New Zealand Journal of Geology and Geophysics abstracts
Lahar history and hazard of the Tongariro River,
northeastern Tongariro Volcanic Centre, New Zealand
SHANE J. CRONIN
V. E. NEALL
A. S. PALMER
Department of Soil Science
Massey University
Private Bag 11 222
Palmerston North, New Zealand
Abstract Lahar deposits beside the Tongariro River have been
mapped and dated using andesitic and rhyolitic marker tephras. Coupling the
stratigraphic record obtained with that of the Tongariro and Ruapehu ring
plains has enabled reconstruction of the history of lahars along the Tongariro
River. This forms the basis of a lahar hazard map for the entire catchment. Six
lahar hazard zones, with assigned recurrence intervals ranging from 1 in
35 yr to 1 in >15 000 yr, have been mapped. Lahar deposits
between the ages of 14.7 and 9.8 ka cover the greatest areas, while
younger lahar deposits are confined to lower surfaces closer to the present
river channel. Holocene lahar deposits along the Tongariro River are not as
well preserved as older units, probably because the Holocene lahars were
confined to a more deeply incised channel and were more readily eroded
following emplacement. All recorded post-11.85 ka lahars in the Tongariro
catchment were derived from Ruapehu volcano. The Mangatoetoenui Stream has been
the conduit for the greatest number of Holocene lahars and for all of the
historic ones. Most of Turangi is built on a surface which has not been
inundated by a lahar since c. 10 000 yr ago. However, the area identified
where high risk affects the greatest population is a part of Turangi, which was
inundated by a lahar less than 1850 yr ago. The infrastructures at greatest
risk include the State Highway 1 bridge across the Mangatoetoenui Stream and
the Rangipo Dam and power station.
Keywords volcanic hazards; volcanic risk; lahar hazard map;
lahars; Ruapehu volcano; Tongariro volcano; Tongariro River; late Quaternary
New Zealand Journal of Geology and Geophysics, 1997, Vol. 40: 383-393
0028-8306/97/4003-0383 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (1191K); (scanned from paper original: notes about this process)
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