Why would my charger start throwing sparks?

Last night while I was listening to this really cool broadcast, I had my laptop plugged into the charger and charger plugged in to the wall. Out of nowhere the charger started throwing sparks. At first I thought it might be static electricity from the blankets, but when I realized it was coming from the cord and wasn’t stopping I unplugged it. Some of the plastic on the cord is melted now. Of course I’m planning to get a new charger, but what would cause something like this? Also, if I have had the laptop less then a year would this be covered on the warranty?