The Geology Of Kilimanjaro

Published: 12th May 2009
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Kilimanjaro lies on a tectonic line intersection 80km. east of the tectonically active Rift Valley. The activity which created this stratovolcano dates back less than a million years and the central ash pit on Kibo, the highest volcanic centre, may be only several hundred years old. Steam and sulphur fumaroles here are indicative of residual activity. Stratovolcanoes are formed when erupted ash and cinders mix with lava flows and cool to produce a steep conical formation. These types of volcanoes usually take tens of thousands of years to materialize and may consist of a number of lava forms including dacite, basalt and andesite to name but a few.

On the Marangu Route you will more than likely come across a number of small cone shaped hills. These are known as 'parasitic cones' and are quite simply formations that are the product of offshoots of the main lava flow. In the event that you elect to do the optional Saddle Walk, you will pass a cliff face that appears to be stained with black and white stripes. Entitled Zebra Rock, this unusually patterned formation is the result of mineral rich rain water flowing down from the rocks above and streaking the almost black lava cliff white in places.

The formations on Kilimanjaro are not limited to volcanic rock alone, but also include incredibly impressive glacial configurations. While the sheets of ice on the mountain reflect the sun's rays from above, typical Weather Patterns on the mountain ensure the heat from the ground melts the ice from below, resulting in the formation of intricate undercuts and overhangs.

Thousands of years ago, whole sheets of ice covered the mountain all the way down to almost 3000 feet. Today they can be seen only near the peak, and scientist predict that sadly within the next 15 years the snow cap may just disappear completely, confining the sight of the Great White Mountain to the pages of literature and the memories of those lucky enough to see it in it's glory.

Shira and Mawenzi were two other areas of volcanic activity. Both became inactive before Kibo. The Shira volcanic cone collapsed leaving the Shira Ridge as part of its Caldera Rim. Mawenzi has been heavily eroded to leave a mass of steep-sided ridges and summits, particularly dramatic on the infrequently-seen eastern side.

Kibo is the best preserved centre; it has three concentric craters and the outer crater rim rises to Uhuru Point - the chief summit. The middle, Reusch crater contains the main fumaroles and in its centre the 130m deep and 400m wide Ash Pit. The outer crater has been breached by lava flows in several places, the most dramatic of these being the Western Breach.

The ash and lava covered slopes of Kibo are mainly gentle-angled from the steep, glaciated precipices which defend its southern and south-western flanks. The impressive rock walls on Kilimanjaro and Mawenzi are generally composed of lavas and ashes.

Deep gorges (barrancos) have been carved into the soft rocks and ashes 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.

Numerous parasitic cones extend east-west across Kilimanjaro; some are located near the Mandara Hut (Maundi Crater offers a fine view point), while others lie just north of the Shira Route.

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 forming moraine ridges, clearly visible now on the southern flanks down to about 4000m. At present only a small fraction of the glacial cover remains.

The remnants of the ice cap can be seen as the spectacular ice cliffs of the Northern and Eastern Icefields, and the longest glaciers are found on the precipitous southern and south-western flanks. If the present rate of recession continues the majority of the glaciers on Kilimanjaro could vanish altogether in the next 50 years.

For more information on climbing Kilimanjaro or visiting Tanzania's mountains click Climb Kilimanjaro with Mountain Kingdom Safaris


Roy J Hinde M.Sc. is a former research scientist who now is a director of Wild Things Safaris Ltd and runs the marketing for MK safaris Climb Kilimanjaro.

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