduce gravity erosion?

To reduce gravity erosion, it is important to use vegetation with strong root systems, reduce water infiltration through evapotranspiration, and avoid activities that compact soil, such as overuse of machinery or walking on wet soil.

How does soil compaction contribute to erosion?

Soil compaction reduces water infiltration, leading to increased surface runoff. This runoff can erode the soil, particularly on slopes, contributing to both water and gravity erosion.

What are some methods to prevent or reverse soil compaction?

Methods to prevent or reverse soil compaction include limiting heavy machinery use on wet soil, practicing deep tillage carefully to avoid creating deeper compaction layers, and using mulches to protect the soil surface and improve biological activity.