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1 New Zealand Journal of Geology and Geophysics ISSN: (Print) (Online) Journal homepage: The Schmidt hammer as a relative age dating technique: Potential and limitations of its application on Holocene moraines in Mt Cook National Park, Southern Alps, New Zealand Stefan Winkler To cite this article: Stefan Winkler (2005) The Schmidt hammer as a relative age dating technique: Potential and limitations of its application on Holocene moraines in Mt Cook National Park, Southern Alps, New Zealand, New Zealand Journal of Geology and Geophysics, 48:1, , DOI: / To link to this article: Published online: 22 Sep Submit your article to this journal Article views: 911 View related articles Citing articles: 32 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 10 December 2017, At: 09:37

2 105 New Zealand Journal of Geology & Geophysics, 2005, Vol. 48: /05/ The Royal Society of New Zealand 2005 The Schmidt hammer as a relative-age dating technique: potential and limitations of its application on Holocene moraines in Mt Cook National Park, Southern Alps, New Zealand STEFAN WINKLER Geographisches Institut Universität Würzburg Am Hubland D Würzburg, Germany stefan_w_winkler@yahoo.no Abstract The use of the Schmidt hammer for the relativeage dating of boulder and bedrock surfaces is outlined. Two examples of the application of the Schmidt hammer for the dating of Holocene moraines in Mt Cook National Park, Southern Alps, New Zealand, confirm the potential of this method. With this technique it is possible to differentiate between Holocene moraines of different age (especially those built up since c yr BP). The results show partial differences to those obtained from other dating techniques in previous work. Keywords Schmidt hammer; relative-age dating; Holocene; glacier variations; Southern Alps; New Zealand INTRODUCTION As the behaviour of glaciers depends directly on changes of their mass balance caused by climate change, it is necessary to reconstruct former glacier variations before forecasts of the impact of future climate change can be made. Therefore, the potential of glaciers as indicators of past and present climate change can only be utilised if the Holocene glacier chronology is known in as much detail as possible and with a high spatial and temporal resolution. The Schmidt hammer is a relative-age dating technique that can be used for dating glacial landforms and deposits (Matthews & Shakesby 1984; McCarroll 1991a). Relativeage dating techniques are mainly used when absolute-age dating methods, for example radiocarbon dating, either are unavailable or have ambiguous interpretation. For instance, radiocarbon dating of organic material can only be used when the sites have been directly linked to a distinct glacier front position. Apart from general uncertainties on the interpretation of radiocarbon dating (cf. Matthews 1984), there is rising doubt about whether the detailed chronology of glacier variations derived from radiocarbon dating of buried soils and plant remains at the Tasman Glacier (cf. Burrows 1980; Burrows &Gellatly 1982; Röthlisberger 1986; Gellatly G03030; Online publication date 23 March 2005 Received 9 September 2003; accepted 1 March 2004 et al. 1988) is representative for the glacial history of the Holocene in the Southern Alps (Kirkbride & Brazier 1998; Winkler2001). In this paper, the Schmidt hammer as a method for the relative-age dating of boulder or bedrock surfaces, and its application during field measurement, will be presented. The Schmidt hammer can be used as part of a "multiproxy approach" with lichenometry and (if possible) radiocarbon dating of associated deposits (Winkler et al. 2003). Lichenometry has the potential to date moraines with a precision of up to 5-10 yr, but cannot be used for dates extending further back than c. 500 yr (Innes 1985; Matthews 1994). By contrast, Schmidt hammer measurements can be applied to moraines formed during the whole Holocene, or even Late Glacial. However, time resolution is less precise. The potential of the Schmidt hammer and its limitations will be shown by dating Holocene moraines in Mt Cook National Park in the Southern Alps of New Zealand, and by comparing these dates with those from previous studies using different methods. METHODOLOGY Schmidt hammer characteristics The Schmidt hammer (official name: "Beton-Prüfhammer Original Schmidt") was developed for the simple mechanical in situ test of the hardness of concrete. Subsequently, the Schmidt hammer has been a successful relative-age dating technique and widely used on glacially eroded bedrock surfaces, boulders embedded in glacial deposits, or talus (Day & Goudie 1977; Day 1980; Matthews & Shakesby 1984; McCarroll 1987,1989a,b, 1991a,b,c;Nesjeetal. 1994; Winkler & Shakesby 1995; Evans et al. 1999; Winkler 2000a). Along with methods of measuring weathering-rind thickness (Chinn 1981), the measurement of surface hardness of rock surfaces using the Schmidt hammer reveals information on the duration of their exposure to atmospheric weathering processes. When the Schmidt hammer is pressed on a rock surface, a spring-suspension driven pin bounces with a calibrated energy (Type N model) of N m on the surface. A rebound-value (r-value), determined by the hardness and compressional strength of the rock surface tested, is obtained (for technical details, see Proceq 1977). Used as a relativeage dating technique, no further treatment of the original r-values is necessary. However, the instrument has to be checked regularly to ensure it is still calibrated correctly. The instrument itself, with its weight of c. 1 kg and its compact size, is easy to carry and quite robust. Field measurements Potential sources of error of the Schmidt hammer are mainly caused by factors other than the time of exposure affecting

3 106 New Zealand Journal of Geology and Geophysics, 2005, Vol. 48 Stocfelngf.il.ii. :' Fig. 1 Map of the study area in Mt Cook National Park. The locations of the study areas on the Hooker and Mueller Glaciers (Fig. 2 and 3) are outlined.

4 WinkleræSchmidt hammer dating, Mt Cook 107 Fig. 2 Morphological sketch map of the foreland of Mueller Glacier. Rivers and lakes are drawn in dark grey, the valley sides in light grey. PB» marked! scaup the degree of surface weathering and rock surface hardness (Winkler 2000a). Ideally, only the same rock types should be tested because different original surface hardness and weathering resistance will affect the Schmidt hammer measurements (McCarroll 1987). In this study, all tests were restricted to the massive sandstone of the Torlesse Group (Spörli & Lillie 1974; MacKinnon 1983). The instrument should be applied vertical, or almost vertical, in order to produce consistent r-value readings (Proceq 1977; Day 1980). The rock surfaces being tested should be smooth, as high surface roughness causes lower r-values (Williams & Robinson 1983). Lichen- or moss-covered surfaces must be avoided, as well as the edges of boulders, joints, or cracks (McCarroll 1989a,b). If boulders embedded in a fine matrix (e.g., boulders in till) are tested, no displacement or movement of the boulder should take place during the test procedure (Winkler & Shakesby 1995). Different recommendations for the number of boulders necessary at each test site, as well as the number of bounces per boulder for optimal measurement, are given in the literature (Matthews & Shakesby 1984; McCarroll 1987). In this study, the sample size (n) was 50 with one bounce on each boulder. By using a large number of boulders for testing, petrographic inhomogeneities, microclimate variations, and other possible factors influencing the weathering rate on rock surfaces exposed at the same time are minimised. Sample sites on moraine ridges should always be kept small, and if possible, several test sites should be marked out on the same moraines. Results and interpretation The r-values obtained from a single sample site can easily be presented using a histogram. For a site where boulders or bedrock have the same exposure time, one would expect a gaussian normal distribution of the r-values. However, in some circumstances there may be skewed and/or bimodal distributions. The latter may occur if previously weathered boulders have been incorporated into the moraine during its formation (McCarroll 1989b).

5 108 New Zealand Journal of Geology and Geophysics, 2005, Vol. 48 Table 1 Dating of M "c" at Mueller Glacier (southeastern foreland). Author(s) Date for M "c" Method Lawrence & Lawrence (1965) Burrows (1973) Gellatly (1984) Winkler (this study) before AD 1754/ AD ± 387 yrbp 1830 ± 476 yrbp 2940 ± 765 yr BP c (2350?) yr BP dendrochronology lichenometry 2 weathering rinds 3 Schmidt hammer 1 Minimum age only. 2 Uses Lawrence and Lawrence's dates as fixed points. 3 Following the method of Chinn (1981). Table 2 Selected results of Schmidt hammer tests on M "c" at Mueller Glacier. Sample site Location (southeastern foreland Mueller Glacier) r-values: mean and SEM 1 Median 0 Skewness Kurtosis M "c" single ridged part 2 M"c ' outer ledge 3 M"c" outer ledge M"c" outer ledge M"c" outer ledge M"c" outer ledge M1 M2 M2 M2 M3 M3 M4 M ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± Standard error of mean at 95% confidence (a = 0.05) (cf. Swan & Sandilands 1995). 2 Single ridged part of M "c" close to White Horse Hill (see Fig. 2). 3 In sections with more than two individual ridges/ledges (see Fig. 2), "outer ledge" stands for the outermost ledge ("inner ledge" for the innermost) Table 3 Selected Kruskal-Wallis H-tests at Mueller Glacier. Sample sites H 1 H2 Interpretation M"c" H< c ² at a = 0.8 (20% confidence) M"c" 4 andm H > c ² at a = 0.01 (99% confidence) 1 Result of Kruskal-Wallis H-test (cf. Swan & Sandilands 1995). 2 Adjusted H due to frequent occurrence of tied ranks (following Schönwiese 1992). 3 Degrees of freedom (φ = k- 1). 4 Representative sample sites only.

6 WinkleræSchmidt hammer dating, Mt Cook 109 When comparing different test sites, a statistical mean and/or the median is usually calculated using all individual r- values for the whole sample site. To be able to judge the quality of the results and identify possible methodological errors or petrological inhomogeneities, these data are accompanied by additional statistical information, usually the standard error of the mean (SEM) at 95% confidence (a = 0.05) (Matthews & Shakesby 1984; McCarroll 1989a,b; Winkler 2000a). Further statistical treatment (e.g., Kruskal-Wallis H-test) is possible, and sometimes necessary (see below). A few centuries (c. 300 yr) is commonly stated as the maximum time resolution for relative-age dating using the Schmidt hammer (Matthews & Shakesby 1984; McCarroll 1987), although Evans et al. (1999) mention an accuracy of just ±100 yr in Iceland. However, Schmidt hammer measurements cannot be used for an age differentiation of moraines formed during single advance periods (e.g., the Little Ice Age). On the other hand, the entire Holocene can be covered by this method and single advance periods clearly detected (Matthews & Shakesby 1984; McCarroll 1989a,b; Winkler & Shakesby 1995; Winkler 2000a). An age-prediction curve for Schmidt hammer measurements can be constructed where talus or moraine ages are also available from radiocarbon dates (Nesje et al. 1994; Evans et al. 1999; Aa&Sjåstad2000). EXAMPLES OF APPLICATION Pre-Little Ice Age moraine at Mueller Glacier Mueller Glacier, located east of the Main Divide of the Southern Alps close to Mt Cook, is a 13.9 km long valley glacier of 22.5 km 2 in total area (Chinn 1996) (Fig. 1, 2). Thirty-seven percent of the entire glacier surface is covered with supraglacial debris (Chinn 1996), making the position of the glacier front difficult to detect accurately. An expanding proglacial lake, which is continuously enlarging, has formed at the glacier snout during recent years. The inner parts of the Mueller Glacier foreland are dominated by huge lateral moraines ("alpine type" lateral moraines following the classification of Winkler & Hagedorn 1999). There is a fine sequence of latero-frontal moraines present on the glacier foreland (Fig. 2). The inner moraines of this moraine sequence (M 1-5) have already been recognised as of Little Ice Age origin, although there are differences between earlier attempts to date those moraines (Lawrence & Lawrence 1965; Burrows & Lucas 1967; Burrows & Orwin 1971; Burrows 1973; Gellatly 1982,1984,1985). The oldest of the inner Little Ice Age moraines has been dated using lichenometry to c. AD (Winkler 2000a, 2004). In the southeastern foreland there are three moraines outside the Little Ice Age sequence (see Fig. 2). Foliage Hill (named M "a" here) and the complex lateral moraine system of White Horse Hill (M "b") predate the Little Ice Age (White Horse Hill at least in its older parts; cf. Gellatly 1982,1984). The inner and smallest of those older moraines (M "c"), is morphologically different to M "a" and M "b", and is not as obviously of pre-little Ice Age origin. Burrows & Orwin (1971) and Burrows (1973) dated this moraine to AD 1750, but this age is likely to be too young (see Winkler 2000a,b for full discussion). Gellatly (1982, 1984) interpreted this moraine as a multi-ridge moraine complex built up during at least three individual glacier advances between 1490 ± 387 and 2940 ± 764 yr BP (cf. Table 1). Winkler carried out extensive Schmidt hammer testing on M "c". Apart from the several metres high moraine flanks that had to be excluded from testing because of a dense vegetation cover, the entire blocky moraine was tested. Separate measurements were made both on the inner and the outer ridges (ledges) of this complex moraine. The Schmidt hammer testing was done for two purposes: firstly, to confirm the assumed pre-little Ice Age origin of this moraine; and secondly, to ascertain whether there is a measurable age difference between the inner and the outer parts of this moraine. If there is an age difference of up to 1450 yr, as Gellatly (1982,1984) suggested, one would expect a statistically significant difference between the individual ridges of M "c". Results The results show that M "c" can be identified as a pre-little Ice Age moraine. All measurements show significantly lower means than those measured on the inner, Little Ice Age moraines (Table 2). A Kruskal-Wallis H-test reveals that M "c" and the oldest Little Ice Age moraine (M1) show a statistical significant difference in r-values and, therefore, in age (Table 3). In addition, Gellatly's (1982, 1984) interpretation of M "c" as a multi-ridge moraine complex with a considerable age difference seems unlikely. There was no statistical significant difference between the individual ridges tested on M "c" (Table 3). The Schmidt hammer readings gave low standard errors (a sign of successful application; cf. McCarroll 1991b; Winkler 2000a). Contrary to Gellatly (1982, 1984), there was not even a detectable trend of lower Schmidt hammer readings on the outer and supposed older individual ridges (Tables 2,3). The variation of means is similar to the results on the Little Ice Age sequence (Table 2). As it seems realistic, in view of the morphology of M "c" compared to M "a" and M "b" (and the Little Ice Age moraines), that the individual ridges were formed during minor oscillations, M "c" should be interpreted as having been built up during one advance period of (max.) yr duration. Complex lateral moraine at Hooker Glacier Hooker Glacier is a 12.3 km long valley glacier of c km 2 in area (Chinn 1996) and is located in Hooker Valley at the foot of Mt Cook (Fig. 1,3). The snout of the Hooker Glacier (which has 25.1 % of its surface covered in debris) is actively calving into a c km 2 proglacial lake that has been enlarging since the late 1980s (Warren & Kirkbride 1998). As a result of a series of years with positive net balance, the retreat of Hooker Glacier has recently slowed down and ceased (Chinn pers. comm.; pers. obs.). Several moraine ridges of different height and morphology can be found on the glacier foreland of Hooker Glacier (Fig. 3). The most impressive is a complex lateral moraine system in the eastern foreland that is composed of up to seven detectable individual ridges (the inner three of Little Ice Age origin, named LM 1-3 here, and four outer ridges, named LM "a"-"d": see Fig. 3). It has been classified as an "alpine type" lateral moraine (sensu Winkler & Hagedorn 1999) that has been built up by "accretion" (following Röthlisberger & Schneebeli 1979). The outer individual ridges ascend from the shore of the proglacial lake up to 150 m above the lake level, and are partly covered by wide talus cones (Fig. 3).

7 110 New Zealand Journal of Geology and Geophysics, 2005, Vol. 48 Fig. 3 Morphological sketch map of the foreland of Hooker Glacier. Dimension and stepwise lower boundaries of those talus cones give morphological evidence that this complex lateral moraine system was built up over successive advances. Burrows (1973) dated the individual ridges of the complex eastern lateral moraine (apart from the outermost ridge) by using lichenometry. His estimated date of AD 1275 for LM "b" suggests a pre-little Ice Age origin for the outer ridges. However, Winkler (2000a, 2004) found that Burrows overestimated lichen growth at Mueller Glacier, and that lichen growth also seems to be slightly slower at the Hooker Glacier. Gellatly (1984) dated LM "a" (the outermost moraine ridge) to 3350 ± 870 yr BP using weathering-rind thickness data (and LM "d" to 1830 ± 476 yr BP). Burrows (1973) dated LM "d" to 16th/17th century AD, showing analagous differences in dating as at the Mueller Glacier. The inner ridges (LM 1-3) have been recognised as of Little Ice Age origin by using lichenometry (LM 1: c. AD 1740; Winkler 2001, 2004). Winkler carried out Schmidt hammer readings on all of the individual ridges. Results The results show that LM "a"-"d" are of pre-little Ice Age origin (Fig. 4, Table 4). A Kruskal-Wallis H-Test reveals that LM "d" and LM 1 show a statistical significant difference in age at a = (99.9% confidence, Table 5). In addition, the Little Ice Age origin of LM 1-3 has been confirmed by statistical significance testing. Although the interpretation is limited by some methodological problems which occurred during testing of the outer ridges (e.g., the possible existence

8 WinkleræSchmidt hammer dating, Mt Cook 111 Fig. 4 Results of Schmidt hammer measurements on different ridges of the eastern lateral moraine complex at Hooker Glacier. Results are given as means with 95% confidence intervals. Hooker Glacier: eastern lateral moraine LM1 LM2 LM3 e o B B p a B B B Sample sites of boulders deposited by rockfall), these outer ridges seem to be formed during at least two individual advance periods. The difference in means between LM "a" and LM "d" are high (Table 4). Statistical testing reveals a significant age difference at a = 0.05 (95% confidence, Table 5). On the other hand, Kruskal-Wallis H-tests and standard errors open for a grouping of LM "a"/lm "b" and LM "c"/lm "d", respectively (Tables 4, 5). The outer ridges could possibly form two pairs of ridges, each representing one advance period (of c yr). This view is supported by observations during fieldwork (morphology, patterns of vegetation, degree of cover by talus). However, restricted testing means that more than two older advances for the outer ridges cannot completely be ruled out. Table 4 DISCUSSION This application of the Schmidt hammer in the Southern Alps of New Zealand can be regarded as successful. Standard errors were usually lower than those experienced in other regions such as Norway (cf. Matthews & Shakesby 1984; McCarroll 1989a; Winkler 2000a) or the Austrian Alps (Winkler & Shakesby 1995). This implies, supported by statistical testing (see above), that the maximum resolution of the Schmidt hammer (i.e., c yr) can be achieved here. The bouldery character of most of the moraines meant that there were usually sufficient boulders to keep test sites small. It was possible to reproduce the results over successive field seasons. However, on some steep lateral moraines, the higher number Selected results of Schmidt hammer tests on the eastern lateral moraine system at Hooker Glacier. Sample Location (eastern lateral sites moraine Hooker Glacier) r-values: mean and SE Median Skewness Kurtosis LM "a LM "a LM "a LM b LM b LM "c LM "c LM "d ± ± ± ± ± ± ± ± LM1 LM1 LM2 LM2 LM2 LM2 LM3 LM3 LM ± ± ± ± ± ± ± ± ± Table 5 Selected Kruskal-Wallis H-tests at Hooker Glacier. Sample sites H H* φ Interpretation LM "a" and LM "b" LM "a" and LM "c" LM "a" and LM "d" LM "b" and LM "c" LM "b" and LM "d" LM "c" and LM "d" LM "d" and LM H < c ² at a = 0.65 (35% confidence) H > c ² at a = 0.15 (85% confidence) H > c ² at a = 0.05 (95% confidence) H > c ² at a = 0.1 (90% confidence) H > c ² at a = 0.05 (95% confidence) H < c ² at a = 0.55 (45% confidence) H > c ² at a = (99.9% confidence)

9 112 New Zealand Journal of Geology and Geophysics, 2005, Vol. 48 of loose boulders that had to be rejected for testing resulted in somewhat larger test sites. Boulders that were not consolidated could have experienced post-depositional movement. As the principles of dating rock surfaces by their degree of atmospheric weathering are basically the same, Schmidt hammer measurements can initially be compared with the results from relative-age dating by measurements of weathering-rind thickness (Gellatly 1984) (Table 6). However, these show major differences with the dating and interpretation of M "c" at Mueller Glacier. One possible explanation could be a higher precision/resolution of the weathering-rind method. However, the results and their statistical testing presented here for M "c" and the comparison with the Little Ice Age moraines make it unlikely that an age difference of c yr given by Gellatly (1982,1984) should not be found in the Schmidt hammer data that even show minor signs of age differences among the Little Ice Age moraines (i.e., a period of c yr). Fundamental criticism of Gellatly's (1982,1984) application of the weathering-rind technique is stated by McCarroll (1991c), especially of the dating curve used for the weathering-rind thickness. McCarroll (1991c) suggests that the time intervals (and resolution) given arise from coincidence and are not statistically consolidated. Schmidt hammer measurements cannot give a precise absolute dating of the moraines tested. They show primarily age differences that allow a grouping of the moraines (see Fig. 4,5,6). A dating curve based on the relationship between r-values and confirmed moraine ages is needed for any more detailed age estimation. Apart from general problems involved in the construction of such a dating curve (Fig. 7), Table 6 regional problems arise in finding suitable calibration points (apart from the Little Ice Age moraines). Birkeland (1982) dated M "a" at Mueller Glacier (Foliage Hill) to yr BP (using weathering-rind thickness and soil development). Gellatly (1984) dated the same moraine to 7200 ± 1870 yr BP. Both datings are correlations, and no absolute dating (e.g., radiocarbon dating) is actually available for this moraine. One possibility for calibration points are the Birch Hill moraines at Lake Pukaki formed during the Late Glacial deglaciation (McGregor 1967; Chinn & Coates 1993; Denton & Hendy 1994; Ivy-Ochs et al. 1999). However, Porter (1975) reported a debris flow covering the Birch Hill moraine at its key locality c yr BP. Schmidt hammer measurements carried out at this location show considerable differences in means between the Birch Hill sample sites (Table 7). Significant age differences have been confirmed by a Kruskal- Wallis H-test at a = (99.9% confidence). The possibility of the Birch Hill data representing two different ages (date of moraine formation c yr BP and the debris flow) has been taken into account with the construction of the dating curve. Comparisons between absolute chronologies from this region (e.g., Röthlisberger 1986; Gellatly et al. 1988) with the Schmidt hammer data and its age estimation presented here (Table 8), show that a date of c yr BP, as given by Porter (2000) for the onset of Neoglaciation in the Southern Alps, can be supported by the Schmidt hammer readings for M "a" at Mueller Glacier (Foliage Hill) if the younger age (5200 yr BP using linear function 2; cf. Fig. 7) is taken. This would imply that M "b" (White Horse Hill) is in its oldest parts c yr Comparison between r-values and weathering-rind dating (Gellatly 1984) at Mueller Glacier. Location 1 Age (after Gellatly 1984) M5 M1 M "c" M "b" M "a" <100yrBP 580±150yrBP 1490 ± 387 yrbp ± 765 yr BP ±870 yrbp 7200 ± 1870yrBP 1 See Fig Age difference between innermost and outermost ridge. 3 Representative sample site (cf. Tables 2, 7). r-values: mean and SE Sample sites ± ± ± ± ± Table 7 Selected results of Schmidt hammer tests at the Birch Hill moraines (Lake Pukaki) and M "a" (Foliage Hill) and "b" (White Horse Hill) at Mueller Glacier. Sample sites Location r-values: mean and SE Median 0 Skewness Kurtosis Birch Hill Birch Hill Birch Hill ± ± ± M "a" M "a" M "a" ± ± ± M 'V 1 M "b" ± ± Outermost part of the complex White Horse Hill.

10 WinkleræSchmidt hammer dating, Mt Cook 113 Fig. 5 Results of Schmidt hammer measurements on different 65 moraines in the foreland of Mueller Glacier and on the Birch Hill ro moraines at Lake Pukaki. 55 Mueller Glacier: southeastern foreland Sample sites 70 Hooker Glacier - Mueller Glacier Hooker Glacier: eastern foreland LM 2 LM 3 Hooker Gl.: western and southern foreland Mueller Gl.: northeastern foreland Mueller Gl.: southeastern foreland Sample sites Fig. 6 Comparison of Schmidt hammer measurements on different moraines in the forelands of Hooker Glacier and Mueller Glacier with possible correlations. Fig. 7 Age estimation for the pre- Little Ice Age moraines at Mueller Glacier taking (1) the weathering rate as a linear function, (2) the Little Ice Age moraines at Mueller Glacier and the Birch Hill moraines at Lake Pukaki as calibration points, and (3) the petrology of both sites as comparable. The disturbance of the Birch Hill moraines by a landslide is taken into account and measurements were therefore separated (cf. text). Arrows indicate the dating of M "a", "b", and "c" using all calibration points (linear function 1: y = x ; r 2 = 0.963). The range of age estimation is given by two different functions, one (linear function 2: y = x ; r 2 = 0.989) with all older Birch Hill sites excluded and the other (linear function 3: y = x ; r 2 = 0.991) with all younger Birch Hill sites excluded. Age estimation I datings with linear function 1 j V V Age (yr BP)

11 114 New Zealand Journal of Geology and Geophysics, 2005, Vol. 48 old and, if judged by its complex morphology, possibly formed during more than one advance (if not by a non-climatic event like a gigantic rockfall on the glacier surface). In addition, M "c" would have been formed c yr ago. However, if all calibration points of Birch Hill are taken into account, Foliage Hill and White Horse Hill turn out to be considerably older (M "a" c yr BP; M "b" c yr BP; M "c" c yr BP). Due to the age differences within the Birch Hill data (see above), the younger age estimations (i.e., linear function 2), seem more likely. At least four major Neoglacial advances (including the Little Ice Age) can be detected at the Mueller and Hooker Glaciers on the basis of morphological evidence in form of moraines. Even if there is the possibility of one or two more advances (represented in the Hooker lateral moraine; see above), this number of advances is less than that obtained by Röthlisberger (1986) from his absolute (radiocarbon) chronology for the region. Most of the advances reported by Röthlisberger (1986) were detected exclusively at Tasman Glacier and a few sites at its lateral moraines. Apart from possible methodological errors when dating fossil alpine soils (cf. Matthews 1984), as well as the possible disturbance of the dated organic material by post-depositional erosional processes on this type of "alpine" lateral moraines (cf. Blair 1994), there is doubt Tasman Glacier should be regarded as a key locality for the Southern Alps (see especially Kirkbride & Brazier 1998; cf. Porter 2000). Kirkbride & Brazier (1998) pointed out that the number of confirmed major Holocene advances at Tasman Glacier is far higher than at any other investigated glacier in this region. The Schmidt hammer data presented here support the latter view and this method has the potential to improve the glacial history of the Southern Alps. CONCLUSIONS 1. Schmidt hammer measurements are a useful relative-age dating technique and can successfully be applied to the dating of Holocene moraines in the Southern Alps of New Zealand, provided methodological precautions are taken into account. 2. On the basis of Schmidt hammer readings, (at least) three pre-little Ice Age moraines can be identified at both the Mueller and Hooker Glaciers. Contrary to previous studies, a pre-little Ice Age moraine (M "c") at Mueller Glacier has to be interpreted as being built up during one advance period only. 3. Although no precise absolute dating is possible by this method, an age of c yr BP (M "a"), c yr BP (M "b"), and c yr BP (M "c") are suggested for the three pre-little Ice Age moraines at Mueller Glacier. A correlation between the pre-little Ice Age moraines at Mueller Glacier and Hooker Glacier can be supported by the Schmidt hammer readings. 4. The number of Neoglacial advances at Mueller and Hooker Glacier confirmed morphologically by moraines is substantially lower than the number given by Rbthlisberger's (1986) absolute radiocarbon chronology from the Tasman Glacier. ACKNOWLEDGMENTS Most of the fieldwork was carried out in 1999 and 2000 when the author was in receipt of a personal grant from the Deutsche Forschungsgemeinschaft (DFG, contract WI1701/1). This support is gratefully acknowledged. The author is also grateful to Trevor Chinn (NIWA, Dunedin), Michael Crozier (Victoria University of Wellington), Blair Fitzharris (University of Otago, Dunedin), and Wendy Lawson and Ian Owens (both University of Canterbury, Christchurch) for local information and valuable discussions during fieldwork. Agnes Pohle, Ariane Walz (both University of Würzburg), and Kathrine Falch (University of Bergen, Norway) assisted during fieldwork. Christine Elliott (University of Canterbury, Christchurch) and Ian Owens kindly improved the language of this article. Two anonymous referees gave valuable comment on earlier versions of the article. REFERENCES Aa AR, Sjåstad JA Schmidt hammer age evaluation of the moraine sequence in front of Bøyabreen, western Norway. Norsk Geologisk Tidsskrift 80: Birkeland PW Subdivision of Holocene glacial deposits, Ben Ohau Range, New Zealand, using relative-dating methods. Geological Society of America Bulletin 93: Table 8 New Zealand Holocene glacier advances (chronologies mainly for Tasman Glacier). Burrows (1980) Röthlisberger (1986) Gellatlyetal. (1985) Burrows & Gellatly (1982) Winkler (this study) 1 c yrbp 6th millennium BP yrbp yr BP yrbp yrbp c. 860 yr BP c. 680 yr BP c. 555 yr BP c. 340 yr BP <250 yr BP yrbp 5100 yrbp yrbp 3700 yrbp yr BP yr BP yr BP 1800 yrbp yrbp yr BP 1050 yrbp 900 yrbp 700 yrbp yr BP yr BP no data 5000 yrbp yr BP 3700 yrbp yr BP yr BP yrbp 1500 yrbp 1100 yrbp 900 yr BP yr BP yrbp 8000 yrbp 4500 yr BP 2500 yr BP 1800 yrbp 1000 yrbp 800 yr BP 550 yr BP 300 yr BP no data c yr BP 2 c yr BP 3 c yr BP 4 mid 18th century AD 1 Mueller and Hooker Glacier only yr BP? (alternative dating; cf. text) yr BP? (alternative dating; cf. text) yr BP? (alternative dating; cf. text).

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