<P> Most geologically young mountain ranges on the Earth's land surface are associated with either the Pacific Ring of Fire or the Alpide Belt . The Pacific Ring of Fire includes the Andes of South America, extends through the North American Cordillera along the Pacific Coast, the Aleutian Range, on through Kamchatka, Japan, Taiwan, the Philippines, Papua New Guinea, to New Zealand . The Andes is 7,000 kilometres (4,350 mi) long and is often considered the world's longest mountain system . </P> <P> The Alpide belt includes Indonesia and southeast Asia, through the Himalaya, and ends in the Alps, Spain and Atlas Mountains . The belt also includes other European and Asian mountain ranges . The Himalayas contain the highest mountains in the world, including Mount Everest, which is 8,848 metres (29,029 ft) high and traverses the border between China and Nepal . </P> <P> Mountain ranges outside these two systems include the Arctic Cordillera, the Urals, the Appalachians, the Scandinavian Mountains, the Altai Mountains and the Hijaz Mountains . If the definition of a mountain range is stretched to include underwater mountains, then the Ocean Ridges form the longest continuous mountain system on Earth, with a length of 65,000 kilometres (40,400 mi). </P> <P> The mountain systems of the earth are characterized by a tree structure, where mountain ranges can contain sub-ranges . The sub-range relationship is often expressed as a parent - child relationship . For example, the White Mountains of New Hampshire and the Blue Ridge Mountains are sub-ranges of the Appalachian Mountains . Equivalently, the Appalachians are the parent of the White Mountains and Blue Ridge Mountains, and the White Mountains and the Blue Ridge Mountains are children of the Appalachians . </P>

What is a continuous series of underwater mountains called