  We have observed the occurrence of dendritic flux avalanches in an amorphous
film of Mo$_{84}$Si$_{16}$. These events are understood to have a
thermomagnetic origin and involve the abrupt penetration of bursts of magnetic
flux taking place within a limited window of temperatures and magnetic fields.
While dc-magnetometry allows one to determine the threshold fields for the
occurrence of the thermomagnetic instabilities, magneto-optical imaging reveals
the spatial distribution of magnetic flux throughout the sample. Conducting
appropriate experiments, typical for this goal, avalanches were confirmed to be
a characteristic of this material, ruling out the otherwise admissible
possibility of an experimental artifact or a feature related to defects in the
film. After the present observation, a-MoSi can be included in the gallery of
superconducting materials exhibiting flux avalanches when in the form of thin
films, a characteristic that must be carefully taken into consideration when
one plans to employ films of those materials in applications.
