INTERVIEW with Mac Swinford, Assistant Chief
Division of Geological Survey
What do you do to support sustainable development in Ohio?
As a geologist, I document the geology of Ohio by producing geologic maps. A geologic map, through the use of lines and colors, is an efficient and effective method of conveying a tremendous amount of geologic research and data onto one image. The map allows the reader to focus on the geology in a specific location and in a regional context. Our division generates many different types of geologic maps in print and Internet formats.
What type of geologic information do these maps contain?
Maps showing two basic types of geologic formations or materials are important in Ohio: maps of bedrock formations and maps of glacial sediments. Bedrock formations, formed in or near ancient seas, are hundreds of millions of years old and glacial sediments, left behind by the receding glaciers, are ten to hundreds of thousands of years old. Bedrock formations include sandstone, limestone, shale, siltstone and dolomite; glacial sediments include clay, silt, sand and gravel.
Glacial sediments, called glacial drift, cover bedrock formations in various thicknesses throughout the glaciated part of the state. In the unglaciated southeastern part of the state, the land surface and the bedrock surface are essentially the same.
How are your maps used for sustainable development?
Geologic maps have many users and uses related to sustainable development including the mining of resources for building materials and energy production and the planning of construction projects and local land use planning.
For example, maps that display the distribution of bedrock formations are used by mineral explorationists to search for deposits of high-calcium limestone for use in cement products. A drift-thickness map reveals where the limestone is covered by thin overburden in the form of glacial deposits. Overburden must be removed before extracting the limestone, so knowing where glacial deposits are thinnest can save money and reduce environmental disruption.
Glacial-geology maps also show where economic deposits of sand and gravel can be obtained for a sand and gravel operation such as the one depicted in the photo to the left. These same maps can show where thick deposits of clay-rich glacial till exist, which are good locations to site solid-waste disposal facilities or from which to obtain clay for their construction.
Most of Ohio’s population lives on glacially deposited sediments and it is important to know about these deposits for land-use planning. Lakes, once present in front of glaciers, produced clay-rich deposits that are notoriously unstable and represent geohazards to construction.
For example, the photo below shows the destruction of westbound lanes of I-70 during heavy rains in September, 1986 in Muskingum County where locally derived, clay-rich red mudstone was used to fill in the valley. It is also important to know that geologic maps can show if a shale-rich formation is present and might be susceptible to landsliding where exposed on steep hillsides. This would alert an engineer where slope-stability problems might occur on a construction site.
How are maps used for energy production?
A majority of Ohio’s electricity comes from coal mined in Ohio and our maps show the distribution and thickness of individual coal beds so the coal can be extracted safely and economically. We also have maps that show the oil and gas bearing formations deep below Ohio’s land surface. They depict, as best as possible, the depth, thickness and character of petroleum bearing formations. Geologists exploring for oil and gas deposits rely on this information to focus their drilling efforts.
We have also produced maps showing where a formation called the Ohio Shale exists. Thick deposits of black, carbon-rich shale present at or near the surface in a north-south oriented belt through the center of Ohio could be a potential energy source, if it becomes economically viable to extract petroleum from shale.
How do you make geologic maps?
Economic development has created opportunities to collect data, especially data useful for making bedrock-topography maps and glacial drift thickness maps. Water-well logs, oil and gas well logs and bridge-borings are the majority of data, because drillers commonly note the depth that bedrock was encountered.
Outcrops of exposed bedrock and glacial drift can also supply data. Some bedrock formations, such as those of the Cambrian period from which oil and natural gas can be extracted, can range from 1,000 to 10,000 feet below the surface. Detecting depth to these formations may require indirect geophysical techniques such as seismic reflection.
After data has been gathered and plotted on a map, the map-maker connects points of equal elevation to draw contour lines. Software programs provide ways to digitize data and produce maps that can be easily downloaded from the Internet. For those who want more detailed information about a specific area of the state, our division offers surface and sub-surface geology maps that are 1/24,000-scale, where 1 inch represents 2000 feet.
What is most challenging about your job?
The challenge over my career has consistently been making geology relevant to the non-geologist. Using a few maps and basic geologic principles, I can show how geology is part of our everyday lives, whether it is energy or earthquakes, landscape or landslides, mining or minerals; all of these items rely on knowing the basic geologic framework. Getting this message across to policy-makers, private industry, and the ordinary citizen is important and represents a constant challenge for the science of geology.