The Human Impact on Slopes

Slopes are vital landforms to manage, for the sake of agriculture and safety by avoiding natural hazards. Their stability, or lack thereof, which can have grave repercussions, depends on the angle of the slope as well as the strength of materials on it. Human activities can have a large influence, both positively and negatively, through creating or destroying stability, and the nature of this influence must be understood so it can be managed properly.

The management of slopes requires constant attention. Due to weathering and erosion, and their increased severity due to global warming, slopes are constantly changing, regardless of human activity, and so they must be monitored and managed to preserve their stability and prevent disasters. It is not simply a case of not damaging slopes, but of active intervention.

There are several human activities which make slopes more stable. Mechanical engineering is often a preferred method, either by ‘pinning’, the attaching of concrete blocks or panels to a rock face to prevent and control the risk of rockslides and falls, or ‘cut-and-fill grading’, which stabilises slopes by removing soil from the top of slopes and relocating it to the base to prevent undercutting.

In 2004, there was a Europe-wide eco-engineering drive to preserve slopes and improve their stability across the continent, both for conservation purposes and to lessen the natural hazard posed. This drive discovered that afforestation, when targeted effectively, dramatically increased slopes’ sheer strength through the binding of soil by tree roots. This showed that biological engineering could be utilised too.

Conversely, of course, many human activities can negatively affect slope stability. Most famously, deforestation, as the opposite of afforestation, reduces the sheer strength of slopes as the soil is not bound. Given the massive amounts of deforestation occurring, with 42 million trees felled each day, this suggests the human impact on slope stability is damaging.

This far from the only harmful human activity either. Atmospheric pollution, through the emission of CO2, sulphur dioxide, and nitrogen oxides, creates more acidic rain, which therefore will chemically weather the minerals contained within the rock. Furthermore, higher temperatures due to human-caused greenhouse gas emissions will lead to more total precipitation, which also increases the level of chemical weathering. As the rock minerals are broken down, the sheer strength of the slope will decrease as internal cohesion is reduced. The higher total precipitation, and thus higher slope water content, will reduce the friction between soil and rock particles in the slope, further reducing internal cohesion, as well as saturating the soil at the top of the slope, adding weight and therefore increasing the sheer stress experienced, making mass movements more likely.

With 3.25 billion tonnes of minerals extracted per year, mining is another human threat to slope stability. Mining, by digging into the rock of a slope, necessarily decreases its cohesion. In addition, fresh rock surfaces become exposed that then experience erosion and weathering, decreasing their sheer strength and stability. This consequently makes these slopes more susceptible to landslides.

The adverse impacts of mining on slope stability, and the disastrous consequences, are best demonstrated by the Aberfan Disaster of 1996, the worst mining disaster in British history. One of the mining tips was above a mountain spring, meaning it was saturated with water and had little internal cohesion: after a torrential downpour, an avalanche of liquified slurry tore down the mountain at up to 30-40mph, killing 144 people.  

Overall, the impact of humanity on slope stability worldwide is a negative one. Despite human efforts to increase slope stability, or combat our own negative impact, deforestation occurs at a far greater rate than afforestation, and mining for minerals essential to the functioning of modern society is unlikely to slow down – not to mention the indirect harm caused to slopes by climate change. Meanwhile, mechanical engineering is expensive and limited in its usage to stabilise slopes. Not only is the current impact on slope stability negative, but this is unlikely to change any time soon.