B-type volcanic earthquakes at White Island have almost all their energy in the band 0.5–4 Hz, around a dominant spectral peak of about 2 Hz. A high degree of similarity in the waveforms suggests that the earthquakes originate from a volume of about 100 m 3, and that the process that generates them is repetitive. At a distance of 1 km from the active crater the particle motion of B-type events suggests an initial P-wave, followed 0.5 seconds later by a horizontally polarised S-wave and then a wave of unknown type. The exact mechanism for B-type events is unknown, however, the absence of higher harmonics implies they cannot be caused by the resonance of gas or magma within a pipe-like structure, and the P- and S-waves suggest a simple shear-induced rock fracture in a hot ductile medium.