Photograph by Chris Johns
Lava spews out of a fissure in the Virunga mountains in the Democratic Republic of the Congo. The Virunga chain is part of the East African Rift Valley system, which marks the boundary between two plates: the Nubian plate to the west and the Somalian plate to the east. The rift valley is a classic example of a divergent plate boundary.
Hot Lava, Mount Etna
Photograph by Carsten Peter
A river of molten lava flows through a channel in hardened lava after an eruption at Mount Etna in Sicily, Italy. Mount Etna, one of Europe's most active volcanoes, was created by the subduction of part of the northward-moving African plate beneath the Eurasian plate.
Thingvellir National Park, Iceland
Photograph by Crispin Rodwell/Alamy
Hikers walk in the shadow of cliffs in Iceland's Thingvellir National Park. The divergent Mid-Atlantic Ridge rises above sea level at Thingvellir, with the North American plate to the west and the Eurasian plate to the east.
Photograph by W.A. Rogers
Offset streams cut into the Carrizo Plain along the San Andreas Fault in California. The fault, which runs more than 700 miles (1,100 kilometers), is the boundary between the Pacific and North American tectonic plates. The stretch of the fault that runs through Carrizo Plain is very well defined because the land is arid and the fault has not been significantly eroded.
Photograph by Louis Maher
The Sheep Mountain anticline in Bighorn Basin, Wyoming, is part of the Rocky Mountains. The mountain chain was formed during a period of intense plate tectonic activity, about 70 million to 40 million years ago. Anticlines are folds that arch upward, with older rocks in the center and younger rocks on the outside.
Raplee Ridge, Utah
Photograph by Michael Collier
Raplee Ridge, part of the Monument Upwarp in southeastern Utah, is a long, narrow, folded anticline that formed about 70 million to 50 million years ago.
Photograph by Emory Kristoff
An eelpout fish swims near tubeworms at the Mid-Atlantic Ridge in the Atlantic Ocean. The Mid-Atlantic Ridge is an example of a divergent plate boundary and is an area where new seafloor is being created.
Photograph by Al Giddings
A cloud of hydrothermal fluids streams from a black smoker, or mineral chimney, along the Mid-Ocean Ridge off the west coast of Mexico. Black smokers are common to spreading zones in plate boundaries. Chimneys are made of lead, iron, manganese, and zinc sulfides, through which spew superheated ocean water. They also harbor exotic life-forms, far below the reach of sunlight.
Photograph by Peter Essick
Sunrise warms the icy southern end of the Andes during a rare break in the weather in Chile's Torres del Paine National Park. The Andes mountains, which span the entire western coast of South America, formed when the Nazca plate subducted under the South American plate.
Dallol Volcano, Ethiopia
Photograph by Carsten Peter
Sulfur, salt, and other minerals color the crater of Dallol volcano, part of the Danakil Depression in Ethiopia. At 157 feet (48 meters) below sea level, Dallol is Earth's lowest land volcano.
Lake Natron, Tanzania
Photograph by George Steinmetz, National Geographic
An airplane casts a shadow over the red waters of Lake Natron in Tanzania, part of the East African Rift Valley. The water's red hue is due to algae that live on salts spewed from nearby volcanoes. The East African Rift Valley system begins in northern Syria and extends across East Africa into Mozambique.
Persian Gulf Plate Activity
Photograph by Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC
In the Persian Gulf, two tectonic plates collide. The Arabian plate (lower left) is running up on the Eurasian plate (upper right). The Persian Gulf (top) and the Gulf of Oman (bottom) were once the site of a rift, a place where two plates pull apart from each other, and the Indian Ocean filled in the widening gap between the two plates. However, the process then reversed, and about 20 million years ago, the gulf began to close up. The collision of the two continental plates gives Iran its mountainous terrain.
Rift Escarpments, Eritrea
Photograph by Chris Johns
A mosque dominates the farming villages of Adi Caieh, Eritrea. Rift escarpments in the distance, now heavily eroded, once adjoined the Arabian Peninsula before the Red Sea opened. The escarpments shifted when the continental crust moved west, as the Red Sea formed in stop-start action during a 30-million-year period.
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