Physical parameters (14): conservation of mass
Geometrical constriction exists between reservoir and conduit.
If mixture of constant density
rmixt3 = rmixt1 ;
w3. = w1. S1 / S3 
S1  = p Rch2; Rch = few km
S3  = p Rcond2; Rcond = few 10 m
S1 / S3 = 104
Vesiculation: S2  = S3 ; w3. = w2. rmixt2 / rmixt3 
rmixt = (1 - a). rliq + a. rgas a : gas volume fraction
a3 = 0.99
a2 = 0
w3. = w2. (1 - a2 ) / (1 - a3 ) = 100 w2
large velocity at the vent, either due to bubble or
contraction at the conduit