Ōrewa College (Tony)
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Saturday 31st July
Section on beach where stream enters sea.
Very safe environment for practicing basics measurements:
channel velocity; penetration measurements of sands and muds; penetration measurements of siltstones and mudstones; pH; conductivity/water quality; change in salinity/conductivity at increasing distances from ocean (concept of brackish water and consequence on drinkability of water as SL rises); temperature; water clarity; texture of sediments; texture of rocks; quadrats to determine biodiversity in each habitat type
Range of ripple types including wave action and channel flow
Alternating siltstones and mudstones – The Waitemata Group rocks are mainly turbidites. Mass flow deposits with sandstone at the base, fining up towards the mudstone. You should see that the bases of the sandstones are erosional and whereas the contact between sandstone and mudstone should be gradational. The whole sequence was deposited in a relatively short period on time in the early Miocene, 20 million years ago.
measure thickness of several layers of the alternating silt/mudstones using log technique and tool. Estimate the thickness of mudstone layers in a cliff sequence and using an approximate mud accumulation rate of 1 cm per 100 years, estimate how long it took for the cliff sequence to be deposited on the seafloor, 20 million years ago. Why do we not also include the thickness of the sandstone beds to help estimate the time taken to deposit the sequence?
good site for an ‘assessment’ eg previous skills introduced could be tested here, this could be an end of module assessment
Sand dunes walk to groyne and King Tide wharf
Lots of potential for profiles. Historical significance (removal of rocks and subsequent drowning)
Introduction to concept of citizen science (possible learning objective for every student to make a contribution to a citizen science project – truck loads covering ‘every’ potential interest)
Bush walk – Eaves bush
Feel this is a ‘must’ and could link to producing own classification/identification charts
Potential to practice fresh water testing techniques identified above
Sunday 1st August
Estuary at low tide
Absolutely ideal location for Orewa. Several single lesson options:
Measure channel velocity across its width. Complete profile
Measure channel velocity at different times wrt high/low tide
Identification of ripple types, the energy environment that they represent, the types of habitat they are associated with (mud/sand/mixed flats). Straight and curved and curved in two directions
Identification of life assemblages (low energy muds and live cockles)
Identification of death assemblages (high energy sands/silts with few live cockles)
Identification of environments not suitable for life assemblages (sandy high energy)
Sediment profile on sand flats showing about 20cm of sand (approx. 40 years to deposit) with mud beneath. Mud contains similar proportion of cockles – but none living as they represent ancient layers (greater than 40 years). Concept of habitat changes over time as estuary matures and potential link to mātauranga Māori.
Identification of other scientists at work and potential to repeat similar practice (Tony to send details)
ID of flora on Crocodile Island – field guide available
ID of burrows and shell imprints preserved in iron oxide – first stage of fossilization
Animal tracks (future trace fossils)
Storm water sump
Great location for sampling and testing in class – phosphates, nitrates, water quality, pH, conductivity, dissolved oxygen, metallic content (runoff), salinity
Eels! Test water entering sump and preferred location of eels
Potential to link with Outdoor Ed and high element of adventure
Re-write several LO’s around concept of ‘Skills Paper’ if required in the future
Drones and GIS – focus of next or subsequent field day?
SL change is an obvious big picture concept to pursue – (car park flooding, King Tide Project). Council predictions of inundation.
The Waitemata Basin The third prominent feature formed during the first 10 myr of phase four in the region was a deep sedimentary basin centred on Auckland and southern Northland (Fig. 6.10). This is called Waitemata Basin (after Waitemata Harbour), and its deposits form most of the cliffs along the north coast of Manukau Harbour and between Maraetai and Leigh, including those along the Waitemata Harbour, North Shore and Whangaparaoa Peninsula. The sedimentary deposits that you see in these cliffs comprise an alternation of sandstones, typically 30–50 cm thick, which stick out of the cliff; and mudstones, generally 10–20 cm thick, which recede. Each sandstone was deposited in the space of a few hours from a sediment gravity flow called a turbidity current, while each mudstone accumulated very slowly over a period of hundreds or thousands of years.
This kind of sedimentary sequence is known by the German derived word flysch (pronounced ‘flish’ or, if you are a language purist, ‘fleesh’). Boxes 6.5 A, B explain the formation of these deposits in more detail. The landscape that existed before the formation of the Waitemata Basin was carried below sea-level by rapid subsidence, so quickly that coastal landforms like cliffs and sea stacks were buried by sediment before erosion had time to remove them. As a result, today we can see the interesting sequence of strata from beach gravels through shallow-water fossiliferous sediments to deep-water mudstones and finally to flysch, wrapping around old sea stacks made of basement greywacke. Because of the westerly tilt that was imparted to Northland 15 myr ago, we see these basal contacts mainly along the eastern coast of Auckland and Northland, where they occur mainly between basement greywackes and Waitemata strata. Good places to see them are on the north-western coasts of Motutapu Island, Mathesons Bay, and Goat Island Bay by the marine reserve at Leigh. While these sedimentary layers would have been more or less horizontal at the time of deposition, they are seldom horizontal when you see them now. This is because of the tectonic movements that accompanied the uplift of the basin 15 myr ago, and also because of movements of the sediment pile that accompanied the subsidence of the basin. Northland and Auckland were in the subduction earthquake zone at this time (Chapter 2). A wide variety of rock structures has resulted from these movements – Boxes 6.6 A–G illustrate some of the things to look out for. The flysch features (Box 6.5 A, B) recur many times throughout New Zealand in different sedimentary basins of different ages. However, the Auckland rocks (known as the Waitemata Group) contain one unique kind of deposit, known as Parnell Grits (after Parnell Point in Auckland). These are strata that are thicker and darker than the surrounding sandstones and mudstones, and they contain a high proportion of pieces of lava, sometimes small pebbles, and sometimes boulders and house-sized blocks, as at Waiwera, Mahurangi Harbour, and Army Bay on Whangaparaoa Peninsula. They originated as sector collapses on the Waitakere, Kaipara and other volcanoes, and were brought into the Waitemata Basin by a different type of sediment gravity flow called a debris flow (Box 6.7). As noted in Chapter 3, the New Zealand sector of the Pacific Ring of Fire underwent a big shake-up 15 myr ago and simplified itself to a single subduction zone/trench/volcanic arc located outside of the Northland–Auckland region. The effects in Auckland and Northland were that the arc volcanoes switched off, the Waitemata Basin was uplifted again, and everywhere north of the mouth of the Waikato River (Port Waikato) was tilted a few degrees to the southwest.
Parnell Grit beds occur within Waitemata Group flysch through most of the Waitemata Basin. Generally thicker and darker than the enclosing flysch, they are named from Parnell Point, where an 8-metre bed dips westwards behind the Parnell Baths. The dark colour rejects a high content of volcanic debris, but they also contain ripped-up blocks of Waitemata flysch, and sometimes shells of shallow-marine organisms. They have an abrupt lower contact on flysch, and an internal organisation in which particle size increases upwards to a maximum around 50 cm from the base, and then decreases upwards to the top of the bed. Maximum volcanic particle size varies from one centimetre to small house size, while rip-ups can be up to 90 metres long. Like flysch, Parnell Grits were deposited by sediment gravity flows, but of a different kind – these were non-turbulent debris flows that originated on the Waitakere and Kaipara volcanoes (Box 6.1). Box 9.2 B describes debris flows (’lahars’) on andesitic volcanoes above sea level (flowing wet concrete is a debris flow); and also the much bigger debris avalanches that occur when sectors of the volcanic cone collapse. Parnell Grit flows resulted when debris avalanches from the two volcanoes entered the sea, picked up near-shore shells, took up sand and water, and became large submarine debris flows. They were able to carry blocks of lava up to 20 m across at least 70 km into the basin and to scour the sea bed to acquire the rip-ups. However, there is little sign of scour where they deposited the Parnell Grit beds on the flat basin floor. The difference between a Parnell Grit bed and a lahar deposit above sea level (Box 9.2 B) is that Parnell Grits lack large floating boulders near the top – the uptake of sea water reduced the overall strength of the flow. In fact, many Parnell Grit flows left all of their heavy debris behind, and carried only fine material to the point of deposition. The best places to see coarse-grained Parnell Grits are south of Waiwera beach and east of Army Bay, Whangaparaoa Peninsula.
Kaipara Harbour Lookout https://www.geotrips.org.nz/trip.html?id=404
Waiwera Parnell Grit https://www.geotrips.org.nz/trip.html?id=404
Only accessible 3 hours either side of low tide. 200 m walk down beach then across low-lying foreshore rocks to view the sequence in the cliffs and high tidal exposures for another 200 m.
Only accessible 3 hours either side of low tide. Walk around foreshore rocks at base of cliffs for 200-400 m examining the rocks. Some access is on sand and some requires clambering over moderately easy rocky shore platforms. Be aware that if you reach the second beach north of Long Bay you may encounter nudists on the beach.
Coal Mine Bay https://www.geotrips.org.nz/trip.html?id=352
Walk west over low-lying foreshore rocks and sand for 400-600 m examining the rock exposures in the cliffs and high tide rocks as far as Coal Mine Bay.
Folds and faults at Whangaparāoa https://www.geotrips.org.nz/trip.html?id=221
Walk east from the car park along the beaches and over the extensive rock shore platforms. Only accessible at low tide or half tide.
Storm water sump
Completed a number of water quality tests at the storm water sump (phosphates, nitrates, water quality, pH, conductivity, dissolved oxygen, metallic, salinity). Plume coming in from submerged pipe, had lower readings than ‘stream’ coming in along drain. Possible indication that plume was due to recent rain fall/ certainly an opening for an investigation.
Tests indicated that the inlets are high in nitrates and phosphates but dissolved oxygen was with aan healthy range.
Potential to use this site to ‘practice’ using the ‘kit’ – see below.
Followed the drain to estuary. Successful measurement of salinity – zero at point of entry and around 20% just a few metres away. This is a good location to discuss impact on drinking water following just a small rise in SL.
It also seems appropriate to include the salinity tester in the ‘kit’ as it will have multiple applications. Students could make their own concentrations in the classroom by dissolving table salt in water. They could also investigate the effects of temperature on measurements.
Returned to estuary (1hr after high tide – no access). Probable that work could be done on estuary at 3.5 to 4 hrs either side of high tide.
Discussed ideas for activities that could occur within a lesson.
Discussed potential kit
- Equipment that Matt is already familiar with (tape measures, etc ) and has ideas for use
- ‘Sciencie’ gear – quadrat & trowel, pH strips, pH test kit, salinity tester, drinkability tester, grain size comparator, ID sheets