From UPSC perspective, the following things are important :
Prelims level : Various rift valleys mentioned in the newscard
Mains level : Intra-continental drifting
- The recent scientific evidence has given a glimpse of the Earth’s changing contours—the African continent is splitting into two.
Africa is splitting
- A place near Nairobi, Kenya had a large crack on the ground that appeared during an intense spell of rain and flooding.
- The crack is 57 km long which is a locus of a future ocean formation.
- Such an event happened 138 million years ago when the South American and African continents separated to give rise to the current South Atlantic Ocean.
- All such signs on Earth’s surface point to a totally new landscape, which resembled how it looked like when it was formed 4.5 billion years ago one huge continent.
- The farthest scientists can predict is that 250 million years from now all continents will unite again in one supercontinent and then will break apart again along the future rift systems.
Why such cracks?
- At first, geologists thought the crack in Kenya was formed due to “erosion of soft soils infilling an old rift-related fault.
- They later revealed that the crack had existed for quite some time, but was filled with ash from Mount Longmont, a volcano nearby.
- The rain had washed away the ash to expose the crack. This triggered a debate whether the crack was a part of the East African Rift system.
Rift in systems
- Rifts are the regions of extension of the crust and the lithosphere.
- Continental changes take place at the boundaries of tectonic plates which are divisions of the uppermost layer of the Earth and swim around on the fluid mantle layer below it.
- The extension may develop to a stage when two plates split apart, like in the example of the Red Sea and the Gulf of Aden. So continental rifts are potential places where new oceans are expected to form.
- These plates periodically crash into each other, giving rise to earthquakes and volcanic eruptions when the intensity is less over short periods of time.
- Over longer periods of time, they create all the geological and geographical features that we find on Earth like mountains, valleys and oceans.
- One of these processes is an intra-continental rift system which acts between tectonic plates and can give rise to rift valleys or even new oceans.
- The African Rift Valley, which is between Ethiopia and Kenya, is a classical example of this geodynamic process.
- There, volcanism, earth-quakes and fracturing of the Earth’s surface result from the enormous forces that tear the eastern portion of the African continent apart.
East African rift system
- The East African rift system is more active in terms of volcanism and it is connected to the global ocean rift (ridge) system through the Afar-Red Sea—Gulf of Aden triple junction.
- The Red Sea and the Gulf of Aden are the rifts along which two continents break apart and new oceanic flow is formed.
- There are numerous rift systems around the world but the most active ones are the East African rift, Baikal rift, West Antarctic rift, Rio Grande rift, the Rhine Graben rift system in Europe and Shanxi rift system in China.
- When such geographical features become prominent enough they reshape the way the planet looks.
- The rifts undergo massive geological changes—shoulders of rifts grow and get eroded by rain and melting snow.
- At the same time, the axial parts of rifts subside and get filled with sediments, which gets eroded from the shoulders.