(Köfels, Umhausen, Ötztal, Nordtirol, Tirol, Österreich)
Landslide (8000 years ago), with ductile deformation at very high strain rate in a narrow shear zone: intense friction raised temperature to melting, leading to the formation of a pumiceous glass thin layer.
The glass resulted from friction thermometamorphism of biotite-amphibole gneisses and not from volcanism or shock.
Ref.:
Eur. J. Mineral., 1993, 5, 893-902.
