East African Rift

The East African Rift (EAR) is an active continental rift zone in East Africa. It is a massive area where the Earth's crust is actively splitting apart. This process is part of a much larger tectonic system. In the past, this system was known as the Great Rift Valley. It extends far north into Asia Minor, a region called Anatolia. The rift is a developing divergent tectonic plate boundary. This means two large pieces of the Earth's crust are moving away from each other.

At this boundary, the African plate is splitting into two new plates. These are called the Somali plate and the Nubian plate. They move apart at a rate of about 8 to 9 millimeters every year. The rift system is complex and includes three microplates. These are the Victoria microplate in the north, and the Rovuma and Lwandle microplates in the south. The Victoria microplate is actually rotating anti-clockwise. This rotation happens because of the different strengths of the lithospheric regions nearby.

Scientists have different ideas about how this rift formed. In 1972, some researchers thought differences in crustal density caused it. However, since the 1990s, evidence has supported the idea of mantle plumes. These are columns of hot material rising from deep inside the Earth. A more recent theory from 2009 suggests a feedback loop. In this model, magmatism and plate tectonics work together. As the lithosphere thins, it creates volcanic activity. This magmatic activity then thins the lithosphere even more. Eventually, the thinning crust behaves like a mid-ocean ridge.

The rift follows several different paths across the continent. North of the Afar triple junction, it splits into two directions. One path goes west to the Red Sea Rift. The other path goes east to the Aden Ridge in the Gulf of Aden. South of the triple junction, there are two main branches. The Eastern Rift Valley, or Gregory Rift, includes the Main Ethiopian Rift. It runs through Kenya and into northern Tanzania. The Western Rift Valley includes the Albertine Rift. This branch passes through the Democratic Republic of the Congo, Uganda, Rwanda, and Burundi.

Volcanic activity is a major feature of this rift system. Many famous mountains, like Mount Kilimanjaro and Mount Kenya, were created by the EAR. Some volcanoes are very active. Erta Ale in Ethiopia has had a summit lava lake since at least 1906. Another unique volcano is Ol Doinyo Lengai. It is the only active natrocarbonatite volcano on Earth. Its lava is very runny, with a viscosity similar to olive oil. The rift is also the largest seismically active rift system on Earth. Most earthquakes occur near the Afar Depression. In the last century, some earthquakes reached a magnitude of 7.0.

The rift system also has a massive impact on the global climate. High elevations like the Ethiopian Highlands catch more rainfall than the dry lowlands. Large lakes in the rift, such as Lake Victoria, create water vapor. This vapor affects weather patterns across East Africa through lake breeze systems. The east-to-west river valleys also influence the wind. They can accelerate winds toward Central Africa. This helps keep the Congo Basin rainforest rainy while making East Africa drier. The rift also affects the Somali Jet, which is a major wind system in the Indian Ocean.

Finally, the East African Rift is a vital site for studying human history. The rapidly eroding highlands fill the valleys with sediments. This environment is excellent for preserving fossils. Many bones of hominid ancestors have been found here. One famous example is "Lucy," a partial skeleton found by Donald Johanson. She lived over 3 million years ago. Other important discoveries include 10-million-year-old apes like Chororapithecus abyssinicus. These fossils help scientists understand how humans evolved over millions of years.