Regional Monowai Seamount lies at the northern end of the
Kermadec Arc north of
New Zealand, in the Southwestern Pacific Ocean about halfway between
Tonga and the
Kermadec Islands. The Kermadec Arc is the southern part of the about long
Tonga-Kermadec arc; this volcanic arc contains about 12
volcanic islands and at least 37
submarine volcanoes, which occur about every . Many of these volcanoes were only recently discovered and are poorly studied;
hydrothermal activity has been observed at many. The
Osbourn Trough and the
Louisville seamount chain are being subducted close to Monowai Seamount and might have influenced the development of the seamount and the volcanic arc and
back-arc in general. Monowai Seamount is one of the most active volcanoes in the Kermadec arc; two other active volcanoes are
Raoul Island and
Rumble III while
Clark,
Rumble V,
Healy,
Brothers,
Volcano-W,
Macauley, and
Giggenbach are hydrothermally active.
Local Monowai Seamount is a large volcano which consists of an wide conical
stratovolcano that rises from the
Tonga-Kermadec Ridge in a part of the ocean with a depth of to a depth of less than below sea level; the exact depth of the summit is subject to changes owing to the ongoing volcanic activity. This activity is also responsible for frequent changes in its morphology with up to height variation recorded between surveys made in 1998, 2004 and 2007. Recent volcanic activity has smoothed the slopes of the Monowai Seamount and covered them with
lapilli sand and
scoria in some places. Migration of the summit vent has formed a long ridge at the top of Monowai Seamount, and aligned vents and radial ridges occur on its slopes as well. To its north-northeast lies a large and deep
caldera that is elongated in the northwest-southeast direction; the Monowai Seamount as a whole has a similar elongation. The caldera appears to consist of two nested calderas, the outer of which is the largest in the northern Kermadec arc with a surface area of . although an origin as one single long-lived caldera is also possible. This caldera is the largest in the Kermadec volcanic arc. The rim of the caldera lies at a depth of about .
Parasitic cones occur around the caldera, and a cone is also found within the inner caldera and appears to be about high
resurgent dome; additional cones can be found on the caldera floor which is covered by sediments. On Mussel Ridge, a ridge located within the caldera and close to its southwestern margin, seafloor observations have found cemented
volcanic ash, dispersed rocks,
mud,
pillow lavas,
pillow tube lavas, and
talus. Another about high cone is situated between the Monowai cone and the caldera. Both Monowai Seamount and Monowai Caldera rise from a lava shield and the entire volcanic complex covers an area of about .
Hydrothermal activity including
venting at temperatures of less than occurs at Mussel Ridge where several low-temperature vents can be found; additional venting occurs on the Monowai Seamount main cone and satellite vents on its flanks; deep hydrothermal
plumes hint at additional vents at greater depths. In addition to "true" hydrothermal fluids, the slopes of Monowai are the sources of non-hydrothermal plumes that probably originate from
landslides or when material is remobilized by eruptions. == Geology ==