The existence of multiple amorphous states, or polyamorphism, remains one of the most debated phenomena in disordered matter, particularly regarding its microscopic origin and impact on glassy dynamics. Profiting of the enhanced data quality provided by brilliant synchrotrons, we combined high pressure x-ray photon correlation spectroscopy and x-ray diffraction to investigate the atomic dynamics-structure relationship in a ${\mathrm{Au}}_{49}{\mathrm{Cu}}_{26.9}{\mathrm{Si}}_{16.3}{\mathrm{Ag}}_{5.5}{\mathrm{Pd}}_{2.3}$ metallic glass at room temperature. We identify a structural and dynamical crossover near 3 GPa, marked by avalanchelike massive atomic rearrangements that promote the system toward increasingly compact atomic cluster connections. This crossover superimposes a pressure-induced acceleration of the atomic motion recently reported and signals the onset of a transitional state, potentially linked to the nucleation of a different phase within the glass, characterized by the coexistence of two amorphous states with distinct relaxation processes. These results provide evidence for a sluggish, continuous polyamorphic transformation, even in the absence of marked structural discontinuities.

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• High-pressure studies
• Glasses
• Glassy systems
• Metallic glasses
• X-ray diffraction
• X-ray photon correlation spectroscopy