Adsorption of Au at 800°C results in a dramatic change of the regular step morphology of 4° vicinal Si(001): the surface decomposes into areas which are perfectly flat with a (001)-orientation and (119) facets. Extremely straight superterraces with a length limited only by the size of the sample (here 4 mm) and a width ranging from 400 nm up to 4 mm are formed by massive Si mass transport. The extreme aspect ratio of 1:10 000 of this submicron structures is attributed to a localized nucleation. The nucleation and formation process during Au adsorption has been studied using low energy electron microscopy (LEEM) and shows a strongly anisotropic growth with a speed of propagation of the superterraces of up to 100 mm/s. Proportional to the Au coverage the width and area of (001) terraces increases. The steps of the vicinal surface are accumulated in irregular step bunches. With further increasing Au coverage the step bunches are transformed into well defined (119) facets. Light diffraction and microscopy have been used to characterize ex situ the macroscopic large scale features of the facet structure.