We investigate the viscous fingering instability that arises when air is
injected from the end of an oil-filled, compliant channel. We show that induced
axial and transverse depth gradients foster novel pattern formation. Moreover,
the steady propagation of the interface allows us to elucidate the nonlinear
saturation of a fingering pattern first observed in a time-evolving system
(Pihler-Puzovic et al. PRL 108, 074502, 2012): the wavelength is set by the
viscous fingering mechanism, but the amplitude is inversely proportional to the
tangent of the compliant wall's inclination angle