  The sources of the observed ultra-high energy cosmic rays must also generate
ultra-high energy neutrinos. Deep inelastic scattering of these neutrinos with
nucleons on Earth probe center-of-mass energies $\sqrt{s} \sim 100$ TeV, well
beyond those attainable at terrestrial colliders. By comparing the rates for
two classes of observable events, any departure from the benchmark (unscreened
perturbative QCD) neutrino-nucleon cross-section can be constrained. Using the
projected sensitivity of the Pierre Auger Observatory to quasi-horizontal
showers and Earth-skimming tau neutrinos, we show that a `Super-Auger' detector
can thus provide an unique probe of strong interaction dynamics.
