Geography of Roads.

Today we feature the Nairobi-Nakuru highway.

The A104 highway straddles the Eastern escarpment of the Rift valley, linking the capital with Nakuru city on the valley floor.

The scenery is stunning all along the route but danger lurks too.

A thread 🧵

The journey starts in Nairobi where the highway heads West towards Gitaru.

Right from the outset, the highway faces an ascent up the highlands of the Rift valley. The elevation starts from Chiromo junction (1700m) to the viewpoint at 'Flyover' junction (2700m), 64km away.

Contextualization of the Kijabe mudslide tragedy from a geographic perspective.

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https://twitter.com/C_NyaKundiH/status/1784937546725658722

Kijabe escarpment is located between Limuru and Naivasha, the section famously referred to as viewpoint.

The ridge at the top of the escarpment where the Nakuru highway passes has an elevation of 2600m while Mai Mahiu, less than 5km away as the crow flies, is 1900m asp.

Ngong river is reportedly the most polluted river in Kenya.

The river flows through informal settlements and Industrial Area where it is polluted by human and industrial waste.

In this thread, we'll trace the river from source to discharge and the various pollution points. Ngong river originates in Motoine forest near Dagoretti. It flows next to the Southern bypass until the Ngong road interchange where it enters the Ngong road forest.

Ngong river then flows within Ngong road forest and enters Kibera in Soweto where the pollution starts.

December 21 is summer solstice in the Southern Hemisphere. Today is the day when the earth is at its maximum tilt to the south and the Sun’s rays are directly overhead at the Tropic of Capricon.

It might not feel like it but today is the start of 3 months of sunny weather in 🇰🇪 The southern tilt of the earth on its axis exposes the southern hemisphere to more sunlight and causes winter in the less exposed northern hemisphere.

Daylight hours increase further South. Nairobi 1.2°S (12h 12m), Capetown 34°S (14h 25m) and South pole 90°S (24hrs daylight).

Mau forest complex is the biggest closed-canopy forest block in Kenya. It is the source of numerous rivers including Mara river which sustains the Mara-Serengeti ecosystem.

Google Earth's timelapse feature gives a sorry picture of the forest's destruction since 1984.

Thread. Mau has several forest blocks. The sections to the East, South and South West have suffered the biggest loss of forest cover since 1984.

The first timelapse shows the loss of forest cover in Maasai Mau, largely located in Narok County

Nguruman escarpment is located on the southern-most section of Kenya's western Rift Valley escarpment.

The valley floor (650m) contrasts sharply with the steep scarp walls that peak at 2300m.

Ewaso Nyiro south flows down the scarp towards Lake Natron.

THREAD. Access to Nguruman is via a murram road that passes over Lake Magadi.

The landscape in this southern part of Kenya is one of outstanding Rift valley features. Volcanic mountains (Ollorgesaille, Gelai) reflect on the glassy surface of RV lakes with huge escarpments on the flanks

The poor quality of air in Nairobi is a matter that needs urgent action by policy makers in Kenya.

These two photos show the exact same view before and after the rains. The dense layer of smog over the eastern side of the city blocks out the view of Mt. Kilimambogo.

THREAD. Nairobi has dangerously high level of toxic particles in the air. As per sensors.africa air quality tracker, Nairobi has particle levels that are 70% higher than the WHO recommended safe levels.

This is a damning statistic for a city that host @UNEP

Storm clouds gather over Nairobi.

Nairobi experiences relief rainfall. This occurs when moist air vapour is blown in from the Indian ocean. Increase in altitude inland and the resultant decrease in temperature causes the air to condense and form clouds that rain over highlands. Relief rainfall occurs over highlands in Kenya including the highlands east & West of the Rift valley as well as Mt. Kenya. The graphic below highlights the inland movement of moist air from the ocean and precipitation in the highlands.

Lake region experiences convectional rain

A map showcasing the tree cover in Kenya (average canopy height of 3m).

While Kenya has limited forest cover (only 6%) the country has a significant canopy coverage that is not necessarily forest. @KeForestService classifies forests as areas having > 30% tree cover.

Thread. It goes without saying that the areas with the highest average canopy height and forest coverage are the main water towers in the country (Mt. Kenya, Aberdares, Mau and Cherangany Hills).

Mt. Elgon on the Uganda border also ranks in this category.

Prosopis juliflora or Mathenge is an exotic drought-resistant tree of American origin that has been widely used for afforestation in Northern Kenya.

A thread on how the aggressive tree species has proved destructive to the pastoralist economy. The trees have pods that are eaten by livestock and spread over large areas where they quickly grow. The deep tap roots of Mathenge trees ensures the trees stay evergreen once they take root.

The tree particularly thrives along water sources such as rivers banks & flood plains.

Lake Chala is a caldera lake that is found along the Kenya-TZ border near Taveta town.

The caldera was formed when a small volcanic hill erupted and collapsed on itself. Ground water from the nearby Mt. Kilimanjaro (pictured) seeped from underneath and fills the crater to date. Lake Chala has a depth of about 90m with a further 170m from the lake surface to the crater rim. This makes for a rather deep crater of almost 300m, akin to the Mt. Longonot crater.

A hydrological map of Kenya with colour-coded watershed areas.

In this thread, we'll highlight the source of each river, the watershed area and the direction of flow. The rivers of Kenya flow from three main sources: the escarpment and highlands east of rift valley (Aberdares), highlands west of the rift valley (Mau) and Mt. Kenya.

Mt. Elgon & Kilimanjaro on the border with our neighbors also act as sources of rivers that flow within Kenya.

The @Space_Station flies some 400kms above earth. In this video, the ISS flies from the Iberian Peninsula to Kenya on a bright, moonlit night.

We've taken some screenshots and tried to highlight some of the cities and geographical features visible.

THREAD. The flight starts above Spain and Portugal.

Mediterranean cities are visible due to their bright city lights including it's largest city, Barcelona as well as Northern Italy's largest city, Milan.

Europe's highest mountain, the Alps mark a dark patch North of Italy.

Millions of years ago, Mt. Kilimambogo erupted and the viscous lava found its way to the nearby Athi river. The lava flowed along the river valley for 300km, shifting the river and creating one of the longest lava flows in the world, the Yatta plateau.

Thread. Athi river flows right next to Yatta plateau throughout the plateau's 300km length. The flat-topped 100m high Yatta forms a natural boundary between Kitui & Makueni counties. The plateau is visible for long stretches along the Mombasa-Nairobi highway.

Image c/o @KivindyoMusyoki