Volcanic Rock on Kilimanjaro

by Debra Bouwer

If you were hoping to read a blog about climbing Kilimanjaro to the exciting sounds of Alikiba then sorry to disappoint. As much fun as it is to have songs from porters radios, rocking out rhythmic music as they pass you by, calling “mambo, pole pole,” this is about the true grit of Kilimanjaro; the rocks.

This vast mountain is situated near the fault-line of two tectonic plates, and began to form about a million years ago as the shifting planes thinned the crust of the earth’s surface. Like two pieces of velcro being pulled and ripped apart other with mighty force they tore under the pressure. Over time, molten lava which had been bubbling and boiling from the earths cauldron started to oose up and out of their volcanic cones, initially creating calm gentle slopes. However continued and larger eruptions radically changed the face of the landscape, caused by not one, but three Volcanoes. They are Shira and Mawenzi, which are extinct, and Kibo, the one we climb, which is still dormant. Shira was the first to erupt and stopped about 500 0000 years ago, eventually collapsing to form the massive 6200ha Shira Plateau.

Next, came Mawenzi, blasting around 500cu km of volcanic rock and stone from beneath the ground into the air and onto the surrounding plains. Not much remains of the crater today except a 5149m high horse shoe crescent shaped from her eroded flank. Adding to her craggy character are narrow jagged ridges known as dyke swarms, which stretch down from her summit.

The last of the three to wake from her slumber was Kibo, seemingly the most angry of the three, progressively blasting ever more violent eruptions from her manic centre which pushed the Kilimanjaro massive higher and higher to around 5900m. Shira, which at that stage sported a caldera was quickly filled in by massive lava flows from Kibo. It is not an easy plateau to see unless you are going along Shira Route, otherwise the best way to catch a glimpse is to look back down towards Shira camp as you reach the half way point to Lava Tower. Either way, the remaining jagged peaks of its edges can easily be seen on the right of Shira Camp.

Mawenzi Peak from across the saddle

Now many of us who have climbed or wish to climb Kilimanjaro are not geologists, and like me, have probably not opened a textbook on geology since high school. However on my second climb up Kilimanjaro I became increasingly curious about the different volcanic (igneous) rocks we were seeing on the mountain, partially started by our wonderful guide who himself, had a fascination with obsidian.

This amazing volcanic stone was formed when the force of lava was pushed up with such ferocity that it hit cold air faster and rapidly cooled to create the hard glass like sheen that we see on it today. The largest patches of obsidian I have ever seen on the climb are from Machame camp up to Shira Plateau, around the Plateau itself and around the Shira caves. This dense shiny black rock was honed into shapes by the early Wachaga people of the mountain about 200 000years ago, to create bowls, rings and arrow heads. Of course Obsidian deposits are not limited to this area. They are all over Kilimanjaro but if you want to see some of the best then look around the caves.

Speaking of caves, these are another amazing source of information about volcanic activity. The caves that we see along the Rongai route and on the Northern Circuit and Shira, especially Shira Cave mentioned on most tourist maps, are actually lava blisters.  As bizarre as that may sound they are formed when gasses beneath the lava flow expand and push up, causing the crust of the lava to swell and burst. There are many of these caves on the mountain, but perhaps they most fascinating are what are known as Lava Tubes. In 2011 a team of researchers headed to Kibo to find evidence of Lava Tubes and managed to identify a surprising number of them.

If you are heading along Shira, Machame or Lemosho routes then your next big point of interest apart from Shira Plateau – a now extinct caldera, will be Lava Tower. The area south of Lava tower is a maze of towering tendrils of weathered lava rock.

Lava Tower is aptly named given that it is a column of rock that juts up like a massive thumb on the landscape. It was formed in the late Pleistocene era around 129,000 and c. 11,700 years ago. What makes this tower particularly interesting is that it is the remains of a volcanic plug. These fascinating land formations occur when volcanic magma hardens inside a vent on an active volcano. The remaining cooled lava becomes the plus and over time, some of the lava rock becomes eroded exposing a hard pillar of erosion resistant rock. On Kilimanjaro, this pillar of rock stands 90m tall.  It is also not surprising that the energy used to create this reflects in the energy taken by climbers to reach this point, most of who feel the effects and altitude when they finally arrive here.

Now if this does not get you curious then the infamous Barranco wall will. Feared by many to be this “indomitable sheer rocks face,” which puts dread in most climbers (don’t believe what you read), the wall is actually the result of a massive landslide caused by underlying volcanic activity. In fact, the word Barranco means a deep ravine or canyon. So if you happen to go via this infamous wall on your climb, and reach the “kissing rock,” remember that about 100 000 year ago beneath you would have been gentle rising slopes.

Left: A view of Barranco Wall was you approach it from Lava Tower Right: Climbers already on the Barranco Wall not far from the base.

Having been exposed to massive lava outcrops on the way to Lava Tower, Obsidian deposits and then Barranco Wall, by the time you start heading for your final camp your eyes will be well trained for the next fascinating rock formations. Above Karanga Camp as well as at Barafu itself are massive sections of slate or Basalt. Slate is interesting as it is actually caused by changes to other rock forms through heat and extreme pressure. Added to that is the fact that is developed perpendicular to the direction of compression and it is for this reason that we sometimes see large chunks almost growing upright out of the ground, (such as those below).

Given that Kilimanjaro is actually three volcanoes and different ages, it is not surprising to see different features across the landscape as you climb to Uhuru Peak on Kibos’ crater. Of course regardless of the route you take the volcanic stone scree above 5000m is, in addition to the altitude, is what makes the pull to summit that much tougher. However for those people heading along the Marangu, Rongai or Northern routes, a different type of rock lava is often seen near Kibo. Of course most people will miss it on the midnight ascent but watch out for it on the way down. To get clear images of the rocks below I placed them on my summit jacket to seperate them from the rock forms around then. What it came to the larger rocks it was understandably, not possible.

This is known as Scoria. It tends to have a reddish tinge to it caused by high temperature oxidation of iron in the lava. Some pieces are brown and others purplish red. Most pieces have large bubbles in them, which is actually dissolved gases and in fact, the white very porous one is the one we call pumice.

There is no denying that you are standing on the rim of a volcanic crater, when you stand at Uhuru Peak. However what many people do not realise is that what you are standing on is the rim of only one of Kibo’s three craters. In fact once you pass Stella Point en route to summit and come around the first rocky outcrop, if you look far right you can just make out the other crater rim. Not far from the summit board, albeit entailing a steep descent into the outer crater and then a further 70m ascent, is Reusch Crater and Ash pit. Reusch crater is about 1300m wide and within that lies Ash Pit, one of the most circular vents in the world at 140m in diameter. If there was any doubt about Kibo being dormant, all you have to do is stand on the edge of Reusch crater and if the wind blows in the right direction, you will easily smell the sulphur exuding from deep below.

What is particularly interesting though and often not directly visible from the route, is that the section between Kibo running toward Mawenzi and down to the south west of Marangu are a series of about 250 parasitic cones, which are cone-shaped accumulations of volcanic material not part of the central vent of a volcano. They formed from smaller eruptions from unstable fractures below.

Over each and every successive climb little changes on Kilimanjaro, save for the progressively vanishing glaciers. Increased glacial melt brings new wash aways and climatic conditions give rise to endless erosion. Every now and then a massive chunk of stone comes crashing down from Lava Tower making it less stable than before to the extent that Park authorities have banned anyone from climbing it. The massive valleys and endless groves of scenecio, magical lush forests around her base and the endless mists that roll in and out across the mountain make Kilimanjaro one of the most beautiful mountains to climb. Yet let us remind ourselves when we climb this sleeping beauty that she is not stratovolcano for nothing, for beneath her seemingly calm demeanour lies a hotbed of activity.

Article by Debra Bouwer

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