Mass Movement

Mass Movement

The downslope movement of loose soil, mud, and rock under the influence of gravity.

Regolith

The loose layer of broken rock, soil, and debris covering the solid bedrock.

The Main Trigger

Heavy rainfall, which saturates the ground, making the regolith heavier and lubricating it so it slides easily.

Classification

Grouped by speed (Slow vs. Fast) and water content (Dry vs. Wet).

Soil Creep

The slowest form of mass movement, moving down gentle slopes at less than 1 cm per year.

How Soil Creep Works

Rain causes soil particles to expand and move straight up; when the soil dries out, particles contract and fall slightly further down the slope due to gravity.

Evidence of Soil Creep

Tilted fences, telegraph poles, gravestones, curved trunks of trees, and terracettes.

Landslides

The rapid movement of a massive amount of dry regolith, rock, and soil straight down a steep slope or cliff face.

How Landslides Work

Often triggered by earthquakes, coastal erosion, road building, or sudden heavy downpours.

Real-world Impact of Landslides

Destroys roads, crushes buildings instantly, and changes the coastline.

Mudslides

A rapid, liquid-like surge of saturated soil, mud, and rock rushing down a steep slope or valley.

How Mudslides Work

Heavy rainfall completely saturates a hillside, causing soil to lose its grip on the bedrock and turn into a thick liquid ('slurry').

Real-world Impact of Mudslides

Block roads, destroy crops, and can bury entire villages at the base of mountains.

Bog Bursts

A specific type of mudslide that occurs in upland blanket bogs when a thick layer of peat becomes completely waterlogged and bursts downhill.

How Bog Bursts Work

Heavy autumn rain fills the peat bog, trapping water under the surface which builds up pressure until it bursts, sending peat mud down the mountainside.

Irish Example of a Bog Burst

The Meenbog Bog Burst (Co. Donegal, 2020) where peat rolled down a hillside, knocking over wind turbines and polluting local rivers.