Pre-conference tephra data workshop – Hands-on session II: tephra excursion, Okareka Loop Road (29 January 2023)

Abstract

Hands-on session to trial StraboSpot with a field excursion to tephra section on Okareka Loop Road near Rotorua. The guide documents the stratigraphy of the section and also includes information on the wider picture of rhyolitic volcanism in the Taupo Volcanic Zone and pedogenic upbuilding of soils on tephra deposits and the formation of clay minerals in them. Supported by the Commission on Tephrochronology (IAVCEI).

Full text

IAVCEI Scientific Assembly
Rotorua, New Zealand
29 Jan–3 Feb 2023
Commission on Tephrochronology (COT)
Pre-conference Tephra Data Workshop
Hands-on session II:
Tephra excursion, Okareka Loop Road
Sunday 29 January, Rotorua, New Zealand
Excusion leaders
David J. Lowe and Tehnuka Ilanko
School of Science, University of Waikato
Hamilton, New Zealand

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Citation: Lowe, D.J., Ilanko, T. 2023. Pre-conference tephra data workshop – Hands-on session II: tephra excursion,
Okareka Loop Road (29 January 2023). Commission on Tephrochronology, IAVCEI Scientific Assembly, Rotorua, New
Zealand. School of Science, University of Waikato, Hamilton. 25 pp.

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Itinerary and NZ tephra studies
We will travel to a section adjacent to the driveway of a pumice quarry (RNL Quarry) on Okareka Loop Rd. It
is about 8 km from the Millennium Hotel in Rotorua (Figs. 1–3). Departure is at 8.15 am from the hotel; we
aim to return by 1.00 pm. We have allowed 3–3.5 hours at the section, which is fenced off from the adjacent
roadway. We have a mid-morning refreshment and toilet break scheduled at nearby Redwood Forest Visitor
Centre (at the site marked “Redwoods Treewalk” on Fig. 1 below). Lunch location/timing to be advised.
A review of tephra studies in New Zealand has been prepared for the conference by Hopkins et al.
(2021a). The first comprehensive modern tephra database for New Zealand was developed by Hopkins et al.
(2021b). A review of gobal tephra studies, centred on the role and importance of the “Commission on
Tephrochronology”, and including aspects of New Zealand work, is provided by Lowe et al. (2022). Ages and
compositions of the main rhyolitic tephras in New Zealand younger than c. 50,000 cal yr BP are covered by
(e.g.) Smith et al. (2005), Lowe et al. (2008, 2013), Danišík et al. (2020), and Hopkins et al. (2021a, b). A
climate event stratigraphy – from the NZ-INTIMATE Project – is reported by Barrell et al. (2013). See also
tables and diagrams later in the field guide.
Fig. 1. Main route for today’s excursion to RNL Quarry entrance, Okareka Loop Rd.
NOTES & ILLUSTRATIONS RELATING TO
TEPHRA SECTION AT OKAREKA LOOP RD

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Fig. 2. Topographic map of the landscape southeast of Lake Rotorua (NZ Topo Map online). Arrow indicates field site.
Fig. 3. Google Earth image showing Okareka Loop Rd and location of section at RNL quarry. The site is located at
38°10’7.19’’ S 176°19’29.25’’ E and is at ~450 m asl. Modelled mean annual rainfall is from 1525 to 1654 mm.

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At the section, we will see tephras derived from vents centres associated with the Okareka Embayment
rhyolite domes (Fig. 4), as well as from the Tarawera Dome Complex and Rotomā Embayment (Fig. 5). These
tephras (eight in total) are shown in Figure 6.
Fig. 4. Rhyolite domes associated with the Okareka Embayment and their relationship to ‘stop 4’ = entrance to RNL
quarry. See map below for references.
Fig. 5. Okataina Volcanic Centre, including the Okataina (Haroharo) caldera complex, dome complexes and known
volcanic vents including those for the Rotorua tephra as indicated in yellow (after Nairn 2002; Cole et al. 2010, 2014).

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a

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Fig. 6. Annotated photographs (a–c) showing the stratigraphy and ages of units at the Loop Rd section. The stratigraphy
of pre-Rotorua tephra deposits (6c) partly follows Nairn (1992). In Fig. 6c, an angular uncomformity lies at the base of
the loess on the paleoslope alongside subhorizontal Okareka tephra. Within Okareka and Te Rere tephras, thin iron pans
and redox concentrations or segregations (Fe, Mn oxides), including blue-black pyrolusite, and redox depletions (low
chroma colours, i.e. pale grey–white colours), are secondary redoximorphic features (Hewitt et al. 2021). The shower
bedding in the Rotorua tephra contains numerous diastems (very short breaks in deposition). Photos: D.J. Lowe.
c
b

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General stratigraphy of Okareka Loop Rd section
The following units are evident in the sequence (Fig. 6) from the base upwards:
(1) early tephras (Te Rere, 25.1 cal ka; Okareka, 23.5 cal ka) and thin interbedded loess within the
remnant top of a small, buried hill-top at the base of the sequence;
(2) the buried hill itself, the formation of which represents a period of erosion that occurred during the
last glacial period, and remnants of a (reworked?) tephra draping the (paleo)hillslope (Rerewhakaaitu,
17.6 cal ka);
(3) the thick (~4.5 m), bedded pumice lapilli tephra (with lithics) mantling the hill (Rotorua, 15.6 cal ka),
the top of which is pedogenically modified to form a distinct orange soil (this orange soil material is
evident throughout Rotorua basin and in road cuttings such as along SH 5 to the west of Rotorua); and
(4) at least four younger tephras and soil horizons overlying the buried soil on the Rotorua tephra:
Waiohau (14.0 cal ka), Rotomā (9.4 cal ka), Kaharoa (c. 1314 ± 10 CE/AD), and Rotomahana Mud
(of the Tarawera eruption, 10 June 1886).
The thick Rotorua tephra is particularly distinctive here. The source vent(s) lie to the southeast beneath
the Trig 7693 and Middle domes of the Okareka Embayment (Fig. 4). The isopach map (Fig. 7) shows how
Rotorua tephra thickens closer to the vent(s), and also that much of it was dispersed towards the northwest
(Nairn 1980). The tephra deposits to the northwest represent deposition from an early explosive phase of the
Rotorua eruption sequence (phase 1 on the isopach map) involving a ~20-km-high plinian eruption plume that
must have lasted for at least 3.5 hours, but no more than 3-4 days (Kilgour and Smith 2008). The unit A0
represents the phreatomagmatic, initial ash that is locally dispersed and not found beyond 5 km from the
inferred vent area. The second phase of the eruption sequence, which lasted for 3–6 years, involved the
growth of the Trig 7693 and Middle domes and intermittent explosive eruptions that seem to have generated
thin tephra deposits blown to the southeast (denoted as phase 2 on Fig. 7) (Kilgour and Smith 2008).
Fig. 7. Isopach map for the Rotorua tephra (modified from Kilgour and Smith 2008; Lowe et al. 1999; Shane et al. 2003
and various references for the Waikato and Auckland regions) with thicknesses in centimetres.

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The Te Rere tephra also derives from nearby source vent(s) in the Okareka Embayment (Fig. 4) beneath
the Northern and Eastern domes (Nairn 1992). The remaining tephras seen at the Loop Rd section are from the
Tarawera Volcanic Complex, 15 km to the southeast, except the Rotomā tephra, which was derived from the
Rotomā Rhyolite Complex, 25 km to the northeast (Fig. 5). The youngest tephra is Rotomahana Mud,
deposited during the later part of the short-lived Tarawera eruption on the morning of 10 June 1886, that
forms the land surface (see Rowe et al. 2021).
Additional information, figures, and tables
Note about soil formation (pedogenesis) on tephra deposits, and importance _____________________ p09
Fig. 8. Evidence of environmental change since c. 25 cal ka __________________________________ p09
Fig. 9. Relationship between environmental conditions and the formation of allophane _____________ p10
Fig. 10. Idealized model of the relative depth of burial of paleosols and their alteration _____________ p11
Fig. 11. Diagram illustrating retardant vs. developmental upbuilding pedogenesis _________________ p12
Fig. 12. Tarawera eruption and tephra isopach maps ________________________________________ p13
Fig. 13. Isopach map, Kaharoa tephra ____________________________________________________ p14
Table 1. Main rhyolitic tephras of Rotorua-Tarawera area ≤25.4 cal ka __________________________ p15
Table 2. Marker tephras of NZ, mineralogical assemblages, eruption temperatures, oxygen fugacity ___ p16
Table 3. Glass major element compositions of NZ marker tephras _____________________________ p17
Fig. 14. Taupō Volcanic Zone and Bay of Plenty relief map __________________________________ p19
Fig. 15. Map of tephra-producing centres of the North Island, NZ _____________________________ p20
Fig. 16. Stratigraphy, ages, and volumes of key eruptives from rhyolitic volcanic centres ___________ p21
Fig. 17. Photo: Oturoa Road, Ngongatahā. Tephras in loess deposits allow dating of climate events ___ p22
References _________________________________________________________________________ p22
Acknowledgements __________________________________________________________________ p25
Note about soil formation (pedogenesis) on tephra deposits, and stratigraphic importance
A distinctive feature of many tephra-derived soils is the multilayered nature of their profiles which attests to
building up the landscape via the deposition of tephras from numerous eruptions. The notes below mainly
follow Hopkins et al. 2021a (p. 178–180).
Soils of the region are described by Rijkse (1979) and S-MAP ONLINE
(https://smap.landcareresearch.co.nz/). The dominant weathering product in them is the nanocrystalline
mineral, allophane (± ferrihyrite), together with halloysite formed under drier climates on older deposits
(Churchman and Lowe 2012; McDaniel at al. 2012; Hewitt et al. 2021) (Figs. 8 and 9). Where allophane
predominates, Allophanic Soils (New Zealand Soil Classification: Hewitt et al. 2010, 2021) or Andisols (Soil
Taxonomy: McDaniel et al. 2012; Soil Survey Staff 2022) are the usual high-level classifications (orders).
Fig. 8. Evidence of environmental change since c. 25 cal ka based on phytolith and clay mineral data from analyses of
buried soil horizons on rhyolitic tephras at Te Ngae, near Rotorua (after Churchman and Lowe 2012).

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Fig. 9. Relationship between environmental conditions and the formation of allophane and other minerals on tephra
deposits (and some other materials) according to the silicon-leaching model and the availability of aluminium (from
Hewitt et al. 2021, after Churchman and Lowe 2012).
Almost all soil textbooks describe only the ‘classical’ formation of soil horizons in a profile through
various processes that gradually deepen the profile as a downward moving ‘front’ on a pre-existing parent
material on a stable land surface with nil (or negligible) additions to the surface. Such soil formation, referred
to as topdown pedogenesis, proceeds by effectively modifying a pre-existing parent material to a greater or
lesser extent according to a range of factors that dictate a range of processes and their impacts. In such a
scenario, the soil profile originates via a two-step process: step 1, accumulation (or exhumation) of a ‘new’
parent material at the land surface, followed by step 2, the modification of the parent material by soil-forming
processes and weathering, the latter mainly involving the dissolution of glass and crystals by hydrolysis and
precipitation of the dissolution products as clays (Fig. 9) (e.g., Hodder et al. 1990; Churchman and Lowe
2012) to form soil horizons, thus generating a soil profile.
However, in North Island landscapes where tephras have been repeatedly deposited, many of the soils are
formed by upbuilding pedogenesis. This is the ongoing formation of soil via topdown processes whilst tephras
(or loess, alluvium, etc) are simultaneously added to the land surface. In this scenario, step 1 and step 2 occur
together (not sequentially) so that the soil profile deepens as the land surface rises concomitantly over time.
The profiles become multi-layered soils that reflect this interplay of geological versus pedological processes
(Cronin et al. 1996; Lowe and Tonkin 2010; McDaniel et al. 2012; Hewitt et al. 2021). The frequency and
thickness of tephra accumulation, and other factors, determine how much impact topdown processes have on
the ensuing soil-horizon development and profile character. Where a thick tephra layer is deposited (e.g., ~50
cm or more), or the rate of accumulation of multiple thin additions is exceptionally rapid, the antecedent soil
is suddenly buried and isolated at depth (becoming a buried paleosol) (Fig. 10), and soil formation begins
again on the fresh materials at the new land surface. This process is retardant upbuilding pedogenesis
(because the original soil’s development has been permanently ‘retarded’ by its sudden/rapid burial).

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Fig. 10. Idealized model of the relative depth of burial of paleosols and their alteration by pedogenic processes acting
from the surface downwards (arrows). Once a paleosol is isolated by relatively deep burial, any changes may be regarded
as largely diagenetic, not pedogenetic (Churchman and Lowe 2012) (modified after Schaetzl and Sorenson 1987).
In other situations, typically at distal sites where individual tephra-fall beds are usually thin (a few
millimetres or centimetres in thickness), the rate of accumulation is incremental and sufficiently slow to allow
topdown pedogenesis to keep operating as the land slowly rises. This process is developmental upbuilding
pedogenesis. Figure 11 illustrates these two ‘end members’ (retardant vs developmental) of upbuilding
pedogenesis.
The pivotal concept – concurrent deposition and pedogenesis – was originally proposed by Taylor (1933,
p. 195), who stated that ‘soil-forming processes are continuous’ during the ‘slow addition of dust from
eruptions of the intermittent type’. Thus, topdown pedogenesis continues whilst thin tephras and cryptotephras
accumulate but its impacts are lessened because any one position in the sequence is not exposed to surface-
dominated pedogenesis for long before it becomes buried too deeply for these processes to be effective
(Hewitt et al. 2021). Thin tephra layers preserved in sediments of nearby lakes or bogs provide unequivocal
evidence of persistent incremental tephra accretion to adjacent soil/land surfaces (Fig. 11, far right) (e.g.,
Alloway et al. 1992; Selby and Lowe 1992; Damaschke et al. 2017; Lowe 2019). This history thus leaves the
profile with a weakly-weathered soil fabric inherited from when the tephra deposits were being modified at
the surface as part of an A and/or upper subsoil (AC, AB, or Bw) horizon. The terms ‘developmental’ and
‘retardant’ upbuilding were coined by Johnson and Watson-Stegner (1987) and Johnson et al. (1990) as part of
their dynamic-rate model of soil evolution whereby soils are envisaged to evolve by ‘ebb and flow’ through
time (Schaetzl and Thompson 2015).
Note that buried soil horizons, even when only very weakly weathered, mark soil formation that took
place when the tephra was at the land surface and stratigraphically represent a disconformity; the boundary
between the top of a buried soil and the succeeding tephra deposit is a paraconformity that marks a period of
non-deposition (Neall 1972; Howorth 1975; Hopkins et al. 2021a).

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Can you see how the Okareka Loop Rd sequence displays the impacts of upbuilding pedogenesis, and
how the buried soil horizons mark the passage of time and thus represent unconformities?
Fig. 11. Diagram illustrating the difference between retardant upbuilding pedogenesis (Rotomahana soil at left) at Brett
Rd versus mainly developmental upbuilding pedogenesis (Tirau soil at right) at Tapapa Rd, and how these differences
relate generally to tephra thickness and distance of site from volcanic sources. Tephra thicknesses usually decline
exponentially away from source. Stratigraphy is after Huang et al. (2021). Core depicted at far right represents tephra
layers (some of which are named) preserved in Lake Okoroire, which is ~10 km from the Tapapa Rd profile (Lowe
1988). Tephra abbreviations: Tr, Tarawera (Rotomahana Mud); Ka, Kaharoa; Tp, Taupo; Wo, Whakaipo (c. 2.8 cal ka);
Wk, Whakatane; Ma, Mamaku; Op, Opepe (c. 10.0 cal ka); Rm, Rotomā; Wh, Waiohau; Rr, Rotorua; Rk,
Rerewhakaaitu; Ok, Okareka; Kk, Kawakawa (Oruanui) (see Table 1). L = loess.
Mainly retardant upbuilding pedogenesis
The Rotomahana soil at Brett Rd, which is adjacent to Lake Rerewhakaaitu near Mt Tarawera, represents essentially a
stack of ‘mini’ soil profiles (each a buried paleosol), one atop the other. Five such ‘mini soil profiles’ are evident in the
photo as indicated.
Mainly developmental upbuilding pedogenesis
The Tirau soil at Tapapa Rd, which is in the eastern Waikato region and ‘upwind’ of the main tephra source volcanoes,
represents mainly incremental, slow additions of tephra and/or loess to the land surface so that (weak) topdown
pedogenesis has effectively kept pacee as the land gradually rises. The rate of addition of tephra and loess to the land
surface since Kawakawa tephra (Kk) was deposited averages ~6 mm per century (i.e. ~1500 mm in 25,400 cal yrs),
comparable to slow loess deposition in some parts of New Zealand. A corollary is that every part of the profile (above
Kk) has been a soil A horizon at one time.

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Fig. 12a. Map of Tarawera area showing locations of the main craters of the 10 June 1886 fissure eruption across
Tarawera Volcanic Complex, Rotomahana Crater (including pre-eruption lakes Rotomahana and Rotomakariri), and
Waimangu craters (after Lowe et al. 2002). Locations of villages and associated fatalities (numbers in parentheses, total
~120) are based on Keam (1988) and Lowe et al. (2001) (there was an additional death at an unknown locality). Fatalities
were all Māori apart from six Europeans at Te Wairoa and one European and three Māori at Waingongongo. On the night
of the eruption nearly half of Te Ariki’s 27 residents were camped at Pink Terrace (Te Otukapuarangi). Inset shows
eastern North Island and documented limits of tephra fallout from the eruption (based on maps by Thomas 1888). Ash
fell on several ships at sea, the farthest being Julia Pryce (c. 300 km) and S.S. Waimea (c. 1000 km) north of North
Island (Keam 1988). Lorrey and Wolley (2018) used historic data recorded during Ferdinand v. Hochstetter’s 1859
survey to locate the sites of Lake Rotomahana’s former sinter terraces (see also de Ronde et al. 2016, 2019; Keir 2019).
Fig. 12b. Isopach map of 1886 Tarawera scoria fallout (in cm). x = location
where scoria occurs mixed with Rotomahana Mud but does not form a discrete
layer (from Walker et al. 1984). See also Rowe et al. (2021).

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Fig. 13. Isopach map of Kaharoa tephra fallout blown firstly southeastward then northwestward to generate the elongated
lobate fallout pattern (after Pullar et al. 1977; Lowe et al. 1998; Sahetapy-Engel et al. 2014; Ratcliffe et al. 2020).
Magma types based on Smith et al. (2005) and Shane et al. (2008) (see Table 3). The tephra isochron has been extended
using cryptotephra occurrences in peats and lake sediments in the Waikato and Auckland regions (Gehrels et al. 2010;
Newnham et al. 2018; unpublished data). The Kaharoa tephra provides an aproximate settlement datum in northern New
Zealand for early Polynesian arrival in the late 13th century CE (Newnham et al. 1998; Hogg et al. 2003; Lowe and
Newnham 2004; Hopkins et al. 2021a).

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Table 1 Summary of main rhyolitic tephras deposited in the Rotorua-Tarawera region during the last c. 25,400 cal years
and their general physical properties.
Name*
(
s
ource volcano)
¶
Date or age
Description
Tarawera Tephra (Tr)
(Tarawera)
10 June 1886 Comprises basaltic scoria (Tarawera Scoria) with occasional
rhyolite clasts and/or fine greyish brown ‘muddy’ ash
(Rotomahana Mud). Mud was dispersed more widely than
the scoria.
Kaharoa Tephra (Ka)
(Tarawera)
1314 ± 12 CE/AD
(636 ± 12
cal yr BP)
Fine to coarse white to grey ash, with occasional dense
(hard, hard-to-crush) pumice, rhyolite, obsidian and basalt
lapilli. Contains abundant biotite. Black A horizon (contains
charcoal from Pol
y
nesian and/or earl
y
European burnin
g
)
Taupo Tephra (also known
as Unit Y) (Tp)
(Taupo)
232 ± 10 CE/AD
(1718 ± 10
cal
y
r BP)
Creamy coloured coarse ash with plentiful shower-bedded
pumice lapilli (crushable). Non-welded ignimbrite unit
always associated with charcoal fragments.
Whakatane Tephra (Wk)
(Haroharo)
5526 ± 145
cal yr BP
Shower-bedded pale yellow coarse ash, overlying a fine to
coarse rhyolitic (pale grey) ash. Rich in cummingtonite.
Reddish-brown uppermost horizon (sometimes with basaltic
Rotokawau tephra c. 4 cal ka).
Mamaku Tephra (Ma)
(Haroharo)
7940 ± 257
cal yr BP
Loose, coarse yellowish-brown pumice ash grading into a
weakly shower bedded coarse ash/lapilli.
Rotoma Tephra (Rm)
(Haraharo)
9423 ± 120
cal yr BP
Shower-bedded fine grey to yellowish brown ash with coarse
ash layers, cummingtonite. Marked by a dark Ah horizon at
top, sometimes with charcoal, or podzolised.
Waiohau Tephra (Wh)
(Tarawera)
14,009 ± 155
cal yr BP
Grey fine and coarse shower-bedded ash. Distinctive v. fine
cream ash layer at the base. Usually has well developed
yellowish-brown or greyish upper soil horizon. Deposited a
few centuries before late-glacial cool episode (NZce-3)§.
Rotorua Tephra (Rr)
(Okareka embayment)
15,635 ± 412
cal yr BP
Shower-bedded pumiceous yellowish lapilli or blocks
(gravel/cobbles). Occasional rhyolitic lithics. Deposited at
start of late-
g
lacial mild episode (NZce-4).
Rerewhakaaitu Tephra
(Rk)
(Tarawera)
17,496 ± 462
cal yr BP
Yellowish-brown ash grading down into tephric loess.
Contains abundant biotite. Marks transition from Last
Glacial to post-glacial conditions (Termination I);
reafforestation of re
g
ion occurred soon after deposition.
Okareka Tephra (Ok)
(Tarawera)
23,535 ± 300
cal yr BP
Yellowish brown ash contains abundant biotite. Typically
encased in yellowish to olive brown tephric loess.
Te Rere Tephra (Te)
(Okareka embayment)
25,171 ± 964
cal yr BP
Yellowish-brown ash (typically encased in yellowish to olive
brown tephric loess).
Kawakawa Tephra (Kk)
(also known as Oruanui)
(Taupo)
25,358 ± 162
cal yr BP
Olive brown to pale yellowish-brown ash (typically encased
in yellowish to olive brown tephric loess), always fine
grained and somewhat ‘sticky’ in situ. Deposited just before
interstadial D (NZce-9). Product of a supereruption (Barker
et al. 2021).
*Terminology is based mainly on Froggatt and Lowe (1990) and Wilson (1993, 2001). Bayesian-modelled ages mainly
from Lowe et al. (2013), Vandergoes et al. (2013), and Peti et al. (2021). Descriptions generalised because character may
differ from proximal to distal locations and from site to site. The region has additionally received distal tephras from
Taupō and Tuhua (Mayor Island) volcanic centres (Fig. 13) and has been ‘dusted’ regularly with andesitic tephra fallout
from numerous eruptions at Tongariro Volcanic Centre and Egmont Volcano (Taranaki Maunga), most recently in the
1995-96 Ruapehu eruptions.
Ages are given in calibrated or calendar (cal) years (95% probability range) before present (BP), ‘present’ being
1950 in the 14C timescale. Calendar dates for the Kaharoa and Taupō eruptions have been determined by
dendrochronology and 14C wiggle-match dating (Hogg et al. 2003, 2012, 2019). An age is reported in years BP (e.g.,
14,000 cal yr BP) whereas a date is a calendrical date (e.g., 1314 CE/AD). Note: ka = x1000 years (e.g., 14 cal ka =
14,000 cal yr ago).
§NZ climate event stratigraphy of Barrell et al. (2013)

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Table 2 Ferromagnesian mineralogical assemblages and magma temperatures and oxygen fugacities of 22 marker
tephras erupted since c. 30,000 cal. yr BP in New Zealand (from Lowe et al. 2008).
Tephra name Relative abundances of
ferromagnesian mineralsa
Eruption
temperatureb
(° C)
Oxygen
fugacity fO2
(NNO)c
Taupo Volcanic Centre (rhyolitic) (see Fig. 6)
Taupo (Unit Y) Opx >> Cpx 862 ± 17 -0.17 ± 0.11
Whakaipo (Unit V) Opx 785 ± 10 -1.06 ± 0.12
Waimihia (Unit S) Opx >> Hbe 816 ± 10 -0.72 ± 0.08
Unit
K
Opx 822 ± 16 -0.59 ± 0.11
Opepe (Unit E) Opx >> Cpx 812 ± 18 -0.54 ± 0.17
Poronui (Unit C) Opx >> Cpx
Karapiti (Unit B) Opx >> Cpx + Hbe 788 ± 33 -0.75 ± 0.24
Kawakawa/Oruanui Opx > Hbe 774 ± 12 -0.14 ± 0.10
Poihipi Opx > Hbe > Bio 771 ± 6 0.07 ± 0.10
Okaia Opx > Hbe 789 ± 17 0.21 ± 0.09
Okataina Volcanic Centre (rhyolitic)
Kaharoa T1
d
T2
Bio >> Hbe >> Cgt ± Opx
Bio >> Cgt > Hbe ± Opx
731 ± 10 0.09 ± 0.14
Whakatane T1
T2
T3
Hbe > Cgt > Opx
Hbe > Cgt > Opx
Opx > Hbe > Cgt
746 ± 13
737 ± 9
770 ± 5
0.33 ± 0.09
0.29 ± 0.11
0.52 ± 0.05
Mamaku Hbe > Opx >> ± Cgt 735 ± 19 0.18 ± 0.13
Rotoma T1
T2
T3
Cgt > Hbe > Opx
Hbe > Opx > Cgt
Opx > Hbe > Cgt
752 ± 19
752 ± 19
752 ± 19
0.47 ± 0.12
0.47 ± 0.12
0.47 ± 0.12
Waiohau Opx > Hbe 762 ± 23 0.36 ± 0.22
Rotorua T1
T2
Opx > Hbe >> Cpx
Bio > Hbe >> Opx
871 ± 10
745 ± 30
1.11 ± 0.13
0.17 ± 0.20
Rerewhakaaitu T1
T2
T3
Opx > Hbe
Hbe + Bio >> Opx
Opx > Hbe
721
750 ± 18
-0.31
0.43 ± 0.14
Okareka T1
T2
T3
Opx + Hbe >> Cgt
Hbe + Bio >> Opx
Opx > Hbe
759 ± 20
724 ± 14
794 ± 12
0.30 ± 0.20
0.05 ± 0.15
0.82 ± 0.08
Te Rere T1
T2
T3
Opx + Hbe
Opx + Hbe + Bio > Cpx
Opx + Hbe
801 ± 24
708 ± 3
1.43 ± 0.16
-0.07 ± 0.01
Tuhua Volcanic Centre (peralkaline rhyolitic)
Tuhua Aeg > Cpx > Opx ± Aen ± Rie ±
Hbe ± Olv(fa) ± Tuh
Tongariro Volcanic Centre (andesitic)
Okupata Opx > Cpx >> ± Olv(fo) ± Hbe ~900-1100
Egmont Volcano (Taranaki Maunga) (andesitic)
Konini Hbe > Cpx >> ± Opx ~950

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Footnotes Table 2
aOpx, orthopyroxene (mainly hypersthene); Cpx, clinopyroxene (mainly augite); Hbe, hornblende; Cgt, cummingtonite;
Bio, biotite; Aeg, aegirine; Aen, aenigmatite; Rie, riebekite; Olv, olivine (fa, fayalite; fo, forsterite); Tuh, tuhualite.
bPre-eruption temperature data (mean ± 1 standard deviation).
cOxygen fugacity data reported in NNO units relative to the NiNiO buffer.
dT1–T3 represent separate magma types (early to late eruptive phases, respectively) identified by Smith et al. (2005) for
some Okataina eruptive episodes.
Table 3 Glass major element compositions of 22 tephras erupted since c. 30 cal ka (from Lowe et al. 2008).

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Fig. 14. Topographic relief model illustrating the broad physiographic regions in the Bay of Plenty-Taupō region. The
‘geomorphic’ Taupō Volcanic Zone (TVZ) comprises an area of largely volcanic hills and lakes and covers a similar area
(but not exactly equivalent) to the ‘volcanologic’ TVZ (defined by vent locations only) (from Leonard et al. 2010).

20
Fig. 15. Map of North Island showing the locations and ages of most of the main tephra-producing calderas, volcanic
centres, fields, or stratovolcanoes (cones) active during the Quaternary or shortly before (from Hopkins et al. 2021a). The
calderas in central Taupō Volcanic Zone (TVZ) are overwhelmingly rhyolitic with Mangakino and Taupō being
supervolcanoes; Taranaki Maunga and Tongariro Volcanic Centre are andesitic; Tuhua (Mayor Island) is peralkaline
rhyolite; and the locally distributed tephras from Auckland Volcanic Field are basaltic. The plate tectonic setting
(Leonard et al. 2010) and various other features are also shown, including marine core locations in which tephra-fall
deposits (including some cryptotephras) have been recorded. BF, buried forest at Pureora (see Hogg et al. 2012, 2019;
Lowe and Pittari 2021); H, Haroharo Volcanic Complex; T, Tarawera Volcanic Complex.

21
Fig. 16. Stratigraphy, ages, and volumes (dense-rock equivalent, DRE) of eruptives derived from three rhyolitic centres
in central TVZ (Okataina, Taupō, Maroa), and from Mayor Island (Tuhua), since ~50 cal ka. One eruptive (Earthquake
Flat) from Kapenga Volcanic Centre is additionally depicted within the early eruptives of the Okataina sequence. From
Hopkins et al. (2021a).

22
Fig. 17. Grey loess deposits ~4 m thick on Oturoa Road near Ngongatahā that were deposited in the last glacial coldest
period between c. 31,500 and c. 15,600 years ago. Such loess is widespread around the Rotorua region. Named tephra
layers provide ages (in thousands of years ago) for New Zealand climate events (NZce) 10, 8, and 6, being the coldest
periods or stadials (Barrell et al. 2013). From Lowe et al. (2012, 2015). Age on Okareka tephra from Peti et al. (2021).
Rerewh. = Rerewhakaaitu.
Based on calculations from 18 sites throughout New Zealand, and assuming minimal loss by erosion or dissolution,
net accretion rates of loess since the eruption of Kawakawa (Oruanui) tephra c. 25,400 cal yr BP, and prior to the
Holocene, have mostly been c. 3–10 mm per century (Lowe et al. 2015). The fastest rates are 15–25 mm per century
where deposition was enhanced by turbulence, and the slowest is <1 mm per century (Eden and Hammond 2003). Rates
of incremental loess accumulation – during which topdown pedogenesis continues – at this site and others in the Rotorua
basin range from an average 5 mm per century (between Unit L and Kawakawa tephra), to 20–25 mm per century (from
Kawakawa to Rerewhakaaitu tephra). At other sites loess deposition continued until the Holocene at an average of 10
mm per century (after Rerewhakaitu tephra) (Lowe et al. 2012). These rates (~5–25 mm per century) are sufficiently
slow for topdown soil-forming processes to continue to operate as the land surface gradually rises ‘millimetre by
millimetre’, generating subsoil features that are only weakly developed. Such loess is thus a sediment-soil (Lowe and
Tonkin 2010).
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Acknowledgements
We thank RNL Quarries for providing access to the tephra section at the quarry entrance, Josh Hughes and Richard
Melchert for support with transport and section preparation, Steve Kuehn and Kristi Wallace for tephra workshop
planning and logistical support, Ellen Nelson (University of Wisconsin-Madison) for leading the StraboSpot exercise at
the outcrop, Adrian Pittari for information about the Loop Rd sequence, and Dave Palmer for providing modelled rainfall
data. In preparing this guide and leading the trip, DJL and TI acknowledge support from MBIE Endeavour Fund Smart
Ideas (grant UOWX1903), the Marsden Fund (grant UOW1902), and the Earthquake Commission (EQC) (contracts
15/U713 and BIG 012 2020). These funders and others are supporting the tephra seismites research project based at the
University of Waikato, Hamilton (https://tephra-seismites.com/). TI additionally acknowledges support from the local
organising committee that enabled her attendance as an ECR plenary speaker at the IAVCEI Scientific Assembly. The
guide is an output of the Commission on Tephrochronology (COT) of the International Association of Volcanism and
Chemistry of the Earth’s Interior (IAVCEI).