The Sonman Mine Explosion

Literature isn't the only source of weird and wonderful events that could act as plot points.

In 1940, the Sonman Mine near Portage, Pennsylvania was the site of a large explosion that killed an estimated 63 miners. Rescue was severely hampered by a methane gas buildup that filled the tunnels, especially around the area called Right No. 16 heading where the explosion is said to have been centered.

While this can easily be explained as a gas explosion, it could also be a coverup for something far more sinister.

Mines can be a good source of mythos related investigations as you never quite know what could have been in those tunnels. In this case there are a few likely variants on this tale

1) The investigators are called in after the explosion to investigate some odd findings in the mining company's rescue attempts; possibly some body parts that couldn't possibly belong to any of the workers, or part of a strange carving.

2) The more fun one is to have the investigators called in to look at something uncovered in the tunnels during the mining. This could be something as simple as an odd mineral or some cave markings in a sealed cave; all the way up to carved tunnels uncovered during the excavation. To explain the disaster, you're likely going to want to have something really nasty hiding in there that needs lots of explosives to stop it escaping.