Monogenetic volcanic field

Transcription

[Radio interviewer] David why is Rangitoto Island on your itinerary? [David Bellamy] Well, you know, it's one of those places which one has heard about as being almost a model of understanding the development of young vegetation. I mean here you've got an area which was -- well most people would say -- destroyed by volcanic activity, but I like to think it was rejuvenated. Out came all these new rocks and then the whole process of succession starts again. And of course it has been well documented, it is something one has read about, and again to actually see it for the first time is going to be quite exciting. [Narrator] Auckland's landscape is dotted with 48 volcanoes, all within about 20 kilometres of the city centre. Further signs of volcanic activity are also apparent on a number of islands in the Hauraki Gulf. Auckland's volcanoes erupted comparatively recently. The oldest, where the Auckland Domain is now situated, is about 150,000 years old. The youngest, Rangitoto Island, finished erupting about 600 years ago. It is located only eight kilometres from downtown Auckland. Auckland's volcanoes are 'monogenetic'. This means that having already erupted, they are unlikely to do so again. Instead, new volcanic activity is more likely to create fresh outlets in nearby areas. The Auckland region is likely to experience volcanic activity again, but where and when is anyone's guess. When Rangitoto Island erupted, it spewed out as much lava as all the other Auckland volcanoes combined. Its symmetrical cone and wide-spreading lava flow make the island one of Auckland's iconic symbols. The highest volcano on the Auckland isthmus is Maungawhau, or Mt Eden. It stands at nearly 200 metres high. The terracing and pits of earlier Māori settlement remain, and its summit is a tourist lookout point. Māngere mountain, which is over 100 metres high, and was also settled by Māori, dominates the landscape of South Auckland. Rangitoto Island first began about 700 years ago with a series of submarine eruptions. As these continued over a century or so, a volcanic cone gradually emerged from the sea. Subsequent eruptions laid layers of scoria and lava on the slopes of the emerging island, building it up into the distinctive volcanic cone you can see today. Many of these eruptions, witnessed by Māori living on Motutapu Island and other nearby areas, would have been spectacular. Rangitoto's name refers to 'the bloody sky of Tamatakapua', which is probably a reference to the pyrotechnic displays that accompanied the island's creation. When Rangitoto's eruptions finally ended, the island cooled and the rivers of lava flowing from its summit gradually solidified. Sometimes the molten material escaped, creating curious. Today a number of lava 'tunnels' can be seen near the top of Rangitoto, measuring up to 50 metres long. These can easily be explored with a torch. As Rangitoto cooled, the island remained a barren expanse of lava and scoria. Nothing grew on the rocky surface until enough wind-blown material accumulated among the rough rocks to enable plant life to establish. Today, Rangitoto supports the country's most extensive pōhutukawa forest. Up to 200 other plant species are found on the island, including northern rata, orchids and more than 40 different types of fern. Once the eruptions stopped on Rangitoto, Māori occupied it and lived here until the island was purchased in 1854 for 15 pounds by the colonial government. For many years basalt and scoria quarried from the island helped build Auckland. In 1890 the island became a reserve, and it became used mainly for recreation. Today, Rangitoto is easily accessible by ferry from Auckland. You can walk along its roads, and climb up to the summit or take at a tractor 'train'. Although forest is found on much of the island, some parts are still expanses of lava and scoria. These are stark reminders of Rangitoto's recent creation -- and just how vulnerable Auckland might be to renewed volcanic activity.