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| Titel |
Late Holocene landscape change history related to the Alpine Fault determined from drowned forests in Lake Poerua, Westland, New Zealand |
| VerfasserIn |
R. M. Langridge, R. Basili, L. Basher, A. P. Wells |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 12, no. 6 ; Nr. 12, no. 6 (2012-06-26), S.2051-2064 |
| Datensatznummer |
250010934
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| Publikation (Nr.) |
 copernicus.org/nhess-12-2051-2012.pdf |
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| Zusammenfassung |
| Lake Poerua is a small, shallow lake that abuts the scarp of the Alpine
Fault on the West Coast of New Zealand's South Island. Radiocarbon dates
from drowned podocarp trees on the lake floor, a sediment core from a
rangefront alluvial fan, and living tree ring ages have been used to deduce
the late Holocene history of the lake. Remnant drowned stumps of kahikatea
(Dacrycarpus dacrydioides) at 1.7–1.9 m water depth yield a preferred time-of-death age at
1766–1807 AD, while a dryland podocarp and kahikatea stumps at 2.4–2.6 m yield
preferred time-of-death ages of ca. 1459–1626 AD. These age ranges are
matched to, but offset from, the timings of Alpine Fault rupture events at
ca. 1717 AD, and either ca. 1615 or 1430 AD. Alluvial fan detritus dated from
a core into the toe of a rangefront alluvial fan, at an equivalent depth to
the maximum depth of the modern lake (6.7 m), yields a calibrated age of AD
1223–1413. This age is similar to the timing of an earlier Alpine Fault
rupture event at ca. 1230 AD ± 50 yr. Kahikatea trees growing on
rangefront fans give ages of up to 270 yr, which is consistent with alluvial
fan aggradation following the 1717 AD earthquake. The elevation levels of
the lake and fan imply a causal and chronological link between lake-level
rise and Alpine Fault rupture. The results of this study suggest that the
growth of large, coalescing alluvial fans (Dry and Evans Creek fans)
originating from landslides within the rangefront of the Alpine Fault and
the rise in the level of Lake Poerua may occur within a decade or so of
large Alpine Fault earthquakes that rupture adjacent to this area. These
rises have in turn drowned lowland forests that fringed the lake.
Radiocarbon chronologies built using OxCal show that a series of massive
landscape changes beginning with fault rupture, followed by landsliding, fan
sedimentation and lake expansion. However, drowned Kahikatea trees may be
poor candidates for intimately dating these events, as they may be able to
tolerate water for several decades after metre-scale lake level rises have
occurred. |
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