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Chapter Two: Mining Coal
As information mounts about the area, depth, and quality of the coal seams,
the mining company decides if and when to begin mining. Mine planners make many
decisions, including which kinds of surface or underground mining to carry out, what
machinery needed, and where to put access roads and camps for the workers. They
must also gauge the effects of the mine on the local surroundings and environment,
get permission from landowners, determine the likelihood of people protesting,
costs, time schedules, and how much coal might sell for when it arrives, among other
aspects of the operation.
Surface Mining
At a surface mine, any layer of soil and rocks, called the
overburden
, is removed
to reveal the coal. Enormous machines like diggers, bulldozers, and excavators lift
and move the overburden, which is usually stored to put back later when the area is
repaired or “rehabilitated.” Explosives may loosen very hard rock.
Then
excavators
start to cut away the coal. Dragline excavators are like cranes
with a vast bucket at the front, which is lowered to the surface and then pulled
toward the excavator with a dragline so it gouges up the coal. The excavator
swings around and dumps the coal onto a conveyor or waiting truck, then turns
back to take another bite. Bucket-wheel excavators have a huge rotating wheel
with many buckets, on the end of a long arm. The arm swings against the vertical
coal “cliff ” or face and eats its way in, with the coal falling onto a conveyor. The
whole excavator moves along on tank-like caterpillar tracks or huge “feet.”
Big Muskie
Dragline excavators for coal mines are among the biggest moveable machines
ever built. Ohio’s “Big Muskie” was almost 400 feet (120 meters) long, 222 feet
(68 meters) high, and weighed over 13,000 tons (11,800 metric tons). Its bucket
held more than 300 tons (270 metric tons) of coal. It was in action from 1969 to
1991, when it was retired because the mines it worked produced coal unsuited
to new environmental laws. In 1999, “Big Muskie” was cut up, providing
enough steel to make the equivalent of 9,000 cars.