Age of the Auckland Volcanic Field: a review of existing data

Abstract

Determining magnitudeÁfrequency relationships, a critical first step in assessing volcanic hazard, has been hampered in the Auckland Volcanic Field (AVF) by the difficulty in dating past eruptions from the field's c. 50 centres. We assessed 186 age determinations from 27 centres for reliability and consistency. Results indicate that only three centres (Rangitoto 0.6 ka; Mt Wellington 10 ka; Three Kings 28.5 ka) are reliably and accurately dated. Eight are reasonably reliably dated within a small age range: Crater Hill, Kohuora, Mt Richmond, Puketutu, Taylors Hill and Wiri Mountain (all 32Á34 ka); Ash Hill (32 ka); and Purchas Hill (11 ka). Tephrochronology of lake sediments and relative ages from stratigraphic relationships provide age constraints for a further 9 and 11 centres, respectively. Although recent ArÁAr studies show promise, ages of AVF centres generally remain poorly understood; this has implications for any statistical treatment of the distribution of volcanism in the AVF.

Auckland's green volcanic heart: groundcover vegetation and soils of the Auckland volcanic cone reserve network

“…The cone was formed by eruption which from stratigraphic evidence also occurred 28,500 years ago (Lindsay et al 2011). Again, the predominant vegetation is grassland, although there is a small area of trees on the north-eastern slopes.…”

“…The Maungakiekie reserves are mostly grassland with scattered trees and are currently grazed by sheep (approximately 13 stock units/ha), with 300 kg/ha superphosphate applied every second year (Dodd et al 2011). Maungawhau is the highest volcanic cone of the Auckland volcanic field at 196 m asl, erupting 28,000 years ago (Lindsay et al 2011). It is encompassed by the 28 ha Mt Eden Domain which is dominated by grassland on its upper slopes but a developing forest on its lower slopes.…”

“…Maungarei (135 m asl) is one of the youngest cones of the Auckland volcanic field, erupting only 10,000 years ago (Lindsay et al 2011). The reserve that includes this cone is the Mt Wellington Domain (27 ha) and is almost completely grassland.…”

“…Maungakiekie probably erupted 28,500 years ago (Lindsay et al 2011) with three craters and extensive lava flows. The Maungakiekie reserves are mostly grassland with scattered trees and are currently grazed by sheep (approximately 13 stock units/ha), with 300 kg/ha superphosphate applied every second year (Dodd et al 2011).…”

“…These cones are part of the Auckland volcanic field which is a dormant basaltic volcanic field underlying much of metropolitan Auckland. Fifty-three eruption centres ranging in age from approximately 250,000 to 600 years since eruption have been identified in this field (Searle & Mayhill 1981;Homer et al 2000;Hayward et al 2011a,b;Lindsay et al 2011). …”