"We should be able to tap into this gas as an energy source."
You can and it is(well the heat not the gas), it's called geothermal energy. You shoot water down a hole, the hot ground turns it to steam and you use that to spin a turbine to produce electricity.
The gas is a noxious mix of toxic elements that make dirty coal technology look as clean as solar power. I'm not sure how you would use the sulfurous gases as anything but a giant fart gun.
Just a side note, another one that threatens to go off on a massive scale is Long Valley
http://volcano.und.nodak.edu/vwdocs/volc_images/north_america/california/long_valley.html
There's a geothermal plant on the island of Hawaii that everyone hates. They were planning to make a bunch more; don't know what came of it. It stunk, sounded horrible, made everyone around it sick.