  We consider a variation of Griffith's analysis of rupture, one which
simulates the process of hydrofracturing, where fluid forced into a crack
raises the fluid pressure until the crack begins to grow. Unlike that of
Griffith, in this analysis fluid pressure drops as a hydrofracture grows. We
find that growth of the fracture depends on the ratio of the compliances of the
fluid and the fracture, a non-dimensional parameter called $\alpha_0$ here. The
pressure needed to initiate a hydrofracture is found to be the same as that
derived by Griffith. Once a fracture initiates, for relatively low values of
the model parameter $\alpha_0$ ($\alpha_0 \leq 0.2$) the fracture advances
spontaneously to a new radius which depends on the value of $\alpha_0$. For
$\alpha_0 \leq 0.2$ further fluid injection is required to increase the
fracture radius after spontaneous growth stops. For the case where $\alpha_0 >
0.2$ each increment of fracture growth requires injection of more fluid. For
the extreme case where $\alpha_0 = 0$ our results are the same as Griffith's,
i.e., a fracture once initiated grows without limit.
