Publication Date:
2017-04-04
Description:
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 1.7–1.9m water depth yield a preferred time-ofdeath
age at 1766–1807 AD, while a dryland podocarp and
kahikatea stumps at 2.4–2.6m 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. 1230AD±50 yr. Kahikatea
trees growing on rangefront fans give ages of up to 270 yr,
which is consistent with alluvial fan aggradation following
the 1717AD 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.
Description:
FRST project Impacts of Plate Tectonics
in New Zealand (PLT): Alpine Fault earthquake geology (PGST
Contract CO5X0702).
Description:
Published
Description:
2051-2064
Description:
3.2. Tettonica attiva
Description:
JCR Journal
Description:
open
Keywords:
Alpine fault
;
drowned forest
;
Lake Poerua
;
New Zealand
;
04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
;
04. Solid Earth::04.04. Geology::04.04.02. Geochronology
;
04. Solid Earth::04.04. Geology::04.04.03. Geomorphology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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