The influence of vulcanicity on drainage features of Uganda

• Vulcanicity led to the formation of lava dammed lakes as L. Mutanda, chahafi, Muhehe and L. Bunyonyi. Such lakes were formed when lava flew from adjacent volcanic eruptions (Birunga volcanoes) overflew and solidified in former tiver courses thereby forming a series of lakes.
• Vulcanicity lead to formation of explosion crater which later filled with water to form crater lakes such as L. Katwe. They were formed when violent volcanic eruption chiefly composed of gases and gaseouswater vapour blow up the country rock into small fragments which rise high and later fall and accumulate around the hole forming a raised rim around depression. When these depressions are filled with water say from rain crater lakes are formed.
• Vulcanicity also formed crate lakes on the top of volcanic cones such as Mt. Elgon and Muhavura. Such crate lakes are formed when seconndary violent eruption blows on the top of volcanic cones leaving behind a funnel shaped depression. The depressions were filled with water to form crater lakes.
• Volcanicity also formed Caldera lakesfor example on top of Napaka mountain. A Caldera is a wide crate that exceeds 1km in diameter. There are two ways through which calderas could be formed. In the first place, it can be formed by a process called cauldron subsidence or basal wreck. During eruption, a lot of magma is poured out due to high pressure such that there is a big empty space (chasm) left unfillled under the volcano. The weight of the overlying volcanic top becoms great and therefore it collapses into the space/chasm nelow leaving a wide depression.

Alternatively, calderas are formed when a violent eruption blow off the top of the volcano leaving a wide depression which is filled with water e.g.Napak caldera lake

• It formed volcanic mountains such as Mt. Elgon is a watershed for numerous rivers flowing on either direction to form a radial drainage pattern such as R. sironko, Namatala, Sisiyi and R. Manafwa.
• Vulcanicity also formed hot springs at Norot in Karamoja, Kitagat Sempay, Rwagimba in western Uganda. A hot spring involves the natural flow of hot water from the rocks of the ground.
• A sill is an intrusive vulcanic features that influence development of drainage feature in Uganda by obstructing river flow leading to the formation of water falls along R. Nile and R. Sezibwa.

On the other hand, vulcanicity has negatively affected development of drainage because in some cases it formed porous soils such as pumice which have reduced surface drainage in Kisoro districts. For example Chuho springs sustains water to a stream which flows only for 30 meters and then disappears due to porosity of the under ground soils.