By 2030, ensure the conservation of mountain ecosystems, including their biodiversity, in order to enhance their capacity to provide benefits that are essential for sustainable development

Mountains are landforms made from rock and earth that rise high above the surrounding terrain. A mountain range is a series or chain of mountains that are close together. Generally, mountains are higher than 600 metres. A landform less than 600 metres high is called a hill.

Mountains exist all over the world, including the oceans. They cover one-fifth of the Earth’s land surface and occur in 75 percent of the world’s countries. Mountains are home to approximately one-tenth of the world’s people. More than half of the world’s freshwater originates in mountains, and all the world's major rivers are fed from mountain sources.

Mountains are formed through tectonic forces or volcanic activity:

• Volcanic mountains form when molten rock from deep inside the Earth erupts through the crust and piles up on itself. When magma pushes the crust up but hardens before erupting onto the surface, it forms so-called dome mountains. Wind and rain pummel the domes, sculpting peaks and valleys. The domes are then shaped by weathering and erosion. Sometimes volcanic eruptions break down mountains rather than building them up.
• Other types of mountains form when stresses within and between tectonic plates lead to the cracking and faulting of the Earth's surface, which forces blocks of rock up or down.

Mountains erode slowly through the action of rivers, weather conditions and glaciers.

Mountains often serve to define the borders of countries. Their height can influence weather patterns, stalling storms that roll off the oceans and squeezing water from the clouds. Rugged landscapes can provide refuge and protection for fleeing or invading armies. High elevations have colder climates than at sea level. These colder climates strongly affect mountain ecosystems, meaning that different elevations have different plants and animals. Because of their less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction and recreation.

The main causes of environmental damage in mountain areas are large numbers of tourists, deforestation and excessive road vehicle use.

Skiing activities threaten the balance of delicate ecosystems, and the cumulative environmental impacts of skiing are considerable. The development of ski infrastructure poses particular problems. Attempts to reduce environmental impacts in popular areas (such as restrictions on parking) may succeed, but only at the cost of shifting the problem elsewhere.

The impacts of skiing and the development of skiing infrastructure include:

• forest clearance and the increased incidence of avalanches;
• the visual degradation of landscapes (especially when concrete and plastic replace natural wooden barriers);
• loss of habitats and the disturbance of endangered species (lifts, off-piste skiing, the use of all-terrain vehicles and the compaction of snow on the slopes disturb many rare animals);
• sewage disposal and water pollution (the chemicals used in preparing ski slopes lead to higher nitrogen and phosphorous levels, and therefore to water pollution);
• exhaust fumes from cars and buses, which kill trees and wildlife;
• the production of artificial snow, which involves the unsustainable use of water; and
• erosion and damage to sensitive vegetation due to skiing in sparse snow conditions.

Another significant impact of tourism in mountainous regions is erosion caused by trampling, off-road driving and mountain biking. These activities need to be managed by zoning and other land-use planning measures.

Mountains are the last remaining areas in Central and Eastern Europe that are relatively untouched by human activity. They support a wealth of biodiversity.