  The order of the vortex state in La_{1.9} Sr_{0.1} CuO_{4} is probed using
muon spin rotation and small-angle neutron scattering. A transition from a
Bragg glass to a vortex glass is observed, where the latter is composed of
disordered vortex lines. In the vicinity of the transition the microscopic
behavior reflects a delicate interplay of thermally-induced and pinning-induced
disorder.
