Abstract:The inland valleys of New Zealand's South Island were heavily glaciated during the last glacial cycle. Subsequent fluvial incision has eroded out glacial deposits from the valleys in many locations, making it difficult to reconstruct glacial dynamics and chronology. The Brabazon and Butler Downs lie in a fault-controlled intra-montaine basin that has been largely protected from fluvial erosion and the area contains extensive evidence for multiple glacial margins. This paper presents a detailed glacial geomorph… Show more
“…From the stratigraphic outcrop, we can resolve that the surface features have little continuity into the subsurface stratigraphy. At least on the lower slopes, they indicate the last phase of activity in the area.Figure 6Geomorphic features of the Butler Downs (modified from Borsellino et al, 2017). The numbers refer to the stratigraphic outcrops; (1) Bush Stream, (2) Scour Stream, (3) Tui Lake, and (4) Zig-Zag Track.…”
Section: Discussionmentioning
confidence: 98%
“…Geomorphic features of the Butler Downs (modified from Borsellino et al, 2017). The numbers refer to the stratigraphic outcrops; (1) Bush Stream, (2) Scour Stream, (3) Tui Lake, and (4) Zig-Zag Track.…”
Section: Discussionmentioning
confidence: 99%
“…The Butler and Brabazon downs comprise a broad valley shoulder that bears remarkably well-preserved glacial geomorphology (Borsellino et al, 2017). The landforms preserve detailed records of ice recession within the Rangitata valley upstream of the Rangitata Gorge.…”
Stratigraphic evidence and extensive optically stimulated luminescence (OSL) geochronology from an 18-km-long reach of the middle Rangitata Valley, South Island, New Zealand, provide evidence for at least six distinct glacial advances during the last glacial cycle. These include four well-constrained Marine Oxygen Isotope Stage (MIS) 3 and 2 advances at ca. 38 ka, ca. 27 ka, ca. 21 ka and at 18 ka, as well as less well-constrained advances in MIS 4 and/or early MIS 3. Ice occupied a farther downvalley reach of the Rangitata from 38 ka to after 18 ka, indicating that near-full glacial conditions persisted for most of the last 20 ka of the last glaciation, though the glacier still fluctuated significantly, as reflected by the numerous distinguishable advances. Global or regional cooling alone cannot explain the persistence of near-maximum glacial conditions for this extended period, nor can it explain the occurrence of the largest advances ca. 32 ka. Instead, we invoke the northward expansion of the westerlies during MIS 3 as the cause for the early widespread glaciation, wherein enhanced westerly flow under moderate cooling maximised glacial extents. Local insolation favoured extended MIS 3 glaciation until ca. 32 ka. Increasing summer insolation gradually reduced glacial extents after ca. 28 ka.
“…From the stratigraphic outcrop, we can resolve that the surface features have little continuity into the subsurface stratigraphy. At least on the lower slopes, they indicate the last phase of activity in the area.Figure 6Geomorphic features of the Butler Downs (modified from Borsellino et al, 2017). The numbers refer to the stratigraphic outcrops; (1) Bush Stream, (2) Scour Stream, (3) Tui Lake, and (4) Zig-Zag Track.…”
Section: Discussionmentioning
confidence: 98%
“…Geomorphic features of the Butler Downs (modified from Borsellino et al, 2017). The numbers refer to the stratigraphic outcrops; (1) Bush Stream, (2) Scour Stream, (3) Tui Lake, and (4) Zig-Zag Track.…”
Section: Discussionmentioning
confidence: 99%
“…The Butler and Brabazon downs comprise a broad valley shoulder that bears remarkably well-preserved glacial geomorphology (Borsellino et al, 2017). The landforms preserve detailed records of ice recession within the Rangitata valley upstream of the Rangitata Gorge.…”
Stratigraphic evidence and extensive optically stimulated luminescence (OSL) geochronology from an 18-km-long reach of the middle Rangitata Valley, South Island, New Zealand, provide evidence for at least six distinct glacial advances during the last glacial cycle. These include four well-constrained Marine Oxygen Isotope Stage (MIS) 3 and 2 advances at ca. 38 ka, ca. 27 ka, ca. 21 ka and at 18 ka, as well as less well-constrained advances in MIS 4 and/or early MIS 3. Ice occupied a farther downvalley reach of the Rangitata from 38 ka to after 18 ka, indicating that near-full glacial conditions persisted for most of the last 20 ka of the last glaciation, though the glacier still fluctuated significantly, as reflected by the numerous distinguishable advances. Global or regional cooling alone cannot explain the persistence of near-maximum glacial conditions for this extended period, nor can it explain the occurrence of the largest advances ca. 32 ka. Instead, we invoke the northward expansion of the westerlies during MIS 3 as the cause for the early widespread glaciation, wherein enhanced westerly flow under moderate cooling maximised glacial extents. Local insolation favoured extended MIS 3 glaciation until ca. 32 ka. Increasing summer insolation gradually reduced glacial extents after ca. 28 ka.
“…There is no defined source area/scar of a larger landslide at the proposed damming site (S3.2) and both surface material and morphology of the terminal moraine complex are comparable to contemporary ones in other valleys (e.g. Borsellino et al, 2017). Even if we reject its capacity to act as a lake dam we have no doubt that the area constitutes a moraine system subsequently modified by glaciofluvial erosion and slope processes (Figs.…”
Section: An Alternative Model For a Non-glacial Lake Speightmentioning
“…A number of glacial-geomorphological studies have recently been published on both individual river basins in New Zealand (Borsellino et al, 2017;Evans, 2008;Wallace, 2001) and regionally in the central Southern Alps (Barrell et al, 2011). The Ahuriri River valley lies to the south and outside of the boundary of the existing central Southern Alps mapping.…”
Detailed geomorphological mapping of ice-related and post-glacial landforms is widely used to explain past glacial fluctuations and dynamics. Here we present the first detailed glacial geomorphological description of the landform assemblages produced by the former Ahuriri Glacier, Southern Alps, New Zealand (44°15 ′ S, 169°36 ′ E). The Southern Alps of New Zealand experienced multiple episodes of glaciation during the Late Quaternary with large mountain glaciers in many valleys, but very little is known about the Ahuriri River valley, one of the main tributaries of the Waitaki River. We selected a region extending approximately 45 km downstream from the headwaters of the Ahuriri River covering an area of about 532 km 2 . Our goal was to create a detailed 1:38,000 scale glacial geomorphological map of this area and provide a geomorphological context to support future geochronological work. Glacial geomorphological mapping was performed by combining several field investigations and remote sensing surveys. We provided high-resolution spatial information for all the glacial-related landforms shown on the map (see main Map). The distribution of post-glacial landforms in the middle and lower section of the main valley outline at least three advances or stillstand phases of past glaciers and suggesting the maximum length (∼41 km) of the former glacier during the Last Glacial Maximum. Most of the tributary valleys were also probably covered by ice at this time. Other prominent but smaller size moraine landforms, mostly in the tributary river valleys, also suggest relatively small, post-glacial advance phases of former glaciers.
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