Most homeowners insurance policies have exclusions that make them worthless when the home is damaged by common geologic problems such as floods, earthquakes, landslides, mine subsidence, cavern collapse and expansive soils. When a home is damaged the homeowner often is surprised that his “all perils” policy has these exclusions.
The Illinois Geological Survey has a publication titled: Karst Landscapes of Illinois. From the publication “Two conditions are necessary for karst landscapes (green areas on map): (1) Soluble rocks, generally limestone and dolostone, must lie at or near the surface of the ground. (2) The loose soil covering the soluble bedrock must be thinner than about 50 feet.”
The Florida Geological Survey has an informative poster titled “Florida’s Sinkholes”. It shows their geographic distribution, explains how they form, describes different sinkhole types, explains why they are a hazard and explains what to do if a sinkhole occurs near your home.
Did you know that most homeowners insurance policies do not cover damage from any type of subsidence? That includes collapse from sinkholes, oil production, ground water pumping and underground mining activity. Most insurance companies offering homeowners coverage exclude almost any type of geologic hazard from coverage – unless you make specific arrangements to acquire it yourself.
Last week a sinkhole opened beneath a home in Florida while the occupants were sleeping. One man’s bed fell into the sink and the efforts of family and rescue workers were not successful in retrieving him. Now he is presumed dead and demolition equipment is there to remove the structure while the sinkhole continues to enlarge. Injuries from sinkholes are rare but this situation shows how suddenly they can occur.
Did you know that the NOAA website has a tabulation of “Watches, Warnings and Advisories” for each of the 50 states? These include blizzard warnings, avalanche warnings, fire weather watches, wind advisories and much more.
The Illinois Geological Survey has published a Google map that allows you to zoom in on historic mining activity across the state. The map supplements a large collection of .pdf documents that show information about the mines and the coal seams in which they were developed.
“About 840,000 acres of Illinois land have been undermined for coal and other minerals. About 178,000 acres of residential and other built-up land in llinois lie close to underground mines and may be susceptible to subsidence.” Quoted from the publication’s introduction. This publication is a good companion to the mine maps described in the post above.
The Arizona Geological Survey has maps showing subsidence in the Holbrook area where a salt deposit in the subsurface is dissolving. Subsidence of up to a few centimeters per year are occurring in some areas.
The Arizona Department of Water Resources is tracking land subsidence in a number of Arizona communities. Historic and recent subsidence maps are being published on the web. Shown below is a portion of a subsidence map for Tucson for the 1993 to 2000 time interval.
“The Earth’s crust beneath the Mississippi Delta sinks at a much slower rate than what had been assumed. [...] However, these subsidence rates are small compared to the rate of present-day sea-level rise.” Quoted from the National Science Foundation press release.
Groundwater pumping was curtailed around Venice several decades ago but the city is still subsiding at a rate of about 2mm per year. Combine that with a sea level rise of 2mm per year and the city is still in trouble.