Another Saturday excursion was planned to Rangitoto. We went with two Area Office couples. I had been looking forward to this trip as it involved hiking and a glimpse at the geology of the area formed in the recent past.
From Devonport Ferry terminal, we took one of several daily ferries to the island. It then took us a little over an hour to hike to the top of the volcano. The first three pictures are of the island and our arrival. Our pace was set to accommodate our fitness levels. Nevertheless, our seemingly methodical pace was not far off the majority of the trekkers.
Rangitoto was formed by a series of eruptions between 550 and 600 years ago. The eruptions occurred in two episodes, 10–50 yrs apart, and are thought to have lasted for several years during the later shield-forming episode. The first episode erupted most of the volcanic ash that mantles Motutapu Island next door, and produced the lower, northern cone. The second episode built most of Rangitoto, erupting all the lava flows and main scoria cone at the apex. The 2.3 cubic kilometres of material that erupted from the volcano was about equal to the combined mass-produced by all the previous eruptions in the Auckland volcanic field, which were spread over more than 250,000 years.
In 2013, scientists said new studies showed Rangitoto had been much more active in the past than previously thought, suggesting it had been active on and off for around 1000 years before the final eruptions around 550 years ago. Civil Defence officials said the discovery didn't make living in Auckland any more dangerous, but did change their view of how an evacuation might proceed.
The volcano is not expected to become active again, although future eruptions are likely within the volcanic field. Subsidence back down the throat during the cooling process has left a moat-like ring around the crater summit, which may be viewed from a path which goes right round the rim
and up to the highest point.
The island was purchased for ₤15 by the Crown in 1854, a very early date in New Zealand's colonization by Europeans, and for many years served as a source of basalt for the local construction industry. It was set aside as a Recreation Reserve in 1890, and became a favourite spot for day trippers. Some development occurred nonetheless. In 1892, salt works were created on 5 acres (20,000 m2) near Mackenzies Bay. The wharf and summit road were opened in 1897, with another road linking the summit to Islington Bay by 1900. For over 30 years (from 1898 to 930), scoria was quarried from near the shoreline on the west side of Islington Bay as building material for Auckland. From 1925 to 1936, prison labour built roads on the island and a track to the summit.
Islington Bay was formed in the South East area of the island. Formerly known as Drunks Bay, it was used as a drying out area for inebriated crews before they ventured out of the gulf. The bay is very popular with Auckland 'boaties' as a refuge, as it is quite sheltered from the prevailing south west winds. In summer it is not unusual to find 30 boats anchored overnight.
A number of Māori myths exist surrounding the island, including that of a 'tupua' couple, children of the Fire Gods. After quarreling and cursing Mahuika, the fire-goddess, they lost their home on the mainland because it was destroyed by Mataoho, god of earthquakes and eruptions, on Mahuika's behalf. Lake Pupuke (see earlier blog) on the North Shore was created in the destruction, while Rangitoto rose from the sea. The mists surrounding Rangitoto at certain times are considered the tears of the tupua.
Military installations were built during World War II to support the Auckland harbour defences and to house U.S.. troops or to store mines. The most visited remains of these installations is the old observation post on the summit. Not much remains of this, but serves as a great vantage point of the surrounding area. The northern shore of the island was used as a wrecking ground for unwanted ships, and the several wrecks are still visible at low tide.
Baches (small holiday houses) were built around the island's edge in the 1920s and 1930s. We walked along the beach trail and observed a number of them. The legality of their existence was doubtful from the start and the building of further baches was banned in 1937. Most have since been removed because of the ban and because the island has become a scenic reserve. However some 30 of the 140 baches remain as of 2010, and some are being preserved to show how the island used to be, once boasting a permanent community of several hundred people, including a good number of children. The buildings included some more permanent structures, like a seawater pool, built of quarried stones by convict labour, located close to the current ferry quay.
I am making better use of the camera I acquired before the mission. The picture to the right is at full magnification and is take of an office or apartment complex near where we live in Takapuna, proabably twenty kilometres away,as the crow flies.
In some parts of the island, fields of lightweight, clinker-like black lava stones called scoria are still exposed, appearing very recent to a casual eye. About 200 metres from the top of the mountain, on the eastern side, we walked to and then through one of seven known lava tubes — tubes left behind after the passage of liquid lava. The more accessible of the caves are signposted. Lava tubes are formed when low-viscosity molten lava known as pahoehoe flows and cools on the outside due to contact with the ground and air, to form a hard crust allowing the still-liquid molten lava to continue to flow through inside.
At Rangitoto, the large tubes are cave-like. A flashlight made entry into the caves a possibility. The longest known cave is about 50 m long.
There are virtually no streams on the island so plants rely on rainfall for moisture. It has the largest forest of
pōhutukawa trees in the world, as well as many
northern rātā trees. In total, more than 200 species of trees and flowers thrive on the island, including several species of
orchid, as well as more than 40 types of fern
The island is considered especially significant because all stages of succession from raw
lava fields to abundant flora is taking root. As lava fields contain no soil of the typical kind, windblown matter and slow breaking-down of the native flora are still in the process of transforming the island into a more habitable area for most plants (an example of
primary succession). This is one of the reasons why the local forests are relatively young and do not yet support a large bird population. However, the
kākā, a New Zealand-endemic parat, is thought to have lived on the island in pre-European times.
Goats were present on Rangitoto in large numbers in the mid 19th century, but were eradicated in the 1880s. Fallow deer were introduced to Motutapu in 1862 and spread to Rangitoto, but disappeared by the 1980s. The brush-tailed rock-wallaby was introduced to Motutapu in 1873, and was common on Rangitoto by 1912, and the brushtail possum was introduced in 1931 and again in 1946. Both were eradicated in a campaign from 1990 to 1996. We saw some traps along the way, clearly designed to trap small rodents without harming them.
