Collapse and reconstruction of Monowai submarine volcano, Kermadec arc, 1998–2004

Monowai submarine volcano is one of the three most historically active volcanoes of the Kermadec arc. Repeat multibeam surveys of Monowai Cone from September 1998 and September 2004 and T wave data recorded by the Réseau Sismique Polynésien network for the same period document the collapse and subsequent regrowth of the cone within this 6‐a period. Grid differencing of the two bathymetric data sets, acquired 6 a apart, reveals that a landslide ∼2230 m long occurred between the surveys, within which a postcollapse cone and talus ridge (∼0.023 km 3 in volume) subsequently formed. The volume of this collapse, minus postcollapse construction, is ∼0.085 km 3 . We interpret an unusual, strong‐amplitude T wave event on 24 May 2002 as recording “hot landsliding”, where the 100‐ to 160‐m‐thick collapse has “unroofed” the uppermost parts of the vent conduit, with the subsequent explosive interaction, and cooling, of hot magma and volcaniclastic rubble with ambient seawater. This interpretation is consistent with the lack of emergent events, sharp onset, and large amplitude of the 24 May 2002 T waves. The subsequent >2500 T wave events, between November 2002 and September 2004, occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures, which are interpreted as recording the regrowth of an ∼90‐m‐high cone back to a near‐1998 elevation, at an average rate of 47 m a −1 . This study provides (1) a lower bound for frequency‐magnitude relationships of landsliding for submarine arc volcanoes and (2) estimates of 0.013 km 3 a −1 of submarine cone growth during eruptive cycles.