After Us
Erosion (Earth Primer #4)
- By Giacomo Sartori
(Countryside in Algeria, photo by Giacomo Sartori)
Cultivated soil is very fragile—just a bit of water running over the surface is capable of stripping away its thin upper layers, which are the most rich and fertile. The soil is then deposited at the base of the slopes, where the water slows, or poured into creeks or rivers that will carry it to the sea. In either case (and both often happen simultaneously), it is a permanent loss. And if the water streams down violently, it tears away all the best soil, opening up rivulets and deep ravines, eating up a stunning amount of earth, annihilating the labor of thousands of years through which the soil had been formed from stone. Steep slopes are not needed; water builds up energy from even minimal height differences,...