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