Volcanic dunes
Volcanic dunes of the Rangipo ´Desert´, with widely spaced bristle tussock, Rytidosperma setifolium and islands of shrubby vegetation (Susan Wiser)
Volcanic dunes comprise drifting sand (0.06 - 2mm) derived from lahar and tephra deposits that accumulate on volcanic ring plains during major eruptive phases and are reworked by aeolian and fluvial redistribution during intervening quiescent periods. These processes have led to dune formation, in both sheltered positions and where plants have arrested the drift of sand, and associated deflation (lag) surfaces. The ‘hummock dunes’ tend to be low and isolated from one another, in chaotic systems of mounds and hollows and occur within a matrix of lag gravel. Despite adequate rainfall (>1200 mm/year), the very windy climate, low humidity and coarse, gravelly and sandy soils have produced a drought-prone desert-like environment.
While other dunes in western North Island are originally derived from volcaniclastic material the proportion that is of laharic origin is minor and these dunes are mostly influenced by coastal processes. They are therefore included in Active sand dunes. The Inland sand dunes of the South Island are formed from non-volcanic material.
Synonyms
Volcanic sandfields (Atkinson 1981), volcanic gravelfields (Atkinson 1981).
Where do they occur?
Volcanic dunes are restricted to the Rangipo ‘Desert’ on the south-eastern fringe of Mt Ruapehu on the Volcanic Plateau in the central North Island.
Notable flora and fauna
Threatened plants include the declining species Pimelea microphylla.
Threat status
Endangered (Holdaway et al. 2012)Threats
Invasion by lodgepole pine (Pinus contorta), mouse-ear hawkweed (Pilosella officinarum [Hieracium pilosella], marram grass (Ammophila arenaria), and tree lupin (Lupinus arboreus) is of some concern. Invasion of volcanic dunes by the latter two species parallels their behaviour on coastal sand dunes. NZ Defence Force exercises (mainly shelling and off-road vehicle tracking) may also have a negative impact.
Further reading
Atkinson IAE 1981. Vegetation Map of Tongariro National Park, North Island, New Zealand. Wellington, New Zealand Department of Scientific and Industrial Research.
Cockayne L 1908. Report on a botanical survey of the Tongariro National Park. Wellington, Department of Lands. 42 p.
Cockayne L 1911. Report on the dune-areas of New Zealand, their geology, botany and reclamation. Wellington, Department of Lands. 76 p.
Donoghue SL, Neall VE 2001. Late Quaternary constructional history of the southeastern Ruapehu ring plain, New Zealand, New Zealand Journal of Geology and Geophysics, 44: 439-466.
Edgett KS, Lancaster N 1993. Volcaniclastic aeolian dunes: Terrestrial examples and application to martian sands, Journal of Arid Environments 25: 271–297.
Palmer BA, Purves AM, Donoghue SL1993. Controls on accumulation of a volcaniclastic fan, Ruapehu composite volcano, New Zealand. Bulletin of Volcanology 55: 176-189.
Purves AM 1990. Landscape ecology of the Rangipo Desert. Unpublished MSc thesis, Massey University, Palmerston North, New Zealand.
Links
A day in the desert (The World According to me)
In the Shadow of Giants (New Zealand Geographic)
Volcanic ash makes sand dunes on the Island of Hawai`i (USGS)
The volcanic dunes of the Central Plateau (Department of Conservation)
Volcanic Dunes of the Rangipo Desert (OurFuture)
Volcano Watch: Sand dunes related to past explosive eruptions (Hawaii 24/7)