The Maryland Department of Transportation State Highway Administration is committed to helping motorists have a safe commute. Our crews are constantly working to address any issues that could interfere with travel, and sinkholes can certainly have an impact. SHA lead geologist Lijun Zhang talked to us about them, and where they occur.
What exactly is a sinkhole?
A sinkhole is a depression, hole or void in the ground caused by some form of collapse of the surface layer. It can vary in size from small depression to large craters that can swallow cars or buildings, a few feet to several hundred feet across and deep. Sinkholes may be utility-related or geological . Geological sinkholes can pose significant hazards, especially in areas where they are common. In Maryland, geological sinkholes with hazardous potential mostly occur in Frederick, Washington, Carroll counties and portion of Baltimore County.
Why do sinkholes occur?
Sinkholes occur due to a variety of natural and human activity factors that destabilize the ground leading to a collapse. There are geological sinkholes, which stem from bedrock and utility related sinkholes that result in human activities.
Geological sinkholes commonly occur in areas where the bedrock is soluble, such as limestone, dolomite, etc. In those cases, rainwater seeps through the soil and dissolves the bedrock. Over the time, this creates underground cavities. When these cavities become too large, the ground above them can collapse into a void. Karst landscapes – commonly found in those Maryland counties mentioned in the first answer – are prime areas for dissolution sinkholes. Geological Sinkholes can form gradually or suddenly, and they can have significant impacts on the environmental and human structures.
Utility related sinkholes stem from human activities, such as not properly compacting subgrade soil that leads to surface runoff infiltrating the ground through cracks. A void is formed and over time, the layer collapses due to loading on the ground surface. Yes, certain types of geography are more prone to sinkholes due to specific geological and hydrological conditions. Karst landscapes and limestone terrains are the most classic examples.
The media reported a sinkhole on MD 90 this summer. There was another on I-270 in 2022. Were they both sinkholes?
We can still call them sinkholes, but they are not geological sinkholes. Both were caused by subgrade soil failure, which is soil not being properly compacted. The sinkhole at MD 90 in Worcester County could have been caused by rainwater infiltrating through the pavement crack in the ground, forming a void. The sinkhole at I-270 in Montgomery County was caused due to an underground cracked pipe that caused the fill soil above the pipe to wash away and form a void.
Shanteé Felix is a Media Relations Manager at the Maryland Department of Transportation State Highway Administration.
