Wikibooks: Historical Geology/Deserts

• Format: Book
• Language: English
• Subjects: Antarc*; Antarctic; Antarctica; Arctic
• Online Access: https://en.wikibooks.org/wiki/Historical_Geology/Deserts

In this article we shall discuss the forces that shape deserts and discuss how geologists can use this knowledge to identify rocks that are the lithified remains of former deserts. We shall use some terms that have been introduced in previous articles on [[sedimentary rocks]] and [[mechanical weathering and erosion]] the reader who has not already read these articles may find it useful to go back and do so. =Definition of a desert= A desert is an area of low rainfall. A desert by this definition is not necessarily hot there are some areas of Antarctica that are considered deserts. Nor does a desert necessarily conform to our stereotype of being sandy a sandy desert is known as an erg . =Causes of deserts= The immediate cause of a desert is by definition lack of rainfall. This itself can have a number of causes which are not mutually exclusive an area can be a desert for more than one reason. High pressure deserts . In zones of high atmospheric pressure the ability of air to contain moisture is increased resulting in little rainfall. Examples include the Sahara Arabian Thar and Kalahari deserts and the desert regions within the Arctic and Antarctic circles. Mid continent deserts . Areas in the middle of a continent can receive little rainfall simply because rain originating from evaporation of seawater will tend to fall before it can reach the middle of a large continent. Modern examples are the Turkmenistan Gobi and Great Australian deserts (the Great Australian Desert is also in a region of high pressure). Rain shadow deserts . Rain will tend to break over mountains so the presence of mountains can prevent rain from the sea from coming inland. Examples of rain shadow deserts include the Mojave desert in the rain shadow of the Sierra Nevada the Patagonian desert in the rain shadow of the Andes and the Iranian desert in the rain shadow of the Zagros mountains. Upwelling deserts . Finally a desert may be by the coast and not in the rain shadow of any mountains but be adjacent to where a cold current of water rises ...