50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

TECTONIC AND NON-TECTONIC CAUSES
OF EARLY HOLOCENE RELATIVE SEA
LEVELCHANGEWITHINA
TRANSGRESSIVE ESTUARY ON A
SUBDUCTION MARGIN, PAKARAE RIVER,
NORTH ISLAND, NEW ZEALAND.
Kate Wilson 1 , Kelvin Berryman 2 , Tim Little 1 ,
Ursula Cochran 2 & Nicola Litchfield 2 .
1 Victoria University of Wellington, PO Box 600,
Wellington.
2 Institute of Geological and Nuclear Sciences, PO
Box 30368, Lower Hutt.
(K.Wilson*gns.cri.nz)
The highest Holocene marine terrace at Pakarae,
North Island, New Zealand, corresponds with the
maximum Holocene marine flooding surface. This
terrace is underlain by a sequence of estuarine,
fluvial and marine sediments that were deposited
under rising eustatic sea level (SL) conditions.
These sediments are presently exposed at elevations
up to 20 m above modern mean SL as a result of
tectonic uplift. This sedimentary sequence provides
an opportunity to study the paleoenvironmental
development of incised valleys under conditions of
rising SL and tectonic uplift. The stratigraphy is
valuable for comparison with traditional facies
models of incised valley infills, which were
developed exclusively from studies on stable
coasts. We use sedimentology, macropaleontology
and micropaleontology (benthic foraminifera) to
reconstruct the paleoenvironments that
accompanied infilling of Pakarae valley and to
estimate the frequency, magnitude and timing of
uplift events that occurred during the depositional
period (c. 10,500 – c. 7,000 cal. yrs BP).
We divide the Pakarae valley infill sequence into
eight bio-lithofacies, each relates to a particular
paleoenvironment. These are grouped into four
paleoenvironmental facies: barrier, estuarine,
estuary-head delta and fluvial. The basal fluvial
facies, the immediately overlying estuary-head
delta facies, and the capping barrier facies correlate
well with models of incised valley infill from stable
coasts and indicate that the complete sequence of
valley infill is probably present within the Pakarae
outcrops. However the middle section of the
Pakarae stratigraphy displays alternations of
estuarine and fluvial facies. This contrasts both
with models of incised valley infill and with
individual estuary infill studies; which predict that
only central estuary basin sediments should be
present between the transgressive estuary-head
delta and the barrier facies.
The whole Pakarae sequence is compressed relative
to the amount of accommodation space estimated to
have been created by eustatic SL rise during the
depositional period. Only a small proportion of this
can be explained by compaction, most of this
important difference is the result of tectonic uplift
during deposition. Supplemented by detailed
microfossil studies and radiocarbon dates, we
identify which facies transitions within the middle
section are tectonic and non-tectonic in origin. One
uplift event of at least 2 m occurred between 8695 –
8376 cal. yrs B.P. One or two uplift events occurred
after deposition of the Rotoma tephra at ~ 9500 cal.
yrs B.P and before 9255 – 8990 cal. yrs. B.P. Our
data extends the paleoseismic history of this
important location which has one of the highest
uplift rates along a subduction margin without an
historical record of subduction earthquakes.
ORAL
IMPACTS OF TEPHRA FALL ON A DAIRY
FARMING OPERATION AT
REREWHAKAAITU, EASTERN TAUPO
VOLCANIC ZONE, NEW ZEALAND
T.M. Wilson 1 &J.W.Cole 1
1 Natural Hazards Research Centre, Department of
Geological Sciences, University of Canterbury,
Christchurch, New Zealand
(tmw42*student.canterbury.ac.nz)
Much of New Zealand’s dairy farming industry,
central to New Zealand’s economy, is based in the
central North Island, in or near the Taupo Volcanic
Zone, and is highly vulnerable to tephra fall.
A vulnerability analysis was undertaken of,
‘Tulachard’ a study farm at Rerewhakaaitu, eastern
Taupo Volcanic Zone, to assess the susceptibility of
dairy farm’s infrastructure and operational
processes to tephra fall. ‘Tulachard’ was
particularly appropriate as it is close to Tarawera
Volcano. Power supply, water supply and ability to
use the tractor were identified as the most
vulnerable elements to ‘Tulachard’s’ ability to
respond and recover from tephra fall. One of the
most vulnerable components of a milking shed is
the condenser used for cooling milk because of its
exposed nature and requirement for circulating
outside air. An air conditioning condenser, similar
to condensers used in milk cooling systems, was
laboratory tested where it performed moderately
well when inundated with dry tephra, but rapidly
failed with wet tephra.
A telephone survey of the Rerewhakaaitu dairy
farming community established their perceptions of
the risks faced from volcanic hazards. Although all
respondents were aware of volcanic hazards, over
half did not believe their farm would be affected by
a volcanic eruption in their lifetime. None had
prepared for a future volcanic eruption. This has
important education implications for key
organisations that would be affected if dairy farms
were affected by eruptions.
50 th Kaikoura05 -95- Kaikoura 2005