Plant & Equipment

Children of the Loess

Shortly after the Great Midwestern Flood of 1993, I undertook a project to map the surficial geologic materials – the sediments left by glaciers, water and wind – near St Joseph, Missouri.

During the ice age a massive glacier extending down from Canada covered the area around St Joe. The ice deposited many tens of feet of black clayey deposits called till. Rivers in the valley bottoms reworked that till, mixed it with other sediment washed to the rivers from the adjacent uplands, and deposited it as alluvium. But the most conspicuous material in the area is loess (rhymes with fuss), a fine soil created by the glacier and deposited by the wind.

The glacier ground some rock into silt, tiny particles no bigger than the diameter of a hair. Meltwater from the glacier carried the silt downstream and deposited it on floodplains. Wind picked up the silt and deposited it as dunes along the ancient waterway that became today’s Missouri River. The prevailing winds were from the northwest, so most of the deposits ended up on the east (Iowa and Missouri) side of the river. Those windblown deposits are referred to as loess.

The end result of this geologic activity was a unique landscape called the Loess Hills. The hills form a 321km long band, up to 24km wide, running north-south along the Missouri River, extending from north of Sioux City in Iowa southward to near St Joseph, Missouri.

{{image2-a:r-w:200}}Although loess is quite common, the Loess Hills are unusual because the loess is extraordinarily thick, as much as 60m in some places. Nowhere else in the world, except near Shaanxi in China, is loess thicker than in the Loess Hills.

Loess has a natural tendency to slump on steep slopes. Over tens of thousands of years, erosion created a landscape of narrow undulating ridges flanked by steep slopes and numerous side spurs. The intricately carved terrain of the Loess Hills makes them a rare geologic wonder that can be experienced via the Loess Hills National Scenic Byway. If you are in that neck of the woods, it certainly is worth a ride along the byway.

As you ride through the Loess Hills, you are apt to see deep road cuts where the loess stands in near vertical faces on either side of the road. You can also see steep cliff faces in loess in some places along the Missouri River, such as in St Joe.

This brings us to the tiny subject of this article. Some of the road cuts or cliff faces expose “loess kindchen”, which is German for “children of the loess”. As rainfall or snowmelt percolates through the loess, it dissolves the calcium carbonate in the soil. When the calcium-rich water reaches a nucleus, such as a snail shell fragment, the calcium carbonate precipitates out, forming a concretion around the nucleus. The concretions commonly are irregularly shaped nodules of calcium carbonate, many of which resemble tiny dolls, hence their name.

The existence of loess kindchen is dependent on local groundwater and soil conditions. When present, sometimes you can find them peeking out of near vertical road cuts and bluffs. Over time they may erode out of the bluffs, where they collect in streams at the base of the bluffs.

While the Loess Hills are a true geologic wonder, the tiny loess kindchen make the area all that more fascinating.

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