Volcanic tremor and activity at White Island, New Zealand, July‐September 1991

Abstract

A short, intense sequence of volcano‐tectonic earthquakes preceded a period of strong volcanic tremor at White Island volcano, New Zealand, in July—September 1991. The tremor was initially harmonic with clear higher harmonics, but after 3 days was gradually replaced by broadband non‐harmonic tremor. Good examples of both harmonic and non‐harmonic tremor were recorded. Shock waves were observed in the eruption column of May 91 vent from early August, coinciding with the period of non‐harmonic tremor. The harmonic tremor is interpreted to have been due to a standing wave vibration in vesicular magma in the conduit beneath May 91 Vent, and the non‐harmonic tremor to open‐vent degassing activity near the top of the vent.

Keywords:

• volcanic tremor
• White Island
• volcano seismicity
• eruptive activity