Tall structures play an important role in the economic well-being of mountainous regions. They serve to distribute hydroelectric energy (power line transmission towers), generate tourist income (cableway pylons) and protect important infrastructure from natural hazards (trees). It is not uncommon for these structures to be destroyed by the air-blast of a powder avalanche. In this paper we investigate the shock response spectra of an asymmetric steel structure subjected to powder avalanche impact. We perform a spectral analysis of measured accelerations in the in-plane (avalanche flow) and cross-plane (normal to avalanche flow) directions. The structural eigenfrequencies in each direction are likewise calculated using a simple finite element model consisting of three-dimensional beam elements. Mode superposition is then used to reconstruct the measured accelerations, velocities and displacements in order to identify the magnitude and duration of the powder avalanche loading. From the analysis we find that the powder avalanche must contain high-frequency, short-duration blasts (f > 2 Hz) of moderate magnitude (p ≈ 1-10 kPa). High frequency blasts are also present in the cross-plane, transverse flow direction. This result, however, does not exclude the existence of longer duration blasts, which, because of the frequency mismatch, cannot excite the measurement pylon. It appears the high-frequency content of the cloud attenuates to endanger low-frequency structures (f ≈ 1 Hz) such as trees at the lateral edges of the flow, or hanging cables located well above the core. The shock response of a specific structure therefore depends on its location relative to the avalanche core, depending on how the blast-structures dissipate in time and space. Because the powder cloud contains a wide range of blast frequencies, tall structures are vulnerable to the action of the powder cloud, even if they are located well outside the avalanche core.