Missouri's Icy Past

Nothing, not even diesel-powered, Detroit iron, moves earth as effectively as glacial ice.

Like giant bulldozers, ancient glaciers plowed across northern Missouri, dramatically altering the landscape as part of a relentless, natural renovation project that occurred nearly 500,000 years ago. These thick rivers of ice left behind a blanket of mixed rock, sand and clay as they pushed innumerable tons of earth southward into the glacial melting zone.

Glacial Effects in Northern Missouri

The sheer amount of land covered by glaciers became apparent to me when a geologist showed me a fist-sized, dull brown mineral sample he found in a stream bed south of St. Joseph. It was taconite, a type of iron ore, from the Mesabi Range in northeastern Minnesota.

The sheer amount of land covered by glaciers became apparent to me when a geologist showed me a fist-sized, dull brown mineral sample he found in a stream bed south of St. Joseph. It was taconite, a type of iron ore, from the Mesabi Range in northeastern Minnesota.

It arrived here during one of two early glacial advances, known as the Nebraskan and the Kansan, when vast ice sheets worked like gigantic conveyor belts to carry a variety of rocks and minerals south from the northern U.S. and southern Canada. When the climate warmed, the ice melted and deposited minerals like taconite as far south as St. Joseph. The mineral in my hand had traveled nearly 500 miles!

Large boulders in northern Missouri provide an even more impressive testament to the power of glaciers. Called "erratics" by geologists, they are so novel that many are noted in Thomas Beveridge's book, "Geologic Wonders and Curiosities of Missouri." An erratic northwest of Milan in Sullivan County is about as tall as a basketball goal and measures 20 feet wide by 24 feet long. Its estimated weight is about 384 tons.

Even that pales in comparison to some of Missouri's other glacial artifacts. For example, main channels of ancient rivers and streams in Missouri's northwest corner once drained primarily from west to east, rather than north to south, as our streams do today. Their valleys were buried under till, a mixture of clays, sands and gravels left by melting glaciers. Only after the Kansan and Nebraskan ice sheets disappeared did the Missouri River attain its present course in this region.

Today, wells are drilled into these buried ancient river channels. In northern Missouri, the water quality from these sites is better 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 from a soap-like substance in its roots. Only one kind of insect, the yucca moth, can pollinate yucca flowers. Once the yucca moth provides this service, it lays its eggs in a seed case, providing a ready food source for its larvae. Some of the seeds survive to produce the next generation of plants.

Skeleton weed, also found here, has tiny leaves, giving it a bare, almost skeleton-like appearance. The plant has numerous small, roundish growths on its stem. These galls-sometimes mistaken for fruits-are formed when a small wasp or fly lays its eggs on the plant's stem. These and other plants more typically found on the Great Plains give Missouri's loess hill prairies their unique character.

Glacial Effects in the Ozarks

Evidence of glacial effects in the Ozarks is more subtle. Glaciers never extended as far south as the Missouri Ozarks, but they did affect this region indirectly. The Ozarks climate was colder and moister during glacial events, providing hospitable conditions for plants and animals that moved in from areas farther north and northeast. Some of these plants and animals survive today in caves, springs and other isolated damp, cool areas.

After glaciers retreated, conditions became warmer and drier. However, cool, wet conditions still occur on some north-facing bluffs, in springs and in bog-like areas, called fens. These sites provide relatively small, secluded places that moderated the more extreme conditions in surrounding areas.

Northern wildlife species, such as wood frogs and four-toed salamanders, survive in these isolated places, providing living evidence that glaciers widely influenced Missouri's natural history. Biologists call these species, "glacial relicts," but they are part of the modern day mosaic of Ozarks life. Four-toed salamanders live along spring-fed creeks in scattered sites in southeastern Missouri. Predators grasping this salamander by its tail may not get a full meal. The appendage easily breaks off next to its body, giving the animal a chance to escape.

Wood frogs favor cool, north-facing wooded hillsides. Males call between early February and late March, depending on weather conditions. They have a short breeding period, and their calling occurs only at select breeding ponds and lasts only a few nights. In his book, "The Amphibians and Reptiles of Missouri," Tom Johnson describes their call as being similar to the quacking of a duck. This sound may be overpowered by choruses of spring peepers calling at the same time.

Northern bedstraw, harebell and northern white violet are plants found only on moist, shaded ledges and in crevices along narrow ravines and streams.

Snake-mouth orchid, green twayblade orchid, queen of the prairie and marsh bellflower survive in fens. Here, groundwater seeping from underlying bedrock into overlying soils provides the cool, moist conditions that have allowed these plants to survive over centuries.

The northern brook lamprey, channel darter and mottled sculpin are fish species which live mainly north and northeast of Missouri, but have outlying populations in Ozark streams. In his book, "The Fishes of Missouri," Bill Pflieger reported that all three species are thought to have survived in the Ozarks as glacial relicts.

Relict insect species in the Ozarks include two species of stonefly and at least two kinds of caddis flies living in the cool waters of large Ozark springs.

Glaciation had a lasting effect on Missouri. Look around at the relict species of animals and plants living in the Ozarks. Marvel at the boulders and pebbles carried into the northern part of the state from distant landscapes. They, along with the loess hills and the dramatically altered courses of river channels in northwest Missouri, are all links to an icy past.