Development of lichenometric dating curves for highland scotland

Lichenometric dating of debris flow deposits in the scottish highlands

(1983) – lichenometry in dating recent glacial landforms and deposits, southeast iceland. the same tephra has been observed on a fláajökull moraine with a lichenometric date of 1871 (evans et al.. 2 – lichen growth ‘curves’ published from measures carried out in north and south iceland. in other areas, many of the authors who have published their results from studies conducted in iceland have presented age-size scatterplots that they called lichen ‘growth curves’ (e.. (2010) – a review of lichenometric dating of glacial moraines in alaska. while the age of two contiguous moraines is well constrained between 1721 and 1755 through the identification of an aeolian layer that (i) shows the absence of tephra k 1721 (deposited after the katla volcano eruption between may and august 1721) and (ii) shows the presence of tephra layer k 1755 (idem, eruption active between october 1755 and february 1756); the lichenometric analysis of 550 thalli on one moraine and 717 thallus on the other indicates a date of 1854 in one case and 1831 in the other, using several methods (largest lichen, five largest lichens, size-frequency). it has been widely used as it is thought to be a statistically more robust and reliable dating technique, as it considers a whole lichen population and includes a large number of measurements (200-5000, 1000 being recommended in bradwell, 2009), which enables identifying anomalous growth/large lichens. a range of lichen dating ‘curves’, most using the yellow-green rhizocarpon lichen, have been published in connection with icelandic geomorphic studies (most of these refer to the lichen at species level viz. these scatterplots should thus be described as lichen dating ‘curves’. most of the ‘curves’ are based on linear regression plots, although some are polynomial (thompson and jones, 1986) or logarithmic (bradwell, 2001a, b and 2004a, b), taking into account the different phases of lichen growth (establishment, juvenile, maturation, maturity; bradwell and armstrong, 2007). increasing awareness of methodological limitations of the technique, together with more sophisticated data processing, has led some authors to claim that lichenometric 'ages' are robust and reliable. in some cases, dating matches; in others the non-availability of tephra doesn’t offer the possibility of a comparison. (2007) – testing the size-frequency-based lichenometric dating curve on fláajökull moraines (se iceland) and quantifying lichen population dynamics with respect to stone surface aspect. (2005) in the vestfirðir show that lichenometry may provide fairly accurate ages over a short period of time, in the most recent years/decades, later deteriorating to become a relative dating tool. moreover, the reliability of lichenometric dates is discredited by their lack of correspondence with tephrochronologic data, whatever the lichenometric method used. authors also used their geomorphic studies to test new approaches to lichenometry dating (e. other cases, disparities in dating can reach several hundreds of years.. (1994) – lichenometric dating: a review with particular reference to “little ice age” moraines in southern norway.

Development of lichenometric dating curves for highland scotland

confronting the results from several studies conducted in common places (se iceland for instance) show that lichenometry is a relevant relative dating technique, but not that an efficient absolute dating tool. At the end, absolute dates proposed in the literature are not very trustworthy, and lichenometry should be used for relative dating only. even lichens measured in close proximity with the same technique show significant differences in lichen growth, as shown by the ‘curves’ developed by caseldine (1983), häberle (1991) and kugelmann (1991) in the vicinity of the skíðadalur valley in north iceland. 2 principal dating technique(s) used: ll (largest lichen); 5ll (five largest lichens); sf (size-frequency distribution); lc (lichen cover); u2 (goodness-of-fit); gev (generalised extreme value).. 6 – relative dating using lichenometry and vegetal cover on boulders to discriminate recent snow-avalanche deposits from those dating back at least to the end of the little ice age on the bakkasel site, fnjóskadalur, northern iceland (modified from decaulne and sæmundsson, 2010 ; background image samsýn). such a disparity, unquestionable due to tephrochronological evidence, arises even though the lichenometric techniques are apparently robust: lichens grow on stable surfaces, and show coherent populations according to the size-frequency relationship, and the regional growth curve is well constrained. the direct use of any existing dating ‘curve’, derived from whatever statistics, leads to very different derived surface dates, as shown by mckinsey et al. here i propose to group these ‘curves’ in two geographical areas, one referring to north iceland, and the other referring to south iceland, to highlight their clear differences.. 3 – differences in lichenometric dating results on moraines from outlets of the vatnajökull ice-cap, south-east iceland, according to different authors using different measuring techniques and data processing. as a consequence it is proposed that transfer or adaptation of existing ‘curves’ out of its original area should be avoided. provides a suitable means of dating recent debris‐flow activity on alpine colluvial fans.. 2 – lichen growth ‘curves’ published from measures carried out in north and south iceland. reviews of the different lichenometric methods applied worldwide, the reader should refer to innes (1983a, b and 1985b), matthews (1994), jomelli et al.. 3 – differences in lichenometric dating results on moraines from outlets of the vatnajökull ice-cap, south-east iceland, according to different authors using different measuring techniques and data processing. this minimizes the risk of under- or overestimating the age of analysed surfaces due to the misinterpretation of a lichen-dating curve constructed in a different environment. (2004) – re-dating the moraines at skálafellsjökull and heinabregsjökull using different lichenometric methods: implications for the timing of the icelandic little ice age maximum. whilst far less numerous studies have applied lichenometry to soil erosion quantification (buckland, 1994), debris-flow dating (caseldine, 1991; decaulne and sæmundsson, 2003; decaulne et al. (1986) – rates and causes of proglacial river terrace formation in southeast iceland: an application of lichenometric dating techniques.

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Development of lichenometric dating curves for highland scotland

thus, lichenometric analysis proposes an age 100 to 150 years younger that the date imposed by tephrochronology. (2009) – lichenometric dating: a commentary, in the light of recent statistical studies. such ‘curves’ are therefore not truly representing the growth of lichens as it doesn’t follow the development of one individual thallus through time, ignoring population dynamics on the rock surface, as pointed out by e. (2010) – establishing lichenometric ages for nineteenth- and twentieth-century glacier fluctuations on south georgia (south atlantic). directly comparing landform ages resulting from these ‘curves’ is not easy, as it requires deciphering the robust ‘curves’ from the possible wrong ones, as the quality of the data is hardly evaluated from the literature. it is worth considering whether lichenometry is best considered a relative or absolute dating tool., this review has shown that lichenometry is a relative dating technique that can be used, when caution is taken, as an absolute dating technique, with some uncertainty, for recent periods less than about 100 years well documented by a large number of reference surfaces. (2009) – lichenometric dating: a commentary, in the light of recent statistical studies. the latter two ‘curves’ are also amongst the longest constructed, going back over 130 years. (1990) – a review of dating methods and their application in the development of a chronology of holocene glacier variations in northern iceland. (2010) – establishing lichenometric ages for nineteenth- and twentieth-century glacier fluctuations on south georgia (south atlantic). therefore, lichenometric ages provided in areas subject to recurrent fallout are suspect., (1991) – dating recent glacier advances in the svarfaðardalur-skiðadalur area of northern iceland by means of a new lichen curve. (2007) – testing the size-frequency-based lichenometric dating curve on fláajökull moraines (se iceland) and quantifying lichen population dynamics with respect to stone surface aspect. the recent shift of the debate toward methods did not improve lichen use for dating landforms, and occulted the biology of lichens. such ‘curves’ are in fact built from the measure of several individual lichens of various sizes growing on rock surfaces that have been exposed for different periods of time, at a given time. common aim of many applied lichenometric studies is dating various geomorphological processes or related landforms with closely limiting numerical ages. öræfi fallout (1362) is also shown as it concerns an area where many lichenometric studies have been carried out (compiled from gronvold et al.

Development of lichenometric dating curves for Highland Scotland

A new lichenometric dating curve for southeast iceland

this minimizes the risk of under- or overestimating the age of analysed surfaces due to the misinterpretation of a lichen-dating curve constructed in a different environment. here i propose to group these ‘curves’ in two geographical areas, one referring to north iceland, and the other referring to south iceland, to highlight their clear differences. in iceland, most lichenometric studies have been performed in proglacial environments to date moraine sequences (e. increasing awareness of methodological limitations of the technique, together with more sophisticated data processing, has led some authors to claim that lichenometric 'ages' are robust and reliable. reliability and number of adequate reference surfaces for dating calibration is essential (innes, 1984, 1985a). therefore, it is proposed that lichen dating ‘curves’ should ideally be limited to studies at valley-scale or even smaller, owing to numerous micro-climate differences (e. (ed): dating in exposed and surface contexts, new mexico university press, albuquerque, 185-212. recently, two other lichenometric approaches have been introduced in iceland; both are based on complex statistical treatments of lichenometric data: (i) the u² statistic (orwin et al. (2005) in the vestfirðir show that lichenometry may provide fairly accurate ages over a short period of time, in the most recent years/decades, later deteriorating to become a relative dating tool. adoption of any existing curve for new dating assessments should only be performed with caution, as the lichen habitat and growth conditions can change drastically across short distances (<1 km). reliability and number of adequate reference surfaces for dating calibration is essential (innes, 1984, 1985a). the inconsistency of results and methods has led some authors to ignore lichenometric dating in iceland in the study of the little ice age (for instance grove, 2003). m (1973) – does the size of lichen thalli really constitute a valid measure for dating glacial deposits? Increasing awareness of methodological limitations of the technique, together with more sophisticated data processing, has led some authors to claim that lichenometric 'ages' are robust and reliable. therefore, lichenometric ages provided in areas subject to recurrent fallout are suspect. however, lichenometric results are often simplistically interpreted in iceland: there, contrasting environments are found over very short distances, and a wide range of geomorphic processes impede rock surface stability; in addition, and as seen previously, the validity of many measurements can be questioned as lichenometric ages do not always accord with tephrochronologic ages. (2010) compared bayesian results with the largest one and the five largest ones; they obtained the same trends and conclusions, except the dates were different: lichenometry is an effective relative dating tool, not an absolute one, which is also the conclusion rosenwinkel et al. overall, the slope of ‘curves’ built in southern iceland is steeper during the first decades of lichen growth, suggesting a faster growth of the lichen.

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(1994) – dating and interpretation of rock glaciers using lichenometry, south tröllaskagi, north iceland. on a site north of mýrdalsjökull, joint observations of lichens and tephras enabled testing the validity of absolute lichenometric dating for the moraine formation. (1991) – lichenometric dating, lichen population studies and holocene glacial history in tröllaskagi, northern iceland. provides a suitable means of dating recent debris‐flow activity on alpine colluvial fans. (1986) – rates and causes of proglacial river terrace formation in southeast iceland: an application of lichenometric dating techniques. lichenometric methods have been applied in iceland to date a range of different surfaces (tab. (1990) – a review of dating methods and their application in the development of a chronology of holocene glacier variations in northern iceland. (2004) – re-dating the moraines at skálafellsjökull and heinabregsjökull using different lichenometric methods: implications for the timing of the icelandic little ice age maximum. suggestions for improving future lichenometric work can be made, as (i) associating one lichenologist is required to ensure the correct identification of lichen species on the studied landforms, leading to (ii) detail the identification key for rhizocarpon in different icelandic environments; (iii) to create a repository gathering rhizocarpon specimens that (iv) will be used to teach non-lichenologists to recognize the lichens in the field, especially to the party members who will be measuring lichens on selected landforms in the field; (v) revisiting the same sites and repeating the measure of the exact same individual thalli to better capture their true growth and to take into account their mortality, on the reference surface and on the geomorphic surfaces to be dated; (vi) to reduce the scale of investigation at small areas where environmental conditions do not vary and were control points are available; (vii) to avoid growth ‘curve’ transfer from one area to another several kilometres away, with latitudinal and altitudinal changes; reference growth curves should be built at local scales, not regional ones., a controversy arose in the literature, focussing on lichenometric dating of the little ice age maximum in southern iceland. öræfi fallout (1362) is also shown as it concerns an area where many lichenometric studies have been carried out (compiled from gronvold et al. lichenometry is a relative dating technique as the technique does not provide the time brackets tephrochronology does. such ‘curves’ are therefore not truly representing the growth of lichens as it doesn’t follow the development of one individual thallus through time, ignoring population dynamics on the rock surface, as pointed out by e. (1999) – a comparison of the lichenometric and schmidt hammer dating techniques based on data from the proglacial areas of some icelandic glaciers. (ed): dating in exposed and surface contexts, new mexico university press, albuquerque, 185-212. they all attempted to limit the potential source of lichen growth rate variations that led to dating errors, for example by forcing thresholds in size measurements (thompson and jones, 1986), or selecting the face of boulders they sample (evans et al. is an inexpensive well-established calibrated-dating technique using lichen size to determine the relative or absolute age of exposed surfaces (beschel, 1950, 1973). furthermore, lichen growth ‘curves’ should be living, meaning that the dataset of control points should be measured again and again with time, especially when short time periods are considered in a specific area.

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Extremely low lichen growth rates in Taylor Valley, Dry Valleys

let’s arbitrary take the example of the age range offered from all ‘curves’ for a 10 mm large thallus: in south iceland, a 10 mm thallus results in a predicted ‘age’ range of 23 (maizels and dugmore, 1985) to 36 years (bradwell, 2001a); this difference is far larger in north iceland, with ‘ages’ ranging from 9 (häberle, 1991) to 41 years (caseldine, 1983); in this latter instance, the minimal age of 9 years for lichens with a 10 mm long-axis presents two problems: (i) a growth rate of the thallus of almost 1 mm. lichenometry is a relative dating technique as the technique does not provide the time brackets tephrochronology does. in some cases, dating matches; in others the non-availability of tephra doesn’t offer the possibility of a comparison. of the aim of most lichenometric studies in iceland is to date proglacial landforms, notably moraines, the spatial distribution of investigated sites is uneven. existing growth curves can be used, provided that anomalous thalli are excluded and allowances are made for differences in the growth rates of rhizocarpon alpieola and rhizocarpon section rhizocarpon thalli. recently, two other lichenometric approaches have been introduced in iceland; both are based on complex statistical treatments of lichenometric data: (i) the u² statistic (orwin et al.. 2 – lichen growth ‘curves’ published from measures carried out in north and south iceland. suggestions for improving future lichenometric work can be made, as (i) associating one lichenologist is required to ensure the correct identification of lichen species on the studied landforms, leading to (ii) detail the identification key for rhizocarpon in different icelandic environments; (iii) to create a repository gathering rhizocarpon specimens that (iv) will be used to teach non-lichenologists to recognize the lichens in the field, especially to the party members who will be measuring lichens on selected landforms in the field; (v) revisiting the same sites and repeating the measure of the exact same individual thalli to better capture their true growth and to take into account their mortality, on the reference surface and on the geomorphic surfaces to be dated; (vi) to reduce the scale of investigation at small areas where environmental conditions do not vary and were control points are available; (vii) to avoid growth ‘curve’ transfer from one area to another several kilometres away, with latitudinal and altitudinal changes; reference growth curves should be built at local scales, not regional ones. other cases, disparities in dating can reach several hundreds of years., 2008), or to test techniques against the findings of other dating methods, such as validating the age estimates by comparing lichenometric ages against tephrochronological ages (e. 2 principal dating technique(s) used: ll (largest lichen); 5ll (five largest lichens); sf (size-frequency distribution); lc (lichen cover); u2 (goodness-of-fit); gev (generalised extreme value). 2 principal dating technique(s) used: ll (largest lichen); 5ll (five largest lichens); sf (size-frequency distribution); lc (lichen cover); u2 (goodness-of-fit); gev (generalised extreme value). directly comparing landform ages resulting from these ‘curves’ is not easy, as it requires deciphering the robust ‘curves’ from the possible wrong ones, as the quality of the data is hardly evaluated from the literature. the same tephra has been observed on a fláajökull moraine with a lichenometric date of 1871 (evans et al. they all attempted to limit the potential source of lichen growth rate variations that led to dating errors, for example by forcing thresholds in size measurements (thompson and jones, 1986), or selecting the face of boulders they sample (evans et al. however, the lichenometrical analysis proposes that the moraine dates from 1871 (evans et al. based on the results of over 35 published studies, lichenometry has been widely applied in iceland, proposing numerical ages (absolute dating) and relative ages (relative dating) of different surfaces. Increasing awareness of methodological limitations of the technique, together with more sophisticated data processing, has led some authors to claim that lichenometric 'ages' are robust and reliable.

Lichenometric dating of debris-flow deposits on alpine colluvial fans

therefore, it is proposed that lichen dating ‘curves’ should ideally be limited to studies at valley-scale or even smaller, owing to numerous micro-climate differences (e. it is worth considering whether lichenometry is best considered a relative or absolute dating tool. overall, the slope of ‘curves’ built in southern iceland is steeper during the first decades of lichen growth, suggesting a faster growth of the lichen. in other areas, many of the authors who have published their results from studies conducted in iceland have presented age-size scatterplots that they called lichen ‘growth curves’ (e. the number of studies conducted adjacent to glaciers represents almost 80 % of all lichenometric studies conducted in iceland (fig. m (1973) – does the size of lichen thalli really constitute a valid measure for dating glacial deposits?. 6 – relative dating using lichenometry and vegetal cover on boulders to discriminate recent snow-avalanche deposits from those dating back at least to the end of the little ice age on the bakkasel site, fnjóskadalur, northern iceland (modified from decaulne and sæmundsson, 2010 ; background image samsýn)., 2008), built on the size-frequency technique, enables the user to identify multiple lichen populations growing on complex multi-event landforms; the u² statistic is a relative dating technique with a strong spatial component, recognising the surfaces with similar lichen cover, i. Based on the results of over 35 published studies, lichenometry has been widely applied in Iceland, proposing numerical ages (absolute dating) and relative ages (relative dating) of different surfaces. such a disparity, unquestionable due to tephrochronological evidence, arises even though the lichenometric techniques are apparently robust: lichens grow on stable surfaces, and show coherent populations according to the size-frequency relationship, and the regional growth curve is well constrained. furthermore, lichen growth ‘curves’ should be living, meaning that the dataset of control points should be measured again and again with time, especially when short time periods are considered in a specific area. most authors having worked in iceland were aware of the rough icelandic nature, and aimed at finding a proxy that could date landforms they observed, lacking all source of accurate dating. the direct use of any existing dating ‘curve’, derived from whatever statistics, leads to very different derived surface dates, as shown by mckinsey et al. Moreover, the reliability of lichenometric dates is discredited by their lack of correspondence with tephrochronologic data, whatever the lichenometric method used.. (1995) – preliminary results from the lichenometric study of the nautárdalur rock glacier, tröllaskagi, northern iceland. at the end, absolute dates proposed in the literature are not very trustworthy, and lichenometry should be used for relative dating only., (1991) – dating recent glacier advances in the svarfaðardalur-skiðadalur area of northern iceland by means of a new lichen curve. as a consequence it is proposed that transfer or adaptation of existing ‘curves’ out of its original area should be avoided.

Research paper (PDF): Lichenometric dating of slope movements

for instance in tröllaskagi, north iceland, lichenometric studies date frontal moraines deposits (e. recent results comparing lichenometric dates with tephrochronologic ones over the same surfaces (table 3 - kirkbride and dugmore, 2001, 2008; kirkbride 2009) clearly establish that lichenometry is severely flawed as a dating technique in several cases., 2008), built on the size-frequency technique, enables the user to identify multiple lichen populations growing on complex multi-event landforms; the u² statistic is a relative dating technique with a strong spatial component, recognising the surfaces with similar lichen cover, i. at the end, absolute dates proposed in the literature are not very trustworthy, and lichenometry should be used for relative dating only. it has been widely used as it is thought to be a statistically more robust and reliable dating technique, as it considers a whole lichen population and includes a large number of measurements (200-5000, 1000 being recommended in bradwell, 2009), which enables identifying anomalous growth/large lichens., this review has shown that lichenometry is a relative dating technique that can be used, when caution is taken, as an absolute dating technique, with some uncertainty, for recent periods less than about 100 years well documented by a large number of reference surfaces. there is no evidence for a large increase in debris‐flow activity in the late 19th century, as has been found in scotland.. (1995) – preliminary results from the lichenometric study of the nautárdalur rock glacier, tröllaskagi, northern iceland. authors also used their geomorphic studies to test new approaches to lichenometry dating (e. moreover, the reliability of lichenometric dates is discredited by their lack of correspondence with tephrochronologic data, whatever the lichenometric method used.. (2010) – a review of lichenometric dating of glacial moraines in alaska. At the end, absolute dates proposed in the literature are not very trustworthy, and lichenometry should be used for relative dating only. while the age of two contiguous moraines is well constrained between 1721 and 1755 through the identification of an aeolian layer that (i) shows the absence of tephra k 1721 (deposited after the katla volcano eruption between may and august 1721) and (ii) shows the presence of tephra layer k 1755 (idem, eruption active between october 1755 and february 1756); the lichenometric analysis of 550 thalli on one moraine and 717 thallus on the other indicates a date of 1854 in one case and 1831 in the other, using several methods (largest lichen, five largest lichens, size-frequency). is an inexpensive well-established calibrated-dating technique using lichen size to determine the relative or absolute age of exposed surfaces (beschel, 1950, 1973).. 3 – differences in lichenometric dating results on moraines from outlets of the vatnajökull ice-cap, south-east iceland, according to different authors using different measuring techniques and data processing. (1985) – lichenometric dating and tephrochronology of sandur deposits, sólheimajökull area, southern iceland.. 6 – relative dating using lichenometry and vegetal cover on boulders to discriminate recent snow-avalanche deposits from those dating back at least to the end of the little ice age on the bakkasel site, fnjóskadalur, northern iceland (modified from decaulne and sæmundsson, 2010 ; background image samsýn). these scatterplots should thus be described as lichen dating ‘curves’.

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A standard Rhizocarpon nomenclature for lichenometry - INNES

existing growth curves can be used, provided that anomalous thalli are excluded and allowances are made for differences in the growth rates of rhizocarpon alpieola and rhizocarpon section rhizocarpon thalli. (1999) – a comparison of the lichenometric and schmidt hammer dating techniques based on data from the proglacial areas of some icelandic glaciers. the number of studies conducted adjacent to glaciers represents almost 80 % of all lichenometric studies conducted in iceland (fig. such ‘curves’ are in fact built from the measure of several individual lichens of various sizes growing on rock surfaces that have been exposed for different periods of time, at a given time. through examples, the validity of lichenometry as an absolute dating method is questioned.. 3 – differences in lichenometric dating results on moraines from outlets of the vatnajökull ice-cap, south-east iceland, according to different authors using different measuring techniques and data processing.. 6 – relative dating using lichenometry and vegetal cover on boulders to discriminate recent snow-avalanche deposits from those dating back at least to the end of the little ice age on the bakkasel site, fnjóskadalur, northern iceland (modified from decaulne and sæmundsson, 2010 ; background image samsýn). on a site north of mýrdalsjökull, joint observations of lichens and tephras enabled testing the validity of absolute lichenometric dating for the moraine formation. however, the well-documented recent times in iceland might help building up lichen population monitoring that would give light on population dynamics on features built by geomorphic processes, helping at better understand the influence of mortality on the building of lichen growth ‘curves’ and its potential toward dating curves. this lichen recognition issue may result in lichenometric ‘curves’ that encompass a number of species all with differing growth rates (innes, 1985b), and to the illusion that lichenometry is a handy technique easily usable in the field, leading several generations of geomorphologists to apply a technique without mastering the craft, ignoring its prerequisite, i. (1985) – lichenometric dating and tephrochronology of sandur deposits, sólheimajökull area, southern iceland. let’s arbitrary take the example of the age range offered from all ‘curves’ for a 10 mm large thallus: in south iceland, a 10 mm thallus results in a predicted ‘age’ range of 23 (maizels and dugmore, 1985) to 36 years (bradwell, 2001a); this difference is far larger in north iceland, with ‘ages’ ranging from 9 (häberle, 1991) to 41 years (caseldine, 1983); in this latter instance, the minimal age of 9 years for lichens with a 10 mm long-axis presents two problems: (i) a growth rate of the thallus of almost 1 mm.. (1994) – lichenometric dating: a review with particular reference to “little ice age” moraines in southern norway. even lichens measured in close proximity with the same technique show significant differences in lichen growth, as shown by the ‘curves’ developed by caseldine (1983), häberle (1991) and kugelmann (1991) in the vicinity of the skíðadalur valley in north iceland. Based on the results of over 35 published studies, lichenometry has been widely applied in Iceland, proposing numerical ages (absolute dating) and relative ages (relative dating) of different surfaces. (1983) – lichenometry in dating recent glacial landforms and deposits, southeast iceland. most of the ‘curves’ are based on linear regression plots, although some are polynomial (thompson and jones, 1986) or logarithmic (bradwell, 2001a, b and 2004a, b), taking into account the different phases of lichen growth (establishment, juvenile, maturation, maturity; bradwell and armstrong, 2007). in iceland, most lichenometric studies have been performed in proglacial environments to date moraine sequences (e.

however, the lichenometrical analysis proposes that the moraine dates from 1871 (evans et al. öræfi fallout (1362) is also shown as it concerns an area where many lichenometric studies have been carried out (compiled from gronvold et al., 2008), most authors basing their own research on the previous publication of lichenometric work without questioning the validity of earlier work (tab. confronting the results from several studies conducted in common places (se iceland for instance) show that lichenometry is a relevant relative dating technique, but not that an efficient absolute dating tool. (2002) – dating of the fláajökull moraine ridges, se-iceland; comparison of the glaciological, cartographic and lichenometric data. thus, lichenometric analysis proposes an age 100 to 150 years younger that the date imposed by tephrochronology. most authors having worked in iceland were aware of the rough icelandic nature, and aimed at finding a proxy that could date landforms they observed, lacking all source of accurate dating. a range of lichen dating ‘curves’, most using the yellow-green rhizocarpon lichen, have been published in connection with icelandic geomorphic studies (most of these refer to the lichen at species level viz. of the aim of most lichenometric studies in iceland is to date proglacial landforms, notably moraines, the spatial distribution of investigated sites is uneven.. 2 – lichen growth ‘curves’ published from measures carried out in north and south iceland., 2008), or to test techniques against the findings of other dating methods, such as validating the age estimates by comparing lichenometric ages against tephrochronological ages (e. based on the results of over 35 published studies, lichenometry has been widely applied in iceland, proposing numerical ages (absolute dating) and relative ages (relative dating) of different surfaces. however, lichenometric results are often simplistically interpreted in iceland: there, contrasting environments are found over very short distances, and a wide range of geomorphic processes impede rock surface stability; in addition, and as seen previously, the validity of many measurements can be questioned as lichenometric ages do not always accord with tephrochronologic ages. the recent shift of the debate toward methods did not improve lichen use for dating landforms, and occulted the biology of lichens. (1991) – lichenometric dating, lichen population studies and holocene glacial history in tröllaskagi, northern iceland., a controversy arose in the literature, focussing on lichenometric dating of the little ice age maximum in southern iceland. lichenometric methods have been applied in iceland to date a range of different surfaces (tab. there is no evidence for a large increase in debris‐flow activity in the late 19th century, as has been found in scotland.

(2010) compared bayesian results with the largest one and the five largest ones; they obtained the same trends and conclusions, except the dates were different: lichenometry is an effective relative dating tool, not an absolute one, which is also the conclusion rosenwinkel et al. recent results comparing lichenometric dates with tephrochronologic ones over the same surfaces (table 3 - kirkbride and dugmore, 2001, 2008; kirkbride 2009) clearly establish that lichenometry is severely flawed as a dating technique in several cases. (1994) – dating and interpretation of rock glaciers using lichenometry, south tröllaskagi, north iceland. (2002) – dating of the fláajökull moraine ridges, se-iceland; comparison of the glaciological, cartographic and lichenometric data., 2008), most authors basing their own research on the previous publication of lichenometric work without questioning the validity of earlier work (tab. the inconsistency of results and methods has led some authors to ignore lichenometric dating in iceland in the study of the little ice age (for instance grove, 2003). reviews of the different lichenometric methods applied worldwide, the reader should refer to innes (1983a, b and 1985b), matthews (1994), jomelli et al. whilst far less numerous studies have applied lichenometry to soil erosion quantification (buckland, 1994), debris-flow dating (caseldine, 1991; decaulne and sæmundsson, 2003; decaulne et al. Moreover, the reliability of lichenometric dates is discredited by their lack of correspondence with tephrochronologic data, whatever the lichenometric method used. common aim of many applied lichenometric studies is dating various geomorphological processes or related landforms with closely limiting numerical ages. the latter two ‘curves’ are also amongst the longest constructed, going back over 130 years. öræfi fallout (1362) is also shown as it concerns an area where many lichenometric studies have been carried out (compiled from gronvold et al. adoption of any existing curve for new dating assessments should only be performed with caution, as the lichen habitat and growth conditions can change drastically across short distances (<1 km). 2 principal dating technique(s) used: ll (largest lichen); 5ll (five largest lichens); sf (size-frequency distribution); lc (lichen cover); u2 (goodness-of-fit); gev (generalised extreme value). for instance in tröllaskagi, north iceland, lichenometric studies date frontal moraines deposits (e. however, the well-documented recent times in iceland might help building up lichen population monitoring that would give light on population dynamics on features built by geomorphic processes, helping at better understand the influence of mortality on the building of lichen growth ‘curves’ and its potential toward dating curves. through examples, the validity of lichenometry as an absolute dating method is questioned. this lichen recognition issue may result in lichenometric ‘curves’ that encompass a number of species all with differing growth rates (innes, 1985b), and to the illusion that lichenometry is a handy technique easily usable in the field, leading several generations of geomorphologists to apply a technique without mastering the craft, ignoring its prerequisite, i.