Missouri's Icy Past

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Published on: Dec. 2, 2001

Last revision: Nov. 10, 2010

than that of wells drilled into bedrock. The sand and gravel sediments found in these buried stream channels also yield higher water flows, which allows wells to recharge more quickly.

The river bluffs in this corner of the state also owe their origins to glacial influences. Ice sheets from later glacial advances, known as the Wisconsinian and Illinoisian, did not reach most of Missouri. However, when the climate warmed again, meltwater from northern glacial ice carried silt into streams and rivers flowing through this region.

The volume of water flowing down the Missouri River during warm summers flooded its valley from bluff to bluff. Where water slowed down, suspended particles dropped out and covered the floodplain with silt. Because the area was flooded for most of the growing season, few plants grew there, so there was little vegetation to help anchor the soil.

Each year, as freezing temperatures returned in winter, glacial melting stopped and reduced the water flow in the river, allowing the floodplain to dry. Prevailing winds blew the silt into the adjacent uplands where it formed dune-like loess hill bluffs. Miniature versions of these ancient dust storms were visible in the Missouri River Valley during the winter following the flood of 1993.

Loess (pronounced, "luss") is a German word that, roughly translated, means "loose and crumbly." That's a good description of this highly erodible soil. Though loess deposits exist along the entire length of the Missouri River in our state, they are especially deep and prominent in Atchison and Holt Counties north of St. Joseph. Over the centuries, rain water has chiseled into piles of loess that rise nearly 200 feet above the Missouri River floodplain. Steep, angular hills formed and became home to one of our states rarest natural communities, the dry prairie.

Loess hill prairies are found near the tops of south- and west-facing slopes. Exposure to prevailing winds, near-constant sunlight and rapidly draining loess soils create harsh living conditions for animals and plants. Similar conditions are found on Ozark glades, but glade soils are seldom more than a foot deep.

In Missouri, several plant species that are common farther west on the Great Plains grow only on loess hill prairies. Most have waxy or hairy leaf surfaces, or their leaves are very small. These features are thought to help minimize water loss.

One of the most distinctive of these plants is soapweed. A type of yucca, the plant's common name comes

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