I e-mailed the Handy Husband several messy pictures and he talked with the dealer (who had just serviced the car on Monday for $1400!). They say it was a radiator hose or clamp that blew. They are sending a tow truck.
Some better news, after a doctor's visit: Frank's wrist is slightly better and is only sprained. He has an ace bandage instead of the splint. Yay!
Since I am now carless, and Frank's wrist is too sore to use the stick shift, I am going to steal his car for the weekend! He can drive his dad's automatic truck if he has to.