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Chapter Two: Mining Coal
As coal is cut from one strip, the overburden is
cleared ahead of it, and then put into the dug-out
area behind it, known as backfill. About two-
thirds of US surface mines use this method.
Open pit mining uses similar machines to
dig coal from a huge hole or pit, which gets wider
and deeper until the coal runs out. Contour
mining follows the coal seam along the contour
or slope of a hillside. Again overburden is
removed, the coal excavated, and the overburden
and leftovers, or spoil, from the second cut fills
the first one. This style is typical of rolling hills
with exposed coal seams, as in the Appalachian
Mountains. Less common methods are pit mines,
augers, and dredging (see sidebar).
Another more recent method is
mountaintop removal (MTR), or mountaintop
mining (MTM). If there are coal seams in
the lower levels of a hill or mountain, the soil and rocks above—perhaps 1,000
feet (almost 300 meters) high—are “sliced off ” by diggers and excavators, as
overburden. The exposed coal is then dug out. In some areas, the overburden is
dumped into nearby valleys or hollows. The result is that the whole landscape is
flattened. The overburden may also be replaced in an effort to remake a hill or
mountain, lower than the original, as an attempt at “rehabilitation.” This mining
method has caused huge controversy, as explained later.
Underground (Deep) Mining
Several types of mine are used to get at coal seems deep underground. In a
drift
mine,
the tunnel goes straight into a hillside. In a
slope mine,
the tunnel angles down
to follow a sloping coal seam. In a
shaft mine
, vertical tunnels or “shafts” go straight
down. Usually there are two or more shafts, for workers and machines to go in, for
Rarer Forms of
Surface Mining
• Pit mines
have narrow
holes or pits dug into
steeply dipping coal
seams.
• Auger mining
uses an
auger—a huge drill-type
device like a massive
corkscrew, perhaps 7
feet (2 meters) wide. It
churns into the seam
and carries the coal
out.
• In
dredging
, coal or
other minerals are
scooped up by a crane
with a large bucket,
which sits on a floating
ship or barge.