The lavas have significant amounts of carbonate but very low calcium and magnesium levels. The surrounding bedrock is composed of alkaline, sodium-dominated trachyte lavas that were laid down during the Pleistocene period. The alkalinity of the lake can reach a pH of greater than 12. High levels of evaporation have left behind natron ( sodium carbonate decahydrate) and trona (sodium sesquicarbonate dihydrate). Temperatures at the lake are frequently above 40 ☌ (104 ☏). The surrounding area receives irregular seasonal rainfall, mainly between December and May totalling 800 millimetres (31 in) per year. The lake is a maximum of 57 kilometres (35 mi) long and 22 kilometres (14 mi) wide. It is quite shallow, less than three metres (9.8 ft) deep, and varies in width depending on its water level.

The lake is fed principally by the Southern Ewaso Ng'iro River, which rises in central Kenya, and by mineral-rich hot springs.

Numerous near-white salt-crust 'rafts' pepper the shallowest parts of the lake (inset). Fault scarps and the Gelai Volcano can also be seen.

Elevation of lake natron tanzania