The geology and major habitats of the Singita Lebombo concession

Kruger National Park | July 2018

The Kruger National Park is a geological wonderland. Some of the oldest rocks in the world can be seen in this iconic game reserve. A geological map of the Kruger shows that the main rock types are organised into broad bands, oriented in an approximately north-south direction. The park can therefore be basically divided into the older granitic rocks (estimated to be between 3.5 – 2.5 billion years old) on the western side of the reserve and the basaltic rocks (estimated to be around 250 million years old) on the east.

Separating the two major divisions of rocks is a thin strip of sedimentary ecca shale which runs down the centre of the park. In some areas of the western side of the park there are patches of gabbro (an intrusive igneous rock). On the eastern side the Lebombo hills (rhyolite) form the border between South Africa and Mozambique.

The Singita Lebombo concession is an extremely beautiful part of the Kruger Park. The concession can be divided into two main areas, namely the high-lying rocky areas and ridges, and the lower lying grassy plains.

The western half of the concession, and the far northern area, is characterized by extensive open grasslands and plains. The underlying rock in this area tends to be basalt, which is an extrusive igneous rock

(a type of volcanic rock that was formed from the rapid cooling of lava that was exposed to the surface of the earth. Due to rapid cooling process these rocks do not generally have large crystal structures). Basalt is a dark coloured rock that erodes fairly easily forming grassy plains. The soils produced from this rock tend to be clay-based. Due to the fact that clay soils expand when wet and shrink and crack when dry it makes it very difficult for trees to establish their roots there. In our area the dominant tree-type in the basalt grasslands is knobthorn (Acacia / Senegalia nigrescens). Knobthorn are highly favoured by giraffes, who browse extensively on these trees. The basaltic clay soils tend to allow for the growth of highly nutritious grasses such as bushveld signal grass (Urochloa mosambicensis) and red grass (Themeda triandra). These palatable grasses tend to attract herds of grazers such as zebras, wildebeest and buffalos into the area (particularly in summer when the grasses are green). This, in turn, attracts lions. The Singita Lebombo Concession is, therefore, known for reliable lion sightings. The basalt plains are also great habitat for cheetahs, who require open areas in which to hunt. Although there are only a few hundred cheetahs in the entire Kruger National Park the eastern basalt plains tend to support the majority of these stunning cats and we do, fairly regularly, see them in our concession.

Towards the centre of the concession, below the ridges, there is a depression (lower-lying basin) bordering the non-perennial Xinkelengane drainage (riverbed), which runs from north to south through the concession. This area is characterized by more sodic (salty) soils. The high salt content in the soils here means that very few plants can grow in this area. The grass tends to be quite short, although very palatable to grazers, and the dominant trees that grow along the Xinkelengane drainage are Delagoa thorns (Acacia / Senegalia welwitschii) and leadwood trees (Combretum imberbe). This area is very open and sparsely vegetated. This habitat tends to attract quite a few grazers and is also a good place to look for lions and cheetahs. This area is very pretty and, in summer when the new green grass just starts to shoot, it looks similar to an open park land or golf course.

To the east of the central depression are the Lebombo hills. These hills form some spectacular cliffs in the central area of the concession. The Lebombos consist predominantly of the rock type known as rhyolite. This rhyolite is estimated to be between 120 – 180 million years old. Rhyolite is an extrusive igneous rock

(similar to basalt, although it is more resistant to weathering and therefore the Lebombo ridges tower over the basalt plains to the west of them). Rhyolite has a similar composition to granite and has a fair amount of quartzite in it. Due to the fact that it cooled down rapidly when it solidified it tends to have smaller crystals than granite. The Lebombo hills are a long, narrow range of hills that run in a north/south direction from just south of Shingwedzi Camp (a public camp in the north-eastern part of the Kruger National Park) all the way down the eastern side of the park (forming the border between Mozambique and South Africa) and south into the province of Natal. This ridge of hills is approximately 800 kilometres (500 miles) long.

 

The Lebombos consist of a series of parallel ridges interspersed with steep-sided valleys and plateaus through which seasonal streams have cut into the rocks. These streams only tend to flow during the summer rainfall season. The rhyolite rocks in the hills tend to be quite angular in shape and may have amygdales in them. Amygdales are vesicles in volcanic rocks, formed from bubbles of escaping gas, that have become filled with light-coloured minerals such as quartz and calcite. The rhyolite rocks may also show signs of flow-banding.

 

The vegetation in the Lebombo hills tends to be quite varied and includes both broad-leafed trees as well as thorn trees. The cliffs are often covered in large euphorbia trees / candelabra trees (including Euphorbia confinalis and Euphorbia cooperii). These are spectacular, poisonous, succulent-type, candelabra-shaped trees that are reminiscent of some type of cactus. On the cliffs and in the rocky areas one can also find some amazing large-leaved rock figs (Ficus abutifolia). These trees are also known as “rock-splitting figs” because the roots often grow through the cracks in the rocks and as they grow bigger and bigger they can cause the rocks to split apart. These fig trees do have fruits that are edible to monkeys, baboons and many frugivorous birds such as green pigeons. The Lebombo hills tend to attract quite a few browsing animals such as kudus, giraffes and others. We are fortunate enough to also see a few rupiculous (living on or amongst rocks) antelope including klipspringers and the elusive, shy, Sharpe’s grysbok. This is also great habitat for leopards, although many of them are shy and not easily seen.

In the southern part of the concession there is a spectacular ridge of rocks on the Lebombo hills (Lebombo and Sweni Lodges look on to and face towards this ridge). This particular ridge is known as “the Granophyres” and is made up of rounded, column-like rocks that perch on top of one another. Granophyre is a type of hypabyssal igneous rock (a volcanic rock that solidified underneath the soil, as opposed to rhyolite and basalt which solidified above the surface of the soil, but not as deep underground as granite which is known as a plutonic igneous rock). Since the granophyre rock solidified underneath the surface of the soil it cooled down slower than the basalt or rhyolite and therefore has slightly bigger crystals in it. This type of rock tends to have higher concentrations of quartzite crystals in it, which causes it to be more resistant to weathering. As a result, the granophyre ridge protrudes above the surrounding rhyolite ridges. The geological formation of the granophyres is known as a dyke. A dyke occurs where a vertical crack under the surface of the soil is filled with volcanic magma, which then cools down fairly slowly and forms a wall-like ridge. The particular type of granophyre rock that occurs in this area is known as Tshokwane granophyre and is named after the area to the south of our concession, where there is a public picnic site known as Tshokwane. Special trees found on the granophyres include wooden bananas (Entandrophragma caudatum) and pod mahogany trees (Afzelia quanzensis). The granophyre rocks are younger than the rhyolites.

 

 

In the far north-eastern corner of the concession there is a large hill known as “Big View Hill”. When one is standing on top of this hill one has extensive views westwards across the grasslands and bushveld of the Kruger National Park. It is a stunning view. On a clear day one can see right across the park and one can even see the Drakensberg mountains that form the escarpment of the country. On top of Big View Hill one can see numerous rounded pebbles lying about.

 

The shape of these pebbles indicate that they were weathered by moving water. It has been suggested that these rocks and stones were deposited here during the Cretaceous period (after the Gondwanaland breakup, +- 65million years ago). During this time, the area was covered in tropical vegetation, ferns etc, and the escarpment was at that stage much closer to the Lebombos and the coast. Rainfall was much higher then and the whole area was essentially a high energy riverine environment with numerous rivers rising on the escarpment and flowing eastwards. It is possible that there was a large inland water-body or lake there in which these pebbles accumulated. These pebbles are predominantly sedimentary rocks. (Sedimentary rocks are rocks where weathered rock material such as stones, dust, sand or clay are put under pressure for a long period of time and therefore join together to form a new rock. Some sedimentary rocks are formed when chemicals that are in solution in the soil-water are brought to the surface by capillary action and then are cemented together when the water evaporates) such as chert or banded ironstone.

It would not be complete to talk about the habitats within the Lebombo concession without referring to the various drainage lines, rivers and water points. The Lebombo concession is generally referred to as a “dry concession”. There are no perennial or permanently flowing rivers in the concession. The two main rivers that flow seasonally through the concession are the N’wanetsi River and the Sweni River. Both of these rivers originate within the Kruger National Park and the waters therein are therefore generally unpolluted. Both of these rivers flow from west to east and the confluence of the two rivers lies just to the east of the two lodges.

The N’wanetsi River passes in front of Lebombo Lodge, whereas the Sweni is the river in front of Sweni Lodge. During summer (our rainy season) both of these rivers flow, but during our winter months they both dry up. There are usually a few areas or pools that hold water throughout the year and therefore provide water for the animals. Two of these pools that usually contain water throughout the year are Puff Adder Pool (named after a highly venomous viper-like snake) and Dumbana Pool. Both of these two pools are in the N’wanetsi River and are formed by rocks damming the river-course like natural dam walls. The N’wanetsi River is dammed up in two places close to Lebombo Lodge by two weirs. These weirs were built many years before Singita got the concession and it is because of these weirs that there is usually water in front of the two lodges. These semi-permanent areas of water tend to attract quite a few animals in the dry months and provide areas where animals such as crocodiles and hippos can be seen.

 

Although we do not have access to the major portion of the Sweni River (it flows in front of the Sweni public picnic site) we do have access to fairly long portion of the N’wanetsi River, and the roads nearby the river are some of our major game-viewing roads in the concession, attracting lots of animals particularly during our winter and spring months. It is along the main drainage lines that we find the larger trees in the area. Although the riparian vegetation is not very thick, and in fact is non-existent in many areas where the banks of the rivers lead straight into the grasslands. Some of the bigger trees that can be found in places along the banks of the rivers include fever trees (Acacia / Vachellia xanthophloea), sycamore figs (Ficus sycamorus), weeping boerbeans (Schotia brachypetala) and apple-leaf trees (Philenoptera violaceae).

The N’wanetsi River enters the concession from the western border of the concession (the S41 public road), in the basalt areas, and flows towards the rhyolite cliffs of the Lebombo hills where it is diverted south towards Lebombo Lodge. Just in front of the lodge the river turns east, cutting through the granophyres and the Lebombo hills and exits the country (South Africa) into Mozambique at a place that we know as the N’wanetsi Poort. Where the river exits the Kruger National Park the habitat is characterised by large hills, steep valleys and cliffs. This is one of the most scenic areas in the concession and is a great place to stop to watch the sun setting over the bushveld.

Throughout the Lebombo hills are valleys with temporary / seasonal streams. Most of these streams flow from east to west, where they join either the N’wanetsi River or the Xinkelengane Drainage. Some of these streams include the Ntsibisane Drainage, the Xinenene Drainage, the Nhlangulene Drainage and the Nkayanini Drainage. The most important of these drainages for game-viewing purposes is the Xinkelengane. Most of the year this riverbed is dry, although it does flow after heavy rains. This drainage line is bordered by the central depression on the western side and the Lebombo hills on the east. This river / stream runs from the northern border of our area, through the middle of the concession southwards towards the N’wanetsi River.

On the far western side of the concession there is a fairly large dam known as Gudzani Dam. The public have access to the dam wall from the S41 public road. This dam is one of the most popular game-viewing sites in the Kruger Park. Fortunately, Singita have private access to the northern part of the dam from the eastern side. This dam tends to attract a lot of animals, which come down to drink there during the drier months. In 2016 and 2017 this dam dried up completely during the drought. At present the water in the dam is receding, although there will probably be a little bit of water in it all the way through winter this year. This dam used to house a few hundred hippopotami, but unfortunately that number dropped substantially as a result of the drought. There are also quite a few large Nile crocodiles in the dam. During the drier months large herds of buffalos are sometimes attracted to come and drink there from the Basalt grasslands to the west of the concession. These herds, in turn often draw lions (particularly the Shishangaan and Mountain prides) to the dam.