In the northern Mid-Atlantic Ridge, the North American plate and the Eurasian plate are splitting apart at a rate of about 2. Over millions of years, the Mid-Atlantic Ridge has formed rift valleys as wide as 15 kilometers 9 miles. Like many underwater rift valleys, the East Pacific Rise is dotted with hydrothermal vents. Geologic activity beneath the underwater rift valley creates these vents, which spew super-heated water and vent fluid s into the ocean.
Continental Rift Valleys. Very few active rift valleys are found on continental lithosphere. The Baikal Rift Valley is formed by a divergent plate boundary, where the Amur plate is slowly tearing itself away from the Eurasian plate, and has been doing so for about 25 million years.
The Amur plate is moving eastward at a rate of about 4 to 5 millimeters. The West Antarctic Rift is one of the most difficult rift valleys to study, because it lies beneath the massive Antarctic Ice Sheet , which can be more than 2 kilometers 1. The Rio Grande Rift separates the Colorado Plateau , which is generally moving in a clockwise direction, from the older part craton of the North American plate.
The most well-known rift valley on Earth is probably the so-called " Great Rift Valley System " which stretches from the Middle East in the north to Mozambique in the south. The area is geologically active, and features volcano es, hot spring s, geyser s, and frequent earthquake s.
Today, however, the Great Rift Valley exists as a cultural concept, not a scientific one. The northern part of the system is the Jordan Rift Valley. Millions of years ago, the Arabian Peninsula was connected to Africa. Seafloor spreading caused the Arabian and African plates to rift apart. The Indian Ocean flooded the rift valley between the continents, creating the Red Sea. Today, Africa and Asia are connected by the triangle of the Sinai Peninsula. East African Rift. The Western Rift is one of the most biodiverse regions in Africa, featuring a narrow corridor of highland forest s, snow-capped mountains, savanna s, and chains of lake s and wetland s.
Rift lake s, formed as freshwater floods rift valleys, often mark rift valley systems. More than a billion years ago, for instance, the North American plate began a rifting process. A triple junction formed in the middle of the young continent, and deep rift valley developed.
Freshwater drained and collected in this rift valley, creating a lake. After millions of years, however, the rift failed. Today, the remains of that ancient rift lake, Lake Superior, rest atop one of the oldest and deepest rift valleys in the world. Lake Baikal, the rift lake over the Baikal Rift Valley in Siberia, is the deepest and oldest freshwater lake in the world.
The deepest parts of Lake Baikal are 1, meters 5, feet , and are getting deeper every year. In addition, over the past 25 million years, layers of soft sediment have accumulate d on the lakebed.
The actual floor of the rift valley is more than 5 kilometers 3 miles deep. Lake Baikal also has the largest volume of liquid freshwater in the world—a staggering 23, cubic kilometers 5, cubic miles. Although the Dead Sea is not the world's deepest lake, the deep Jordan Rift makes it the lowest land elevation on Earth.
Unlike Lake Baikal, however, the Dead Sea is not a true rift lake as it was not formed entirely by the rift beneath it. The so-called Dead Sea Transform is a geologically complex area, where tectonic plates interact in many ways.
The most famous rift lakes in the world may be the series of narrow, deep rift valleys in the East African Rift known simply as the Rift Valley lakes. The Rift Valley lakes, stretching from Ethiopia to Malawi, are sites of amazing biodiversity.
Only Lake Baikal is deeper and holds more water. Like many freshwater Rift Valley lakes, Lake Tanganyika is home to hundreds of endemic species of cichlid fish. Rift valleys are typically deep and narrow. Photograph by Emory Kristof, National Geographic. African Great Lakes. Antarctic Ice Sheet. Also called a collision zone. Great Rift Valley system. Horn of Africa. Also called the geosphere. Middle East. Also called an alkaline lake. Also known as a composite volcano.
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Plate Tectonics. View Article. View Video. View leveled Article. Educational Resources in Your Inbox. Rifts exhibit a very distinctive topography, characterised by a series of fault-bounded depressions surrounded by higher terrain.
In the East African system, a series of aligned rift valleys separated from each other by large bounding faults can be clearly seen from space. Not all of these fractures formed at the same time, but followed a sequence starting in the Afar region in northern Ethiopia at around 30m years ago and propagating southwards towards Zimbabwe at a mean rate of between 2.
Although most of the time rifting is unnoticeable to us, the formation of new faults, fissures and cracks or renewed movement along old faults as the Nubian and Somali plates continue moving apart can result in earthquakes. However, in East Africa most of this seismicity is spread over a wide zone across the rift valley and is of relatively small magnitude.
Volcanism running alongside is a further surface manifestation of the ongoing process of continental break up and the proximity of the hot molten asthenosphere to the surface. The East African Rift is unique in that it allows us to observe different stages of rifting along its length. To the south, where the rift is young, extension rates are low and faulting occurs over a wide area. Volcanism and seismicity are limited. Towards the Afar region, however, the entire rift valley floor is covered with volcanic rocks.
This suggests that, in this area, the lithosphere has thinned almost to the point of complete break up. When this happens, a new ocean will begin forming by the solidification of magma in the space created by the broken-up plates.
Eventually, over a period of tens of millions of years, seafloor spreading will progress along the entire length of the rift. The ocean will flood in and, as a result, the African continent will become smaller and there will be a large island in the Indian Ocean composed of parts of Ethiopia and Somalia, including the Horn of Africa.
Dramatic events, such as sudden motorway-splitting faults can give continental rifting a sense of urgency.
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