CHAPTER 7.2 DESERTS Most of the weathered debris in deserts is the result of mechanical weathering.

This debris consists of unchanged rock and fragments of minerals.

Little moisture, few organic acids, and few decaying plants.

Chemical weathering exists but S-L-O-W-L-Y.

Water in the Desert? Sure! Ephemeral = temporary (streams are intermittent and dry most of the year.

Flash flooding = happens because there are few plants to absorb or slow the run off so rain waters from storms flow quickly into dry stream beds and just as quickly end when the storm ends.

Death Valley

Arid regions have ephemeral streams that do not flow out of the desert to the ocean like streams in other areas. They have INTERNAL DRAINAGE because most streams dry up long before they reach the oceans.

China

Like the alluvial fan at the mouths of rivers that empty into the oceans, desert storms create rushing waters that carry enormous amounts of sediment in a fan-like shape when it reaches gentler slopes.

Copper Canyon, Death Valley

Occasionally, water can flow out into a basin creating a shallow PLAYA LAKE that lasts only a few days or weeks. After the water evaporates or infiltrates it leaves a dry lake bed called a PLAYA.

Exceptions to the rule…

Colorado River

Nile River

The Nile crosses 3000 km of the Sahara without

a single tributary adding

to it.

Water vs. Wind

WIND EROSION WATER EROSION

Water Wins!