Rocks in East Africa: Types, Formation, and Economic Importance"
Discover the different types of rocks in East Africa, their formation processes, and their economic significance in construction, mining, and industry.
What is a rock?
A rock can be defined as an aggregate of particles composed of one or more minerals, forming the major part of the carth's crust. It may be unconsolidated such as sand, clay or consolidated such granite, limestone and coal. A given rock is usually composed of two or more minerals, and usually many minerals are present. However, a few rock varieties consist almost entirely of one mineral. Most rock of the earth's crust is extremely old in terms of human standards, the times of formation ranging back many millions of years. But rock is also being formed at this very hour as a volcano emits lava that solidifies on contact with the atmosphere.
Classification of rocks according to origin
Rocks can be classified under three groups according to their mode of formation. These are:
1. Igneous rocksa.
2. Sedimentary rocks
3. Metamorphic rocks
IGNEOUS ROCKS
Igneous rocks are one of the three main types of rocks, the other types being sedimentary rocks and metamorphic rocks. Igneous rocks are also known as fire formed rocks. They are formed when molten or partially molten material, called magma cools and solidifies. Magma is molten rock that forms in the interior of the earth. It is generated when rock deep underground melts due to the very hot temperatures and high pressures inside the earth. The hot temperature is generated by radioactivity and geo-chemical reactions. Because magma is lighter than the surrounding rock, it tends to rise towards the earth's surface. The rising process is also as a result of magma moving toward lower pressure regions.
When magma rises and does not reach the earth's surface, it cools slowly and solidifies to form intrusive igneous rocks. On the other hand, when magma rises and reaches the earth's surface, it cools rapidly to form extrusive igneous rocks. The character of igneous rocks depends on two main features; first, the physical circumstances under which cooling and solidification took place and secondly the chemical composition of the molten rock from which the rock solidified.
The cooling of magma
Different types of igneous rocks are formed due to different rates of cooling. If magma cools in large masses deep in the earth's crust, the process is slow and the resulting rocks are compact, course in texture and large crystalled. They are known as plutonic rocks. Examples include granite, diorite and gabbro. The intrusive rocks can be exposed at the surface by denudation. Examples include granite at Seme Location in Kisumu, Mubende, Kalongo (Pader), Nakasongola, Soroti and Maragoli.
Where the molten material rises along lines of weakness and cracks in the country rocks and cools near the earth's surface, hypabyssal rocks are formed. In this case, cooling is more rapid than in the case of plutonic rocks. Medium sized crystals are formed e.g. quartz and dolerite. Examples include dykes cutting across the Rufigi River, kimberlites in northern Tanzania, sills along the Arua- Packwach road and dolerite in the Athi Plains and Doinyo Sabuk area in Kenya.
illustration of a vulucanic eruption
Rocks, which result from the cooling of magma, which has been poured onto the earth's surface, are called volcanic rocks. They cool rapidly to form small crystalled rocks e.g. rhyolite, andesite, basalt and obsidian. These rocks form mountains such as Elgon, Kilimanjaro and Kenya and highlands such as in Kigezi and Kenya Highlands.Pyroclasts on the other hand consist of igneous materials but fragmented in character. They have been thrown out from a volcanic vent and include fragments of solid lava, cinders, ash and dust more or less consolidated e.g. around Mounts Muhavura and Elgon.
lava Flow from Volucanic eruption.
Chemical composition.
Igneous rocks also vary according to their chemical composition in the following ways. Igneous rocks with a high proportion of silica, exceeding 65 percent are said to be acidic e.g. granite and obsidian rocks that occur at the Ntumbi and Rungwe mountains in the Mbeya region of Tanzania.
Where the amount of silica is low, the rocks are said to be basic e.g., the basalt forming the lava plateaus like the Yatta in eastern Kenya and Kisoro plateaus in south western Uganda. Rocks having intermediate silica content are said to be ultra basic e.g. the andesite rocks in South Nyanza and porphyries rocks in the Athi Plains of Kenya. Generally, acid rocks are light in colour and weight while the basic rocks are darker and heavier.
SEDIMENTARY ROCKS
These are rocks derived from pre-existing rocks formed by the accumulation and consolidation of materials deposited by running water, wind or ice. Sedimentary rocks are also derived from depositions of organic remains of plant and animal life. The deposition takes place on either dry land like valleys and lowlands or under water such as in lakes, rivers, oceans and seas. Sedimentary rocks occur in layers, which indicate where one phase of deposition has ended and another begun. Most layers are horizontal or gently dipping and have been deposited over hundreds or millions of years.
For example, when an igneous rock is exposed at the surface of the earth, it is subjected to the processes of earth-sculpture, carried on by weathering, erosion (by wind, running water, waves and ice) and deposition. The result is that an igneous rock may be broken down. The products broken down are transported elsewhere and then laid down or deposited in layers or strata either on dry land or under water. These deposits are consolidated or cemented by addition of overlying weights and in various other ways to form solid sedimentary rocks.
Sedimentary rocks may be classified according to their mode of origin into mechanically. organically and chemically formed sedimentary rocks.
Mechanically formed sedimentary rocks
These rocks are composed of mineral particles produced by the physical disintegration of rocks (weathering) and their transportation without alteration in the chemical composition of the rocks. This group includes a variety of either course or fine texture rocks formed by the compaction and cementation of detrital sediments such as sand, silt, clay and gravel. Cementing solutions of calcareous, siliceous or ferruginous materials consolidate the materials.
Various rocks are formed depending on the agent of erosion. Sandsone, clay, silt and gravel are mostly transported and deposited by water and ice. Sandstones consisting of grains of sand cemented together usually by lime occur at Lindi, Tanga, Malagarasi and Songea in Tanzania. Silt, clay and gravel occur in Lake Victoria localities such as Kajansi and Kisumu, and along flood plains of rivers such as Ruvuma, Rufigi, Ruvu, and Pangani. Extensive layers of boulder clays or till laid down by glaciers occur on the lower slopes of mountains Rwenzori, Kenya and Kilimanjaro. Sedimentary rocks from wind deposition are called loess and occur in parts of northern Kenya, parts of Karamoja and parts of the Masai steppes of Kenya and Tanzania and in the Serengeti in northern Tanzania.
Organically formed sedimentary rocks
These rocks are composed of remains of dead animals and plants, which are deposited over a long period of time and become compacted into solid rock. Coral limestone rocks are formed from deposits of skeletons of tiny sea creatures called polyps. When they die, their hard skeletons accumulate over long periods of time and get cemented into solid rock. Coral limestone rocks grow layer by layer over thousands of years of deposition. Examples of coral limestone rocks include those forming a fringing reef at Mombasa, Tanga and Dar es Salaam along the East African coast.
Another example is the siliceous rocks formed from the remains of animals such as sponges and radiolaria (a minute organism whose hard parts remain as a complex framework of silica) and of plants such as diatoms. The carboniferous rocks consist essentially of carbon combined with other elements. They are formed from plant accumulations. Coal for example is formed from the accumulation of plants after being transformed into peat and subsequently compressed for example in Ruhuhu valley and Rukwa in south western Tanzania.
Chemically formed sedimentary rocks
These rocks are precipitated or evaporated from solutions of salts. All water falling onto the earth as rain and running over the surface carries salts in solutions. The salts may be precipitated by direct evaporation of water, chemical interaction or by the release of pressure where underground water reaches the surface. The deposition of calcium on beds of streams and in the form of stalactites and stalagmites in caves is a familiar future in the limestone regions of Nyakasura in western Uganda. Other examples include soda ash recovered from Lake Magadi in Kenya and Lake Natron in Tanzania and salt recovered from the sea at Malindi coast and from Lakes Katwe and Kasenyi in western Uganda, Salt pans occur extensively in dry areas of Kenya such as Narok, Wajir, Pokot, and Samburu.
METAMORPHIC ROCKS
These are igneous and sedimentary rocks that have gone through changes both physically and chemically to produce new structures within the rocks. Heat, pressure or both bring about the changes.
Heat within the earth is generated in a number of ways. Radioactivity and geo-chemical reactions produce heat for metamorphism. Magma (molten rock) moving from deep within the earth toward the surface also provides heat for metamorphism. This is seen where there is an intrusion of a mass of igneous rock, so that the near by rocks are affected. The effects result from direct contact between the magma or hot igneous rocks and the country rock.
The magma introduces great amounts of heat into the country rock, leading to re-crystallization and mineral reactions in the rocks nearby. The envelope of contact- metamorphosed rocks around a magma intrusion is called an aureole.
Another source of heat within the earth that can lead to metamorphism is friction between rocks grinding past one another especially along earthquake faults or at plate tectonic boundaries. The changes brought about by heat or thermal metamorphism includes sand stone changed to quartzite and limestone to marble for example at Embu in Kenya.
In addition to heat, pressure within the earth contributes to the formation of metamorphic rocks by changing the texture and mineral density of rocks. Metamorphism bout by pressure is known as dynamic or regional metamorphism. The pressure is usually brought about by earth movements which result in subsiding of blocks of the earth's crust such as in the formation of the East African rift valley by tensional forces.
Furthermore, pressure is caused by continuous deposition of sediments causing the rocks above to compress those below into a smaller, denser form. Slate is a fine-grained metamorphic rock formed from shale or clay sedimentary rock that has been exposed to pressure for example at Wajir in northern Kenya and Nyanza Province in Kenya. Greater pressure forms phyllite, which has a slightly coarser grain size than slate. The surface of a phyllite is visibly scaly and often has a silvery luster e.g. in the Kilembe and Toro regions of western Uganda, and Kigoma in Tanzania.
In other cases, the changes may also be brought about by both heat and pressure. Coal or organic matter is turned into graphite by both heat and pressure. When slate is subjected to great pressure and subsequent heat, it produces schist, a more coarsely foliated rock e.g. at Buhweju in western Uganda and areas around Lake Kyoga. Furthermore, when schist is subjected to more heat and pressure, it produces gneiss, a very coarse rock like in Arua region.
The mineral structure of metamorphic rocks depends both on the type of parent rock and on the amount of heat and pressure present when the rocks formed. Metamorphic rocks may be foliated or non-foliated. Foliated metamorphic rocks have layers or banding e.g. slate, schist and gneiss in Mandera and coastal areas of Kenya. Non-foliated rocks on the other hand consist of rocks which are not layered e.g. marble and quartzite in Nyanza Province of Kenya.
ROCK TYPE IN RELATION TO RELIEF AND LANDFORM DEVELOPMENT IN EAST AFRICA
Igneous rocks
Igneous rocks differ in the silica content hence forming acidic rocks with high silica content and basalt rocks with low silica content. These affect landform development differently. Furthermore, the landforms resulting from igneous rocks can be intrusive; occurring below the earth's surface or extrusive, occurring on the earth's surface. The following landforms are associated with igneous rocks.
Extrusive igneous rocks produce various landforms. All volcanic mountains are formed by the accumulation of magma (or molten igneous rock that forms below the earth's surface) on the earths surface and its solidification. The magma erupts through one or more volcanic vents to form different types of volcanoes.
When magma is ejected onto the earth's surface through a central vent and accumulates around the vent to form different layers of ash and lava (see Fig 6.008), composite volcanoes are formed. They are usually very large with fairly steep sides like Kilimanjaro and Kenya mountains.
Volcanoes are produced when igneous rocks consisting of lava piles up to form volcanic cones or mountains. If the lava is acidic, it forms high and steep sided volcanic mountains like Ntumbi volcano, east of Mbeya town in Tanzania.
It flows over long distances before solidifying. The volcanoes formed are thus low in height but with a very wide base like Marsabit in northern Kenya as well as Nyamulangira close to the Uganda -DRC boarder. Resistant volcanic rocks have formed volcanic necks or plugs at Napak and Tororo in Uganda,
Basic lava as already noted earlier is fluid and mobile. Once it flows out of a fissure, it can flow over a very wide area before solidifying. Repeated processes lead to the formation of a platform of lava high and extensive enough to be called a plateau. The Yatta, Kano and Laikipia plateaus in Kenya and the Kisoro lava plains in south-western Uganda are examples. They show large areas of more or less flat land.
Other extrusive volcanic rock landforms include hollows or depressions found on top of volcanic cones. They include craters e.g. on mounts Longonot, Sabinio, Elgon, Kilimanjaro and Kenya. Most of the crater on Mount Kenya has however been removed by glacial erosion. (See Fig 6.012) Calderas, which are similar to craters but wider, include Ngorongoro in northern Tanzania as well as Menengai and Suswa in Kenya.
Intrusive volcanic rocks lead to the formation of intrusive volcanic landforms such as dykes, sills, batholiths and laccoliths. Generally, intrusive volcanic landforms affect the relief after they have been exposed to the surface by denudation. Depending on the resistance of the rocks, uplands, ridges, depressions, flatlands, trenches and others are formed as later explained in the Chapter of Vulcanicity.
Sedimentary rocks
The dominant relief and landforms associated with sedimentary rocks fall under the followingcategories:
Coral landforms
Coral reefs are ridges or elevated part of a relatively shallow area of the seafloor, approaching the sea's surface. They are composed of the skeletal remains of billions of tiny marine polyps called corals. Over time, sand and rubble fill gaps between the skeletons of various colonies, cementing them together and forming a solid limestone foundation. These coral reefs have formed a barrier along the East African coast from Kenya down to Tanzania and Mozambique. Much of this reef liesbetween 500 meters to over 1000 meters off the shore.
Karst topography
A lot of igneous activity in East Africa involved materials rich in carbonates e.g. the Kambe limestone in Kenya, Tororo and Karasuk (Karamoja) carbonates, and Tanga limestone of Tanzania. In these areas, like other areas with carbonates, chemical weathering particularly the carbonation process produces karst topography. The weak carbonic acid in the groundwater dissolve this limestone into a terrain marked by caves, underground streams, steep valleys, stalactitesstalagmites, cliffs, sink holes, grikes and clints as well as expanses of barren rock and basins. Most of the above features can be seen on the Kambe rocks at Kilifi, Tanga region and Nyakasura in Fort Portal.
Alluvial featuresVarious features have developed from fluvial (river) and lacustrine (lake) deposits. Most of these occurred during the Tertiary and Quaternary periods. The most wide spread are the riverine deposits which include alluvial fans, deltas, flood plains and levees. Floodplains are flat wide deposits of alluvium, river-deposited sediment, on either side of the river channel. During floods, a river overflows its banks and spreads out the sediment near the river to form a floodplain. A number of large rivers in East Africa have flood plains e.g. Rufigi, Ruvuma, Ruvu, Tana and Athi.
Levees are embankment along the course of a river. Natural levees are low banks that are produced by the river during floods when the overflowing of the river decreases the speed of the water and permits the deposit of silt. Rivers in East Africa with levees include Ngaila, Nyando, Yala and Malaba.
Many river valleys end in a delta. Deltas are a fan-shaped accumulation of sediment where the river reaches the sea or lake. They form because the river deposits alluvium more rapidly than it can be removed by the action of waves and coastal currents. Notable examples are the deltas at the mouths of rivers Rufigi, Wami and Tana along the East African coast. Rivers Nile and Semliki form deltas where they join Lake Albert.
Alluvial fans are fan shaped deposits laid down by rivers on land where a river emerges from a steep narrow valley into a wide gentle plain. The Lume fan, formed where River Lume joins River Semliki is a very good example. Others in Uganda can be seen along the banks of the Kazinga Channel while in Tanzania they are found in the Kilombero Valley.
Lacustrine deposits forming flatlands include the Lwera flats around Lake Wamala, swamp deposits around Lake Kyoga, as well as the Kaiso-Kasenyi-Kisegi deposits along the western rift valley floor. Deposits forming beaches are seen at Lutembe, Lido and Nabugabo among others around theshores of Lake Victoria.
Morainic landforms
Moraine is an accumulation of sediment or rock fragments that are deposited by a mass of ice called a glacier. Landforms of glacial deposition include erratics, eskers, kame, kame terraces and drumlins found on Mountains Kilimanjaro, Kenya and Rwenzori as discussed later on in the topic ofGlaciation.
Metamorphic rocks
As already noted, one of the main sources of heat within the earth that can lead to metamorphism is friction between rocks grinding past one another e.g. along tear or strike faults, earthquake faults at plate tectonic boundaries. These movements result in faulting and the formation of fault landforms such as the East African rift valley, block mountains such as Rwenzori, and other fault landforms like escarpments, tilt blocks, fault scarps and fault basins.
Sometimes, bodies of rock produce friction and heat as the two blocks push directly against each other. The end result is the production of folding and its related landforms. In Ankole, founding in addition to granitic intrusions into the Karagwe-Ankole rock system led to the formation of arenas surrounding dome shaped structures.
Metamorphic rocks are in general compact and resistant to erosion. They tend to form highlands when the surrounding rocks have been removed by denudation.
INFLUENCE OF ROCK STRUCTURE AND LITHOLOGY ON THE DEVELOPMENT OF RELIEF AND LANDFORM IN EAST AFRICA
The term rock structure is generally used to meal all ways in which rocks differ from each other in their chemical and physical characteristics. It includes the attitude of rocks, the nature of dips, their faults and folds as well as other characteristics such as hardness or softness, permeability, mineral composition, bedding planes, rock colour and age. The term lithology refers to the detailed and minute physical characteristics of a rock in terms of joints, permeability, colour, beddings and hardness. The following are the major effects of rock structure and lithology on the relief and landforms in East Africa.
Rock resistance
The resistance of a rock to erosion depends on massiveness of the rock. A massive structure is one where there are no joints and water cannot easily penetrate it to cause chemical weathering. Besides, temperature changes cannot easily break the rock. Rocks offering more resistance to denudational forces e.g. resistant granite rocks for example stand out as mountains, highlands, hill and ridges such as the Mubende batholith and the inselbergs at Parabong, Maragoli and Cherangani. On the other hand, less resistant rocks are worn down to form flatlands and depressions e.g. the linear trenches west of Lake Turkana in Kenya.
A slope is that part of the land that rises or falls gradually in the same general direction. Slope development is affected by a number of factors, which include tectonic movement, weather, erosion and gravity. The amount of erosion done on the rocks depends on their resistance.
Rock resistance thus influences the nature of hill slopes. Hills made-up of resistant rocks form convex slopes while those of less resistant rocks form concave slopes.
Mineralogical composition
Mineralogical composition of the rocks e.g. limestone rocks are weathered by the carbonation, a chemical weathering process to form landforms such as grikes and clints at Kambe near Kilifi, and Mwea Peninsular in the Queen Elizabeth national Park, as well as stalactites, stalagmites and pillars in areas such as Nyakasura in western Uganda.
Rock joints.
Rock joints like fault lines in the rift valley region have enabled magma to rise to the surface leading to the formation of volcanic landforms such Mounts Longonot, and Suswa within the Kenyan section of the rift valley. Displacement along rock joints leads to the formation of Block Mountains like Rwenzori and escarpments like Butiaba.
Rock permeability
Rocks, which allow water to seep through them, reduce the amount of erosion on the surface. Permeable or porous rocks therefore form uplands e.g. the limestone rocks forming Sukulu hills in Tororo, Kalyango hills in Fort Portal and Wazo hills in Tanga
Rock beddings.
The degree of dipping or slope of the rocks influences landform development. Denudation is faster on a steep dip slope than on a gentle slope. Steeply dipping slopes low lands while gently dipping landforms form uplands e.g. the western and northern slopes of Tororo rock are steep while those of the south and eastern are gently sloping.
Colour of the rocks
Dark coloured rocks are more susceptible to weathering than light cloured rocks. Dark cloured rocks such as granites expand and contract more than light coloured rocks leading to the formation of exfoliation domes e.g. in Soroti and Kumi in eastern Uganda, Marsabit and Lodwar in northern Kenya as well as Kongwa and Iringa in Tanzania.
ECONOMIC IMPORTANCE OF ROCKS
Soil
Rocks weather to produce soils of varying fertility. For example, the igneous rocks on the slopes of Mts. Elgon, Kenya, Mufumbiro and Kilimanjaro have weathered to produce fertile volcanic soils supporting intensive cultivation and high population densities. Arabica coffee and bananas are grown as a source of food and income for the people. Sedimentary rocks along river valleys and lowlands have weathered to produce fertile soils supporting agriculture e.g. rice growing in the swampy areas of Butaleja, Pallisa, Iganga, Busembatia and Namutumba.
Minerals
Rocks are mined to provide minerals used for a wide range of purposes e.g. diamonds at Mwadui in Tanzania and tin in Kigezi are derived from igneous rocks. Salt mined from Lake Katwe and soda ash from Lake Magadi are derived from sedimentary rocks. Some minerals derived from the rocks such as diamonds and gold are exported thus earning the respective countries foreign exchange. Limestone rocks are used as a source of raw materials for cement manufacturing industries at Tororo, Hima and Bamburi. Mining generates employment and income for the people.
Building materials
Many types of igneous, metamorphic and sedimentary rocks are used as building stone, facing stone, and decorative material. In the Kigezi Highlands and slopes of Mount Elgon, exposed igneous rocks are quarried to provide building stones. Sedimentary rocks provide building materials e.g. coral rocks at Bamburi near Mombasa and Wazo near Tanga are used in the manufacture of cement. Metamorphic rocks such as slate and marble are commonly used as finishing stone in buildings. Roofing slate is obtained at Mandera in northern Kenya while marble from Moroto in Karamoja. Bricks and tiles are made from clay at Kajansi in the Lake Victoria basin and Kamonkoli near Mbale.
Rainfall formation
Igneous rocks form many highlands and mountain areas in East Africa. These highlands receive heavy orographic rainfall which has supported agriculture as well as source of water for the dense populations on the mountain slopes e.g. on the slopes of Mount Kilimanjaro, the Chagga people cultivate Arabica coffee and bananas. Furthermore, the heavy rainfall has also given rise to the growth of forests which are a tourist attraction e.g. Mount Elgon Forest Park.
Energy
Rocks are used as a source of energy. The hot igneous rocks in the Kenyan rift valley have given rise to several hot springs and fumaroles used in the generation of geothermal energy e.g. the Olkaria Geothermal Power Station near Lake Naivasha in Kenya which generates electricity. Coal is derived from sedimentary rock in the Ruhuhu valley is southern Tanzania. Oil and natural have been discovered in the sedimentary rocks in north Kenya and in the Albertine rift valley in western Uganda.
Road construction
Granite chippings are used for non-skid surfacing of major roads such as Kasese-Kampala-Busia- Nairobi-Mombasa road.
Water supply
Water supply is greatly affected by the nature of the rocks. The circulation of ground water, the formation of springs, the sinking of boreholes to reach the water holding strata, the possibilities of natural or artificial reservoirs are all affected by the nature of rocks. The rocks of the floor where reservoirs such as Kindaruna and Kamburu in Kenya are sited are such that leakage due to permeability is impossible or greatly minimized. Most sedimentary rocks are porous thus permits seepage of water and the formation of underground water resources. These are useful water sources in dry climatic areas such as Karamoja and Kiruhura through drilling of bore holes.
Salts
Salts obtained from rocks include rock salt. In East Africa it is obtained from L. Katwe, L. Magadi and at Malindi is used as an ingredient in food for man and cattle. In addition, common table salt marketed for consumption often has small quantities of iodides added to prevent the occurrence of goiter.
Ornamental stories
Rocks containing diamonds, gold and rubies are used as ornaments (precious stones) of great economic significance to the respective countries.
Tourism
Rocks have formed various relief landforms which act as important tourist attractions thus earning the respective countries foreign exchange e.g. the Tororo rock which is an igneous rock, the sedimentary rocks forming coral rocks at Mombasa and Dar es Salaam along the East African coast and karst landforms in limestone rocks at Nyakasura.
Grindstones and millstones
Other useful materials from rocks include millstones and grindstones obtained from granite and metamorphic rocks. In the rural areas of Soroti, Kumi, Kaberamaido and Katakwi, stones are used to grind millet and sorghum used as food.
Education
Rocks form important areas for research or educational purposes especially for students in higher institutions of learning studying geology and geography e.g. at Kilembe and Hima in Kasese,
Short comings of rocks
- The coral limestone rocks at Mombasa, Malindi, Tanga and Dae es Salaam along the East African coasts are sharp and hard and hinder navigation as no vessels can sail across them without being wrecked or damaged.
- Areas with pervious rocks e.g. the limestone rocks which allow water to seep through them at Nyakasura and lava flows at Kisoro often lack surface water hence negatively affecting water supply in the surrounding communities.
- Sand stones and gravel tend to create areas of infertile soils of no agricultural value to man.
- Resistant and outcrop rocks make the construction of roads difficult and expensive hence hindering the development of transport and communication routes e.g. the igneous rocks in Kapchorwa, Bukwo, Kabale and Kisoro. Bundibugyo
- Rocks containing large quantities of clay are non-porous leading to water logging and acidic soils hence limiting the number of crops that can be grown e.g. at Kibimba in Bugiri District.
- Continuous deposition of sedimentary rocks results into young soils of low agricultural value e.g. coastal areas of Tanga in Tanzania.
- Furthermore, the quality of water depends on the types of the rocks e.g. water in limestone areas tends to be hard because of the presence of soluble calcium carbonate.
- Some rocks such as the coral limestone rocks weather to produce infertile soils e.g. the soils referred to as coral wanda in Zamzibar and Pemba. Basalt rocks under humid tropical conditions weather to form laterite soils of low agricultural value like on hill tops of Buganda.
- Rocks act as hiding grounds for dangerous pests and animals that harm man. Like elephants and other animals in the cave rocks on the Kenyan side of Mount Elgon.
- Rocks forming highlands and mountains act as climatic barriers on the leeward sides of these mountains. Having lost their moisture on the windward slopes, the winds descend the leewardas dry wind hence causing little or no rainfall like the south east slopes of Mount Elgon are dry.
- Various types of landslides result from rocks e.g. rock fall involving the falling down of individual rocks and boulders, and rock slide involving the slipping of large masses of rocks over steep slopes are of immediate danger to man and his property e.g. the volcanic rocks in Bundibugyo, Kabale, Mt.Elgon and Mt. Kilimanjaro.
- Many volcanic rocks are formed through the ejection of hot lava, pyroclasts and gasses into the atmosphere which are of immediate danger to the surrounding areas. They lead to death on man and his animals, displacement of settlements, destruction of vegetation among others. The most recent eruption occurred in 2010 in the regions of Nyamulangira affecting areas in Rwanda and Goma in the DR Congo.
- Sedimentary rocks such as coral rocks along the East African coast are a barrier to fishing as the trap and tear fishing nets.
Conclusion
East Africa's diverse rock formations play a crucial role in shaping the region’s geology, economy, and natural landscapes. From the volcanic rocks of the Great Rift Valley to the vast deposits of sedimentary and metamorphic rocks, these geological features support industries such as construction, mining, and energy production. Understanding the formation and distribution of these rocks not only enhances our knowledge of Earth’s history but also helps in the sustainable utilization of natural resources. As East Africa continues to develop, the responsible management of its rock resources will be vital for economic growth and environmental conservation.
FAQs About Rocks with East African Examples
1. What is the definition of rocks?
A rock is a naturally occurring solid composed of minerals, mineraloids, or organic materials. Rocks form the Earth's crust and vary in composition, texture, and formation processes.
Example: In East Africa, volcanic rocks like basalt and granite are common due to the region's active tectonics, especially around the Great Rift Valley.
2. What are the 5 main types of rocks?
Rocks are typically classified into three main types, but additional classifications exist based on specific criteria. The five main types are:
- Igneous Rocks – Formed from cooled lava or magma.
- Example: Basalt, found in Tanzania's Mount Kilimanjaro region.
- Sedimentary Rocks – Formed from compacted sediments over time.
- Example: Sandstone, found in Kenya’s Turkana region.
- Metamorphic Rocks – Formed from heat and pressure altering existing rocks.
- Example: Marble, found in Moroto, Uganda.
- Volcanic Rocks – A subtype of igneous rocks formed from volcanic activity.
- Example: Obsidian, found near Mount Nyiragongo in the DRC (close to Uganda).
- Precambrian Rocks – Some of the oldest rocks on Earth, dating back billions of years.
- Example: Granite from the Buganda-Toro region in Uganda.
3. What does "rocks" mean in slang?
In slang, "rocks" can mean something is amazing, exciting, or impressive.
Example: If a Ugandan musician releases a hit song, fans might say, "That song rocks!" meaning it is excellent.
4. What describes a rock?
A rock can be described based on several characteristics, including:
- Composition (what minerals it contains)
- Texture (smooth, rough, porous)
- Hardness (resistant or brittle)
- Color (varied due to mineral content)
Example: The coral rocks found along the Kenyan coast are porous and light-colored due to their limestone composition.
5. What defines rock?
A rock is defined as a naturally occurring, solid material made of one or more minerals. It differs from soil due to its solid structure.
Example: The volcanic rocks in Rwanda's Virunga Mountains define the rugged landscape and support gorilla habitats.
6. How do you explain rocks?
Rocks are Earth's building blocks, forming through natural processes such as cooling lava, sediment compaction, and heat and pressure changes. They provide materials for construction, industry, and even art.
Example: The Kasese district in Uganda has rich copper-bearing rocks, contributing to mining activities.
7. What best defines rocks?
Rocks are naturally occurring solid aggregates of minerals. Their properties depend on their formation process and composition.
Example: The volcanic rocks in Ol Doinyo Lengai, Tanzania, are unique because the volcano erupts carbonatite lava, unlike typical silicate lava.
8. What is rock and its classification?
Rock is a naturally occurring substance composed of minerals. It is classified into:
- Igneous rocks (formed from lava/magma)
- Sedimentary rocks (formed from compressed sediments)
- Metamorphic rocks (altered by heat and pressure)
Example: Karamoja, Uganda, has both sedimentary (limestone) and metamorphic (gneiss) rocks, important for cement production.
9. What are the properties of rocks?
Rocks have several physical and chemical properties, including:
- Hardness – Some are hard (granite), others are soft (chalk).
- Porosity – Some absorb water (sandstone), others do not (slate).
- Color – Varies based on mineral content.
- Density – Some are heavy (iron-rich rocks), others are light (pumice).
Example: The soft limestone found in Hima, Uganda, is used for cement production.
10. What does "this rocks" mean?
When someone says "This rocks!" they mean something is great, exciting, or fun.
Example: After a successful music festival in Nairobi, someone might say, "This event rocks!" meaning it was amazing.
11. What is the main component of rock?
The main components of rocks are minerals, which vary depending on the rock type. Common minerals include:
- Quartz (in granite)
- Calcite (in limestone)
- Feldspar (in igneous rocks)
Example: The quartz-rich rocks in Busia, Uganda, are associated with gold deposits.
