New Zealand Journal of Geology and Geophysics abstracts
A late Quaternary stratigraphic framework for the northeastern Ruapehu and
eastern Tongariro ring plains, New Zealand
SHANE J. CRONIN
VINCENT E. NEALL
Department of Soil Science
Massey University
Private Bag 11 222
Palmerston North, New Zealand
Abstract The northeastern Ruapehu and eastern Tongariro ring
plains record a complex sequence of episodic lahar sedimentation. Andesitic and
rhyolitic tephrostratigraphy reveals 15 lahar episodes in the northeastern
Ruapehu ring-plain record ranging in age from >65 to 5 ka, and five in
the Tongariro ring-plain record ranging in age from >23 to 14 ka. The
most voluminous and widespread lahar deposition occurred during cool and stormy
climatic periods equivalent in age to marine d18O Stages 2 and 4. In
these periods, accelerated physical weathering on the volcanoes supplied
erosion debris, while large areas of snow and ice acted as sources of water to
form lahars triggered by a variety of mechanisms. Lahar distribution after
c. 22.5 ka was affected by two landform changes in the area at about
this time. First, a large lava flow was emplaced along the boundary between
Ruapehu and Tongariro ring plains shortly before 22.5 ka, effectively
separating the two ring plains since. Second, Last Glacial moraines along the
Whangaehu and Mangatoetoenui Rivers have blocked direct drainage from the
Ruapehu summit region to a large sector of the northeastern ring plain,
including the Upper Waikato Stream, formerly an important lahar path. These
moraines have directed subsequent lahars (after c. 15 ka) along their
current routes (active in 1995) in the Whangaehu and Mangatoetoenui catchments.
Lahar deposition in the study area during this time is linked to large,
explosive andesitic eruptions impacting on catchments where retreating glaciers
provided water for lahar generation.
Keywords Ruapehu volcano; ring plain; volcanic stratigraphy;
lahars; late Quaternary; paleoclimatic change
New Zealand Journal of Geology and Geophysics, 1997, Vol. 40: 185-197
0028-8306/97/4002-0185 $7.00/0 (c) The Royal Society of New Zealand
1997
PDF file of entire paper: medium quality (1236K); (scanned from paper original: notes about this process)
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