Air hammers are a wonderful thing. They make short work of...well...hammering.
Looking at that boulder, no matter what you do, it will take a while. This might take less of a while.
Some other ideas:
acid etching (if it can burn through glass, it will burn through stone)
abrasive material removal (diamond grit?)
very small amounts of thermite (I've seen it burn through granite)
oxy-acetyline torch (it might burn into it)