10 Massive Stargate Plot Holes
2. The Iris
When a wormhole forms in the centre of the Stargate's ring, the distinctive kawoosh (yes, that's the actual name) erupts forward, destroying everthing in its path. Thankfully, its only a couple of metres forward, before it settles back into the main body of event horizon. In the SGC, a metal iris, originally made of titanium before being upgraded to trinnium, closes like the shutter on a camera to prevent anything from getting through the wormhole.
Generally, this should be destroyed as soon as the kawoosh erupts, as it stands directly in its path. However.
This is both a plot hole, but something that has been addressed in the show. In the episode A Hundred Days, Carter explains that because the irish is so close to the surface of the wormhole, it doesn't allow anything - even the kawoosh - room to form, but still allows the wormhole itself to connect.
That may go some way to explaining it away, yet there are still instances where a buried gate can carve a hollow, even underground. Now, this can be accepted as the rock not being close enough to the wormhole to prevent formation - but more likely, it was easier simply to give it a nod and a smile, and accept it for what it is: a seriously cool piece of the Gate!