Geologic Hazards: Earthquakes, Karst Terrain, Radon, Shore Erosion, Landslides, and Mine Subsidence are the Main Ones in Ohio; Volcanic Hazards, Geomagnetic Hazards, Glacier Collapse, and Glacial Lake Collapse Are Other Important Geohazards

     I recently saw that the Ohio Department of Natural Resources (ODNR) had a page about geologic hazards. Thus, this post will focus mostly on Ohio geohazards, which make up most of the total geohazards. They define a geologic hazard as follows:

“A geologic hazard or "geohazard" is a geologic condition, either manmade or natural, that poses a potential danger to life and property.”

     They note that geohazard avoidance or mitigation involves investigating and understanding the geology behind the hazard. Thus, geologic mapping can be utilized as geohazard mapping. Certain rock types are prone to certain hazards.

“For example, maps that show the Columbus Limestone exposed at the surface also depict areas subject to karst development, and maps that show shale-rich Ordovician bedrock present on steep slopes in southwest Ohio also indicate landslide-prone areas.”

 

Shore Erosion

     In Ohio, shore erosion is all about Lake Erie shore erosion, but in coastal states it is oceanic shore erosion that is problematic. That shore erosion is influenced by sedimentation rates, which may be altered by the construction of dams that hold back sediment, increasing the likelihood of erosion. It is also influenced by individual storms. The Ohio page about lakeshore erosion lists the following factors or variables: erodibility of material, soil slope and composition, water level fluctuations, nearshore lakebed shoals and slopes, storm wave energy and duration, precipitation, groundwater and soil conditions, ice cover, shoreline orientation, beach composition, width and slope, and shore protection structures. Thus, there are many factors that must be considered. Ongoing mapping programs are important for assessing shore erosion. For Lake Erie, they note that:

“Erosion within the nearshore is often unnoticed since it occurs under the surface of the water, but it can be a significant cause of major erosive events along Ohio's coast.”

     Coastal erosion is a huge problem around the world where it occurs.

 

Earthquakes

     Earthquake hazards can be mitigated with seismology networks where seismographs are set up to monitor earth movement. This information is vital where earthquakes are common and can be used to predict dangerous earthquakes and to assess epicenter location and depth, which are important for determining future impacts and for defining which faults have slipped. Where earthquakes are likely to occur, there needs to be extensive knowledge of the faults and the likelihood of seismic events.

 

Karst Terrain: Limestone Sinkholes

     Karst terrain is where karstic limestone or dolomite outcrops or is near the surface. This can result in sinkholes that can constrain construction and present dangers to road construction. Groundwater hazards can also be present where groundwater aquifers are in karstic carbonates. In those cases, groundwater can travel much faster and farther than in other kinds of aquifers. Thus, contamination can also travel much faster and farther as well. Normally, soil can filter contaminants and chemically neutralize them over time, but with karst voids, those contaminants often enter groundwater without being filtered and chemically or biologically neutralized.

 

Landslides

     Landslides typically occur where slopes are steep. ODNR notes:

“Landslides occur when a hillside of earth materials destabilizes and moves downslope, which can happen rapidly or slowly over hours, weeks, or even years.”

     As a geologist, I learned about processes like land “creep” and slump erosion. In terms of rocks, shales are more erodible as well as being more subject to landslides than other rocks. The map below shows the regions in Ohio associated with the highest landslide risks. These include regions with steep slopes, areas where shale outcrops, and areas where glacial tills and clays are exposed to lakeshore erosion processes.

 

Radon

     Radon is a geohazard where certain rocks outcrop or occur close to the surface and can outgas radon into basements. Organic black shales, light-colored volcanic rocks, granites, sedimentary rocks that contain phosphate, and metamorphic rocks derived from these rocks are the major sources of radon. I wrote a post about radon in January 2025. Below is an EPA map of areas where radon exposure is a concern.

 

Mine Subsidence and Other Hazards of Abandoned Mine Lands

     Mine subsidence is a problem where there are lots of abandoned underground mines, such as in Eastern Ohio and nearby Appalachian states like West Virginia and Pennsylvania. These can present as large sinkholes. In Ohio, I-70 has been closed at times due to mine subsidence under the freeway. There are quite a few hazards associated with abandoned mine lands, including mine subsidence, landslides of tailings piles, erosion and sedimentation clogging stream channels and culverts, highwalls left over from surface mining, acid mine drainage, and mine openings. Entering mine openings can expose one to “poisonous or explosive gases, oxygen deficiencies, flooded sections, unstable roofs, hard-to-see vertical shafts, venomous insects and snakes and disorienting mazes of mine workings.” When I was young, we used to swim at a place we called Bear Mountain (or Bare Ass Mountain to some), and we used to jump off of a very high highwall. It was a bit dangerous as you had to leap out enough to avoid scraping on the rock, which is how a few people hurt themselves.

     There are two basic types of mine subsidence: pit subsidence and sag subsidence, which are described below:

“There are two types of subsidence: (1) pit, also called sinkhole or pothole, and (2) sag, or trough. Pit subsidence is characterized by an abrupt sinking of the ground surface, resulting in a circular, steep-sided, craterlike feature that has an inward drainage pattern. It is associated with roof collapse of mines that have total overburden – overlying, unconsolidated material and rock – of less than 165 feet, weak roof rock of shale or mudstone, and a ratio of unconsolidated-material thickness to rock thickness that is less than 1:2:1. Pit subsidence does not occur where the thickness of the unconsolidated overburden is more than 90 feet. Sag subsidence occurs as a gentle, gradual settling of the ground surface and is associated with roof collapse, pillar crushing, or pillar crunching of deeper mines (overburden of more than 75 feet). Sag subsidence may fill with water if the surface of the subsidence intersects the water table. Pit subsidence features generally do not hold water because the pit drains in to the underlying mine.”

 

Geomagnetism

     The U.S. Geological Survey monitors geomagnetism, which may present hazards to power transformers. USGS notes:

“Geomagnetic storms generate electrical currents that can damage transformers and cause cascading power failures. By accessing near-real-time information, engineers can adjust operations and avoid potential blackouts or other disruptions.” 

     They use magnetotellurics to map the electrical conductivity of rocks. The map below utilizes nearly 1800 data points across the U.S.

 

Volcanoes

     Areas where there are active volcanoes, such as Hawaii, are major geohazard zones. Geologists study and try to predict when eruptions will occur and how they will occur, whether explosively with massive outgassing or with more gentle lava flows with less pressure. Understanding geology is very important for predicting and mitigating such events. Related hydrothermal phenomena like geysers can also be hazardous.  

Glacier Collapses and Glacial Lake Collapses 

     As occurred recently in Nepal, glacier collapses can be immensely hazardous. In addition to that, the collapse of glacial lakes can also lead to catastrophic downstream flooding as well. 

 

 

References:

 

Geologic Hazards. Ohio Department of Natural Resources. Geologic Hazards | Ohio Department of Natural Resources

Geologic Hazards Science Center. Colorado School of Mines. U.S. Geological Survey. Geologic Hazards Science Center | U.S. Geological Survey

Ohio Karst: Geofacts. ODNR. GF31_Aden_2024.pdf

Mine Subsidence: Geofacts. No. 12. 2010. Mine Subsidence

Recently completed geophysical survey will help protect critical infrastructure from geomagnetic storms and space weather. U.S. Geological Survey. News Release. August 8, 2024. Recently completed geophysical survey will help protect critical infrastructure from geomagnetic storms and space weather | U.S. Geological Survey