1. About geological mapping
  2. Volcanoes of Auckland (ARC)
  3. Hochstetter map - Ferdinand von Hochstetter's 1859 geological map of Aucland
  4. Auckland museum geology booklet - (PDF) geology of Auckland area begins page 15
  5. Wikipedia entry - Auckland Volcanic Field
  6. Wikipedia entry - North Head
  7. Wikipedia entry - Mt Victoria
  8. Learnz virtual field trip 2005 - Auckland Volcanoes (archived material) - username 59, see Mr Keestra for password
  9. Video from LEARNZ website- about North Head etc.
  10. Parnell Grit - paper from the New Zealand Journal of Geology and Geophysics (NZJGG), 2004. Very academic.
  11. Chelthanam Breccia- an excerpt from a 1901 paper from the Royal Society of NZ. This refers to the outcrop of Parnell Grit that we looked at (it seems that in 1901 this was considered to be a different unit)
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northheadnow.jpg
North Head today
northheadprehuman.jpg
3000 years ago

devonport.jpg


360 degree panorama from top of Mt Victoria here (requires Quicktime)
The two images above show North Head today, and my impression of what it may have been like 3000 years ago when the tombolo was being formed. Notice that the sea also comes in further at Ngataringa Bay.



Geological history of the Auckland area (Summary):
  • Deposition, burial, lithification of greywackes. Time = about 140my ago. Not seen in Devonport area, but fragments of greywacke are found in tuff on North Head.
  • Rangitata orogeny and peneplanation: this formed the landscape onto which the sediments of the Waitemata Formation and Parnell Grit were laid down. From about 130my to 30 my ago
  • Probable submergence. 30-22 my, but we saw no direct evidence for this. Rocks laid down by this may have been eroded away at the beginning of the Kaikoura orogeny
  • Deposition of Waitemata Formation and Parnell Grit: 20-10my ago. Implies a rapid downsinking in Devonport area to create a depositional basin. Volcanic fragments in Parnell Grit imply volcanism nearby (probably to the west). We saw no direct evidence of where the sediment source was, but it was probably to the north.
  • Drop in sea level at the beginning of Ice Ages. New drainage patterns emerged on the landscape which formed the hills and valleys of the modern landscape.
  • Eruption of volcanoes: North Head, then Mt Victoria.
  • Rise in sea level 20,000 years ago. Flooding of stream valleys, erosion back of seaward side of Vauxhall area and North Head to form the cliffs of the modern coastline. Deposition of swamp material in Narrow Neck and Cheltanham area.
  • Slight drop in sea level 6000-3000 years ago to form modern tombolo and beaches.




Pictures from the field trip:
vauxhall.jpg
Vauxhall area seen from the top of Mt Victoria

The picture above shows the main landscape features in part of the area we visited, and should be useful in preparing your map.
The area outlined in red represents the 'sandstone high' - this is the remnant of an old, hilly landscape of Waitemata Sandstone formed during the last ice age, then partly drowned by rising sea level and cut back on the seaward side to form the cliffs we saw.
The flat area would have been intertidal muds during the period of slightly elevated sea level about 3000-6000 years ago. At the time of European colonization, much of the golf course area was mangrove or near-shore swamp.
It is difficult to tell from our work exactly where the edge of the lava flows are, except that it is likely to be about the edge of the houses (they would not have built into the swamp). We can also not come up with any definite sign that the comment by EJ Searle in his book, quoted in your resource material, that the sea once flowed through at the top right of the land area. However, considering the about 3 m drop from Vauxhall Rd down to Cheltanham Beach at this point, it seems a little unlikely.
Below is a modified picture showing what this may have looked like before human settlement, at a spring tide (it may have been a few thousand years ago that water level was actually this high, in which case Rangtoto would be missing).

vauxhallretro2.JPG
Vauxhall area pre human


Resources for 2009 write up:
(coming soon, upload problem)



Exemplar

This is and example of the sorts of things you need to include and how to set it out.

Report: The geology of the Achilles Point to West Tamaki Head area
external image Saint_Heliers_In_Auckland.jpg
(click here for image attribution)- image from Wikimedia commons
1. Landscape features
The Achilles Point to West Tamaki Head area consists of cliffs between two beaches, Ladies Bay and Karaka Bay. (seen above from the other side of Tamaki River)
At the top of the cliffs, the land slopes south, away from the sea, so that the cliffs form a ridge line with the cliff tops being the highest points in the area.
Midway between the two beaches is a crater, Glover Park. There is a partial tuff ring around this crater; it is breached to the north by the erosion of the cliffs, and to the west and south-east (at the junction of Maskell and Riddell Roads). The cliff line on either side of the crater has tuff from the crater perched on it, and there are fallen blocks of this tuff on the wave-cut platform at the bottom of the cliffs.
The floor of the crater is now playing fields; these were formed by draining a swamp that occupied the crater floor. It is possible that this is the floor of a former small lake that was drained when the western breach of the tuff cone was formed; it is also possible that this lake drained through the south-eastern breach prior to this. There is an old water tower on top of the most extensive remaining segment of the tuff cone.
Karaka Bay occupies a distinctive ‘cut’ out of the cliffs and lies at the toe of a large landslide.
West Tamaki Head is a resistant headland of Parnell Grit. Between the headlands there is a considerable wave cut platform; it is probable that erosion rates were higher prior to the formation of Rangitoto Island less than 1000 years ago.

2. Rock Units
  • Waitemata Formation: these are interbedded sandstones and mudstones. Sandstone layers are typically from a few cm to about .1.5 m thick. Mudstone layer range from a few millimetres up to about 40 cm thick. Both sandstone and mudstone are soft, easily gouged by a pen-knife. At West Tamaki Head there are layers containing coalified plant fragments, immediately underlying the Parnell Grit at the headland.
  • Parnell Grit Member: this is a member within the Waitemata Formation. It consists of largely volcanic-derived sediments, including fragments of scoria and andesite. It is darker grey and more massive than the sandstones and mudstones within which it is found, and contains joints with calcite mineralization. It is graded, with fragments up to fist-sized at the base to coarse sand sized at the top. Total thickness in this locality is about 15 metres.
  • Tuff: basaltic tuff from the St Heliers (Glover Park) volcano, consisting of about 85% vesicular basaltic fragments. The remaining 15% is mostly Waitemata Formation material, but fragments found on the foreshore include basement greywacke, schist and ultramafic material; presumably these are derived from considerable depths.
  • Recent alluvium: the base of the crater is floored with swampy material. There is no good exposure at this time, but it presumably consists of muds and peats.
  • Gouge material: the boundary of the landslide contains some 2 m of gouge material, derived from Parnell Grit and Waitemata Sandstone and pulverized by the landslide movement. It is clay-rich and soft.


3. Geological History
The oldest unit in the area is the Watemata Formation. According to Searle (1962) this is Miocene in age and was deposited in a NW-SE trending sedimentary basin. The sandstones are turbidity-current deposits, with the mudstones in between having been deposited from mud carried out to sea between turbidity-current events. The Parnell Grit was deposited into this basin as an underwater lahar from some unknown source. Searle (1962) suggests this lay to the north-west. Plant fragments may have been derived from the land mass to the east or from islands to the west (the Waitakere Volcano).
The sediments of the Waitemata Formation are moderately deformed; the study area covers a large, shallow anticline. Deformation is locally more pronounced around the Parnell Grit. It is likely this deformation took place during the general uplift of this area some 8 million years ago (Searle 1962).
The St Heliers volcano erupted with a series of explosions, possibly 50,000 to 100,000 years ago (Cox 1989). At this time, the sea level was considerably lower than at present and the ridge line of the present cliff tops would have sloped as a hillside down to a valley some way below present sea level and perhaps a few hundred metres from the present shore line. The eruption formed a crater surrounded by a tuff cone, the northern part of the cone draped over the top of a pre-existing hill.
Following the eruption it is likely the crater filled with water and became a small lake, The lake probably drained through the south-eastern breach into the stream that now runs through Churchill Park. However, the breach to the west is lower and it seems at some point the lake drained through this breach down to St Heliers beach. The floor of this breach must have eventually cut down to the level of the lake floor and the lake became a swamp and seasonal lake.
Following the end of the last glaciation, some 20,000 years ago, sea level rose. The hillside to the north rapidly eroded back (there was no Rangitoto Island to protect from swells from the Gulf), eventually undercutting part of the tuff cone and allowing blocks of tuff to fall down the cliff. The rate of erosion diminished when Rangitoto formed and the cliff is equilibrating to a steep slope now that the waves are no longer strong enough to undercut it.
Karaka Bay is a large rotational slump, known to have undergone movement in the 1940s. However, the bay existed prior to this so the movement was probably on a pre-existing landslide.


4. Areas for further study
  • The sequence of events forming the swamp of Glover Park is not exactly known and would require cores through the former lake floor to elucidate.
  • The rate of erosion of the cliffs requires further study. There was evidence of recent movement on the track down from Glover Park, and it is likely that this will have consequences for dwellings on the cliff tops.
  • It is possible that there will be further movement on the Karaka Bay landslide.
  • The location of the feeder vent for the volcano is unknown and would require geophysical work to find.

Devonport internal assessment checklist

Tick when you have covered these things:
1.Map
üMap on tracing paper, tidy, coloured pencil
üFrame, north arrow, scale bar
üKey with colours for rock formation, dip/strike, fault and other symbols
üYour name
2.Report
üLandscape features: sandstone high, cliffs/wave cut platform, North Head tuff cone and erosion, other volcanic features, beaches and tombolos
üGeological features:
i.Waitemata sandstone, including plant fossils and Parnell Grit;
ii.Volcanic features (North Head – tuff, scoria, erosion; Mt Victoria scoria cone and basalt flows)
iii.Erosional features – sandstone hill (Vauxhall) with drainage valleys, wave cut bench
iv.Late depositional features – Narrow Neck and Cheltenham low lying areas
üGeological history
i.Deposition of Waitemata Sandstone and Parnell Grit (give time and depositional environment, evidence. Can mention deposition was on unseen greywacke surface).
ii.Sea level drop, erosion to form sandstone hill landscape and drainage features (see diagram in Cox)
iii.Formation of volcanoes
iv.Sea level rise and erosion of coastal features, deposition of intertidal sediments in tombolo areas