Mount Kilimanjaro Geology
Mount Kilimanjaro lies on a tectonic line intersection about 80km east of East Africa’s tectonically active Rift Valley. Many people have been told that Kilimanjaro is a volcano, but that is not strictly true – it’s actually three volcanoes.
Roughly 750,000 years ago, molten lava burst through a gap in the surface of the Great Rift Valley. The great pressure that caused this eruption also pushed part of the Earth’s crust skywards, creating the Shira volcano, the oldest of the volcanoes forming the Kilimanjaro massif, which stopped erupting and became extinct roughly 500,000 years ago. The Shira volcanic cone collapsed leaving the Shira Ridge as part of its Caldera Rim.
Subsequent eruptions over the following 50,000 years gave birth to Mawenzi and Kibo.
Kibo erupted a number of times over the proceeding 100,000 years or so which took its summit ever higher and also brought about the black volcanic rock which today helps make Kilimanjaro such an incongruous and fascinating sight, especially when taken in contrast to the white glacial summit. The main summit point of Uhuru Point is located on Kibo’s outer crater rim.
The striking and imposing rock walls on Kilimanjaro and Mawenzi are generally composed of lava and ash.
While Mawenzi has been significantly eroded over the years, it retains a striking volcanic shape and makes for great photographs on your way to Uhuru Peak.
Deep gorges or barrancos have been cut into the soft rocks and ash of Kilimanjaro. The most impressive of these is the Great Barranco below the Western Breach and the two Barrancos on the east side of Mawenzi.
Kibo’s last volcanic eruption was 200 years ago. Today, it is classified as dormant rather than extinct.
At one stage, most of the summit of Kilimanjaro was covered by an ice cap, probably more than 100 metres deep. Glaciers extended well down the mountain. At present only a small fraction of the glacial cover remains and some estimate that the mountains’ famous glaciers could disappear by as soon as 2030.