The Americas consist of fragments of the former continents of Laurasia and Gondwana, rifted apart in the late Mesozoic and moved westwards away from Europe and Africa. The two separate lithospheric plates of North and South America only became linked together in the late Cretaceous by the orogenic activity which produced the Central American mountain chains (Figure 4.1). Thus, the Americas fall naturally into three parts and it is convenient to discuss their geomorphology under the headings of North, Central and South America.

Information about landforms in the Americas is uneven in amount. Much less research has been done and little has been written about Central and South America compared with North America. This disparity is reflected in the text which follows.

NORTH AMERICA

The work of American geomorphologists has made the geomorphology of North America widely known, and examples from North America have illustrated geomorphological textbooks to the exclusion of comparable examples from other parts of the world. The area of North America is approximately 21.5 million km2, and includes the countries of Canada, USA, Mexico and Greenland. It extends from 25°N latitude to beyond 80°N (over 6000 km) and from longitude 60°W to 170°W, although the main part of the USA lies between 70°W and 125°W, a distance of 4200 km.

The eastern margin of the North American lithospheric plate is a constructive margin, the mid-Atlantic ridge, extending from approximately 20°N to the Azores and then to Iceland.