Crazy manhole cover explosions

We've noticed something weird lately: exploding manhole covers. 

Did you ever think such a thing was possible? Apparently it is: A series of underground explosions in Erie, Pennsylvania blew two manhole covers off in front of a Gannon University building earlier this month. A couple weeks later, an underground explosion in San Francisco blew a manhole cover into the air. Luckily, there were no injuries or damage in either case. The Pennsylvania incident resulted in the shutdown of electric power, but there was no power outage associated with the incident in San Francisco. The cause of the blasts was not determined in either case. 

We did a little research and found out that exploding manholes are actually fairly common. HowStuffWorks has a really cool explanation of the physics behind exploding manholes, including a helpful illustration that shows the forces at work in these explosions. Here's a video of a manhole explosion: 

Crazy stuff! We're not sure if there is any particular insurance angle to this, though we do wonder what would happen if a manhole cover exploded and fell onto a car… or a person. Yikes!