Relativistic hadronic plasmas have an intriguing property known as hadronic supercriticality: they can, under certain conditions, abruptly and efficiently release the energy stored in protons through photon outbursts. These photon flares may have a direct analogy to those observed from compact astrophysical objects, such as Gamma Ray Bursts (GRBs). Here, we investigate for the first time the manifistation and properties of hadronic supercriticality in adiabatically expanding sources. We consider the injection of relativistic protons in an expanding spherical volume with a radially decaying magnetic field and seek the parameters (e.g., expansion velocity) that lead the system to supercriticality. We apply this idea to the GRB phenomenology by assuming that several such blobs are released consecutively from a central engine with random initial conditions that might bring some of them to supercriticality. We superimpose their lightcurves and photon spectra in order to construct a picture of a typical GRB prompt emission. We also provide the all flavour neutrino fluxes expected under the assumptions of this work and compare them with the standard neutrino models for GRBs.