<p>This study presents an experimental investigation into the transition from vortex-induced vibration (VIV) to galloping for a flexible square prism in a cross-flow. Experiments were conducted in a rotating water channel over a wide range of reduced velocities. Several square prisms were studied, and their dynamic responses were characterized by three distinct regimes. For the primary square prism that is the main focus of this study, at low reduced velocities, the prism underwent a stable, low-amplitude VIV, where the oscillation frequency locked in with the vortex shedding frequency. At high reduced velocities, the system entered a pure galloping regime, featuring large-amplitude oscillations at a frequency near the prism’s natural frequency, which was decoupled from the vortex shedding. The key finding of this work is the discovery of a transitional regime characterized by intermittent switching between VIV-dominant and galloping-dominant episodes. During these transitions, the response was observed to switch between stable, low-amplitude VIV and large-amplitude, galloping oscillations that exhibited a complex dual-frequency response. The beam was under almost no externally imposed tension, leading to a response dominated by the beam’s flexural rigidity. As a result, the second-mode natural frequency of the beam was at nearly four times the beam’s first natural frequency. In the primary beam in this study, only the first mode was excited. In other beams that we considered, second-mode VIV response was also observed at higher reduced velocities. This work suggests that in low-tension, bending-dominated flexible square prism, the transition from VIV to galloping occurs through an intermittency mechanism.</p>