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The spacing between the head and the disk in hard disk drives was long considered to be limited by the roughness of the substrate topography. For the current ultrasmooth disks, as the head-media spacing can go even lower, intermolecular forces play a more significant role in the head-disk interaction and interesting new lubricant dynamics on the interface are revealed. We present an experiment where, when the head is flying extremely close to the disk, the head-disk contact develops within a short but finite period of time. The quartic root of the time goes linearly with the fly height or the head-disk spacing. A hypothesis based on lubricant moguls formation and growth is proposed. The ensuring calculation shows reasonable agreement with the data.