One Afternoon or 600,000 Years? Changes to a Farm County's Surface

The Driest Year

1This was the driest year that Nadia Haddad's family can remember on their wheat farm in Crane County. Only 23 cm of rain fell between January and October, about half the usual amount. Many fields were plowed but bare, because the crop sprouted poorly or never came up at all. Crane County sits on a wide, nearly flat plain, cut only by one river valley.

2In April, a windstorm with gusts near 80 km/h swept across the county, and the sky turned brown by midafternoon. When the wind died down, Nadia's father checked the marked stakes the family had pushed into a bare field. About 5 mm of topsoil had blown away in a single afternoon, and neighbors on many farms across the county reported the same. Fine dust from the storm settled on cars and windowsills more than 100 km away.

3In August, a thunderstorm dumped 6 cm of rain in less than an hour onto the hard, dry ground. Water raced across the fields instead of soaking in. Within three hours it had cut a gully 2 m deep and about 500 m long along the edge of one field. Afterward, the bottom of the gully was scattered with chunks of soil and small stones torn from its sides.

4For her science project, Nadia compared these events with slower changes, which are hard to notice in one lifetime and are usually found by measuring and calculating. A county soil scientist told her that in this area about 1 cm of new topsoil forms in roughly 200 years, as rock breaks down and plant remains decay and mix in. Nadia also studied the valley of the Red Willow River, which winds through the county. The valley is about 40 km long and 60 m deep, and geologists estimate the river has been cutting it for about 600,000 years. She organized what she learned in the table below.