Hickman County, Kentucky

GEOLOGIC HAZARDS

There are many concealed faults located throughout Hickman County. Currently there is no evidence that these faults are active. However,

because of the proximity of Hickman County to the New Madrid Seismic Zone, strong earthquake activity is a possibility. Soil creep, slumps, and landslides along steep slopes may occur from erosion or ground motion associated with a strong earthquake.

Areas associated with saturated alluvium and other unconsolidated deposits are subject to liquefaction during a strong earthquake. Alluvium deposits are also subject to flooding. Soils derived from alluvium deposits have a moderate to high shrink swell capacity, which may affect structural foundations and roads. Flood information is available from the Kentucky Division of Water, Flood Plain Management Branch,

www.water.ky.gov/floods/

Landslides and slumps are associated with tall bluffs during strong earthquakes. The bluff pictured above is located just south of Columbus- Belmont State Park on Ky. 58 in Hickman County. The bluff is capped by approximately 30 feet of loess (wind blown) material. Photo by Glynn Beck, Kentucky Geological Survey.

EARTHQUAKE HAZARDS

Peak ground acceleration at the top of rock that will probably occur in the next 500 years in Kentucky

Although we do not know when and where the next major earthquake will occur, we do know that an earthquake will cause damage. Damage severity depends on many factors, such as earthquake magnitude, the distance from the epicenter, and local geology. Information on earthquake effects is obtained by monitoring earthquakes and performing research. Such information is vital for earthquake hazard mitigation and risk reduction.

The most important information for seismic-hazard mitigation and risk reduction is ground-motion hazard. One way of predicting ground-motion hazard is by determining the peak ground acceleration (PGA) that may occur in a particular timeframe. The map above shows the PGA at the top of bedrock that will likely occur within the next 500 years in Kentucky (Street and others, 1996). It shows, as expected, that PGA would be greatest in far western Kentucky near the New Madrid Seismic Zone. Ground-motion hazard maps for the central United States and other areas are available from the U.S. Geological Survey. These maps are used to set general policies on mitigating damage. For example, maps produced by the USGS in 1996 were used to determine seismic design in building codes. For additional information pertaining to earthquake hazards visit the Kentucky Geological Survey website at www.uky.edu/KGS/geologichazards/geologichazards.html

GROUNDWATER

Abundant groundwater is available for domestic, irrigation, and industrial uses in Hickman County, from depths of a few feet down to 750 feet. Generally, depth to groundwater is under 100 feet except in the uplands and in the western part of the county, where water is found in the 100 to 250 foot range. Yields in some of the deeper wells (250-750 feet) are greater than 1,000 gallons per minute, which is sufficient for a community or industrial supply. Groundwater sometimes contains naturally-occurring iron in objectionable amounts from the deeper zones. In some formations with slightly acidic groundwater, a chemical reaction between the groundwater, steel well casing, and pump equipment will produce high iron content in the water. In general, the chemical quality of the water is good. Water from alluvium is generally hard to very hard. Water from the sand and/or gravel, non-alluvium aquifers is considered soft and slightly acidic, with low dissolved solids.

THE LAND

Agriculture is a major part of the Carlisle County economy. There are 122,112 acres in the county and 49,300 of them were planted with either corn or soybeans in 2002 (Kentucky Agriculture Statistics 2002--2003). Photo courtesy of Jerry McIntosh, U.S. Department of Agriculture--Natural Resources Conservation Service.

Approximately 140 chicken houses are in Hickman County. Each house holds about 27,000 birds. Chicken litter associated with these operations is used as a substitute for synthetic fertilizers on row crops. Photo by Glynn Beck, Kentucky Geological Survey.

A typical way to control gully erosion, common in Hickman County, is to construct a grassed waterway with a rock chute outlet. Funding for this structure was provided by the CRP CP-21 program through the U.S. Department of Agriculture Conservation Reserve Program. Photo by Glynn Beck, Kentucky Geological Survey.

A typical cypress swamp in the Obion Creek drainage. Most of Obion Creek drains the Loess Plains ecoregion (Woods, 2002) in Hickman County. Photo by Glynn Beck, Kentucky Geological Survey.