Geography – Earth processes and mass movements | e-Consult

Mass movement hazards are complex phenomena, and their occurrence is rarely attributable to a single cause. While natural factors like rainfall, earthquakes, and geological instability play a significant role, human activities often exacerbate these hazards, increasing their frequency and severity.

Natural Factors:

• Rainfall: Excessive rainfall saturates the soil, increasing its weight and reducing its shear strength. This is a primary trigger for many types of mass movement, particularly landslides and debris flows. For example, the 1999 Boubous landslide in Greece was directly linked to prolonged periods of heavy rainfall.
• Earthquakes: Seismic activity can destabilize slopes, causing landslides, rockfalls, and debris avalanches. The 2010 Haiti earthquake caused widespread landslides, contributing significantly to the devastation.
• Geological Instability: Certain geological formations, such as steep slopes, fractured rock, and unconsolidated sediments, are inherently more prone to mass movement. The Swiss Alps, with their steep, glaciated slopes, are a prime example. Freeze-thaw cycles can also weaken rock structures.
• Volcanic Activity: Volcanic eruptions can trigger landslides, lahars (mudflows), and pyroclastic flows. The 1980 eruption of Mount St. Helens resulted in massive landslides and lahars.

Human Factors:

• Deforestation: Removal of vegetation reduces soil stability and increases runoff, making slopes more vulnerable to landslides. The deforestation in parts of the Amazon rainforest has significantly increased the risk of landslides.
• Agriculture: Unsustainable agricultural practices, such as terracing on steep slopes without proper drainage, can destabilize slopes. Overgrazing can also remove vegetation cover.
• Construction: Construction activities, including quarrying, road building, and building on slopes, can alter slope gradients and destabilize slopes. The construction of roads in mountainous areas often triggers landslides.
• Mining: Mining operations can create unstable slopes and increase the risk of landslides and debris flows. Open-pit mining, in particular, can significantly alter slope stability.

Relative Importance: While natural factors provide the initial trigger, human activities often act as a catalyst, increasing the likelihood and magnitude of mass movement events. In many cases, the interaction between natural and human factors is the most significant driver. For example, deforestation combined with heavy rainfall creates a highly unstable environment.