Lake Assal, located in the central-western region of Djibouti in East Africa, is one of the most saline bodies of water globally. Situated within the scorching Afar Triangle, the lake’s surface lies approximately 155 meters below sea level, making it the lowest point on the African continent. Its salinity is exceptionally high, often measured at nearly ten times that of typical seawater, with concentrations reaching up to 398 grams of salt per liter in deeper areas. This hyper-saline environment results from an active geological setting, specific water input mechanisms, and an extreme climate.
The Geological Source of the Salt
The massive amount of salt in Lake Assal is fundamentally linked to its position within the Afar Triangle, a triple junction of the Great Rift Valley system. This tectonic setting is characterized by continuous crustal spreading, which exposes the area to intense volcanic and geothermal activity. The lake depression sits atop the East African Rift, where the earth’s crust is thin and fractured.
This geological activity constantly introduces massive quantities of minerals and salts into the local rock and groundwater system. As water permeates through the fractured basalt and volcanic rock formations, it leaches out these naturally occurring deposits. Geothermal activity, evidenced by hot springs and fumaroles near the lake, further contributes to this mineral-rich environment, meaning the water entering the basin is already highly saturated with dissolved solids.
How Water Enters the Lake
Lake Assal is classified as an endorheic basin, meaning it has no outflow to any river or ocean, which is key to its salinity. The lake receives very little water from surface runoff or rainfall due to the surrounding region’s extreme aridity and minimal annual precipitation.
The primary water source is subterranean, originating from the nearby Gulf of Tadjoura. Seawater from the Gulf seeps through a highly porous, fractured volcanic ridge separating the ocean from the lake basin. This underground flow travels approximately 10 kilometers before emerging into the lake as geothermal springs. The water entering the lake has a salinity level close to that of normal seawater, but it is enriched with minerals from its journey through the volcanic rock.
The Extreme Concentration Mechanism
The intense process of evaporation is the reason Lake Assal’s water becomes significantly saltier than its seawater source. Located in one of the hottest places on Earth, extreme heat and strong, dry winds drive a remarkably high rate of water loss. The annual evaporation rate is estimated to be between 3.5 and 5 meters of water depth, significantly exceeding the amount of water flowing in. As the water evaporates, it leaves behind all the dissolved salts and minerals, causing the concentration of the remaining liquid to increase dramatically. Since the lake has no outlet, this continuous process results in a liquid brine much higher than the Dead Sea, depositing massive quantities of salt to form thick crusts around the lake edges.