Maroa Caldera

The Maroa Caldera (Maroa Volcanic Centre) is approximately 16 km × 25 km (9.9 mi × 15.5 mi) in size and is located in the north-east corner of the earlier Whakamaru caldera in the Taupō Volcanic Zone in the North Island of New Zealand. Volcanic activity in the caldera commenced over 300,000 years ago and the most recent volcanic eruption within in it was c. 9,400 years BCE.

Its northern rim is to the south of the Waikato River at Ātiamuri. At Ātiamuri the Ohakuri Caldera which had a paired eruption with the Rotorua Caldera is to its immediate north. The eastern boundary is also defined by the present Waikato River and it extends as far south as probably opposite Orakei Korako on the river. The southern boundary is somewhat ill defined given the subsequent deep deposits from the Taupō Volcano but includes a number of domes of which the highest is Maroanui at 897 metres (2,943 ft).

The Maroa Caldera's last major eruption produced 140 km³ (33.6 cu mi) of tephra about 230,000 years ago (230 ka). Its earliest eruption was about 300 ka with decreasing frequency and volume to as recently as 11.3 ± 1.7 ka cal. before present (BP), when an eruption of about 0.25 km³ (0.1 cu mi) occurred from the Puketarata volcanic complex (38°33′02″S 176°03′16″E / 38.550573°S 176.054519°E / -38.550573; 176.054519 to distinguish from another older volcano of this name near Te Kawa). The caldera is now mainly dome lava in filled. In summary going back in time:

• 11,300 ± 1,700 years ago most recent eruption Puketarata tuff ring, which formed with total volume of 0.25 km³ (0.060 cu mi) in a complex multiphase series of eruptions including maar formation
• 229,000 to 196,000 years ago Pukeahua deposits and dome building
• 220,000 years ago unclear where Mokai ignimbrite that outcrop in some of Maroa area comes from
• 229,000 ± 12,000 years ago Ātiamuri deposits from northern Maroa
• 251,000 ± 17,000 years ago onward two large parallel dome complexes developed
• 256,000 ± 12,000 years ago Orakonui pyroclastics from a central Maroa source
• 272,000 ± 10,000 years ago Putauaki pyroclastics from a central Maroa source
• 275,000 to 240,000 years ago small-scale pyroclastic eruptions
• 283,000 ± 11,000 years ago Korotai deposits from northern Maroa
• 305,000 ± 17,000 years ago oldest Maroa dome

Map centered to show selected surface volcanic deposits in area of postulated Maroa Caldera/Volcanic Centre (light green shading, boundary particularly in south-east ill defined). The present surface ignimbrite is various light violet shades which are identical for any single source, but other eruptions may breakup the mutual ignimbrite sheets. Clicking on the map enlarges it, and enables panning and mouseover of volcanic deposits name/wikilink and ages before present for wider volcanic context. The key to the shading of other volcanics that are shown (active in last million years odd) with panning is rhyolite - violet, dacite - purple, basalt - brown, monogenic basalts - dark brown, undifferentiated basalts of the Tangihua Complex in Northland Allochthon - light brown, arc basalts - deep orange brown, arc ring basalts -orange brown, andesite - red , basaltic andesite`- light red, and plutonic - gray. White shading has been used for other postulated calderas (usually subsurface now) including the older overlapping Whakamaru Caldera.