A new lichenometric dating curve for southeast iceland
Lichenometric dating curve
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. gravestones and farm ruins that have been used in iceland are moreover located several kilometres away from the geomorphic landforms that are investigated, and most often located at lower altitude, implying a different environment that do impact the lichen growth. (1991) – lichenometric dating, lichen population studies and holocene glacial history in tröllaskagi, northern iceland. the contrasted environment (temperature and precipitation, wind and snow cover, …) of iceland offers another possible aim that would test latitudinal and altitudinal comparisons of lichen growth to attempt getting answers on the influence of climate on lichen growth in iceland. 2 provides a review of some of the criteria regarding the data robustness, such as lichen identification, proximity of control points and reproducibility of measurements; the proposed ranking is arbitrary, based on these sole criteria, but help extracting the most thorough work that has been carried out in iceland on lichens.. 2 – an evaluation of the robustness of lichen identification and measures in iceland.-1 growth rate presented by the author (häberle, 1991) and (ii) neglects the lag time necessary from the building of the landform and the visible thallus on the newly exposed rockface, which is highly variable, from 7 (decaulne et al. thesis, faculty of science, department of physics, university of iceland, 130 p. 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. (1987) – neoglacial glacier variations in northern iceland: examples from the eyjafjörður area. walls: journals with no new volumes being added to the archive. the linear ‘growth’ curves derived previously by former authors working in iceland represent only part of a curve which has an overall exponential form. the journal includes new ideas,Methods and original research results which may stimulate work within various. since the 14th century, major volcanic eruptions resulting in heavy ash production and consecutive tephra deposition are numerous in iceland.
Lichenometric dating science or pseudoscience
decaulne and sæmundsson (2010) demonstrated with lichens that recent snow avalanches (less than 10 years old) have a shorter runout than snow avalanches triggered during most older times, potentially at the end of the little ice age, from the spatial distribution of newly exposed surfaces of boulders transported by snow avalanches (fig. paper presents a new lichenometric dating curve for southeast iceland. reasons for the non‐linearity of the new dating curve are probably physiological, although climatic change over the last three centuries cannot be ruled out.. (2007) – growth rates of rhizocarpon geographicum lichens: a review with new data from iceland. 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. the technique takes advantage of the radial development of the thallus on the rock, specifically the species within the rhizocarpon subgenus, and has been applied in iceland as well as in other cold environments (golledge et al. more isolated investigations regarding debris-flow and snow-avalanche frequency have been carried out in northwestern and north iceland (decaulne et al. (2010) built a curve that is much more spatially constrained, with 6 reference points located within a 20-km long line, with two additional points located about 30 and 70 km away providing reference ages thought valid for the late 18th century. (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. gravitational spreading a precursor for the stífluhólar landslide (skagafjörður, northern iceland)? as a consequence it is proposed that transfer or adaptation of existing ‘curves’ out of its original area should be avoided. in southern iceland, 75 % of glaciers from the vatnajökull ice cap also experience surging behaviours (björnsson et al. 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.
Lichenometry dating curve
but over such a long distance, lichens are exposed to different microenvironments, even though the global climate of se iceland can be considered as homogeneous. The temporal framework for the curve is based on reliably dated surfaces covering th. (2000) – the tephrochronology of iceland and the north atlantic region furing the middle and late quaternary: a review. in addition to the above mentioned limitations of transferring of a reference growth of rhizocarpon directly to other geomorphic features is the significance of the reference ‘growth curve’. the simplest one, consisting of measuring diameters of large lichens and selecting only the single largest lichen thallus, growing on a surface, follows beschel’s pioneer work (1950); this method has been commonly used in iceland since 1970 (see table 1). Moreover, the reliability of lichenometric dates is discredited by their lack of correspondence with tephrochronologic data, whatever the lichenometric method used., 2005) to over 20 years (caseldine, 1983; maizels and dugmore, 1985; see table 1); the variability in lag time necessary for lichen colonisation of newly exposed bedrock is also an indicator of differential environments that condition lichen growth in north vs. 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. 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. (2004) – climate change and ‘anomalous’ glacier fluctuations: the southwestoutlets of mýrdalsjökull, iceland. for instance in tröllaskagi, north iceland, lichenometric studies date frontal moraines deposits (e. 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). those moraines lichenometrically 'dated' to the second half of the 19th century in iceland may actually pre-date this time by several decades (30-100 years), thus throwing doubt on the exact timing of maximum glaciation during the 'little ice age'. 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, recent history is rich in eruptions that severely affected the icelandic environment (e. (1999) – a comparison of the lichenometric and schmidt hammer dating techniques based on data from the proglacial areas of some icelandic glaciers.. (2008) – identifying moraine surfaces with similar histories using lichen size distributions and the u² statistic, southeast iceland. in bold: studies conducted in north iceland – all other studies were conducted in south iceland1 nombres se référant à la localisation des sites d’étude sur la figure 1 ; 2 techniques principales utilisées : ll (lichen le plus large) ; 5ll (cinq lichens les plus larges) ; sf (distribution taille-fréquence) ; lc (couverture lichénique) ; u2 (qualité de l’ajustement) ; gev (généralisation des valeurs extrêmes) ; (*) recalculé avec les mesures supplémentaires faites en 2009 (0,403 selon la croissance publiée en 2005). reviews of the different lichenometric methods applied worldwide, the reader should refer to innes (1983a, b and 1985b), matthews (1994), jomelli et al.. (1998) – holocene glacier fluctuations of the eiríksjökull ice cap, west central iceland. although this is not a limitation specific to iceland, the thalli of rhizocarpon geographicum (section rhizocarpon) and rhizocarpon inarense (section alpicola) on the same boulder are very difficult to recognize for non-lichenologists without closer examination in the laboratory, although different identification keys exist, either in open access (internet) or in the high latitude literature (hansen, 1995; thomson, 1984, 1997). using both lichenometric techniques, revised dates for moraines on two glacier forelands are presented which shed new light on the exact timing of the little ice age glacier maximum in iceland. most papers dealing with lichenometry in iceland do not describe the lichen(s) that had been used (e. the same tephra has been observed on a fláajökull moraine with a lichenometric date of 1871 (evans et al. (1993) – “little ice age” glaciation of tröllaskagi peninsula, northern iceland: climatic implications for reconstructed equilibrium line altitudes (elas). it is worth considering whether lichenometry is best considered a relative or absolute dating tool.): environmental change in iceland, münchener geographische abhandlungen, reihe b, 12, 31-40. in some cases, dating matches; in others the non-availability of tephra doesn’t offer the possibility of a comparison.
A new lichenometric dating curve for 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). indeed, the effect of volcanic fallouts is unknown on the development of lichens; so far, no study has highlighted the reactions of lichens to burial by ash after volcanic eruptions, or to acid rains due to silicic tephra dispersion in the icelandic atmosphere. 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. on a site north of mýrdalsjökull, joint observations of lichens and tephras enabled testing the validity of absolute lichenometric dating for the moraine formation. most sites from se iceland have been affected by repetitive tephra fallouts, suggesting that volcanic activity might have had a significant disruptive ecological effect on lichen growth and survival. (2002) – dating of the fláajökull moraine ridges, se-iceland; comparison of the glaciological, cartographic and lichenometric data., 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. 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).. (2008) – geomorphic evidence for holocene glacial advances and sea level fluctuations on eastern vestfirðir, northwest iceland. (2012) – surge fingerprinting of cirque glaciers at the tröllaskagi peninsula, north iceland. 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. use of linear ‘growth’ curves in iceland is problematic over time‐spans of more than c. reliability and number of adequate reference surfaces for dating calibration is essential (innes, 1984, 1985a). (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.
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in iceland, few accurately dated surfaces exist and most of them are quite young (>100 years); several authors have already pointed out both in the south (e. therefore, lichenometric ages provided in areas subject to recurrent fallout are suspect. (1990) – a review of dating methods and their application in the development of a chronology of holocene glacier variations in northern iceland. in bold: studies conducted in north iceland – all other studies were conducted in south iceland1 nombres se référant à la localisation des sites d’étude sur la figure 1 ; 2 techniques principales utilisées : ll (lichen le plus large) ; 5ll (cinq lichens les plus larges) ; sf (distribution taille-fréquence) ; lc (couverture lichénique) ; u2 (qualité de l’ajustement) ; gev (généralisation des valeurs extrêmes) ; (*) recalculé avec les mesures supplémentaires faites en 2009 (0,403 selon la croissance publiée en 2005). (2010) – a commentary to ‘asynchronous little ice age glacial maximum extent in southeast iceland’ by chenet et al. (2005) – debris flows triggered by rapid snowmelt in the gleiðarhjalli area, northwestern iceland. the temporal framework for the curve is based on reliably dated surfaces covering the last 270 years, making it the best constrained study of this nature conducted in iceland. the temporal framework for the curve is based on reliably dated surfaces covering the last 270 years, making it the best constrained study of this nature conducted in iceland.): environmental change in iceland, münchener geographische abhandlungen, reihe b, 12, 205-224. walls: journals with no new volumes being added to the archive. (2002) – fungal weathering of basaltic rocks in a cold oceanic environment (iceland): comparison between experimental and field observations.. (2008) – two millennia of glacier advances from southern iceland dated by tephrochronology. (2004) – re-dating the moraines at skálafellsjökull and heinabregsjökull using different lichenometric methods: implications for the timing of the icelandic little ice age maximum.. 2 – an evaluation of the robustness of lichen identification and measures in iceland.
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Fláajökull (north lobe), Iceland: active temperate piedmont lobe
(2008) – late quaternary terrestrial tephrochronology of iceland - frequency of explosive eruptions, type and volume of tephra deposits. these scatterplots should thus be described as lichen dating ‘curves’. tens of scientists and students in field courses, in addition to hundreds of tourists, trample on numerous moraines each year in south iceland, on the southern margins of both mýrdalsjölkull and vatnajökull. 1), most of these have been conducted around the southern margins of vatnajökull (50 %); followed by mýrdalsjökull (22 %), then the tröllaskagi glaciers in northern iceland (21 %), and finally one or two studies around eiríksjökull in west iceland, and adjacent to drangajökull (principato, 2008) in northwestern iceland (buckland, 1994). authors also used their geomorphic studies to test new approaches to lichenometry dating (e. 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. 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. 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. in iceland, most lichenometric studies have been performed in proglacial environments to date moraine sequences (e.* ranks on data robustness extracted from the scientific papers, as sum of the following parameters arbitrary weighted: lichen identification by a lichenologist (l) = 2; key identification (k) = 1; none = 0 point; control point within the valley = 2, within the region 1, no reference surface = 0; repetitive measurements of the very same thalli (rt) = 2, repetitive measurements on the same surface (r) = 1, unique measurement (u) = 0; other information such as lichen used in the study, number of control points and number of lichen measured, and the production of a lichen growth curve (yes or no) are just informative, as extracted from the references cited. 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.. 22 – n° 1 | 2016 : analyses of high energy – low frequency geomorphological events onslopes, fluvial and coastal dynamics in iceland and methodological contributions. however, the lichenometrical analysis proposes that the moraine dates from 1871 (evans et al.. 2 – lichen growth ‘curves’ published from measures carried out in north and south iceland.
The Little Ice Age glacier maximum in Iceland and the North Atlantic
through examples, the validity of lichenometry as an absolute dating method is questioned. caseldine and baker (1998) therefore are probably too optimistic by stating that lichenometry in iceland provides a good opportunity to examine size-frequency distribution since the laki eruption of 1783, as only the western- and north-westernmost parts of iceland have not encounter tephra fallouts, as well as some parts of north and east iceland (fig. the recent shift of the debate toward methods did not improve lichen use for dating landforms, and occulted the biology of lichens. the dating potential of this new curve is tested on surfaces of known age in southeast iceland. (1991) – holocene glacial history of the hörgárdalur area, tröllaskagi, northern iceland. thus, lichenometric analysis proposes an age 100 to 150 years younger that the date imposed by tephrochronology. 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 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). 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. for instance, bradwell (2001a, b) proposes a reference growth curve based on nine reference surfaces ranging from southern mýrdalsjökull to eastern vatnajökull, i. in fact, the growth curve that is developed from direct measurements of a lichen population on the oldest reference surface (anthropic or natural) cannot be taken for an age-size scatterplot as it figures out the growth of survivors only, i. caseldine (1991), caseldine and baker (1998) and kugelmann (1991) mentioned the lack of large lichens in northern iceland, and related it to the production of fine-grained volatile and acid material from the laki eruptions in 1783-84; this might also be valid for southern iceland, where the laki plume delivered the thickest fallout. i am grateful to helgi páll jónsson for providing several of the references i needed regarding historical volcanic eruptions in iceland. other cases, disparities in dating can reach several hundreds of years.
Annual Moraines and Summer Temperatures at Lambatungnajökull
this leads to the second issue, regarding the suitability of control points/surfaces as icelandic environmental conditions can change drastically in very short distances, particularly in glacier surroundings. (1988) – historical development of the proglacial landforms of svínafellsjökull and skaftafellsjökull, southeast iceland. the method has a limitation though, especially if a new event of a bigger magnitude totally covers the previous deposits. use of linear 'growth' curves in iceland is problematic over time-spans of more than c. (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. however, work in iceland shows that the ecological and environmental aspects of lichens impede the quality of the results, with researchers seeking at gaining more accurate dates to understand and better explain the dynamic of different geomorphologic processes. the case study of principato (2008) around drangajökull, in northwestern iceland clearly shows that the ages of landforms derived from kugelmann’s tröllaskagi curve, northern iceland (1991) do not match historical observations. 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.* ranks on data robustness extracted from the scientific papers, as sum of the following parameters arbitrary weighted: lichen identification by a lichenologist (l) = 2; key identification (k) = 1; none = 0 point; control point within the valley = 2, within the region 1, no reference surface = 0; repetitive measurements of the very same thalli (rt) = 2, repetitive measurements on the same surface (r) = 1, unique measurement (u) = 0; other information such as lichen used in the study, number of control points and number of lichen measured, and the production of a lichen growth curve (yes or no) are just informative, as extracted from the references cited. lichenometry is a relative dating technique as the technique does not provide the time brackets tephrochronology does. the late 1980s the size-frequency approach was introduced in iceland, first by caseldine (1990, 1991) in tröllaskagi., (1991) – dating recent glacier advances in the svarfaðardalur-skiðadalur area of northern iceland by means of a new lichen curve. (2010) – asynchronous little ice age glacial maximum extent in southeast iceland. (2011) – a response to dąbski's commentary on asynchronous little ice age glacial maximum extent in southeast iceland [geomorphology (2010), 114, 253-260].A New Lichenometric Dating Curve For Southeast Iceland
size-frequency approach is mainly defended in iceland by bradwell (2001a, b; 2004a, b; 2009), while the gev approach is defended by cooley et al. 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. (2007) – volcanism in iceland in historical time: volcano types, eruption styles and eruptive history. 400 years - in the maritime subpolar climate of southeast iceland. 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.. (1995) – preliminary results from the lichenometric study of the nautárdalur rock glacier, tröllaskagi, northern iceland. (2010) – establishing lichenometric ages for nineteenth- and twentieth-century glacier fluctuations on south georgia (south atlantic). at the end, absolute dates proposed in the literature are not very trustworthy, and lichenometry should be used for relative dating only.. (2006) – the little ice age glacier maximum in iceland and the north atlantic oscillation: evidence from lambatungnajökull, southeast iceland. gravitational spreading a precursor for the stífluhólar landslide (skagafjörður, northern iceland)? the icelandic volcanic parent material varies through this transect, with intrusive, extrusive acid, basic and vesicular characteristics; all of which affect lichen growth, but first of all the lichen colonisation rate.. (2010) – a review of lichenometric dating of glacial moraines in alaska. the icelandic volcanic (basaltic) parent material can be unsuitable for lichen development, particularly if highly vesicular; therefore, sometimes only part of any geomorphic feature can be dateable using lichenometry. 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.
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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. (2009) – lichenometric dating: a commentary, in the light of recent statistical studies. 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. (1985) – the extent of some glaciers in northern iceland during the little ice age and the nature of recent deglaciation. m (1973) – does the size of lichen thalli really constitute a valid measure for dating glacial deposits? this curve is built on accurately dated surfaces, both natural (historically dated moraines or rockfall) and man-made (bridge piers); providing a growth-curve for the whole area. 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 lichen growth and applied lichenometry in southwest and southeast greenland. (1985) – lichenometric dating and tephrochronology of sandur deposits, sólheimajökull area, southern iceland. this paper presents a calibrated dating curve based on the gradient of the size-frequency distribution of yellow-green rhizocarpon lichens. (1994) – dating and interpretation of rock glaciers using lichenometry, south tröllaskagi, north iceland. paper proposes a review of the use of lichenometry in iceland since 1970, using different techniques to solve the chronology of geomorphic processes. 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. (2010) – distribution and frequency of snow-avalanche debris transfer in the distal part of colluvial cones in central north iceland.
When should i get my dating scan appointment | A New Lichenometric Dating Curve for Southeast Iceland the number of studies conducted adjacent to glaciers represents almost 80 % of all lichenometric studies conducted in iceland (fig. these problems are exacerbated in iceland by rapid environmental changes across short distances and more generally by lichen species mis-identification in the field., 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. 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. öræfi fallout (1362) is also shown as it concerns an area where many lichenometric studies have been carried out (compiled from gronvold et al. the journal includes new ideas,Methods and original research results which may stimulate work within various. (1994) – glacial, late glacial and holocene history of the hörgaárdalur area, tröllaskagi, northern iceland. (eds): environmental changes in iceland: past and present, kluwer academic publishers: 203-217. use of lichenometry in iceland raises the issue of absolute vs. decaulne, « lichenometry in iceland, results and application », géomorphologie : relief, processus, environnement, vol. 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. 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. (2004b) – annual moraines and summer temperatures at lambatungnajökull, iceland., 2005, 2010), and a single soil erosion study has been carried out in northwestern iceland.
What is considered first base in dating | Lichenometric Dating in Southeast Iceland: The Size-Frequency 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., a controversy arose in the literature, focussing on lichenometric dating of the little ice age maximum in southern iceland. those moraines lichenometrically ‘dated’ to the second half of the 19th century in iceland may actually pre‐date this time by several decades (30–100 years), thus throwing doubt on the exact timing of maximum glaciation during the ‘little ice age’. (ed): dating in exposed and surface contexts, new mexico university press, albuquerque, 185-212.): environmental change in iceland, münchener geographische abhandlungen, reihe b, 12, 133-145. At the end, absolute dates proposed in the literature are not very trustworthy, and lichenometry should be used for relative dating only. paper presents a new lichenometric dating curve for southeast iceland. this novel approach has gained popularity over the last 20 years and has been applied by several authors in southern iceland (e.. (1994) – lichenometric dating: a review with particular reference to “little ice age” moraines in southern norway. reasons for the non-linearity of the new dating curve are probably physiological, although climatic change over the last three centuries cannot be ruled out. 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. 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. and spatial analysis of rockslides failures in the icelandic westfjords: first results [texte intégral]., 2008), most authors basing their own research on the previous publication of lichenometric work without questioning the validity of earlier work (tab.
Dating tips from my future self | Lichenometry in Iceland, results and application (2002) – the role of biological weathering in periglacial areas: a study of weathering rinds in south iceland. 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). 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. (1986) – rates and causes of proglacial river terrace formation in southeast iceland: an application of lichenometric dating techniques. even in this smaller area the variability of landscapes on which the reference curve was built does not account for variable environmental conditions. is an inexpensive well-established calibrated-dating technique using lichen size to determine the relative or absolute age of exposed surfaces (beschel, 1950, 1973).. 2 – lichen growth ‘curves’ published from measures carried out in north and south iceland. and dugmore (2001, 2008) and kirkbride (2009) investigated in detail glacier front fluctuations in southern iceland.. (2001) – can lichenometry be used to date the “little ice age” glacial maximum in iceland? paper presents a new lichenometric dating curve for southeast Iceland. with this much environmental variability such a curve cannot be used as a reference for the entire area. (1983) – lichenometry in dating recent glacial landforms and deposits, southeast iceland. as for other measurements, a lichen growth curve should be built by measuring again and again the very same thalli on the same reference surface to take into account the establishment of the lichen in a new habitat, as bradwell et armstrong (2007) started.. 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).