can a flood trigger a volcano?
no.
A volcano is triggered from volcanic movement underground. Pressure buildup of lava, or gas, or, earthquakes, or tectonic shifts. All incidences where there is pressure underground, pushing up. Either slow magma leaks, or a giant explosion as the pressure pops the mountain cap.
A flood pouring unto a volcano hotspot, would just potentially cause a violent steam eruption. which is a very different thing.
found this after typing.. "oh, scientists say it could totally happen! the writers were very careful about checking!" "also, it would be a steam eruption, not a volcanic one, they fibbed a little"
The Rings of Power's latest episode, “Udûn,' featured a cataclysm caused by a torrent of water falling onto magma, opting for science over magic.
winteriscoming.net
now, the orcs digging tunnels themselves could trigger an eruption. Say, you have volcanic pressure building. But, its under .5 KM of rock. you dig a tunnel down into that rock... and suddenly you have lets say .2km of rock between the open air, and that giant volcanic bubble of high pressure magma.. Well, NOW that rock is too thin, and the magma can punch through and has a path to go.
well... actually I suppose there is a path for this to work THAT way... one tunnel is going to erupt. but mostly just create a venting tube for safe eruption. you pour water down that tube, and you blow the top of the mountain off with a steam explosion. Now, the entire top of the mountain is an open caldera of free flowing magma.
I'd have to watch the show to see how the hell they got a flood of water UP into a mountain though.