We characterize the spectral broadening performance in silica clad and unclad Tantalum pentoxide (Ta2O5) waveguides as a function of the input pulse central wavelength and polarization, sweeping over a wavelength range from 900 nm to 1500 nm, with an average incident power of 110 mW. The waveguides are 0.7 µm high and between 2.2 and 3.2 µm wide, and the SiO2 top cladding layer is 2 µm thick. We model the dispersion of the higher order spatial modes, and use numerical simulations based on the generalized nonlinear Schrödinger equation to analyze the nonlinear behaviour of the spatial modes within the waveguides as well as the dispersive effects observed in the experiments. We achieve octave spanning supercontinuum with an average power of 175 mW incident on the waveguide at 1000 nm pump wavelength.