Wind Sculpture
Listen in RealAudio
Email your weather question

There are exquisite patterns seen in mountains, prairies and rivers sculpted into the earth. These are among the great examples of the ground giving away to the relentless toouch of the weather. Hi, I'm Dave Thurlow.

This sculpting process as I'm calling it is especially easy to see in much of the western part of the U.S. It's called weathering; a recognition of weather's role in shaping the earth's outer shell, or its crust.

Weathering is a pretty slow process, kind of like sculpting stone with a toothbrush. Something I've never actually tried but I can't imagine it being immediately effective. But, if you stick with it long enough, you might just get something done.

The sculpting of the Grand Canyon for example is the result of about a million years of weathering. The slowest and least detectable step in this weathering process is called chemical weathering. This is when pure rain water with its slightly ionized composition dissolves some of the composite minerals in the rock that holds it together. 500 years barely does anything but 5 million years is another story.

The most noticable changes take place with what's called mechanical weathering. Like when rain water seeps into cracks in rock and then freezes which expands and forces the rock to break. The rock then breaks into pieces big and small which are blown, washed or simply fall into a low spot with the rain water. This creates a stream with churning sand and gravel which scrapes a path for a river to take and get down to some serious erosion. The weather may not work quickly but it beats the hell out of a toothbrush.