New Zealand Journal of Geology and Geophysics abstracts
Late Quaternary constructional history of the southeastern Ruapehu ring plain,
New Zealand
SUSAN L. DONOGHUE
Department of Earth Sciences
The University of Hong Kong
Pokfulam Road, Hong Kong
email: donoghue@hkucc.hku.hk
VINCENT E. NEALL
Institute of Natural Resources
Massey University
Private Bag 11-222
Palmerston North, New Zealand
Abstract A late Quaternary constructional history of the
southeastern Ruapehu ring plain is established from detailed mapping of
volcaniclastic sequences preserved over a 200 km2 area northwest of
Waiouru. Lahar deposits dominate these sequences and form the major surfaces.
Local andesitic tephras, and distal rhyolitic tephras from Taupo and Okataina
Volcanic Centres, are interbedded with the lahar deposits, providing a
framework radiocarbon chronology for these deposits dating back to
c. 22 600 yr BP. Five formations are mapped across the southeastern
Ruapehu ring plain with their respective constructional surfaces: Onetapu
Formation (dated c. 1850 yr BP to Present), Manutahi Formation (dated
c. 5370-3200 yr BP), Mangaio Formation (dated c. 4600 yr BP), Tangatu
Formation (dated c. 14 700-5400 yr BP), and Te Heuheu Formation
(dated c. >22 600-14 700 yr BP). Each formation records a
period of ring-plain aggradation in response to increased sediment influx,
principally by sediment flows associated with syn-eruptive and inter-eruptive
activity. Sector-wide aggradation occurred between c.22 600 and
14 700 yr BP, and during the Last Glacial Maximum (c. 23-13 ka).
Movement along the Desert Road Fault post c. 25 000 yr BP led to more
confined ring-plain aggradation west of the fault. Lithological and
sedimentological characteristics of the lahar deposits, and their
distributions, indicate changing rates of sediment supply and a progressive
northwards migration of source areas and ring-plain sedimentation over time.
This post-c. 22 600 yr BP record of sedimentation and ring-plain
construction is important to deciphering the nature of eruptive and
non-eruptive activity at this volcano and the establishment of an integrated
(tephra and lahar) record of the volcanic history.
Keywords Ruapehu; ring-plain construction; lahars;
syn-eruptive aggradation; inter-eruptive aggradation
New Zealand Journal of Geology & Geophysics, 2001, Vol 44: 439-466
0028-8306/01/4403-0439 $7.00/0 (c) The Royal Society of New Zealand
2001
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