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My name is Wendy Miller, and this blog explains the East African Rift Valley and its properties. To navigate, use the subjects on the right to find seperate topics within the blog.

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Map of the location of East African Rift Valleys

The East African Rift Valley was named "The Great Rift Valley" by the explorer John Walter Gregory in the 19th century. The Great Rift Valley is an incorrect name because it pertains to seperate but related rift systems. The East African Rift is a divergent plate boundary that extends from the Afar Triple Junction southward across eastern Africa through Ethiopia, Kenya, Uganda, and Tanzania (see photo above). The boundary is in the process of splitting the African Plate into two separate plates. Geologists named the plate that makes up the majority of Africa the Nubian Plate, and the Somalian Plate is the smaller of the two that is moving away from the Nubian Plate (see photo below). The two plates together are moving away from the Arabian plate to the north, and the three meet in Ethiopia. The place where the three plates meet is called a triple-junction. Geologists today still debate why and how rifting comes about, but East Africa displays this process extremely clearly. Subterranean forces broke the earth's crust apart and large chunks of the crust sunk between parallel fault lines and forced up molten rock in volcanic eruptions. Many boiling hot springs along the rift prove that volcanic activity is extremely high along the rift system.

Web Sources

Websites used to complete this blog:

http://en.wikipedia.org/wiki/Lake_Malawi

http://www.gadling.com/media/2006/02/lake-malawi.jpg

http://www.merriam-webster.com/maps/images/maps/malawi_map.gif

http://dannysdesktop.themesunlimited.com/Files/nasa/ZaireLakeTanganyika.jpg

http://soundwaves.usgs.gov/1999/11/tanganyikamapLG.gif

http://en.wikipedia.org/wiki/Great_Rift_Valley

http://geology.com/articles/east-africa-rift.shtml

http://www.cotf.edu/ete/modules/rift/rvwhatisriftvalley.html

http://www.geolor.com/East_African_Rift_Valley_geolor.htm

http://www.geology.sdsu.edu/how_volcanoes_work/Unusual%20lava.html

http://frank.mtsu.edu/~fbelton/lengai.html

http://stloe.most.go.th/html/10_index/LOcanada4/403/images/1_2.jpg

http://www.kilimanjaro.cc/mkgeolog.htm

http://volcano.oregonstate.edu/vwdocs/volc_images/africa/mt_kenya.html

http://www.kiliair.com/images/gallerys/kilimanjaro3.jpg

http://photos.igougo.com/images/p248334_Tanzania-01_Doinyo_Lengai.jpg

www.earlham.edu/~graveti/olddoinyolengai.htm

http://en.wikipidia.org/wiki/stratovolcano

http://en.wikipedia.org/wiki/Mount_Kilimanjaro

http://en.wikipedia.org/wiki/Mount_Kenya

http://www.homeless_international.org/doc_images/mtkenyar.jpg

http://www.le.ac.uk/bl/staff/dmh/ew/Exhib5a_LakeBaringo.JPG

http://science.jrank.org/pages/106/Africa-East-African-rift-system.html

http://www.ing.pan.pl/ecga_js/pict_his/LakeMagadi.jpg

Rift Valley Lakes

Rift Valley Lakes

The lakes in eastern Africa that formed because of the rifting that occurs there are some of the oldest, largest, and deepest lakes in the world. Many of these lakes hold fresh water and are ecoregions which are large areas of water that have distinct groups of biological species. The reasoning behind the lakes being ecoregions is the mixture between specific landforms and types of soil. Wikipidia uses Omernik's definition and defines an ecoregion as "areas within which there is a spacial coincedence in characteristics of geographical phenomena associated with differences in quality, health, and itegrity of ecosystems." Other lakes in eastern Africa are composed of alkaline or soda and support extremely specialized organisms. Through Kenya, there is a series of small lakes that are covered by volcanic ash and sediments. These lakes include Lake Baringo and Lake Magadi (see photos below).

Lake Baringo

Lake Magadi. You can clearly see the ash and sediment covering the water.

Specific lakes that have formed in the rift valley of eastern Africa are Lake Malawi, Lake Tanganyika, and Lake Victoria. The elongated shapes of both Lake Malawi and Lake Tanganyika show that they are forming due to the rifting system. Through Kenya, there is a series of lakes that are all covered in volcanic ash and debris

Lake Malawi:

Lake Malawi lies between Malawi, Mozambique, and Tanzania. There are more fish species in Lake Malawi than any other lake in the world, and it is the third largest lake in Africa. It formed on the rift valley where the African Tectonic Plate is splitting in two. The lake is about 40,000 years old. One specific fish that Lake Malawi is famous for is its chichlids. These fish are famous for their bright colors and are often shown in aquariums.

Lake Malawi is circled above on the map

Lake Tanganyika:

Photo of Lake Tanganyika from space

Lake Tanganyika is located in central africa within the East African Rift and is confined by the valley walls (also created by the rift system). It's the largest and deepest lake in Africa. With a depth of about 600 feet, Lake Tanganyika is an extremely important place for the reasearch and study of biological evolution. The lake holds more that 200 species of chichlids (species of fish described above).

Location of Lake Tanganyika shown on a map

The Formation of the Rift System

Formation of the Rift System

Heat flow from the asthenosphere is causing bulges is Kenya and Ethiopia. It’s believed by geologists that these bulges formed because of mantle plumes under the earth’s surface that heat the continent so that it expands and fractures. When these bulges form, they stretch the crust into a series of normal faults. The rift opened about 65 million years ago, and while it's splitting the African continent in two, it's also caused the Red Sea to open into the Indian Ocean. The reasoning behind this occurence is that the Arabian Plate is drifting to the northeast. This drifting has also helped cause the formation of the volcanoes and mountains in East Africa.

Volcanic eruptions usually occur along these rifts, and the lava comes out of the fractures instead of individual volcanoes. This lava spreads around the land in floods. Two branches of this rifting have formed with this process. There is one that heads westward, and the rift filled with water which makes up the African Great Lakes. The other one is parallel to the latter and goes through Kenya to enter Tanzania. It is thought by geologists that the reasoning behind two parallel rifts is the Tanzania craton (ancient metamorphic rock) that was too hard for to be torn, so the rifts branched out and around the craton. The eastern branch of the rift has more volcanism and is characterized by a broad dome.

This photo shows both the eastern and western branches of the rift system. Both rifts surround Lake Victoria.

Major East African Volcanoes

Major East African Volcanoes

The eastern branch of the rift valley is more seismically active than the western branch. More volcanic eruptions occur on the eastern branch because the magma is protruding the earth's surface. According to geologists, the eastern branch has more volcanism and is more seismically active because it is older than the western branch.

Ol Doinyo Lengai Volcano:

Ol Doinyou Lengai is located in northern Tanzania and its name means "Mountain of God" in Massai language. The Mountain of God is 2900 meters steep and is the only volcano on Earth that produces natrocarbonatite lava, meaning it contains more than fifty percent of carbonate content. Natrocarbonatite lava is much cooler than other types of lava, is a highly fluid lava, and contains almost no silicon. Due to its cooler heat and low viscosity, it looks like oil as it flows out of the Ol Doinyo Lengai Volcano during the day, but at night it appears to be more of an orange color (see photos below). Viscosity is a measure of the thickness of lava that is established by stress. The minerals that make up Ol Doinyo Lengai's lava include nyerereiete and gregoryte, and both of these contain a high percentage of sodium and potassium. Natural reactions of the chemicals in the lava when mixted with moisture turns the lava white. These ususual eruptions of low silicate eruptions come from holes or cracks from the cones in or near the base of the volcano. However, the patterns of the volcanoes eruptions still remain a mystery to geologists. The last two eruptions of this sort were from 1966 to 1967 and from 2007 to 2008. The volcano is in its late stages of eruption currently.

The low viscosity of the lava gives it its frothy, oil-like appearance.

Due to its cool heat, the lava of Ol Doinyo Lengai only glows at night.

Below is a link to a YouTube video of Ol Doinyo Lengai erupting natrocarbonatite lava:

http://www.youtube.com/watch?v=3Ck4q1d2-XE

Although there are points where the Ol Doinyo Lengai often produces lava with a low silicone content, there are also periods where the volcano produces more silicate material and thus reduces its viscosity. The lava in these types of eruptions of the Mountain of God is less fluidic and claims the properties of ash.

Mt. Kilimanjaro:

Birth of Kilimanjaro:
Millions of years ago, when lava burst through the surface of the East African Rift, pressure pushed the earth upward creating the Shira volcano which is part of the Mount Kilimanjaro volcano group. The Shira eventually collapsed creating a huge caldera where it stood before. After an eruption of the caldera, the Mawenzi volcano began to form. Unlike the Shira volcano, Mawenzi still holds a similar shape as it did when it formed. An eruption by Mawenzi then caused the formation of Kibo. Eruptions by the Kibo volcano caused greater vertical expansion of Kilimanjaro.

Mt. Kilimanjaro is the tallest inactive strotovolcano in the world, is located in eastern Tanzania and has three volcanic cones named Kibo, Mawenzi, and Shira (mentioned above). A strotovolcano is a tall volcano with many layers of hardened lava, tephra, and volcanic ash. These volcanoes are sometimes called composite volcanoes because of their composite build-up of different layers. Kilimanjaro's peak is at 5,892 meters making it extremely elevated. The highest peak on the mountain is Uhuru peak on the volcano Kibo, and the summit crater of Kilimanjaro measures 1.5 miles across. In the center of Kibo is a smaller cone named Mawenzi. Mawenzi is an older cone with sheer faces on each side. Because of the high elevation and location of Kilimanjaro, it experiences almost every known type of climate. Kilimanjaro, as far as experts know, has been dormant for millions of years.

Because of the tephra content of the volcano (an igneous rock), it has a tephra cinder cone. An explosion that is thought to have occured millions of years ago violently erupted gaseous lava that then turned into cinders. This explosion created the giant tephra cone. The lava from Kilimanjaro is extremely viscous and this explains why Kilimanjaro has so many small craters. The rock also has a high content of silica.

Mt. Kilimanjaro from an aerial view.

Mt. Kenya:

Mount Kenya is located in central Kenya and is just south of the equator. The last eruption of Mt. Kenya was about 3 million years ago. Mt. Kenya is a dome-shaped central volcano. A central volcano is a volcano constructed by the ejection of debris and lava flows from a central point forming almost a symmetrical volcano. Its highest peaks include Batian and Nelion and both are around 5,000 meters high. The original crater was previously higher than its current state, but due to erosion from glaciers, almost 35% of the volcano was worn away. The most common rock that makes up Mt. Kenya is basaltic rocks, an iron and magnesium-rich lava that contains about 50% silica. Similarly to many other volcanoes in the world covered in glaciers, it's estimated that in about 25 years, the ice on Mt. Kenya will melt away. Records of Mount Kenya began in 1873, and since that time, seven out of eighteen glaciers have melted away.

Mt. Kenya