Please note Mt Etna erupted on predicted date 30th July 2011.
The theory of tidal pull and momentum changes in a nutshell is like this
1) There is hot molten magma inside the earth,below the crust
2)The volume of this magma is huge, roughly 3000 odd kms
3)Compared to oceans ,having depth only few kms,this is huge fluid
4)There occurs high tide and low tide inside the crust,exactly like one in oceans
5)On given date when tidal pull is maximum,and have momentum chnage(due to direction change of major planets) this magma breaks the crust
6) If the crust is broken partially.quake occurs.
7) More the pull, more the magnitude of quake
8) If the pressure inside ,comes directly under dorment volcano mouth,it break open the mouth and eruption occurs
9) If eruption occurs on given date ,the quake will be of lesser magnitude than expected( as some of the pressure is released)
Time and again we have noticed that the major quakes and eruption occurs simultenously( the infamous Iceland volcano eruption which have closed the airspace was on the date of major quake in China)
But ...But ... we are not ready to believe this.