Where is it leaking? Normally there is no place that it can come out underneath.
You either have a head gasket failure or the coolant is not circulating. If coolant is puking out of the bottom of the engine (not just a bad hose connection) then you have some major engine work ahead of you....
If you can't determine this stuff yourself, then you need to get a Subaru shop to check it out. Hopefully it's just a rotten hose. If so, replace them all, or others will soon fail. But from what you described, it doesn't sound good. Repeated overheating will wreck an engine.
Good luck.
John Davies
Spokane WA USA
