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Lahar deposit on eastern Mt Ruapehu, central Volcanic Plateau (Rowan Buxton)

Lahar deposit on eastern Mt Ruapehu, central Volcanic Plateau (Rowan Buxton)

This ecosystem comprises a mud flow of water and volcanic material commonly caused by the bursting of a crater lake, eruption from a snow-capped volcano or from prolonged torrential rain. They may include boulders (> 256 mm) but are dominated by finer particles (< 2mm) including much sand, silt, and clay. Composition varies greatly among lahars depending on their source material. They can be many thousands of years old, but this category concerns only recent lahar deposits with minimal vegetation cover of mosses, grasses, and herbs with some shrubs.

Notable flora and fauna

There is no notable flora; fauna is unknown.

Threat status

Not threatened (Holdaway et al. 2012 )


Their location in indigenous matrix reduces weed threat but Pinus contorta  is a problem on the Volcanic Plateau. Lahar deposits are unsuitable for agriculture and not legally available for development. There is limited quantitative information on animal impacts but lagomorphs and possums may be a problem.

Where do they occur?

In association with mountains on the central Volcanic Plateau and Mt Taranaki.

Further reading

Atkinson IAE 1981. Vegetation Map of Tongariro National Park, North Island, New Zealand. Wellington, New Zealand Department of Scientific and Industrial Research.

Clarkson BD 1986. Vegetation of Egmont National Park New Zealand. Wellington, DSIR.

Graettinger AH, Manville V, Briggs RM 2010. Depositional record of historic lahars in the upper Whangaehu Valley, Mt. Ruapehu, New Zealand: implications for trigger mechanisms, flow dynamics and lahar hazards . Bulletin of Volcanology 72: 279-296.

Hodgson KA, Lecointre JA, Neall VE 2007. Onetapu Formation: The last 2000 yr of laharic activity at Ruapehu volcano, New Zealand . New Zealand Journal of Geology and Geophysics 50: 81-99.

Procter JN, Cronin SJ, Sheridan MF 2012. Evaluation of Titan2D modelling forecasts for the 2007 Crater Lake break-out lahar, Mt. Ruapehu, New Zealand.  Geomorphology 136: 95-105.


Disaster  (The Daily Post)

Lahar on Mount Ruapehu, New Zealand  (NASA Earth Observatory)

Lahars from Mt Ruapehu - mitigation and management  (DOC poster)

Lahar video  (DOC)