Cyclic eruptions and sector collapses at Monowai submarine volcano, Kermadec arc: 1998–2007

Abstract

Repeated multibeam bathymetric surveys at Monowai Cone, a shallow submarine basaltic volcano and part of the Monowai Volcanic Center in the northern Kermadec arc, were conducted in 1998, 2004, and 2007. These surveys document dramatic depth changes at the volcano including negative changes up to −176 m from two sector collapses and positive changes up to +138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars. One sector collapse occurred on the SE slope between 1998 and 2004 with a volume of ∼0.09 km3, and another occurred on the SW slope between 2004 and 2007 with a volume of ∼0.04 km3. The volume of positive depth change due to addition of volcanic material by eruption is of the same order: ∼0.05 km3 between 1998 and 2004 and ∼0.06 km3 between 2004 and 2007. During these time intervals, monitoring by the Polynesian Seismic Network detected frequent T wave swarms at Monowai, indicative of explosive eruptive activity every few months. An unusual T wave swarm on 24 May 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys, but no similarly anomalous T waves were detected between 2004 and 2007, probably because the Polynesian Seismic Network stations were acoustically shadowed from the second slide event. We interpret that the sector collapses on Monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano (>20°). Moreover, there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano. Volumetric rate calculations suggest that these two processes may be more or less in equilibrium. The repeated collapses at Monowai are relatively modest in volume (involving only 0.1–0.5% of the edifice volume), have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes, and may be characteristic of how persistently active shallow submarine arc volcanoes grow.

Volcanic evolution of the South Sandwich volcanic arc, South Atlantic, from multibeam bathymetry

“…The scars are similar to that on JCR seamount (PS6), Protector Seamounts (Leat et al, 2010a) and transient scars on submarine Monowai volcano, Kermadec arc (Chadwick et al, 2008). The well-surveyed Monowai volcano slide scars formed by repeated down slope movement of unstable largely fragmental material as smallscale landslides and small mass flows (Chadwick et al, 2008).…”

Underwater acoustic records from the March 2009 eruption of Hunga Ha'apai-Hunga Tonga volcano in the Kingdom of Tonga

“…The most persistent sources are Mata and Monoawai Volcanoes, which lie~630 km to the north and 560 km to the south, respectively. Both are acoustically active throughout the 15-month monitoring period, and both are recognized widely as submarine volcanic systems in states of long-term (VEI~0) eruptive activity (e.g., Chadwick et al, 2008;Wright et al, 2008;Resing et al, 2011;Watts et al, 2012). The ability of the array to track these sites of persistent eruptive activity, as wells as the more ephemeral acoustic noise leading up to and following the Hunga Ha'apai eruption, shows the potential value of including even a sparse hydrophone array as part of any effort to assess volcanic hazards within the arc.…”

Morphometric analysis of the submarine arc volcano Monowai (Tofua–Kermadec Arc) to decipher tectono-magmatic interactions

“…It is the locus of current magmatic activity, having formed a 'regrowth' cone of 0.023 km 3 after a sector collapse event of 0.085 km 3 within a 6 year period (1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) Chadwick et al, 2008). While the caldera complex hosts an active hydrothermal system with low temperature venting (<60˚C) (Leybourne et al, in revision), there is also hydrothermal activity at the stratovolcano.…”

“…The MVC has been extensively surveyed using multibeam echosounder systems in 1986, 1998and 2004Chadwick et al, 2008;Graham et al, 2008). The 30 kHz multibeam echosounder system data acquired in 2004 ( Figures 1B, 1C) provide the basis for this paper.…”

“…We document here the tectono-magmatic interaction at Monowai Volcanic Centre (MVC) in the Kermadec Arc ( Figure 1A), a typical arc volcano that comprises a caldera complex, stratovolcano, extensive cone construction e.g., parasitic cones on the stratovolcano slopes, and extensional faulting (Davey, 1980;Wright et al, 2008;Chadwick et al, 2008;Graham et al, 2008). The MVC has been extensively surveyed using multibeam echosounder systems in 1986, 1998and 2004Chadwick et al, 2008;Graham et al, 2008).…”