Achilles Point (Te Pane o Horoiwi – ''The head of Horoiwi'') is a rocky point on the headland at the eastern end of the small sandy beach named Ladies Bay,
Auckland
Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The List of New Zealand urban areas by population, most populous urban area in the country and the List of cities in Oceania by po ...
, New Zealand. The name 'Te Pane o Horoiwi' can also sometimes refer to the whole headland between St Heliers and Tamaki River estuary. Achilles Point is named after a ship called
HMNZS Achilles (70)
HMNZS ''Achilles'' was a light cruiser, the second of five in the class. She served in the Royal New Zealand Navy in the Second World War. She was launched in 1931 for the Royal Navy, loaned to New Zealand in 1936 and transferred to the new Ro ...
which defeated the
German pocket battleship Admiral Graf Spee in 1939. The headland, from the point round to the Tamaki heads, was previously known as Te Pane o Horoiwi, named after Horoiwi who arrived in New Zealand on the
Tainui canoe (waka).
Ladies Bay is a secluded beach, below steep cliffs, on the headland west of the lookout over Achilles point. Both Ladies Bay and further to the east, the more secluded Gentleman's Bay beach are unofficially places where
nudists can often be found enjoying the sun and sand however the fine for indecent exposure is $200.
The secluded bays are also popular with the male gay community.
Glover Park is an ancient
volcanic crater which erupted more than 45,000 years ago.
The volcanic tuff ring crater is also known in
Māori language
Māori (), or ('the Māori language'), also known as ('the language'), is an Eastern Polynesian language spoken by the Māori people, the indigenous population of mainland New Zealand. Closely related to Cook Islands Māori, Tuamotuan, and ...
as Whakahumu or geologically as the 'St Heliers explosion crater'. It is found in the center of the headland between West
Tamaki Head and the eastern end of St Heliers Bay beach. It was filled in during the 1950s to form a public sports field. Before that it formed a seasonal shallow lake or swamp.
The seaward side of the tuff crater is falling away down the coastal cliffs to 'Gentleman's Bay' far below. The tuff ring is made from ash and ejected material. The cliffs were there before the volcano erupted so the volcanic rock draped over the clay hill that once existed before sea levels rose and began eroding it away to become the steep cliffs we see today. Some volcanic rocks can be found on the beach below – some fragments ejected from deep in the earth, or blocks of tuff ring that were once perched on top of the cliff. Rangitoto Island is directly to the north, however Rangitoto is a recent eruption (600 to 550 years ago) and was not always there to shelter the cliffs from powerful wave action.
There is an old concrete water tower built on the
tuff ring formed around the edge of the crater opposite the seaward side.
Geology
Going east, past Ladies Bay and Gentleman's Bay, we round the West Tamaki Head into the Tamaki Estuary. It is here we find an excellent example of the grey coloured 'Parnell Grit' accessible from Karaka Bay. 'Parnell Grit', is a brittle sedimentary rock containing fragments of
scoria,
andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...
, and
pumice
Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular vol ...
.
At low tide there is an interesting walk from Ladies Bay along the base of the cliffs to St Helier's Bay. The rocky shoreline overlooks the
Waitemata Harbour Waitemata or Waitematā may refer to:
* Waitematā Harbour, the primary harbour of Auckland, New Zealand
* Waitematā (local board area), a local government area in Auckland, New Zealand
** Waitematā Local Board, a local board of Auckland Council, ...
which itself occupies a
drowned valley system cut in
marine sediments
Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles have their origins in soil and rocks and have been transported from the land to the sea, mainly ...
of
Miocene
The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
Age (15–25 million years ago). Generally, around Auckland these soft Miocene sediments are alternating Waitemata series
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates) ...
and
mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
with more massive beds of sandstone sometimes with minor occurrences of limestone.
Geological Map of New Zealand
/ref>
The concretions that can be easily seen, are formed by the action of ground water with dissolved minerals (mainly calcium carbonate of which limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
is made) percolating through the layers. Calcium carbonate is an important component of concrete and fills in the pore spaces between grains of sediment thereby cementing the grains together and making them more durable against erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
.
Glover Park volcano formed from a phreatomagmatic eruption leaving a basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic monogenetic volcanic crater up to in maximum diameter, surrounded except to the north-east by tuff deposits that extend about to the east and south.[ The presence of overlying Rotoehu tephra on a drill ore means the volcano last erupted more than 45,000 years ago, but the age is unclear within a wide range. The cliff retreat with raising sealevels of Achilles Point has meant, as already mentioned, that the tuff deposits up the cliffs,][ as they erode, fall onto the sea rock platform (see photos below). This has resulted in the discovery that a distinctive lithic clast in the tuff that contained shell fragments was strong evidence that the erupted magma traversed the eastern border of the ]ophiolitic
An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.
The Greek word ὄφις, ''ophis'' (''snake'') is found i ...
Dun Mountain-Maitai Terrane
The Dun Mountain-Maitai Terrane comprises the Dun Mountain Ophiolite Belt (also called the Mineral Belt), Maitai Group and Patuki Mélange. The Dun Mountain Ophiolite is an ophiolite of Permian age located in New Zealand's South Island. Prehistori ...
.[
]
References
*''Volcanoes of Auckland: A Field Guide''. Hayward, B.W.; Auckland University Press, 2019, 335 pp. .
External links
Archaeology and History of St Heliers, Auckland.
Geology of the headland
Point to point walkway ARC – St Heliers to Churchill park through the crater at Glover Park
Explanation of concretions
Point to Point walkway. The full point to point walk is approximately 7.5km long, starting at the popular St Heliers Bay and finishing at Point England. Allow three to four hours.
Gallery
;Geological features between Ladies Bay and St Heliers Bay
Image:mudstone sandstone layers.jpg, Sandstone and mudstone layers
Image:Archilles_point_white_closs.jpg, Close up of white siltstone
Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
in cliff.
File:White rock eroding away, between Ladies Bay and St Heliers Bay Auckland.jpg, White rock broken away
Image:Crumbling_white_rock.jpg, Discoloration of crumbling white siltstone layer.
Image:Broken_concretion.jpg, Cross-section of concretion snapped off at cliff wall.
Image:Line_of_concretions.jpg, Concretions all line up in the cliff wall.
Image:AucklandMapHochstetter1859.JPG, 1859 map showing the volcanoes and lava flows. Glover Park volcano is to the upper right on the shores of the Waitematā Harbour.
Image:Archillies point.jpg, The rocks between the point and St Heliers Bay. Layers of sedimentary rock strata
In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...
.
Image:Archilles point white.jpg, The rocks between the point and St Heliers Bay. White siltstone layer.
Image:Archilles concretions scattered.jpg, The rocks between the point and St Heliers Bay. The concretions are scattered and looking like fossilised logs, long after the supporting sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates) ...
has been eroded away by the waves.
Image:Archilles point concretions.jpg, The projections are known as concretions and are all on the same horizontal layer. Sometimes they might snap off. More often, the softer stone erodes away completely, leaving them resting on the surface a few meters lower.
Image:Sandstone mudstone.jpg, Close up of sandstone and mudstone layers
Image:Achilles Point, from the viewing platform.jpg, Achilles Point from the viewing platform - looks like the bow of a ship.
Image:Ladies Bay.jpg, Ladies Bay
Image:Glover park.jpg, Glover Park crater with housing and water tower on the tuff ring
{{Ōrākei Local Board Area
Geography of Auckland
Headlands of the Auckland Region
Hauraki Gulf
Ōrākei Local Board Area