Kilimanjaro Geology

As the world’s largest free-standing mountain, Mount Kilimanjaro is an impressive peak with fascinating geology. Rather than simply a mountain, Mount Kilimanjaro is actually a stratovolcano, which means that it is a huge volcano. In fact, Mount Kilimanjaro is actually three volcanoes! So, what is this massive African multi-volcano peak made up of?

 

Kilimanjaro geology: As a stratovolcano, Mount Kilimanjaro is made up of ash, lava, and rock, with large quantities of basalts and andesites. It began to form nearly 750,000 years ago when molten lava erupted through the Earth’s crust and began to push rock and sediment upwards.

 

Mount Kilimanjaro is Africa’s tallest mountain, standing at an impressive 5,895 meters. It is located in northeastern Tanzania, and as a free-standing mountain, it is not associated with any mountain range. The three volcanos that makeup Kilimanjaro are known as Kibo, Mawenzi, and Shira, with Kibo being the center and tallest of the three.

 

The three peaks have been affected in differing fashion due to the process of erosion over hundreds of thousands of years. Shira has been flattened into a broad plateau, with the remaining rim of the volcanic crater deeply cut into the earth. Mawenzi is much rockier, with a steeper incline, and erosion has cut harsh channels through the rock that makes some places nearly inaccessible.

 

One of the most remarkable features of Mount Kilimanjaro is the glacial summit of Kibo, which gives the peak its snowy cap. These glaciers were once present on the majority of Kilimanjaro, with ice more than 100 meters thick, but due to global warming, these 10,000-year-old glaciers could completely disappear by 2030.

 

To learn more about this fascinating geological behemoth in Africa, read on below.

How was Mount Kilimanjaro Formed?

 

Mount Kilimanjaro’s remarkable geological composition is the result of its volcanic origins. Kilimanjaro sits at the southern portion of the East African Rift system. This system is where some of the Earth’s tectonic plates meet together, and new plates are being formed while old plates are pulling away from each other and creating rifts.

 

As the tectonic plates move and pull away from each other, the brittle outer crust of the Earth begins to crack. The pressure of these moving plates results in ample amounts of volcanic activity, so it comes as no surprise that the East African Rift system is lined with various volcanoes, both dormant and active.

 

About 750,000 years ago, lava burst through cracks in the Earth’s crust created by the shifting tectonic plates. The pressure of the erupting lava pushed the earth upwards, resulting in the Shira portion of Kilimanjaro forming. Shira was volcanically active for about 250,000 years before it collapsed to form a caldera.

 

Shortly after Shira became extinct, another eruption resulted in the formation of Mawenzi. About 460,000 years ago, Kibo was formed by another similar eruption. Kibo continued to erupt, causing it to become the highest portion of Kilimanjaro.

 

The continual eruptions of Kibo significantly contributed to the geological makeup of Mount Kilimanjaro and gave it its unique composition and appearance.

What Sort of Rock is Mount Kilimanjaro Made Of?

 

Due to its volcanic origins, Mount Kilimanjaro is comprised of rock, lava, and ash. This volcanic activity also resulted in the majority of Kilimanjaro’s rocks being mostly composed of silicon dioxide. A large portion of the peak is comprised of andesites. Andesite is formed from volcanic activity and it has a variable color but tends to be grey or blue-grey.

 

More than half of Mount Kilimanjaro’s volume is comprised of basalts. Basalt is a volcanic rock, which when superheated can form lava. Basalt is typically a dark grey or black color, which is why Kilimanjaro has such a striking dark contrast to both the African plain and its glacial cap. Basalt also has a high composition of iron and magnesium and a relatively low composition of silica.

 

Basalt is also the most common rock type in the Earth’s crust, and it is frequently the main component of volcanoes. The volcanic islands of Hawaii are almost entirely made out of basalt, for example.

 

Kibo also has an impressive amount of obsidian. Obsidian is an igneous rock and it usually forms above the Earth’s crust when lava cools so quickly that the atoms within it are unable to form a crystalline arrangement. As a result, obsidian has a smooth surface and looks like dark glass. Obsidian is most commonly black, but it can range from browns to greens to even yellow, blue, or red. Occasionally, two colors can swirl together within the same rock.

What is the Great Rift Valley and What is Its Geology?

 

Mount Kilimanjaro is located within the Great Rift Valley, which is also called the East African Rift System. This rift system is a unique geological wonder. It is a series of rifts covering the Eastern edge of Africa, stretching through Ethiopia, Kenya, Uganda, and Tanzania. These rifts are present because it is here that the Earth’s tectonic plates are pulling away from each other while a new plate is being formed. Studying this area gives insight into how continents break apart.

 

The three main tectonic plates involved here are known as the Nubian Plate, which makes up most of the African continent, the Somalian Plate, which is gradually pulling away from the Nubian plate towards the east, and the Arabian Plate which is to the north. These three plates meet at a Y-shaped junction point called the Afar Triple Junction.

 

As the Nubian and Somalian plates pull away from each other, the region between them thins to form a great rift. Over time, this rift may end up filled with ocean water and form a new narrow ocean but for now, the area is ripe with volcanic activity. This is why Mount Kilimanjaro exists there, as well as several other volcanoes.

 

The Somalian Plate is mostly metasediments and igneous intrusives, which form from magma slowly cooling beneath the surface of the Earth. Due to volcanic activity causing lava to rise above the Earth’s crust, the western edge of the plate is mostly igneous rock such as basalts, rhyolites, phonolites, trachytes, and pumice-dominated ignimbrites.

 

The Nubian Plate is generally comprised of a Precambrian base of meta-sedimentary, meta-igneous, and igneous rocks. On top of this can be found other volcanic sediments and younger sedimentary rock deposits, which is fitting for the area’s tectonic activity.

Is Mount Kilimanjaro an Active Volcano?

 

As mentioned previously, Mount Kilimanjaro is actually comprised of three separate volcanoes: Shira, Mawenzi, and Kibo. Shira was the first of the volcanoes formed and it was thus also the first to go extinct, with its last eruption occurring over 500,000 years ago.

 

Once Shira was extinct, Mawenzi was formed. About 40,000 years after that, another eruption caused Kibo to form. Kibo was very active when it first formed, with multiple eruptions causing it to stretch further skyward until it reached its eventual height of 5,895 meters.

 

Of the three peaks, Kibo is the only volcano still considered to have the potential of volcanic activity. Rather than being classified as extinct, it is considered to simply be dormant. The last major eruption was 360,000 years ago, but it is believed the volcano has probably been volcanically active within the last 10,000 years.

 

While the likelihood of a major volcanic eruption is still rare, there is still a potential of Kibo erupting sometime in the future.

What is a Stratovolcano?

 

Mount Kilimanjaro is considered a stratovolcano, but what exactly does that mean? A stratovolcano, also called a composite volcano, is a type of volcano that has andesite and dacite forms of lava, which tend to be thicker types of lava and cause pressure to build up until the volcano has an explosive eruption.

 

The majority of the Earth’s volcanoes are stratovolcanoes, comprising about 60% of all volcanoes. They tend to be very large and are comprised of half lava and half pyroclastic material. The lava usually flows very slowly, and typically, the supply of magma from the Earth’s mantle is low.

 

Since the magma is generally not overheated or fast-moving, stratovolcanoes tend to have very long stretches of time between eruptions. However, even though they are usually less violent than other types of volcanoes, stratovolcanoes are responsible for more casualties than any other type of volcano.

 

Stratovolcanoes tend to be more devastating for several reasons, but one reason is simply that more humans live closer to stratovolcanoes than other volcanoes. In addition, stratovolcanoes have a higher likelihood of landslides, avalanches, and mudflows, since they are generally comprised of ash and lava which can become easily dislodged by rain and earthquakes. Sometimes, an entire side of a stratovolcano can collapse and cause massive destruction.

 

Examples of other stratovolcanoes besides Mount Kilimanjaro include Mount St. Helens, Mount Fuji, Pinatubo, and Mount Rainier.

What are the Main Lava Formations of Kibo?

 

On Mount Kilimanjaro, Kibo is believed to have five main lava formations which created the towering mountain that stands today. The lava erupted from the Earth’s crust and then cooled as rock to form the bulk of the mountain. The volcanic phases of Mount Kilimanjaro started about 2.5 million years ago, at Shira. About 1 million years ago, the volcanic activity migrated east to Mawenzi and Kibo.

 

The oldest dated rocks on Kibo come from what is known as the Lava Tower group, a lava formation that resulted in a sheet of rock at 4600m high. These rocks are mostly alkaline phonotephrites and tephriphonolites. The rocks found here date back to 482 thousand years ago.

 

Two other lava formations represent the main period of volcanic activity on Kibo. These formations are the Rhomb Porphyry group and the Lent group. The Rhomb Porphyry group occurred between 460 to 360 thousand years ago and is characterized by tephriphonolite and phonolite lava, while the Lent group occurred between 359 to 337 thousand years ago and has aphyric phonolite lava with obsidian.

 

The Caldera Rim group lava phase took place between 274 to 170 thousand years ago and consists mostly of igneous rock such as quartz and feldspar. The final lava formation of Kibo is known as the Inner Crater group, which is comprised almost exclusively of aphyric phonolites, although there are occasional rare aegirine phenocrysts.

Can You Climb Mount Kilimanjaro?

 

The first recorded climb of Mount Kilimanjaro was by Hans Meyer and Ludwig Purtscheller in 1889, and ever since it has been a popular hiking destination for both locals and travelers alike. Mount Kilimanjaro is an appealing hike for many due to the fact it does not require any specialized gear or extensive amounts of experience in order to reach the summit.

 

Kibo’s slopes are relatively gentle, making it a comfortable trek for even inexperienced hikers. There are a number of routes available to reach the summit, meaning that you can select a path depending on your abilities and preferences. To see a list of the paths and descriptions of each, there is a great guide located here.

 

Climbing Mount Kilimanjaro can be remarkable because the short journey will pass through very distinct climates and varied areas of vegetation, leading to some saying “to climb up Kilimanjaro is to walk through four seasons in four days.” Almost every kind of ecological system is found on the mountain, making it a truly fascinating experience.

 

If you are hesitating about the idea of climbing Mount Kilimanjaro, you may be interested to know that one South African, Bernard Goosen, was able to reach the summit of Kibo while in a wheelchair. Goosen used a modified wheelchair but was still able to scale the mountain with barely any assistance.

 

Each year, about 25,000 people attempt to scale Mount Kilimanjaro, with about two-thirds of those trekkers successfully reaching the summit. The most common reason hikers do not reach the peak is due to altitude sickness.

Is Climate Change Affecting Mount Kilimanjaro?

 

On Kibo, the tallest peak of Kilimanjaro, there have been thick glaciers of ice more than 100 meters thick. However, in recent decades, the icy cap of Mount Kilimanjaro has been shrinking.

 

Due to global warming, the snows of Kilimanjaro are evaporating directly into gas. This is devastating to some local farmers, who count on the seasonal meltwater of the icy rivers to provide much-needed water for livestock and farming. The loss of these glaciers will not only mean that Kilimanjaro will lose its picturesque white cap, but the lives of local people will be negatively affected by the absence of a seasonal water source.

 

It is estimated that the mountain’s snow caps have lost over 80% of their mass since 1912, and there is thought that the glaciers may be completely gone by 2033. The melting glaciers also cause hazards for climbers. The warm temperatures cause frozen rocks near the summit to loosen, and these can then fall and kill trekkers who are attempting to reach the top.

 

There is some worry that tourism will drop off if the glaciers disappear from Mount Kilimanjaro. One major attraction of the peak is the novelty of finding such dense ice caps located at the equator, and many visitors are drawn by this uniqueness. These tourists provide a huge revenue source for Tanzania, so if the ice disappears up, so might the potential income from tourists.

What are the Seven Summits, and How Does Mount Kilimanjaro Compare?

 

Mount Kilimanjaro is considered one of the seven summits. These seven peaks represent the tallest mountains on each of the seven continents. Since Kilimanjaro is the tallest mountain in Africa, it makes this list. The peaks of the seven summits are as follows, starting with the tallest mountain in the world:

 

• Everest: Everest is the tallest mountain in Asia, and also the tallest mountain in the world. It stands at an impressive 8850m/29,035 feet.
• Aconcagua: Located in South America, Aconcagua is 6960m/22,834 feet tall.
• Denali: Located in Alaska, Denali is the tallest peak in North America. It is 6,190m/20,310 feet tall.
• Kilimanjaro: As mentioned previously, Kilimanjaro is the tallest mountain in Africa. It has a height of 5895m/19,340 feet.
• Vinson: At 4892m/16,050 feet, the icy Mount Vinson is the highest peak on Antarctica.
• Elbrus: The tallest peak in Europe is Elbrus. Located in Russia, it stands at 5642m/18,513 feet tall.
• Puncak Jaya: Representing the highest peak in Oceania, Puncak Jaya is 4,884m/16,024 feet tall.

 

There is some debate in regard to which peaks should be included on the list of seven summits and whether the list should be increased to eight or even nine summits. The first point of debate is whether to consider only mainland Australia as the continent or whether to include all of Oceania. If only considering mainland Australia, Puncak Jaya would be replaced by Mount Kosciuszko, which is only 2,228m/7,310 feet tall.

 

Another point of contention is whether Elbrus, located in Russia, should be considered part of the European continent since it is close to the border between Europe and Asia and by some definitions of the boundaries it falls entirely in Asia. Those who do not consider it to part of Europe state that Mont Blanc, lying in the Alps, should be the European peak. Mont Blanc is 4,810m/15,781 feet tall.