Hazards

Earthquakes, flooding, and other hazards can take a severe toll on human lives and economic systems. ISGS geologists conduct studies to understand the underlying geologic processes behind these hazards, obtain and compile data to inform stakeholder decisions, and develop maps and other tools that can be used to mitigate risks and reduce losses.

Earthquakes

Illinois averages about five earthquakes a year, mainly in southern Illinois. Many of those on record in the state have small magnitudes of 2 to 4, which do not cause damage but are felt over large areas. No earthquakes have been larger than a magnitude (amount of energy released) of 5.5, and nearly all are located deep in the crystalline basement rocks. None have been found to be associated with wastewater disposal, which in Illinois is performed many thousands of feet above the basement rocks.

The extent of damage to buildings and infrastructure is not only affected by the magnitude and distance from the earthquake but also by the sediment on which structures are built. In Illinois, structures built on loose sediments of river floodplains experience more earthquake shaking than those built on glacial till or bedrock, since these materials amplify the earthquake ground motions. Every property has a unique combination of geologic and structural factors that must be considered to determine how its structures might hold up during an earthquake.

ISGS geologists have been involved in mitigating earthquake hazards in Illinois for decades, taking measurements and providing information on soil characteristics that affect the amplification of earthquake ground motion, such as type and properties of underlying materials, depth to bedrock, slope of the land, and depth to groundwater. These data are used to produce soil amplification and liquefaction susceptibility maps for federal and state governments in developing earthquake hazard computer programs to assess damage levels. These computer programs are used for state and national earthquake exercises and for state and county hazard assessment and mitigation efforts.

Geologists also coordinate earthquake efforts and products through the Central United States Earthquake Consortium, which is a partnership of the federal government and the eight states affected by earthquakes in the central U.S. region. ISGS also serves as a liaison with the Illinois Emergency Management Agency in developing earthquake exercises and response.

Coal mined-out areas

Historically, more than 6,000 coal mines have operated in Illinois, with many more known that have not been located. As of today, there are fewer than 15 mines currently active. Mine subsidence can occur over abandoned mines, creating significant economic damage to homes, businesses, and roadways. Therefore, compiling information on coal mines and mapped extents is important for society.

Information and maps about coal mining in Illinois from over the past 150 years are being compiled by ISGS and are available online via the ISGS Coal Mines in Illinois Viewer (ILMINES), an interactive repository of mine locations in the state. Users can type their address into the map to find abandoned mines in their area and links to pages that have more information about the mine indicated, when available. These data are also accessible via the County Coal Data and Maps page and the Coal Mines Quadrangle Maps and Directories page.

In association with ILMINES, a companion online data archive and library, the ILMINES WIKI, is available. The WIKI contains detailed information, including coal mining statistics, historical mined-out area maps, coal industry information, mine photographs, geologic mine notes, and other data related to coal mining. This research and online publication effort is co-funded by the Illinois Department of Transportation, Illinois Mine Subsidence Insurance Fund, and the Illinois Department of Natural Resources’ Office of Mines and Minerals.

Sinkholes in karst areas

When rock and soil naturally collapse into a crevice in the underlying carbonate bedrock found near the ground surface or into a cave cavity in the carbonate, a sinkhole forms. Only a few small areas of karst are found in northern Illinois. In Jo Daviess, Carroll, Ogle and Lee counties, where the bedrock is typically dolostone, sinkholes are a few tens of feet in diameter.

Sinkholes in the southwestern part of the state with limestone bedrock tend to be larger and are more numerous than in the north. Some sinkholes in St. Clair, Monroe, and Randolph counties southeast of St. Louis, Missouri are more than one-half a mile in diameter, formed by the growth and blending of two or more sinkholes. Other sinkhole areas are along the southern tip of Illinois.

Sinkholes provide a serious hazard for construction of buildings, roads, and other infrastructure.

ISGS provides up-to-date downloadable data about sinkholes for the entire state to inform decisions on community planning and development. Geologists have used Graphic Information System (GIS) databases to interpret the lidar-shaded imagery and distinguish sinkholes from other depressions. Tools they have used included the Illinois Height Modernization Lidar Data and the statewide 1:500,000-scale bedrock geology map layer that defines generalized areas of underlying carbonate bedrock. The sinkhole inventory includes two GIS datasets: Illinois Sinkhole Points (n=21,799) and Illinois Sinkhole Areas (n=138).

Other ISGS resources pertaining to karst areas include:

Caves

Caves are defined as openings in bedrock that are large enough for humans to enter and are long enough for a visitor to experience total darkness. They form when water from rain and snow melt seeps into a fractured and soluble bedrock (limestone or dolostone) that is near the ground surface. As water moves through the fractured rock, it slowly, over thousands of years, dissolves and enlarges pathways along the fractures and bedding planes of the rock. When surveying and studying caves in southwest Illinois, ISGS geologists can find clues to the origin and evolution of the caves and evidence of past major earthquakes, climate change, and flood events.

By systematically mapping and dating cave sediment deposits, geologists are beginning to see correlations among groups of deposits and their relationship to specific historic and prehistoric climatic and seismic events. With these results, ISGS staff have been developing conceptual models of the timing of caves’ initiation, development, and deposition of sediments, stalagmites, and stalactites. Stalagmites and fine-grained sediments have been used to identify paleoclimatic and paleoflooding in the study area, and stalagmites have been used to explore the dating of earthquake activity.

Landslides

Landslides in Illinois are usually non-life-threatening, with only two known deaths, but they pose a significant economic risk due to property damage. ISGS-compiled data have shown that most of Illinois’ reported landslides have been induced by construction, particularly cutting into slopes for roadways, and others occur primarily along most rivers, creeks, and lakes. Some of the natural factors contributing to landslides include the geologic setting, slope angle, precipitation rate, and vegetation loss.

There is no statewide reporting system for landslides in Illinois. Thus, over the years, ISGS geologists have compiled information about landslides, including case histories and photographs, and produced maps that are useful to developers, businesses, and local government agencies.

ISGS staff maintain a database using reports from various government entities, data from staff landslide inventories, and a picture and slide collection. New events are added through field observations and reviews of imagery. A systematic review of imagery for a county in some cases has added more than 50 events for the database, mostly in rural settings. The database also includes the results of analysis, particularly for earthquake-induced landslides.

Flooding

High-resolution digital elevation data have been acquired for all Illinois counties using airborne light detection and ranging (LiDAR) data technologies as part of the Illinois Height Modernization Program. Use of these data collections has proven to be an effective tool for mapping river forecasts for flood emergency response and public safety, implementing flood control, updating floodplain maps and regulations, and conducting levee and watershed analyses.

By comparing LiDAR data from different years, it’s possible to discern land cover and land use changes over time. These change-detection analyses provide planners and developers with accurate measurements for assessing climate change effects on water and biota.

A statewide data viewer and stand-alone county LiDAR data collections can be accessed via the Illinois Geospatial Data Clearinghouse at https://clearinghouse.isgs.illinois.edu/data/elevation/illinois-height-modernization-ilhmp.

ISGS also collaborates with the Illinois State Water Survey’s Coordinated Hazard Assessment and Mapping Program (CHAMP). CHAMP produces flood studies and updates the Federal Emergency Management Agency’s Flood Insurance Rate Maps which show areas that have a 1 percent annual chance of inundation. These maps require regular reassessment to account for changing land uses, topography, and precipitation as new data become available.

Coastal erosion

Erosion can consume hundreds of acres of coastal land in Illinois, costing tens of thousands of dollars for municipalities working to conserve valuable infrastructure and recreational spaces. Researchers in the ISGS Coastal Geology group deploy various technologies and methods to better understand the complex processes driving morphologic changes across beach, dune, wetland, and estuarine systems.