Supercontinua generated in microstructured optical fibre are now used widely. The detailed spectral and temporal behaviour arising from the processes causing the extreme spectral broadening remains of interest particularly where users require temporal stability for specific visible wavelengths generated by a supercontinuum source. The theoretical gravity-like potential model requires NIR Raman self-frequency shifted solitons in the anomalous dispersion region of the fibre to be phase matched with short wavelength dispersive waves travelling in the normal dispersion region of the fibre. This is difficult to probe in the fundamental EM mode of the host fibre as competing wavelength generating and spreading non-linear processes obscure results. Here, specific high order EM modes excited in the fibre generate a spectrally sparse supercontinuum which was investigated using polarization and spatio-spectral mapping to provide unequivocal phase matching evidence supporting the gravity-like trapping model. Further, polarization measurements reveal that the input polarization state is scrambled due to non-linear effects within the fibre during supercontinuum generation, having implications for interferometry using supercontinua.