County residents often associate sinkholes with quarrying, but blasting generally does not aggravate the holes, the county's hydrologist said.
Sinkholes, common in the Wakefield Valley area, are more likely to occur after a heavy rain or after the land has been altered insome way, Thomas Devilbiss said.
"It takes a very long time to form the holes," he told the county's mineral mining committee.
The citizen committee also heard reports Wednesday from the county's landscaper and transportation planner. The committee is doing research for a report on how land around mineral resources should be used.
Sinkholes occur when the soil on the land surface collapses into the subsurface, Devilbiss said.
Shocks and vibrations, such as those caused when quarry operators blast rock off the quarry wall, can cause sinkholes, but that is relatively rare, he said.
Farming, land development, road construction, stormwater management and other alterations to the land also can cause sinkholes, Devilbiss said.
Last month, the nine-member committee sawsinkholes for themselves when they toured land owned by the Arundel Corp. in Medford. The company wants to dig a quarry on the land, but its efforts to get permission from the county have been mired in court since 1988.
One hole they saw measured about 50 feet across and was 25 feet deep. Another measured about 15 feet across and was 8 feet deep. The holes were spotted on aerial photographic maps as long ago as 1952, and have been expanding over the years, a company officialsaid.
Committee member Georgia Hoff of Westminster said her husband's family has been in the New Windsor area for 150 years, and olderfamily members say sinkholes were there before the quarries.
Genstar Stone Products Co. mines two quarry pits in Medford and has plansto dig a third. Lehigh Portland Cement Co., which mines in Union Bridge, also has plans to dig a quarry outside of New Windsor. The Arundel Corp.'s land is near Genstar's pits.
County landscaper Neil Ridgely said quarries need "environmental landscaping" to buffer them for aesthetic and safety reasons.
Plantings must be done early in the planning stages for quarries so the trees and bushes have time to grow, he said.
"We are stewards for the land," Ridgely said. "Really, land belongs to the earth."
The county and its residents must be involved in landscaping around quarries, too, he said.
"Let's not hold quarries completely responsible for all of it," Ridgely said. "You have to take care of your own back yard as well.
"Landscapingwill never be cheaper than it is today."
Landscaping around quarries can include earthen berms, trees, meadows, thorned plants, streams and agriculture, Ridgely said.
Carroll transportation planner Slade McCalip said the county examines several transportation issues when any development, including a new quarry, is proposed.
The issues include the condition of the roads around the development, safety and capacity.
A public hearing sponsored by the committee to take input from citizens on mining issues has been rescheduled for 7:30 p.m. April 2 at the Eldersburg branch of the Carroll County Public Library at 6400 W. Hemlock Drive.
The committee will meet for a work session Tuesday.