50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
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TECTONIC AND NON-TECTONIC CAUSES<br />
<strong>OF</strong> EARLY HOLOCENE RELATIVE SEA<br />
LEVELCHANGEWITHINA<br />
TRANSGRESSIVE ESTUARY ON A<br />
SUBDUCTION MARGIN, PAKARAE RIVER,<br />
NORTH ISLAND, <strong>NEW</strong> ZEALAND.<br />
Kate Wilson 1 , Kelvin Berryman 2 , Tim Little 1 ,<br />
Ursula Cochran 2 & Nicola Litchfield 2 .<br />
1 Victoria University of Wellington, PO Box 600,<br />
Wellington.<br />
2 Institute of Geological and Nuclear Sciences, PO<br />
Box 30368, Lower Hutt.<br />
(K.Wilson*gns.cri.nz)<br />
The highest Holocene marine terrace at Pakarae,<br />
North Island, New Zealand, corresponds with the<br />
maximum Holocene marine flooding surface. This<br />
terrace is underlain by a sequence of estuarine,<br />
fluvial and marine sediments that were deposited<br />
under rising eustatic sea level (SL) conditions.<br />
These sediments are presently exposed at elevations<br />
up to 20 m above modern mean SL as a result of<br />
tectonic uplift. This sedimentary sequence provides<br />
an opportunity to study the paleoenvironmental<br />
development of incised valleys under conditions of<br />
rising SL and tectonic uplift. The stratigraphy is<br />
valuable for comparison with traditional facies<br />
models of incised valley infills, which were<br />
developed exclusively from studies on stable<br />
coasts. We use sedimentology, macropaleontology<br />
and micropaleontology (benthic foraminifera) to<br />
reconstruct the paleoenvironments that<br />
accompanied infilling of Pakarae valley and to<br />
estimate the frequency, magnitude and timing of<br />
uplift events that occurred during the depositional<br />
period (c. 10,500 – c. 7,000 cal. yrs BP).<br />
We divide the Pakarae valley infill sequence into<br />
eight bio-lithofacies, each relates to a particular<br />
paleoenvironment. These are grouped into four<br />
paleoenvironmental facies: barrier, estuarine,<br />
estuary-head delta and fluvial. The basal fluvial<br />
facies, the immediately overlying estuary-head<br />
delta facies, and the capping barrier facies correlate<br />
well with models of incised valley infill from stable<br />
coasts and indicate that the complete sequence of<br />
valley infill is probably present within the Pakarae<br />
outcrops. However the middle section of the<br />
Pakarae stratigraphy displays alternations of<br />
estuarine and fluvial facies. This contrasts both<br />
with models of incised valley infill and with<br />
individual estuary infill studies; which predict that<br />
only central estuary basin sediments should be<br />
present between the transgressive estuary-head<br />
delta and the barrier facies.<br />
The whole Pakarae sequence is compressed relative<br />
to the amount of accommodation space estimated to<br />
have been created by eustatic SL rise during the<br />
depositional period. Only a small proportion of this<br />
can be explained by compaction, most of this<br />
important difference is the result of tectonic uplift<br />
during deposition. Supplemented by detailed<br />
microfossil studies and radiocarbon dates, we<br />
identify which facies transitions within the middle<br />
section are tectonic and non-tectonic in origin. One<br />
uplift event of at least 2 m occurred between 8695 –<br />
8376 cal. yrs B.P. One or two uplift events occurred<br />
after deposition of the Rotoma tephra at ~ 9500 cal.<br />
yrs B.P and before 9255 – 8990 cal. yrs. B.P. Our<br />
data extends the paleoseismic history of this<br />
important location which has one of the highest<br />
uplift rates along a subduction margin without an<br />
historical record of subduction earthquakes.<br />
ORAL<br />
IMPACTS <strong>OF</strong> TEPHRA FALL ON A DAIRY<br />
FARMING OPERATION AT<br />
REREWHAKAAITU, EASTERN TAUPO<br />
VOLCANIC ZONE, <strong>NEW</strong> ZEALAND<br />
T.M. Wilson 1 &J.W.Cole 1<br />
1 Natural Hazards Research Centre, Department of<br />
Geological Sciences, University of Canterbury,<br />
Christchurch, New Zealand<br />
(tmw42*student.canterbury.ac.nz)<br />
Much of New Zealand’s dairy farming industry,<br />
central to New Zealand’s economy, is based in the<br />
central North Island, in or near the Taupo Volcanic<br />
Zone, and is highly vulnerable to tephra fall.<br />
A vulnerability analysis was undertaken of,<br />
‘Tulachard’ a study farm at Rerewhakaaitu, eastern<br />
Taupo Volcanic Zone, to assess the susceptibility of<br />
dairy farm’s infrastructure and operational<br />
processes to tephra fall. ‘Tulachard’ was<br />
particularly appropriate as it is close to Tarawera<br />
Volcano. Power supply, water supply and ability to<br />
use the tractor were identified as the most<br />
vulnerable elements to ‘Tulachard’s’ ability to<br />
respond and recover from tephra fall. One of the<br />
most vulnerable components of a milking shed is<br />
the condenser used for cooling milk because of its<br />
exposed nature and requirement for circulating<br />
outside air. An air conditioning condenser, similar<br />
to condensers used in milk cooling systems, was<br />
laboratory tested where it performed moderately<br />
well when inundated with dry tephra, but rapidly<br />
failed with wet tephra.<br />
A telephone survey of the Rerewhakaaitu dairy<br />
farming community established their perceptions of<br />
the risks faced from volcanic hazards. Although all<br />
respondents were aware of volcanic hazards, over<br />
half did not believe their farm would be affected by<br />
a volcanic eruption in their lifetime. None had<br />
prepared for a future volcanic eruption. This has<br />
important education implications for key<br />
organisations that would be affected if dairy farms<br />
were affected by eruptions.<br />
50 th <strong>Kaikoura</strong>05 -95- <strong>Kaikoura</strong> <strong>2005</strong>