How Coal Is Formed

Read this in 3 minutes

A map of the Allegheny Plateau, which lies underneath western PA, and portions of West Virginia, Ohio, Kentucky & New York
Photo credit: Kmusser via Wikimedia Commons/CC BY-SA 2.5

Oil & coal have been crucial to the economic growth of Washington County, PA. Welcome to the Allegheny Plateau.

The Allegheny Plateau is the western part of the Appalachian Mountains. That mountain range stretches north & south in the eastern U.S. The Allegheny Plateau includes Washington County.

A plateau is an elevated expanse of flat land. A dissected plateau, such as the Allegheny Plateau, started out flat but has been severely eroded over the years by weather, rivers & creeks, making it look like mountains.

The part of the Allegheny Plateau in western PA is unglaciated. When glaciers covered large portions of the earth during ice ages, they didn’t reach as far as Washington County.

When Europeans arrived in North America, the Allegheny Plateau was covered in forests that were largely oak trees. About one-third of the area remains forested. The woodlands support populations of animals, bird, snakes & other reptiles.

The industrial beauty of the Allegheny Plateau is that it is mineral rich, bringing jobs & wealth to the area as it met the high energy needs of the U.S. starting with the Industrial Revolution.

The story of those resources began millions of years ago when the area that is now Washington County was a swamp. The swamp sank. Trees, other plants and animals of the swamp were buried by mud or sand. Tectonic plates that underlie continents lifted up, turning the area back into a swamp. In time, that cycle of being buried underground, uplifted into the sunlight & buried again put a lot of organic material underground where heat & pressure turned it into peat & finally coal.

This plant debris accumulated slowly – fifty feet of accumulated plant debris can take thousands of years to form and produce only 5 feet of actual coal – but consistently for millions of years.

Appalachian Plateau Geology and Landmarks from ThoughtCo.

The Appalachian coalfields – spread over many states – are the largest in the country. The discovery of coal in Washington County brought settlers to mine it. The regional economy depended heavily upon the extraction of coal. Many coal mines have been exhausted & abandoned.

The Pennsylvania Mining Complex, located in Washington and Greene Counties, is the largest active underground coal mine operation in North America. Three large mines in the complex can produce a nearly 30 million tons of coal per year.

Oil is formed underwater when marine life dies & accumulates. It becomes buried. Rising underground temperatures convert that organic matter into hydrocarbons – oil. Massive flows of crude in Washington County in the late 1800s & early 1900s brought an economic boom to the region. The last oil was shipped from the Washington Oil Field in 1916.

The rise of hydraulic fracturing – or fracking – of Marcellus Shale in the U.S. revived the region’s role in the nation’s oil & natural gas industry in the late 1900s & early 2000s.

Coal, oil & fracking have brought jobs & wealth to Washington County for two centuries due to the geography & geology of the region that was shaped long before Europeans or Native Americans lived in the area.