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Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 244, part 3
The Relationship Between Geology and Landslide Hazards of Atchison, Kansas, and Vicinity--page 2 of 9

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Introduction

In 1995, a landslide destroyed two $400,000 homes in Overland Park, Kansas, dramatically underscoring the need for landslide studies in the greater Kansas City metropolitan area. During reconnaissance mapping in 1997, landslides were located along the Missouri River from Kansas City to Wathena, along the Kansas River from Kansas City to Topeka, and along Stranger Creek from the Kansas River to Potter (fig. 1). Based on the reconnaissance and previous damaging landslides in Wyandotte and Johnson counties, a pilot project was initiated to study the landslide hazards of the Kansas City metropolitan area in Kansas.

fig. 1


Fig. 1. Map of northeast Kansas, showing the location of the study area (green shaded area) and locations mentioned in the text.

The objectives of the pilot project were to produce a landslide inventory map (Ohlmacher, 2000) and a landslide susceptibility map for a region near the Kansas City metropolitan area. An inventory map shows the locations of landslides and related features, whereas a susceptibility map ranks the degree to which parts of the study area are prone to future landslides, based on the factors that produced past landslides. (A landslide susceptibility map does not provide information on how often landslides occur, as in a landslide hazard map, or the extent of damages and injuries that might be anticipated from a future landslide event, as in a landslide risk map.) A landslide event is defined as one or more landslides occurring during a limited time frame--for example, during and following a severe rainstorm. A landslide susceptibility map requires detailed information on the factors causing landslides, including slope morphology, geology, and soils. This report presents information on the causal factors collected as part of the pilot study.

Setting

The area around Atchison, Kansas, was chosen as the study area for the pilot project because of its proximity to the Kansas City metropolitan area and the occurrence of landslides (fig. 1). Landslides around Atchison were observed during the 1997 reconnaissance mapping and were reported by a former Atchison city engineer (J. Hixon, personal communication, 1997). One of the reported landslides broke a sewer line south of downtown, and another landslide occurred behind a house near Jackson Park. A map showing the location of landslides and breaks in the sewer line between downtown and Jackson Park was produced by the City of Atchison (unpublished data, 1995). The map shows the locations of five sewer breaks that occurred during the last 10 years. It is not known how many breaks resulted from landslides.

Atchison is presently unaffected, or only marginally affected, by the growth of the Kansas City metropolitan area. Except for some growth in the 1920's and in the late 1990's, both the city and county have seen a slow, steady decline in population, and this decline is projected to continue in the near future (Helyar, 1999). However, new homes being constructed in and to the south of Atchison suggest that growth may be on the rise.

The study area around Atchison lies within the Glaciated Region physiographic province, whereas Kansas City straddles the boundary between the Glaciated Region and the Osage Cuestas. Although this might imply geologic differences between the two areas, the surficial geology around Atchison and Kansas City is fairly similar. The rocks at the surface in both areas consist of glacial drift, loess, bedrock, and alluvium, although the Kansas City area has less glacial drift and more bedrock. The topography of both Atchison and Kansas City is controlled by the Missouri River and its tributaries. Geologic similarities, the potential for population growth, and the proximity to Kansas City made Atchison a suitable location for the pilot project.

Physiography

The study area, which includes the entire City of Atchison and part of Atchison County, was defined as the area covered by the U.S. Geological Survey Atchison West and the Atchison East 7-1/2 minute topographic maps (excluding Missouri) (fig. 1). In general, the study area consists of an area of gently rolling hills to the west and a more rugged, hilly topography to the east, near the Missouri River. The total relief is about 112 m (370 ft), and the greatest local relief, 73.2 m (240 ft), occurs along the bluffs of the Missouri River. The Missouri River and its tributaries--the Independence, White Clay, Brewery, Whiskey, Walnut, and Camp creeks--drain the study area (fig. 2). Steep slopes occur in the bluffs along the Missouri River and its tributaries, where bedrock units of Pennsylvanian age are exposed. The glacial deposits in the western half of the study area have relatively gentle slopes.

fig. 2


Fig. 2. Map of the study area showing the soil associations as defined by the National Resources Conservation Service (Sallee and Watts, 1984). Soil associations are regions with similar soil series, slope morphology, and drainage characteristics.

Soils

Soils are defined differently by geologists and engineers. Whereas geologists (and pedologists) look at soils as the products of the weathering of rock and sediments, engineers consider soil to be a "relatively loose agglomerate of mineral and organic materials and sediments found above bedrock" (Holtz and Kovacs, 1981). This definition includes geologic soils, unconsolidated sediments, and rocks such as loess that can be easily excavated (Kehew, 1995; West, 1995). The engineer's definition of soil is commonly used in studying and describing landslides (Varnes, 1978) and will be used in this report.

The National Resources Conservation Service (NRCS) has published a soil survey of Atchison County that identifies the soil series present in the county and provides some data on soil properties (Sallee and Watts, 1984). A soil series is a class of soils with similar soil profiles including horizons, color, texture, structure, composition, and other properties. Sallee and Watts (1984) recognized 19 soil series in Atchison County. The units used on the detailed soil maps consist of one or more soil series. Additionally, Sallee and Watts (1984) divided Atchison County into seven soil associations based on patterns of soil series, slope, and drainage. Of the seven soil associations, five are found in the study area (fig. 2). These can be lumped into three groups: soils in gently rolling terrain, soils on hilly terrain, and lowland soils.

The western part of the county has gently rolling terrain that exposes soils of the Grundy-Pawnee and Sharpsburg-Shelby associations. These are deep soils, developed on glacial drift and loess, on level to moderate slopes. Deep soils are those where bedrock is at least 152 cm (60 in) below the surface. The Sharpsburg-Shelby Association occurs in areas with slightly more relief than Grundy-Pawnee Association.

The Knox-Armster-Gosport Association is exposed in the hilly terrain in the central portion of the study area. This association consists of shallow to deep soils on strongly sloping to steep hillsides. Gosport Series are thinner and develop on bedrock, Armster Series develop on glacial drift, and Knox Series develop on loess. Knox-Armster-Gosport Association also contains small areas of Vinland Series that develop on shales.

The lowland areas include the floodplains of the Missouri River and its tributaries. In this area, Kennebec-Wabash-Colo and Haynie-Onawa associations are dominant. These are deep soils developed on alluvium, on level to gently sloping land.

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Kansas Geological Survey
Web version December 22, 2000
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