Ben Ohau Range Research Articles

Age constraints of rock glaciers in the Southern Alps/New Zealand – Exploring their palaeoclimatic potential

Two rock glaciers in the valley head of Irishman Stream in the central Ben Ohau Range, Southern Alps/New Zealand, have been investigated using the electronic Schmidt-hammer (SilverSchmidt). Longitudinal profiles on both features reveal a consistent trend of decreasing R(Rebound)-values and, hence, increasing weathering intensity and surface-exposure age on their numerous transverse surface ridges from rooting zone towards the front. Previously published numerical ages obtained by terrestrial cosmogenic nuclide dating (TCND) allowed the calculation of a local Schmidt-hammer exposure-age dating (SHD) age-calibration curve by serving as the required fixed points. Age estimates for the lowermost rock glacier surface ridges fall within the early Holocene between 12 and 10.5 ka and indicate a fast disappearance of the Late Glacial glacier formerly occupying the valley head, followed by the initiation of rock glacier formation around or shortly after the onset of the Holocene. Although it cannot be judged whether the rock glaciers investigated were active within the entire Holocene or only repeatedly during multiple episodes within, their location and intact morphology exclude any substantial glacial activity at Irishman Stream during the Holocene. This has considerable regional palaeoclimatic implications because it opens for the hypothesis that climatic conditions during early Holocene were possibly comparatively dry and favourable for rock glacier initiation, but less so for glaciers. It would also challenge the view that air temperature is the sole major climate driver of glacier variability in the Southern Alps. More work utilising the palaeoclimatic potential of rock glaciers in the Southern Alps is advised.

The anatomy of long-term warming since 15 ka in New Zealand based on net glacier snowline rise

The timing and magnitude of postglacial climatic changes around the globe provide insights into the underlying drivers of natural climate change. Using geomorphologic mapping of moraines, 10 Be surface-exposure dating, snowline reconstructions, and numerical modeling, we quantified glacier behavior during Late Glacial (15–11.5 ka) and Holocene (the past ∼11.5 k.y.) time in the Ben Ohau Range, New Zealand. Glaciers were more extensive during the Antarctic Cold Reversal (ACR), than subsequently, and the margins underwent a punctuated net withdrawal over the Holocene. Numerical modeling experiments that achieve the best fit to the moraines suggest that air temperature during the ACR was between 1.8 °C and 2.6 °C cooler than today, with similar (±20%) prescribed precipitation. After the ACR, a net snowline rise of ∼100 m through the Younger Dryas stadial (12.9–11.7 ka) was succeeded by a further long-term, or net, rise of ∼100 m between ∼11 k.y. and ∼500 yr ago. Glacier snowline records in New Zealand show generally coherent Late Glacial and Holocene climate trends. However, the paleoclimate record in the southwest Pacific region shows important differences from that in the Northern Hemisphere.

Estimation of late-glacial temperatures based on coupled energy balance/ice flow modelling of paleoglaciers in the Ben Ohau Range, Southern Alps, New Zealand

Estimation of late-glacial temperatures based on coupled energy balance/ice flow modelling of paleoglaciers in the Ben Ohau Range, Southern Alps, New Zealand

Evaluation of Lateglacial temperatures in the Southern Alps of New Zealand based on glacier modelling at Irishman Stream, Ben Ohau Range

Climate proxy records from the middle to high latitude Southern Hemisphere indicate that a Lateglacial (15,000–11,500 years ago) climate reversal, approximately coeval with the Antarctic Cold Reversal (ACR), interrupted a warming trend during deglaciation. In New Zealand, some palaeoclimate proxy records indicate a cool episode during the ACR (ca 14,500–12,500 years ago), while others do not express a significant change in climate. Recently published moraine maps and ages present an opportunity to improve the palaeoclimate interpretation through numerical modelling of glaciers. We use a coupled energy-balance and ice-flow model to quantify palaeoclimate from past glacier extent constrained by mapped and dated moraines in the headwaters of Irishman Stream, a high-elevation catchment in the Southern Alps. First, a suite of steady-state model runs is used to identify the temperature and precipitation forcing required to fit the modelled glacier to well-dated Lateglacial moraine crests. Second, time-dependent glacier simulations forced by a nearby proxy temperature record derived from chironomids are used to assess the fit with the glacial geomorphic record. Steady-state experiments using an optimal parameter set demonstrate that the conditions under which the 13,000 year old moraine formed were 2.3–3.2 °C colder than present with the range in temperature corresponding to a ±20% variance in precipitation relative to the present-day. This reconstructed climate change relative to the present-day corresponds to an equilibrium-line altitude of ca 2000 ± 40 m above sea level (asl), which is ca 400 m lower than present. Time-dependent simulations of glacier length produce ice advance to within 100 m of the 13,000 year old terminal moraine, indicating that the chironomid-based temperature forcing and moraine record provide consistent information about past climate. Our results, together with other climate proxy reconstructions from pollen records and marine sediment cores, support the notion that temperatures during the ACR in New Zealand were ∼2–3 °C cooler than today.

Hypsometric analysis to identify spatially variable glacial erosion

[1] Relatively little research has been undertaken on the use of digital elevation models to recognize the spatially variable glacial imprint of a landscape. Using theoretical topographies and a landscape evolution model, we investigate to what extent the hypsometric analysis of digital elevation models may be used to recognize the glacial signature of mountain ranges. A new morphometric parameter, which we term the hypsokyrtome (from the Greek: ipsos = elevation, kyrtoma = curvature), is derived from the gradient of the hypsometric curve. The efficacy of the hypsometric integral and hypsokyrtome is tested through the study of the Ben Ohau Range, New Zealand, whose glacial imprint has been described previously. With a numerical model we further test the geomorphic parameters in describing the morphologies of regions subject to diverse climatic and tectonic conditions. The hypsokyrtome is highly sensitive to glacial erosion, and the maps produced provide insights into the spatial distribution of glacial erosion. We use SRTM data and focus on two alternative geomorphic settings: the European Alps and the Apennines. The former has been affected by both fluvial and glacial erosion while the latter mainly exhibits a fluvially dominated morphology. The correlation between elevations with increased glacial erosion and Last Glacial Maximum (LGM) equilibrium line altitudes (ELAs) suggests the prevalence of a “glacial buzz saw” in the Alps, indicating that climate may put a limit on alpine topography.

Cirque development in a steadily uplifting range: rates of erosion and long‐term morphometric change in alpine cirques in the Ben Ohau Range, New Zealand

AbstractThe intractable obstacle to understanding cirque evolution has been the lack of an independent timescale against which to measure morphometric change. By using known rates of transport and uplift of the Southern Alps, combined with the oxygen isotope record contained in marine sediments, it is possible to estimate the duration of glacial occupancy of cirques in the Ben Ohau Range. The pattern is one of very limited glaciation of the southern range, with glacial occupancy increasing northwards. Map‐based measurement of 18 morphometric properties in each of 92 cirques reveals systematic northward trends in cirque size, form and altitude, which are explained as reflections of increasing cirque ‘age’ (i.e. length of glacial occupancy). Thus, the validity of space–time substitution is demonstrated rather than assumed, and morphometric trends define evolutionary stages of cirque development. For cirques with up to c. 750 ka occupancy, rates of downcutting average 0·29 mma−1 and headwall retreat 0·44 mm a−1. There is no indication of attainment of an equilibrium form within this time: both cirque size and form continue to evolve throughout, with few parameters showing a convergence of value with cirque ‘age’. Some morphometric parameters perform much better than others: the k coefficient of the long‐profile descriptor is the most powerful predictor of cirque ‘age’, and simple measures correlate better than derived measures (e.g. ratios of dimensions). The trends identified concur with some previously published ideas, but for the first time provide empirically quantified rates of change at an appropriate timescale. Copyright © 2006 John Wiley & Sons, Ltd.

Hypsometry of glaciated landscapes

AbstractHypsometry (frequency distribution of elevations) is often used to characterize landscape morphology, traditionally in the context of the degree of fluvial dissection. Recently, the hypsometry of glaciated regions has been used to infer how rates of glacial erosion compare with tectonic uplift rates. However, many factors other than tectonics can also exert a major influence on the hypsometry of a glaciated landscape, resulting in a wide variety of hypsometries. Using examples from the eastern Sierra Nevada, California, the western Sangre de Cristo Range, Colorado, and the Ben Ohau Range, New Zealand, we demonstrate that, all else being equal, the hypsometries of neighbouring basins can indicate the relative degree of glacial modification in each. A selection of drainage basins from the Rocky Mountains shows that the position of the equilibrium line altitude (ELA) within the drainage basin relief is a dominant variable in determining the hypsometry of a glaciated basin. This is a non‐linear effect: once the ELA falls to some critical level, the glaciers scour deeply below the ELA, causing a noticeably different hypsometry. The hypsometry of an arbitrary region encompassing many drainage basins can disguise the variation present in the hypsometries, and thus landforms, of the individual basins. Unique local circumstances, such as the presence of a mountain icefield (Waiho Basin, Southern Alps), substantial hanging valleys (Avalanche Creek, Glacier National Park), a narrow outlet canyon (Sawmill Creek, Sierra Nevada), and isolated geologic structures (Baker Creek, Sierra Nevada), can have a major impact on the hypsometry of an individual basin. Copyright © 2004 John Wiley & Sons, Ltd.

The relationship between climate and rock glacier distribution in the ben ohau range, new zealand

Landforms of ice and debris transport marginal to the glacierized zone of the Southern Alps, New Zealand, have been classified into debris‐covered glaciers, cirque floor lobes, and talus‐derived rock glaciers. Mapping of fossil and active landforms reveals a zonation within the Ben Ohau Range in terms of both landform type and activity status. The dominant distinction of active forms is between relatively ice‐rich forms (glacial origins) in the humid north and relatively debris‐rich forms (periglacial origins) in the more arid south. A secondary altitudinal zonation distinguishes currently or recently active forms at high elevations from fossil forms at lower elevations. Estimates of mean annual precipitation and of the altitude of the –2°C mean annual isotherm indicate that glaciers and active talus rock glaciers are located within the climatic boundaries identified for the European Alps. However, many fossil forms also occur within these boundaries where cirques are broader and shallower. These findings confirm earlier suggestions that permafrost occurs in the Southern Alps, but is restricted to a narrow zone above 2000 m. The study demonstrates the importance of relative ice‐to‐debris fluxes in determining the developmental pathways of landform genesis over both space and time.

The Role of Fluvial and Glacial Erosion in Landscape Evolution: The Ben Ohau Range, New Zealand

A morphometric comparison of valleys has been made for the Ben Ohau Range in the central Southern Alps of New Zealand. The range is undergoing rapid tectonic transport and uplift. The humid north of the range is a glacial trough-and-arête landscape, with a temperate glacial climate. The dry south has rounded divides and plateau remnants dissected by fluvial valleys. Assuming that space–time substitution allows today's spatial valley-form transition to represent evolutionary stages in valley development, the tectonic history allows time constraints to be placed on the rate of transition to an alpine glacial landscape. Morphometric change has been quantified using hypsometric curves, and distance–elevation plots of cirque and valley-floor altitudes. Ancestral fluvial valleys have less concave long profiles but are stepped at altitude owing to the presence of high-level cirques and remnant plateau surfaces, and possess a low proportion of land area at low elevation. Increasing glacial influence is manifest as smoother, more deeply concave long profiles and U-shaped cross-profiles associated with a higher proportion of the land area at lower elevation. The full morphological transition has involved up to 2.4 km of vertical denudation over the 4 Ma lifetime of the mountain range, of which 80 per cent would have occurred by preglacial fluvial erosion. Combining the trajectory of tectonic transport with reconstructed glaciation limits and climatic history, it is indicated that about 200 ka of temperate glacial erosion produces recognizable trough-and areête topography. Mean and modal relief increase where glacial activity is confined to cirques, but decrease when trough incision by ice becomes established as a dominant process in the landscape. © 1997 by John Wiley & Sons, Ltd.

Tectonic hydrothermal gold mineralisation in the outboard zone of the Southern Alps, New Zealand

Abstract Gold‐bearing veins cut a belt of low‐grade (pumpellyite‐actinolite/greenschist facies) schist in the Ben Ohau Range to the east of the Main Divide, in the outboard zone of the Southern Alps continental collisional zone, New Zealand. The schist has been exposed along the currently active Ostler Fault system, which has had c. 5 km of reverse motion since the Pliocene. The veins consist of quartz, ankerite, calcite, chlorite, and pyrite, with minor chalcopyrite and galena. Hydrothermal chlorite contains about 490 ppm Zn, and the gold contains 3–5 wt% Ag. Hydrothermal alteration of host rock is minor apart from Sr enrichment (up to four times background). Fluid inclusions in quartz are aqueous with minor dissolved CO2 and salts (<4 wt% NaCl equivalent), and homogenise at 236–270°C. The veins formed at 300 ± 20°C and 1000 ± 800 bars fluid pressure, probably under a hydrostatic fluid pressure regime. Oxygen and carbon isotopic data (δ18O = +10 to +14; δ13C = ‐6 to ‐10‰) are similar to data from economic metamorphogenic Au deposits of the nearby Otago Schist, but minor meteoric incursion may have occurred. Isotopic data are also similar to veins formed in the inboard zone of the Southern Alps orogen. The Ben Ohau veins demonstrate that gold can be concentrated in low‐grade schists distant from the most active part of the hydrothermal system driven by continental collision.

On the sensitivity of Holocene talus‐derived rock glaciers to climate change in the Ben Ohau Range, New Zealand

AbstractThe morphology and surface ages of talus‐derived rock glaciers are investigated to establish the timing of rock glacier formation in the central Southern Alps. Samples of rock weathering rinds show that all rock glaciers studied were formed during the Neoglacial period, but differences exist between sites in the number of new rock glacier lobes formed by Holocene climatic fluctuations. A qualitative conceptual model is proposed to explain rock glacier formation in terms of two thresholds. An external threshold relates to the presence of a cool climate capable of allowing internal ice to form within talus slopes. An internal threshold relates to the presence of sufficiently thick talus at a site to generate a shear stress capable of overcoming internal friction within the talus/ice mass. The model produces a non‐steady‐state response to explain why unmodified talus, single‐lobed and double‐lobed rock glaciers developed at adjacent sites under the same climatic regime. Individual landforms have different sensitivities to formation, which depend partly on the previous history of talus accumulation and rock glacier activity at a site. The model demonstrates how successive cool climate periods may be fully represented by rock glacier lobes at sensitive sites but under‐represented at insensitive sites. Sensitivity (and therefore climatic representativeness) is favoured by high rates of debris supply. By implication, the timing of formation of rock glacier lobes in regions of prolonged cool climate and low debris production is less likely to correspond to the timing of climatic cooling and more likely to follow the ‘rules’ of deterministic chaos.

Holocene soil chronofunctions, Southern Alps, New Zealand

Field and laboratory data for two soil chronosequences from the high country of the South Island of New Zealand suggest rapid soil formation rates. The areas studied are the Ben Ohau Range and the Mt. Cook area, where mean annual precipitation is about 1 and 4 m, respectively. Most soil ages are estimated from the thicknesses of rock weathering rinds. Soil chronofunctions are derived for indices that depict field profile and color development, and a modified index of profile anisotropy for laboratory data. Out of a possible 21 chronofunctions, 16 are statistically significant (at the 0.05 level) and 8 are from each area. Most (13) of the chronofunctions best fit a power model, and the remaining ones are split between linear (2) and exponential (1) models. Although problems exist in the purity of the chronosequences because other soil-forming factors are not constant, duration of pedogenesis seems to be the most significant factor in explaining the trends. Despite the large differences in mean annual precipitation between the two areas, many of the derived curves for property vs. time are quite similar.

Subdivision of Holocene glacial deposits, Ben Ohau Range, New Zealand, using relative-dating methods

Relative-dating methods measure post-depositional alteration of surficial deposits. Measured in this study are the size of the yellow-green Rhizocarpon lichen, percent lichen cover, weathering-rind thickness, quartz-vein height, surface oxidation, and pitting of clasts. The data are used to subdivide Holocene deposits in the Ben Ohau Range and to suggest correlation with moraines in other parts of the Southern Alps. Glacial and/or rock-glacier deposits of five different ages are identified in the Ben Ohau Range. Ages can be approximated mainly from the rind-development curve of Chinn (1981). From youngest to oldest the deposits are: Dun Fiunary (∼ 100 yr); Whale Stream (∼ 250 yr); Jacks Stream (∼ 3,000 yr); Ferintosh (∼ 4,000 yr); and Birch Hill (∼ 9,000 yr). All but the Whale Stream have been previously named, but data presented here result in improved definitions of mapping units and more accurate age assignment. The present climate of the Ben Ohau Range is increasingly continental to the south. A similar climatic gradient existed for much of the post-Birch Hill Holocene, as shown by the glacial depositional facies: moraines are common to the north, whereas rock glaciers, especially of Jacks Stream and Ferintosh ages, are common to the south. In some areas, rock glaciers that have long been inactive have recently been reactivated. Data from moraines in the Waimakariri Drainage and the Mount Cook, Cameron Valley, and Rakaia River areas improve previous correlations, as relative-dating methods provide age information where 14C ages are either lacking or limiting, or when a single relative-dating method is subject to erroneous interpretation.

Plant succession in relation to periodic soil movements in the subalpine zone of the NE Ben Ohau Range, New Zealand

Abstract Three high country yellow-brown earths (eldefulvic soils) influenced by periodic erosion and deposition were studied in the Twin Stream Catchment, north-east Ben Ohau Range. Six different-aged surfaces were recognised and designated as K0 (youngest surface), KI, K2, K3, K4, and K5 which is the oldest buried surface (after Butler's 1959 nomenclature). Successive cycles of erosion and deposition had buried soils which were recognised by charcoals. 14C dating from a buried soil on the K4 surface was 1115 ±80 yr B.P. Base saturations and phosphorus fractions indicated that the soil on the K1 surface was a less leached soil than the soils on the K2 and K3 surfaces. Plant succession showed a dominant community of Trifolium repens growing on the more recent soils (K1 surface) with sprub communities dominating the older surface (K3).

Geology of the Torlesse supergroup in the northern Ben Ohau Range, Canterbury

Geology of the Torlesse supergroup in the northern Ben Ohau Range, Canterbury

Geology of the Torlesse Supergroup in the northern Ben Ohau Range, Canterbury

Abstract Torlesse rocks in the northern Ben Ohau Range form steeply plunging north-facing structures with steep axial planes trending mostly NNE and NE. In a central belt of the range textural zone 2 (and some zone 3) schists have been developed, probably after the folding, by a mechanism including flattening across the schistosity plane. Fold axes have variable attitudes and plunge north in the non-schistose rocks. In the schists the axes are more strongly aligned and plunge south to give overturned structures and well developed lineations. Decollements with dextral vergence com plicate the pattern of the main structure, the Bush Stream anticline, which is exposed along the crest of the range; they also affect the Whale Stream syncline to the east. Local south-facing folds in the non-schistose rocks of the eastern foothills may indicate earlier stages of structural development. Movement along the Great Groove Fault on the eastern edge of the schist has been complex, possibly changing from a system with a...

Plant Succession in Relation to a Sequence of Hydromorphic Soils Formed on Glacio-fluvial Sediments in the Alpine Zone of the Ben Ohau Range, New Zealand

Five plant communities arc described in relation to plant succession on a hydromorphic sequence of soils formed on recent moraine and glacio-fluvial outwash. The communities progressed from pioneer colonisation, dominated by bryophytcs and Celmisia hectori, to a closed community dominated by Chlonochloa orcophila. Plant succession was marked by a gradual reduction of both calcium and magnesium, and pi I, and an increase in organic carbon. There was a decrease in calcium bound phosphorus, and an increase in both aluminium and iron surface bound phosphorus associated with gleyed soils, and a gradual increase of organic phosphorus. The hydromorphic soils were characterised by periodicity in the form of sedimentation and organic cycles.

Holocene Moraines and Rock Glaciers in the Central Ben Ohau Range, South Canterbury, New Zealand

Young moraines and rock glaciers in the central part of the Ben Ohau Range, about 42 km. south of the highest peaks of the Southern Alps, are briefly described. A new formation, the Ben Ohau Formation, consisting of the Ferintosh, Jacks Stream and Dun Fiunary Members, is proposed for moraines and rock glaciers believed to have been built since the climatic optimum by three minor glacial advances. Moraines, and outwash and fan gravels, deposited during a more extensive pre-climatic optimum advance which was contemporaneous with the Cockburn Glacial Phase (Cochrane) in North America are assigned to the Birch Hill Formation. The sequence of glacial advances recorded in the Ben Ohau Range is compared with that found in western North America.

Holocene Moraines and Rock Glaciers in the Central Ben Ohau Range, South Canterbury, New Zealand

Young moraines and rock glaciers in the central part of the Ben Ohau Range, about 42 km. south of the highest peaks of the Southern Alps, are briefly described. A new formation, the Ben Ohau Formation, consisting of the Ferintosh, Jacks Stream and Dun Fiunary Members, is proposed for moraines and rock glaciers believed to have been built since the climatic optimum by three minor glacial advances. Moraines, and outwash and fan gravels, deposited during a more extensive pre-climatic optimum advance which was contemporaneous with the Cockburn Glacial Phase (Cochrane) in North America are assigned to the Birch Hill Formation. The sequence of glacial advances recorded in the Ben Ohau Range is compared with that found in western North America.