Danger Underground? Coal Mining in Utah

You may have seen the news headlines this summer: six coal miners and three rescue workers were killed when part of the Crandall Canyon Mine, in central Utah, collapsed. (You may even have seen our blog entry about it.) Across the US, around 30 of the more than 79,000 coal miners are killed in accidents at work each year.

If mining can be dangerous, why do we still do it? What makes it risky? How do miners stay safe?

Why do we mine coal? One word: power. Burning coal generates almost 90% of Utah’s electricity. Despite talk about clean, renewable sources of energy, the fact remains that coal is plentiful, cheap, and constant. In the short term, at least, coal is here to stay.

Where’s the risk? Extracting coal in Utah is like scraping the frosting from inside a complex layer cake that’s been smashed, stretched, sat on, and buried. Staying safe means ensuring the tunnels through the coal don’t collapse while people are still using them. But coal is the weakest layer, and the forces on it from the surrounding rock can be uneven and unpredictable. Also, the coal is buried deep, as far as 3,000 feet below the mountainous surface.

To stay safe, miners leave big pillars of coal supporting the roof above their heads. When they finish a section, they collapse the roof to relieve some of the pressure. Sophisticated machines do much of the dirty work, meaning fewer people in harm’s way. Still, it’s a difficult business. “These miners are going places that nobody’s been since the dinosaurs lived on Earth,” says Dave Tabet, of the Utah Geological Survey. “Like astronauts, they accept an inherent risk.”

A typical Utah coal mine. After extracting coal from an area, miners let small sections of roof collapse behind them to relieve pressure from the surrounding rock layers.

Want to know more? Follow the links below for more information about coal mining, Crandall Canyon, and mining in Utah.

Utah Mine Collapses: Caused by a Quake?

This morning, the Deseret Morning News reported that six people may be be trapped in a coal mine near Huntington, UT. Rescuers are searching for the miners, but haven't yet been able to reach them. The miners were trapped when a section of the mine caved in.

As the search continues, scientists are trying to understand what might have caused the incident. Seismograph readings show that close to the mine, there were vibrations in the earth around the time of the cave-in. The jolt measured 3.9 on the Richter Scale.

The hard part is knowing whether there was an earthquake that caused the mine to collapse, or if the collapse itself is what caused the earth to shake.

"Normally, rocks in the Earth's crust are constantly subjected to pressures from all sides. This is called a confining pressure. However, the mining of coal leaves a low pressure zone (empty space). After mining, pressures are still being applied to the rock on all other sides, except at the wall of the tunnel. If the rock is not strong enough to withstand this stress, the wall of the mine tunnel gives way. These "bursts" are well named because there is often no warning and large rocks can be thrown horizontally or vertically, as well as drop from the ceiling during these events. In addition to these relatively small rock bursts, more catastrophic "implosional" failures can also occur on a much larger scale. Sometimes large sections of mines can collapse.

"Mine tremors", rock bursts or mine collapse events, are recorded on seismograph instruments in exactly the same manner that earthquakes are recorded."

-University of Utah Seismograph Stations website

We still don't know what caused today's incident, but the U of U Seismograph Stations say that in the Utah coal belt, about 1/4 of tremors are a result of mining, while 3/4 are natural earthquakes.