ocean trenches and ridges![click to hear](/images/speaker.jpg)
Trench: very deep, elongated cavity bordering a continent or an island arc; it forms when one tectonic plate slides beneath another. Ridge: underwater mountain range that criss-crosses the oceans and is formed by rising magma in a zone where two plates are moving apart.
Mid-Indian Ridge ![click to hear](/images/speaker.jpg)
Mountain range in the middle of the Indian Ocean that separates the African and Australian-Indian plates.
Southwest Indian Ridge ![click to hear](/images/speaker.jpg)
Ridge separating the African and Antarctic plates; it joins the Mid-Indian and Southeast Indian ridges off the coast of Madagascar.
South America ![click to hear](/images/speaker.jpg)
Represents about 12% of the world’s land and is linked to North America by Central America; its features include the Andes in the west and plains and plateaus in east and central regions.
Puerto Rico Trench ![click to hear](/images/speaker.jpg)
Trench located off the coast of Puerto Rico, on the boundary between the South American and Caribbean plates; it features the deepest point in the Atlantic Ocean (27,493 feet).
Peru-Chile Trench ![click to hear](/images/speaker.jpg)
Trench (26,460 feet) bordering South America; the world’s longest trench (3,700 mi), it is located on the boundary between the Nazca Plate and the South American Plate.
Pacific-Antarctic Ridge ![click to hear](/images/speaker.jpg)
Mountain range separating the Pacific and Antarctic plates; it joins the eastern Pacific Ridge off the coast of South America.
East Pacific Ridge ![click to hear](/images/speaker.jpg)
Ridge that marks the boundary between the Pacific and Cocos Islands plates to the north, and the Pacific and Nazca plates to the south.
Aleutian Trench ![click to hear](/images/speaker.jpg)
Trench (25,600 feet) extending from Alaska to the Kamchatka Peninsula; it results from the Pacific Plate sliding beneath the North American Plate.
North America ![click to hear](/images/speaker.jpg)
Its area (9.3 million mi2) represents about 16% of the world’s land; the Central American isthmus is an extension of North America.
Africa ![click to hear](/images/speaker.jpg)
Continent that represents about 20% of the world’s land; two-thirds of its surface lies north of the Equator. Characterized by very hot climates, Mediterranean in the north and south, tropical and arid elsewhere.
Mid-Atlantic Ridge ![click to hear](/images/speaker.jpg)
Ridge about 7,000 mi long, located in the middle of the Atlantic Ocean; some of its mountains reach the surface, forming islands such as Iceland.
Europe ![click to hear](/images/speaker.jpg)
Western extremity of the vast Eurasian continent that, by convention, is separated from Asia by the Ural Mountains; it covers a relatively small area.
Asia ![click to hear](/images/speaker.jpg)
The largest and most populous continent, Asia represents 32% of the world’s land; it is dominated by imposing mountain ranges.
Ryukyu Trench ![click to hear](/images/speaker.jpg)
Trench (24,629 feet) located near the Ryukyu Islands; it marks the boundary between the Philippine Plate and the Eurasian Plate.
Japan Trench ![click to hear](/images/speaker.jpg)
Trench (27,929 feet) located east of Japan, on the boundary between the Pacific Plate and the Eurasian Plate; this zone is marked by intense seismic activity.
Kuril Trench ![click to hear](/images/speaker.jpg)
Trench (34,587 feet) located northeast of Japan; it results from the Pacific Plate sliding beneath the Eurasian Plate.
Mariana Trench ![click to hear](/images/speaker.jpg)
Cavity located near the Mariana Islands, where the Pacific Plate and the Philippine Plate converge; it is the world’s deepest trench (about 36,000 feet).
Philippine Trench ![click to hear](/images/speaker.jpg)
Trench bordering the eastern Philippines, reaching depths of 34,578 feet; it results from the Philippine Plate sinking beneath the Eurasian Plate.
Kermadec-Tonga Trench ![click to hear](/images/speaker.jpg)
Cavity located north of New Zealand, where the Pacific Plate meets the Australian-Indian Plate; it reaches depths of 35,702 feet.
Australia ![click to hear](/images/speaker.jpg)
The world’s largest island (3 million mi2) is sparsely inhabited in spite of its size; because of its isolation, Australia’s wildlife is unique.
Southeast Indian Ridge ![click to hear](/images/speaker.jpg)
Ridge separating the Antarctic Plate from the Australian-Indian Plate; its topography is more regular than the topography of the Southwest Indian and Mid-Indian ridges.
Java Trench ![click to hear](/images/speaker.jpg)
Trench located south of Indonesia, between the Australian-Indian and the Eurasian Plates; it is the deepest point in the Indian Ocean (24,440 ft).