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| Titel |
Recognition and paleoclimatic implications of Late Holocene glaciation on Mt Taranaki, North Island, New Zealand |
| VerfasserIn |
Martin Brook, Vince Neall, Bob Stewart, Rob Dykes, Derek Birks |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050240
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| Zusammenfassung |
| Evidence for the timings of inter-hemispheric climate fluctuations during the Holocene
is important, with mountain glacier moraine systems routinely used as a proxy
for climate. In New Zealand such evidence for glacier expansion during the Late
Holocene is fragmentary and is limited to glaciers in a narrow zone within the centre
of the Southern Alps. Recent high precision work in the central Southern Alps at
the termini of Tasman, Mueller and Hooker glaciers has documented a series of
middle to late Holocene moraine advances which appear to have occurred during
classic Northern Hemisphere warm periods. However, there are issues connected to
palaeoclimatic interpretation of dated moraines in the Southern Alps, namely that: (1)
some glaciers have a calving tendency, and can become detached from climate; (2)
large rock avalanche deposits onto a glacier may affect a glacier’s mass balance, its
frontal variations, and moraine formation, thus obscuring a "true" climatic signal;
(3) the termini of the low-gradient long profiles of valley glaciers experience a
time-lag of >100 years in response to major climate signals. Thus, in order to make
suppositions about Holocene climate-driven glacier advances, it is important to
determine whether advances in the central Southern Alps do reflect regional New
Zealand palaeoclimate, or instead reflect local geomorphological factors. To help
address this, we present the first evidence for Late Holocene glacier expansion on the
North Island of New Zealand in the form of two unconsolidated debris ridges on the
south side of the stratovolcano, Mt Taranaki/Mt Egmont, at ~1920 m asl. The two
ridges are aligned north-south along the western and eastern sides of a small basin
(Rangitoto Flat), which is formed between the main Taranaki cone (to the north), and
the parasitic cone of Fanthams Peak (to the south). The approximate age of the
ridges is constrained by dated eruptive events and the relationship between ridge
locations and the spatial positioning of adjacent volcanic landforms. We propose the
ridges formed as two lateral moraines on the margins of a cirque glacier during the
final construction phase of Fanthams Peak between 3.3 and 0.5 ka BP, during Late
Holocene time. This time interval accords with published cosmogenic 10Be dating of
moraine-building episodes in the Southern Alps, indicating the Mt Taranaki moraines are a
response to the same regional climatic forcings. That glacier advances during the late
Holocene in New Zealand do appear to reflect regional climate forcing is consistent
with contemporary glacier behaviour, as both the Interdecadal Pacific Oscillation
(IPO) and El Niño-Southern Oscillation (ENSO) have been important influences
on glacier behaviour in New Zealand over the past few decades. Indeed, the IPO
switched to a negative mode about 1940 bringing warmer and drier conditions to New
Zealand’s Southern Alps before reverting to a positive, colder, and wetter mode in
1978. These changes are reflected in New Zealand’s glacier length fluctuations. |
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