Crowley's Ridge - Composition and Origin

Composition and Origin

The ridge is primarily composed of the windblown glacially derived sediment known as as loess. It contrasts greatly with the flat table land around it and with the black soil that makes up the delta. It varies from half a mile to 12 miles (19 km) wide and reaches an elevation of 550 feet (170 m) near its northern extremity. The formation is generally thought to have originally been an island between the Mississippi River and Ohio River that became a long low hilly ridge after the rivers changed course millions of years ago. Recent research, however, questions the fluvial origin.

There are loess deposits found along both sides of the Mississippi River Alluvial Valley. These loess deposits are a classic example of periglacial loess. Crowley's Ridge is a natural loess accumulation point. A comparable example of this type of deposit is the Loess Hills in northwestern Missouri and southwestern Iowa.

There is evidence that the area's elevation has increased over the years, suggesting that uplift took place and is still taking place. This alternative explanation posits a link between the ridge and the nearby New Madrid Seismic Zone.