Other types of strip mines return the "overburden" to the areas from which it was taken and recreate what is known as the "approximate original contour."
But because the overburden material swells when it is moved, and since mountaintop removal uncovers so much more area than a traditional strip mine, there is no way to put the material back where it was.
As a result, it is disposed of by layering it in nearby valleys and streambeds, creating a post-mining terrain that is flat to gently rolling, but nothing like the steep hills and narrow hollows that were there originally.
However, the governor's task force found that there have been few scientific studies of the long-term effects of valley fills.
"None of the studies and reports available ... addresses the issue in a comprehensive manner," the task force committee on the environment said.
One committee concluded, however, that the use of mountaintop removal mining has created "a need to add a new level of regulation to mining."
"The use of new technologies that include extensive blasting, large earth-moving equipment and the ability literally to remove the tops of mountains and fill valleys with the spoil requires the consideration of a new level of regulation," the committee said.
"The impact of mountaintop removal mining on the people of the state is real and in some cases very direct and adverse," the committee said.