The USGS works with many partners to monitor, assess, and conduct research on a wide range of natural hazards. USGS science provides policymakers, emergency managers, and the public the understanding needed to enhance family and community preparedness, response, and resilience.
By identifying potential hazards and using USGS hazards science, federal, state, and local agencies can mitigate risk. In addition, USGS science can inform planning for major infrastructure investments and strengthen private property standards and materials, which help make homes and communities more resilient to natural hazards. While everyone should be aware of the hazards that are most prevalent in their community, the annual National Preparedness Month is a great time to learn about all hazards. Two of the lesser-known hazards for most Americans – but which can occur almost anywhere – are landslides and sinkholes.
Landslides occur in all fifty states and every U.S. territory, and cause the loss of life and billions of dollars in damage to public and private property annually. The USGS Landslide Hazard program (LHP) is dedicated to understanding how and why these events occur and how best to make informed assessments of the hazard to inform communities that may be at risk, ultimately helping to save lives and property, and to support the economic well-being of American communities.
Landslide processes and characteristics, such as size, distance travelled, trigger, and speed can vary tremendously, and these differences make understanding landslide events challenging. USGS scientists work to assess where, when, and how often landslides occur and how fast and far they might travel.
United States Landslide Inventory Map – Our understanding of landslide hazards at the national scale is limited because landslide information across the U.S. is incomplete, varies in quality, and is not accessible in a single location. In order to fix these obstacles, USGS scientists produced a website that marks an important step toward mapping areas that could be at higher risk for future landslides. In collaboration with state geological surveys and other Federal agencies, USGS has compiled much of the existing landslide data into a searchable, web-based interactive map called the U.S. Landslide Inventory Map. This database is an important first step to helping assess where, when, and how often landslides occur in the United States.
Every year, land subsidence and collapse – or “sinkholes” – causes significant damage to personal property and public infrastructure. By one estimate, the cost of sinkhole damage to the country is several hundred million dollars annually; however, sinkhole occurrences are often not reported, and the true cost is likely much higher.
One of the more famous sinkhole events occurred on February 12th, 2014. A large sinkhole opened beneath the National Corvette Museum in Bowling Green, Kentucky and damaged or destroyed eight cars. Although the property damage was substantial, the collapse occurred in the early morning while the museum was closed and fortunately no one was hurt.
A much more tragic event occurred a year earlier. A man in Seffner, Florida, lost his life when a sinkhole opened beneath his house and swallowed him while he was in bed.
What exactly is a sinkhole, and why do they occur?
Sinkholes form when the land surface slowly subsides or collapses into pre-existing voids underground – essentially “air pockets” underneath the perceptibly “solid” ground we walk on every day. Such voids are often the result of movement and removal of sediments by water flow, a process known as piping. A sinkhole can occur as a result of natural processes or can be induced by human activities.
Cover-collapse sinkholes may develop abruptly (over a period of hours) and cause catastrophic damages. They occur where the covering sediments contain a significant amount of clay. Over time, surface drainage, erosion, and deposition of sinkhole into a shallower bowl-shaped depression.
Some minerals, such as salt, limestone, or gypsum, in bedrock can dissolve slowly over time and leave open voids within the rock where groundwater flows. These areas are called karst and have characteristic landforms such as caves, sinking streams, and springs in addition to sinkholes.
About twenty percent of the nation has the potential to host karst landscapes. In karst areas, the sediments overlying the bedrock are piped down into the bedrock voids and ultimately carried away by moving groundwater. The surface landforms are the result of voids in the bedrock formed by this process over long periods of geologic time, and as those sediments covering the bedrock are removed, subsidence occurs. The USGS produces geologic and subsurface maps that help managers and others to understand karst regions and identify local areas that may be susceptible to sinkholes.
Where do sinkholes occur?
Although there is not yet an effective method to predict where an individual sinkhole may occur, the USGS produces geologic maps that help to identify regions that may be susceptible to sinkhole formation. However, sinkholes can occur just about anywhere. It all depends on the subsurface geological composition and the characteristics of the area, i.e., type of unconsolidated and consolidated soils, infrastructure, and void dynamics.