Mass Movement Notes

Slope: The angle of the slope affects the likelihood and speed of mass movement.
Tectonic Activity: Earthquakes and other tectonic events can trigger mass movements.
Slope Material: The type of material (rock, soil, etc.) and its properties influence stability.
Human Activity: Construction, deforestation, and other activities can destabilize slopes.
Water Content: Water can increase the weight of the slope material and reduce friction between particles.
Vegetation Cover: Vegetation can stabilize slopes by binding soil particles together with their roots.

Soil on a slope becomes saturated by heavy rainfall, increasing the weight of the regolith.
Often occurs in impermeable areas where water cannot be easily absorbed by the bedrock.
Soil expands when it absorbs moisture and contracts when it dries out, causing slow downhill movement of regolith under gravity.
Waves form in the soil, called terrecettes.
Evidence includes tilted walls, cracked structures, and slanted telephone poles or trees.
Management involves adding plants with roots to anchor the soil or creating artificial drainage paths for excess water runoff.

The movement of rocks downhill under the influence of gravity.
Sudden and fast movement of material.
Can occur after heavy rainfall or freeze-thaw cycles.
Tectonic activity can also trigger rockfalls.
Example: Roads in the Himalayas are regularly blocked after tectonic activity.
Mitigation: Nets can be erected on rock faces to prevent rocks from falling on people or vehicles.

Occurred on November 13, 1985.
The town of Armero was destroyed, killing over 20,000 people (95% of the population).
Nevada Del Ruiz is one of South America’s largest stratovolcanoes.
Volcanologists had noticed seismic activity in the year before the eruption.
The volcano had been dormant prior to the eruption.
The volcano's height meant there was permanent snow cover on the peak.
The lahar was 30 meters high and composed of volcanic ash, debris, and melted ice.
The mixture traveled downslope at speeds exceeding 70 kmph.
5,000 homes were destroyed.
The lahar occurred at night, and many residents were buried in their homes under up to 2 meters of mud.
The town had been ordered to evacuate, but the order was later called off due to a lull in volcanic activity.
Townspeople had been warned of a 100% chance of a lahar if an eruption occurred, but they lacked the technology and expertise to implement an evacuation plan.

Occurs on soft coastlines of loose rock and regolith due to coastal erosion.
The coastline is undercut and moves downslope.
Moderate speed of movement.
Slips along a curved surface that rotates outwards back on itself.
Human activities, like road construction on steep slopes, can cause instability (similar to undercutting).
Associated with landscapes following heavy rain as the soil increases in weight.

Example: Derrybrien, Co Galway, July 2003.
An area of saturated bog moves downslope.
Slow to fast speed.
Occurs mostly during autumn and winter due to high precipitation levels.
Periods of very heavy rain after long periods of very dry weather are associated with bog bursts.
Human activity, such as peat cutting, draining of land for agriculture, and wind farm construction, is also linked to bog bursts.

Very rapid movement of snow downslope.
May occur due to natural events or human activity.
Humans can cause regular avalanches to avoid one large avalanche.
Usually occurs on mountain slopes.
Occurs when the weight of the snow exceeds the slope's capacity to hold it.
Usually occurs if snowfall is greater than 30 cm and on slopes between $30^\circ$ and $45^\circ$ .

*Example: India, 2015.

Slope stability changes from stable to unstable.
Large volume of loose regolith moves downslope.
Causes include loss of vegetation, erosion of slope, weakening of slope, earthquake activity, volcanic eruptions, and human activities.
Fast speed.

Too much pressure (overgrazing) on resources (soil) caused increased mass movement (soil erosion leading to mudflows and landslides).
1990s: Increased subsidies from the EU caused an increase in sheep numbers in Ireland.
Major impact on upland areas, with 30% at risk.
80 mm of rainfall in north Mayo in 2003 resulted in 40 landslides and mudflows in the local area, destroying houses, roads, and bridges.
Farmers unintentionally caused this to happen.
Very little alternatives to make a living.
Subsidies were meant as a positive for the area but led to unintended consequences.

Areas most affected by desertification are regions on the edges of deserts.
The Sahel region lies to the southern end of the Sahara Desert in Africa.
Covers an area of approximately 1,000 km in total.
Stretches from the Atlantic Ocean coast to the Red Sea coast and is located at the southern end of the Sahara Desert.
The desert is growing at a rapid rate.
The region has experienced a population increase in recent years due to high birth and immigration rates.
High population growth increases the demand for food, leading to increased demand for land to cultivate.
Growth of farming and cultivation has led to soil becoming exhausted and exposed to erosion.
Lack of irrigation practices exacerbates the problem.
An increase in the number of animals required for food has also resulted in overgrazing.
Cattle are also seen as a sign of wealth in the region.
Energy needs are satisfied by cutting down trees, contributing to deforestation.