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Lava flows on Rangitoto (Steve Pearce)

Lava flows on Rangitoto (Steve Pearce)

Recent lava flows are recent very coarse deposits of acidic or basic volcanic rock that has issued from a volcano or fissure in the Earth’s surface in fluid form and then solidified. On Rangitoto Island, lava flows are almost completely colonised by pohutukawa (Metrosideros excelsa). The youngest lava flows, such as those on Mt Ruapehu, support only mosses and sparse alpine herbs.

Notable flora and fauna

Threatened plants include the nationally critical fireweed (Senecio scaberulus), the nationally vulnerable purple plume grass (Dichelachne micrantha) and turnip-rooted geranium (Geranium retrorsum), the declining Kohurangi or Kirk’s daisy (Brachyglottis kirkii var. kirkii), Daucus glochidatus, and although skeleton fork fern (Psilotum nudum) is not threatened nationally it is declining locally on Rangitoto (E.K. Cameron, pers. comm.).

There are no threatened or rare fauna associated with this system, although Rangitoto Island once had a flourishing avifauna which might be partially restored (Miller & Craig 1994).

Threat status

Not threatened (Holdaway et al. 2012)

Threats

The main weed on Rangitoto is evergreen buckthorn (Rhamnus alaternus), but moth plant (Araujia hortorum) is an increasing problem on all offshore islands of the Hauraki Gulf. Broom (Cytisus scoparius) has the potential to be a bad weed on the mainland volcanoes. Possums are a threat to Rangitoto, but are unlikely to be significant on the other mountainous lava flows.

Where do they occur?

Several active volcanoes have produced lava flows in the last 1000 years, i.e. Rangitoto Island, Mt Ruapehu, Mt Tarawera, and Mt Taranaki.

Further reading

Hobden BJ, Houghton BF, Nairn IA 2002. Growth of a young, frequently active composite cone: Ngauruhoe volcano, New Zealand.  Bulletin of Volcanology 64: 392-409.

Miller CJ, Craig JL, Mitchell ND 1994. Ark 2020: a conservation vision for Rangitoto and Motutapu Islands.  Journal of the Royal Society of New Zealand 24: 65-90.

Nichol R 1992. The eruption history of Rangitoto: reappraisal of a small New Zealand myth.  Journal of the Royal Society of New Zealand 22: 159-180.

Spurr EB, Anderson SH 2004. Bird species diversity and abundance before and after eradication of possums and wallabies on Rangitoto Island, Hauraki Gulf, New Zealand.  New Zealand Journal of Ecology 28: 143-149.

Links

Lava and Rangitoto  (Nature's Pic images)

Rangitoto (New Zealand Geographic)

Rangitoto Island - Historic volcanic activity  (Te Ara, The Encyclopedia of New Zealand)

Lava  (Wikipedia)