Valleys carved by ice
A river cuts a V-shaped VALLEY, but a GLACIER grinds out a broad U shape. During the last Ice Age, glaciers carved deep valleys along the coast of Norway. When the ice melted and the sea level rose, the sea flooded in, leaving long, narrow inlets with steep walls: a FJORD. Norway's longest, the Sognefjord, runs more than 200 kilometres inland and is over 1,300 metres deep in places, deeper than the sea beyond its mouth. Fjords are also found in New Zealand, Chile, Canada, Greenland and Scotland, where they are called sea lochs.
Canyons, mesas and buttes
A CANYON or GORGE is a deep, narrow valley cut by a river through rock over millions of years, often in dry places where there is little rain to wear the sides down. The Grand Canyon is the most famous, and our national parks page covers it. In the American south-west, where layers of soft rock sit beneath harder rock, erosion leaves flat-topped hills standing above the plain. A MESA is a wide one, Spanish for table; a BUTTE is a narrow one, taller than it is wide, and a BLUFF is a steep cliff or bank, often beside a river.
Roofs, necks and points of land
A PLATEAU is a large area of high, fairly flat land. The Tibetan Plateau, pushed up by the same collision that raised the Himalayas, averages over 4,500 metres high and is often called the roof of the world. A PENINSULA is land almost surrounded by water; the Arabian Peninsula is the largest. An ISTHMUS is a narrow neck of land joining two larger areas, like the one at Panama that joins North and South America. A CAPE is a point of land sticking out into the sea, like the Cape of Good Hope near the southern tip of Africa.
A BASIN is a low area where water collects or drains, like the vast Congo Basin in Africa. A PLAIN is wide, flat, low land, often made of soil laid down by rivers, and some of the best farmland in the world.
When is a hill a mountain?
There is no world rule. In Britain, a height of 2,000 feet, about 610 metres, has long been used as the dividing line, and hill walkers keep lists of the peaks that pass it. A 1995 film, based on a local legend, tells of Welsh villagers who pile earth on top of their hill to push it over the line. In 2008 surveyors found that a real Welsh hill, Mynydd Graig Goch, was just over 2,000 feet after all, and it was promoted to a mountain. A HILL is lower and rounder, a MOUNTAIN higher and steeper, and each has a RIDGE and a SUMMIT.
Craters, cliffs and frozen plains
A CRATER can be made by a volcano or by a meteorite; Meteor Crater in Arizona, about a kilometre across, was blasted out around 50,000 years ago. A CLIFF is a steep rock face, a CAVE a natural hollow underground, and the TUNDRA a flat, treeless landscape of frozen ground in the far north. Our mountains page covers how the biggest landforms are made.