Seismic analysis of the 13 October 2012 Te Maari, New Zealand, lake breakout lahar: Insights into flow dynamics and the implications on mass flow monitoring

Abstract

On 6 August 2012 an eruption of the upper Te Maari vent Tongariro volcano and subsequent debris flow in the Mangatetipua channel created a debris dam and ephemeral lake. The lake reached its maximum volume of 50,000m3 by 13 October, initiating dam breaching at 22:30 NZDT (11:30 UTC) after a period of intense rainfall. The breach eventually grew to 29×12m, causing eroded debris flow sediment and water to remobilize as a lahar. The event, comprising multiple surges, lasted ~30min, and displaced 57,000m3 of remobilized sediment up to 4.5km downstream. To determine the dynamics of the event, the seismic signals generated by the lahar were compared with active seismic source data collected in February 2013. The comparison used a common frequency band range of 3–10Hz to compute amplitude for four near-field seismic stations. For periods with signal-to-noise ratios above 2.0, we obtained lahar amplitude distributions that match best the equivalent active source amplitudes within ~0.5km of the dam breakout. The accumulated seismic energy of the lahar was estimated at 1.93×109Nm, whereas the peak energy was 6.88×107Nm. Results of this work may improve the characterization of future mass flow events in the Te Maari/Mangatetipua area through the calibration of seismic stations used in this study.