Mountains
A mountain is an area of ground much higher than its surroundings, with a narrow peak compared to its base. A hill becomes a mountain if it measures more than 1,000 feet (about 300 metres) from foot to summit. Mountain ranges show where the Earth's crust has been compressed and thickened by the movement of the tectonic plates. Older, heavily eroded mountains can be found in the middle of continents, at the site of tectonic activity in the distant past. The Rocky Mountains were formed as the North American continent accumulated a series of fragments moving from the west. The Urals show where Europe and Western Siberia collided 220 million years ago. Younger, higher mountains are found where tectonic plates are meeting today, such as the Himalayas which lie on the junction of the Indian and Eurasian plates.

The Alps and the Jura Mountains, covered by snow in March 2000.

The Picos de Europa in northern Spain rise to more than 2,500 metres (6825 ft)

In mountain-building episodes, compressive forces cause the crust to buckle, often leaving parallel folds of rock or a complex jumble where layers of rock have been thrust over one another.

The Appalachian fold mountains, cut by the Susquehanna River in Pennsylvania.

Erosion by ice and water wears down the elevated surface, leaving high peaks separated by steep valleys. In the Appalachian Mountains of America's east coast, old folded rock layers have been exposed, and the more resistant layers appear as parallel ridges.

The summit of Mount Rainier, Washington state (4,392 metres, 11,990 feet), like many high mountains, is topped by a permanent glacier.

Mountain-building can be due to volcanic activity as well as compression, with repeated eruptions of lava and ash able to build the cones of high volcanoes. In the Coast Ranges of Western North America, a chain of volcanoes runs the length of the subjection zone where the Juan de Fuca plate is sinking beneath the North American plate. Similar chains of volcanoes are found in South America, Alaska and Japan, circling the Pacific with a "ring of fire".

Links
Qomolangma Feng (Mount Everest)
Fujiyama
Kilimanjaro