WINDS AND DESERTS

• Global Wind Patterns 530
• Wind as a Transport Agent 531
• Wind as an Agent of Erosion 534
• Wind as a Depositional Agent 535
• The Desert Environment 540

AT ONE TIME OR ANOTHER, we’ve all been caught in a wind strong enough to have blown us over, had we not leaned into it or held onto something solid. London, England, which rarely gets strong winds, experienced a major windstorm on January 25, 1990. Winds blowing at more than 175 km/hour ripped roofs off buildings, blew trucks over, and made it virtually impossible to walk on the streets. In deserts, strong winds are much more common, often howling for days on end. Dust storms are frequent, and many winds are strong enough to blow sand grains into the air, creating sandstorms.

Recently, concern over the expansion of Earth’s deserts has increased. Conditions in southern Spain, for example, have become so dry that people there are increasingly wondering whether the Sahara has jumped the Mediterranean Sea and is now encroaching on southern Europe. The process of desertification, in which nondesert land is transformed into desert, has become a major focus of scientists trying to understand Earth’s climate system.

Wind is much like water in its ability to erode, transport, and deposit sediment, and it is capable of moving enormous quantities of sand and dust over large regions of continents and oceans. That is not surprising, because the general laws of fluid motion that govern liquids also govern gases. The much lower density of air makes wind currents less powerful than water currents, even though wind speeds are often much greater than those in currents of water. And there are other differences. Unlike a stream, whose discharge is increased by rainfall, wind transports sediments most effectively in the absence of rain.

In this chapter, we will look at the role of erosion, transportation, and deposition by wind in shaping the surface of the land. We will focus particularly on deserts because so many of the geologic processes that shape those arid environments are related to the work of wind. We will also look at the elements that make up desert landscapes, and how those landscapes are spreading across the globe.