Grades 3–5 · Earth & Space
How can a dry valley floor become covered in salt?
A white salt flat can mark the bottom of a basin with no river outlet to the sea. Rain and streams carry dissolved minerals downhill into that low area. The minerals come partly from rocks along the water’s journey.
In the diagramA closed basin keeps minerals as water evaporatesno river outletwater leaves into the airmineral crust remainsMinerals arrive; water evaporates from a closed basin.
After a flood, a shallow temporary lake may spread over the basin floor. In a dry climate, evaporation can remove water faster than fresh water replaces it. The dissolved material becomes more concentrated as the lake shrinks.
Eventually, minerals form solid crystals and remain on the ground. Repeated flooding and evaporation can build layer upon layer. The salt has accumulated from material carried in, rather than appearing because the ground merely became hot.
Later water can dissolve some of the crust again and move it elsewhere in the basin. Salt flats therefore keep changing. Their formation connects a mineral supply, a closed drainage system and a climate that favors strong evaporation.
About this explanation
Starting knowledge: Know that water can carry dissolved minerals and that evaporation removes liquid water into the air.
Sources
- National Park Service — Salt Flats — Death Valley National Park