At 600 km the river abruptly enters a narrow valley between hills rising some 200 m from the broader valley floor, becoming almost a gorge. About 700 km from source the Luangwa merges with its tributary the Lukusashi after the latter has merged with the Lunsemfwa River coming from the opposite direction, and turns due south through a steep narrow valley: this is its exit from the Luangwa Rift Valley. After only 20 km it emerges from the hills into the broad valley of the Zambezi and meanders over sandy flats about 1.5 km wide in a flood plain of 3–5 km wide. It merges with the deeper Zambezi at Luangwa town.
The Luangwa Rift Valley
This section explains the geomorphology of the Luangwa Valley. It is a rift valley or graben forming a south-west extension of the east African Rift, branching off its Lake Rukwa-Lake Malawi southern section, and reaching almost as far as Lusaka. The junction is not obvious because it filled with material spewed out from an ancient, extinct volcano. There are at least 20 hot springs, characteristic of a rift valley, in the valley or on its escarpments. The Luangwa flows along four-fifths of the Luangwa Rift Valley to the point where it meets the Lukusashi and the Lunsemfwa which has come from the opposite direction. At one time, millions of years ago, there was no way out and the Luangwa Rift filled with a Rift Valley Lake called the Madumabisa Lake, which rivalled Lake Malawi in size. The water of the lake overflowed in a river to the south-west, towards what is now the Kalahari, where it combined with the Okavango, Upper Zambezi, Cuando and Kafue rivers, emptying into the Limpopo River and flowing to the Indian Ocean. Several geological events combined to produce the current river systems. Faulting produced another graben just to the south of the Luangwa Rift, and running east–west: the Zambezi Rift Valley and the Chicoa Trough. A tributary of the Shire River at the south end of the Great Rift Valley then cut back eastwards through the Chicao Trough and Zambezi Valley, capturing the southerly overspill of the Madumabisa Lake. This tributary became the Zambezi, which over millions of years captured the Kafue, Cuando and the upper Zambezi. Faulting lowered the land between the Luangwa Rift and the Zambezi Rift allowing Madumabisa Lake to drain out into the Zambezi in a channel which became the lower Luangwa River.
The Luangwa as a barrier
The Luangwa Rift Valley and rivers within it form a natural barrier, with a very low population density. This, the steepness of the terrain, and the existence of the wildlife reserves have resulted in no highways crossing the valley between the Lusaka-Kabwe roads in the west and the Isoka-Chisenga road in the north, a distance of about 800 km. The lower Luangwa Valley is crossed by just one road, the Great East Road at the Luangwa Bridge, about 10 km south of the Luangwa-Lunsemfwa confluence.
