Surfaces Of Known Age Research Articles

Inverse modeling of lichen growth curves and implications for lichenometric dating

Lichenometric dating represents a quick and affordable surface exposure dating method that has been widely used to provide a minimum age constraint on tectonic and geomorphic landscape changes as well as buildings and anthropogenic landscape changes in various settings during the late Holocene. Despite its widespread usage, this method has several limitations. Major problems relate to the sampling of lichen population on any given rock surface and the modeling of growth curves. In order to overcome these issues, it has been suggested to subdivide the rock surface into some areas and measure the largest lichen thallus on each one. However, how to express the data in terms of a probability distribution function and link it to an age of last exposure of the rock surface are still a matter of debate. Here, we propose a novel approach to the modeling of lichen growth curves by treating lichen growth as a continuous-time Markov process with a time-varying rate and additive Brownian noise. Given the growth rates, the probability distribution of the lichen population at any time can then be obtained by solving the Fokker–Planck equation. This method is illustrated using a dataset from the Huashan area of eastern China, which consists of measurements of the largest thalli on 12 rock surfaces of known age. We first build up the probability distribution of the lichen population for each rock surface based on extreme value theory and then use these to optimize the growth curve by minimizing the Jensen–Shannon divergence. A new method is also proposed to use the growth curve to map a sample of size data from an undated rock surface to the calendar age domain so as to yield a fully probabilistic estimate of the exposure age of the undated rock surface rather than a point estimate. • We propose a novel approach to lichenometric dating. • Lichen growth is modeled using a continuous-time Markov process. • Extreme-value theory is used to model the size distribution. • A MATLAB package for implementing the model is provided.

Lichenometric Dating of Historic Inscriptions on a Rock Outcrop in Coastal Oregon

We estimated the age of inscriptions on a rock outcrop by estimating the ages of lichens that had overgrown the inscriptions. The inscriptions are considered to be historically important, potentially representing some of the earliest European exploration of Neahkahnie Mountain, the highest point along the Pacific coast from Baja California to Strait of Juan de Fuca, Washington. The rock bearing the inscriptions was destroyed by road construction activities in about 1970–1980, but the inscriptions had been photographed with sufficient detail to allow diameter estimates for the lichens on the rock, affording an opportunity for dating based on lichen sizes. Aspicilia and Placopsis are currently the only lichen genera that are common on similar outcrops in the area and form large light-colored discrete individuals with a radial form. We therefore derived a calibration curve for lichen size in relation to age based on Aspicilia and Placopsis sizes on nearby surfaces of known age (road cuts and stone walls), then applied that curve to the diameters of lichens in the photo. Based on the sizes of the lichens on the rock outcrop with inscriptions, the rock face had been available for lichen colonization and growth for > 100 yrs and perhaps shows a pulse of recruitment following extensive wildfires on the immediate coast in the 1840s. Calculated lichen ages are within 25 years of the expected time of US Army exploration of Neahkahnie Mountain under Captain C. C. Augur in the mid-1800s.

Characterisation of faults as earthquake sources from geomorphic data in the Tongariro Volcanic Complex, New Zealand

ABSTRACTAt the southern Taupo Rift, tectonic faults and volcanic edifices have interacted during the last 350 kyr. The NNE-striking Tongariro Volcanic Complex is bounded and displaced by four parallel normal faults: National Park, Waihi, Poutu and Upper Waikato Stream, which collectively define the Tongariro Graben. Offsets of geomorphic surfaces of known age and fault trace geometry were used to characterise the seismic parameters of these faults. Along-strike distribution of fault displacement suggests that these faults could rupture as a whole. However, geomorphic data and geometrical characteristics of surface ruptures suggest that they could also rupture in shorter segments. This study calculates higher slip-rates (∼2.6 ± 0.8 and 2.2 ± 1.9 mm/yr for Waihi and Poutu fault zones, respectively) and greater earthquake magnitudes (up to MW 7.2 ± 0.1 and 6.9 ± 0.1, respectively) than previous studies, suggesting an important seismic hazard for the Tongariro area.

Age assessment and implications of late Quaternary periglacial and paraglacial landforms on Muckish Mountain, northwest Ireland, based on Schmidt-hammer exposure-age dating (SHD)

Schmidt-hammer exposure-age dating (SHD) was applied to a variety of late Quaternary periglacial and paraglacial landforms composed of coarse rock debris on Muckish Mountain, northwest Ireland. Landform ages were determined using a linear high-precision age-calibration curve, derived from young and old control surfaces of known age on the same rock type. The SHD ages represent maximum estimates of the time elapsed since the boulders stabilised and the landforms became inactive. Most ages are also minimum estimates for the start of landform development because older boulders are buried beneath the sampled surface boulders. Ages and 95% confidence intervals obtained for blockfield, boulder lobes and talus indicate these features were likely active during several of the early Holocene cold events evidenced in Greenland ice cores and North Atlantic sediment records. Activity ceased at different times ~9–7ka BP. These landforms are the first indication of a geomorphological response to early Holocene cooling in the oceanic mountains of Ireland. Late Holocene ages, obtained for rock-slope failure run-out debris and debris cone boulders, overlap with shifts to cooler and/or wetter conditions, including the Little Ice Age. Geomorphological impacts associated with these changes in climate have not previously been recorded in the Irish uplands. The SHD results indicate that previously implied timings for the stabilisation of some accumulations of coarse rock debris on mountain slopes are in need of revision.

Holocene Chemical Weathering, Surface Lowering and Rock Weakening Rates on Glacially Eroded Bedrock Surfaces in an Alpine Periglacial Environment, Jotunheimen, Southern Norway

ABSTRACTIndices of the rate of Holocene chemical weathering of pyroxene‐granulite gneiss and peridotite are estimated from bedrock surfaces deglaciated c. 9700 years ago. A mean surface lowering rate for pyroxene‐granulite gneiss of 4.8 ± 1.0 mm ka−1 is estimated from the mean height of upstanding quartz veins, and Schmidt hammer R‐values are used to validate the reference‐surface method. Microrelief development and crack‐widening rates for peridotite are 2.6 ± 1.1 mm ka−1 and 1.8 ± 0.4 mm ka−1, respectively. Well‐developed weathering rinds indicate a mean rind development rate for peridotite of 0.6 ± 0.1 mm ka−1. New indices of rock surface weakening (IRW) and the rock surface weakening rate (WR) are defined in relation to Schmidt hammer mean R‐values. IRW values from weathered and unweathered surfaces of known age are 38.7 per cent for gneiss and 34.1–59.2 per cent (depending on the texture of the weathered rock surface) for peridotite: corresponding WR values are 2.7 R‐units ka−1 and 2.1–3.7 R‐units ka−1, respectively. Our methods and results are evaluated, particularly in relation to previous research and other rock types in Scandinavia. The various indices, being affected in different ways by biochemical and biological mechanical weathering and micro‐erosion, are regarded as complementary aids in the investigation of both the effects of chemical weathering and its rate. Copyright © 2010 John Wiley & Sons, Ltd.

Use of bomb‐14c to investigate the growth and carbon turnover rates of a crustose lichen

.The reliability of lichenometric dating is dependent on a good understanding of lichen growth rates. The growth rate of lichens can be determined from direct measurement of growing lichens or indirect methods by measuring lichens growing on surfaces of known age, although there are limitations to both approaches. Radiocarbon (14C) analysis has previously been used in only a handful of studies to determine lichen growth rates of two species from a small area of North America. These studies have produced mixed results; a small amount of carbon turnover appears to occur in one of the species (Caloplaca spp.) previously investigated introducing uncertainty in the growth rate, while much higher carbon cycling occurred in another (Rhizocarpon geographicum), making the 14C approach unsuitable for estimating growth rates in the species most commonly used in lichenometric dating. We investigated the use of bomb‐14C analysis to determine the growth rate of a different crustose species (Pertusaria pseudocorallina) common to Northern Europe. 14C‐based growth rates were considerably higher than growth rates of morphologically similar species based on direct measurement made at locations nearby and elsewhere in the UK. This observation strongly suggests that a degree of carbon turnover probably occurs in Pertusaria pseudocorallina, and that bomb‐14C analysis alone cannot be used to determine lichen age or absolute growth rates in this lichen species.

Dating young geomorphic surfaces using age of colonizing Douglas fir in southwestern Washington and northwestern Oregon, USA

AbstractDating of dynamic, young (<500 years) geomorphic landforms, particularly volcanofluvial features, requires higher precision than is possible with radiocarbon dating. Minimum ages of recently created landforms have long been obtained from tree‐ring ages of the oldest trees growing on new surfaces. But to estimate the year of landform creation requires that two time corrections be added to tree ages obtained from increment cores: (1) the time interval between stabilization of the new landform surface and germination of the sampled trees (germination lag time or GLT); and (2) the interval between seedling germination and growth to sampling height, if the trees are not cored at ground level. The sum of these two time intervals is the colonization time gap (CTG). Such time corrections have been needed for more precise dating of terraces and floodplains in lowland river valleys in the Cascade Range, where significant eruption‐induced lateral shifting and vertical aggradation of channels can occur over years to decades, and where timing of such geomorphic changes can be critical to emergency planning.Earliest colonizing Douglas fir (Pseudotsuga menziesii) were sampled for tree‐ring dating at eight sites on lowland (<750 m a.s.l.), recently formed surfaces of known age near three Cascade volcanoes – Mount Rainier, Mount St. Helens and Mount Hood – in southwestern Washington and northwestern Oregon. Increment cores or stem sections were taken at breast height and, where possible, at ground level from the largest, oldest‐looking trees at each study site. At least ten trees were sampled at each site unless the total of early colonizers was less. Results indicate that a correction of four years should be used for GLT and 10 years for CTG if the single largest (and presumed oldest) Douglas fir growing on a surface of unknown age is sampled. This approach would have a potential error of up to 20 years. Error can be reduced by sampling the five largest Douglas fir instead of the single largest. A GLT correction of 5 years should be added to the mean ring‐count age of the five largest trees growing on the surface being dated, if the trees are cored at ground level. This correction would have an approximate error of ±5 years. If the trees are cored at about 1·4 m above the ground surface (breast height), a CTG correction of 11 years should be added to the mean age of the five sampled trees (with an error of about ±7 years). Published in 2006 by John Wiley & Sons, Ltd.

Late Holocene solifluction history reconstructed using tephrochronology

Abstract Phases of activity of four solifluction lobes at an altitude of 750–800 m are dated by tephrochronology at Snaefell, central eastern Iceland (64°48′ N 15°33′ E). The sample includes sorted lobes with tread gradients of 3–11° and unsorted (turf-banked terraces) in slope-foot locations. Trenches through lobe fronts reveal detailed internal structures picked out by multiple tephra layers. The tephras V1717, V1477, Ö1362, V870, Hekla-3 (2900 years bp and Hekla-4 (3800 years bp ) provide isochronous surfaces of known age whose deformation and disturbance indicate mass movement and/or cryoturbation of the soil cover. Undisturbed soil including the Hekla-3 tephra indicates an absence of solifluction prior to 2900 years bp . Several centuries after Hekla-3, gravel-rich horizons mark wide-spread frost heave and solifluction of hillslopes. Later stabilization of these lobes allowed the accumulation of aprons of aeolian sediment below lee-side risers. These aprons contain in situ mediaeval tephras, dating the inception of solifluction to a considerable time prior to Norse settlement. The likely period of this first phase of solifluction is the Later Bog Period of the Subatlantic, c. 2500-1000 years bp . The aprons are currently being overridden and deformed by solifluction lobes reactivated in the Little Ice Age.

Lichenometric dating in southeast iceland: the size–frequency approach

The age of recent deposits can be determined using an intrinsic characteristic of the lichen ‘population’ growing on their surface. This paper presents a calibrated dating curve based on the gradient of the size‐frequency distribution of yellow‐green Rhizocarpon lichens. The dating potential of this new curve is tested on surfaces of known age in southeast Iceland. This particular size—frequency technique is also compared with the more traditional largest‐lichen approach. The results are very encouraging and suggest that the gradient can be used as an age indicator, at least on deposits formed within the last c. 150 years – and probably within the last c. 400 years – in the maritime subpolar climate of southeast Iceland. 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.

A Rhizocarpon geographicum growth curve for the Cascade Range of Washington and northern Oregon, usa

Lichen thallus measurements from 22 surfaces of known age on Mount Baker, Mount Hood, and Mount Rainier are used to construct a regional Rhizocarpon geographicum growth curve for the Cascade Range of Washington and northern Oregon. Growth rates determined by measuring the largest thallus diameters on the same surfaces at Mount Rainier in 1976 and 2002 are used for comparison with lichenometric data from Mount Baker and Mount Hood. Similar lichen thallus diameter vs age relationships identified in the data from the three mountains suggest the presence of uniform growth rates over the 400-km range. A regional growth curve developed during our study shows three growth phases of successively slower growth: a rapid phase from 8 to 20 yr, a linear phase from 20 to 145 yr, and a slow phase of unknown duration beyond ca. 145 yr. Uncertainty in lichen growth rates beyond 145 yr limits projection of the curve beyond that age; however, the age range of the constrained growth curve covers an important period of recent climate variability. When applied in appropriate settings, our growth curve can be used to determine numeric ages to ±10 yr for surfaces between 20 and 145 years old in areas where other techniques are not applicable or do not provide unique or well-constrained ages.

Steady, balanced rates of uplift and erosion of the Santa Monica Mountains, California

Topographic change in regions of active deformation is a function of rates of uplift and denudation. The rate of topographic development and change of an actively uplifting mountain range, the Santa Monica Mountains, southern California, was assessed using landscape attributes of the present topography, uplift rates and denudation rates. Landscape features were characterized through analysis of a digital elevation model (DEM). Uplift rates at time scales ranging from 104to 106years were constrained with geological cross‐sections and published estimates. Denudation rate was determined from sediment yield data from debris basins in southern California and from the relief of rivers set into geomorphic surfaces of known age. First‐order morphology of the Santa Monica Mountains is set by large‐scale along‐strike variations in structural geometry. Drainage spacing, drainage geometry and to a lesser extent relief are controlled by bedrock strength. Dissection of the range flanks and position of the principal drainage divide are modulated by structural asymmetry and differences in structural relief across the range. Topographic and catchment‐scale relief are ≈300–900 m. Mean denudation rate derived from the sediment yield data and river incision is 0.5±0.3 mm yr−1. Uplift rate across the south flank of the range is ≈0.5±0.4 mm yr−1and across the north flank is 0.24±0.12 mm yr−1. At least 1.6–2.7 Myr is required to create either the present topographic or the catchment‐scale relief based on either the mean rates of denudation or uplift. Although the landscape has had sufficient time to achieve a steady‐state form, comparison of the time‐scale of uplift and denudation rate variation with probable landscape response times implies the present topography does not represent the steady‐state form.

The Extent of Some Glaciers in Northern Iceland during the Little Ice Age and the Nature of Recent Deglaciation

Lichenometric studies from four glaciers in Northern Iceland are used to determine the dates of their Little Ice Age maxima. In all cases these date to the last half of the nineteenth century and probably marked the maximum Neoglacial extent of the glaciers. Comparison of the pattern of subsequent deglaciation and meteorological records from the area indicates a likely relationship between changes in the mass balance of glaciers in Northern Iceland and mean summer temperatures. LITTLE IS KNOWN about the glacial history of Northern Iceland during the Holocene. Recent studies of Gljufurarjokull, a small valley-head glacier in the Trollaskagi peninsula of Northern Iceland, have demonstrated that it reached its Neoglacial maximum late in the Little Ice Age, only retreating from this position at the end of the nineteenth century (Caseldine, 1983; Caseldine and Cullingford, 1981). In this paper further details of the Gljufurarjokull record are presented and compared with other small glaciers in the region. Lichenometry Dating of the most recent deglaciation at Gljufurarjokull was based on the use of lichenometry, a technique as yet used very little in Iceland (Jaksch, 1970, 1975; Caseldine, 1983; Gordon and Sharp, 1983). Lichenometry utilizes the linear growth rate of certain lichen species such that measurement of the diameter of the largest thallus found at any site can be taken as representative of the age of the substrate on which it is growing. The rate of growth is usually determined from measurements on surfaces of known age and expressed in mma-1 (Lock, Andrews and Webber, 1979). In 1979 a lichen growth curve was derived for Rhizocarpon geographicum agg. from dated abandoned farmsteads in SkitaSalur and applied to the glacier foreland of Gljufurarjokull. This produced linear growth rates of 0.57 mma-1 (using the single largest lichen) and 0.51 mma-1 (using the mean of the 5 largest lichens) for the period 1905-1981. Although it was acknowledged that there could be differences in growth rate between the two valleys this problem could not be fully solved in view of the lack of any dated surface from the foreland. However, comparison with other growth rates for Rhizocarpon geographicum agg. in Iceland has supported the applicability of the results, the more continental area of Northern Iceland showing a slightly lower rate of growth than sites in Southern Iceland around the Vatnajokull ice cap (Table I).

Lichenometric Studies in the Cascade Range of Washington: Establishment of Rhizocarpon geographicum Growth Curves at Mount Rainier

Measurements of Rhizocarpon geographicum thalli on rock surfaces of known age at Mount Rainier National Park permit growth curves to be constructed for andesitic and granitic substrates spanning the last 125 yr. Control points for the younger part of each curve come mainly from man-made structures, whereas older control points are from rock outcrops in the foreland of Nisqually Glacier, an area which as experienced progressive deglaciation since the early 19th century. The growth curves indicate an initial period of very rapid growth until thalli reach about 10 mm diameter, after which growth proceeds at an exponentially decreasing rate for the next century. Growth rates are slightly faster for andesitic substrates than for granite. If extrapolated, the curves should be useful for dating substrates as much as 3 to 4 centuries old with an accuracy of + 20 yr or better. However, the curves are applicable primarily between altitudes of about 1000 and 1700 m; below this zone growth rates are higher, whereas above it lichenometry may be of limited value because of widespread lichen kill during the early 19th century along the crest of the Cascade Range.

Holocene glacial variations in Sarek National Park, northern Sweden

Detailed mapping of well‐preserved moraine systems fronting 17 small alpine glaciers in Sarek National Park in Swedish Lapland reveals two Holocene intervals of prolonged glacier expansion, each involving a complex of minor fluctuations. The younger interval, which corresponds to the Little Ice Age, experienced advances that culminated about A.D. 1916–1920, 1880–1890, 1850–1860, 1800–1810, 1780, 1700–1720, 1680, 1650, and 1590–1620. The older expansion interval, which probably centered around 2500 14C yr B.P., experienced several minor fluctuations spread through about 600 years.Lichen data collected on moraine systems in Sarek are internally consistent from glacier to glacier. Lichen measurements on surfaces of known age in Sarek and nearby Kebnekaise match closely, allowing moraine correlations between these areas. Several older expansion intervals are recorded in the Kebnekaise Mountains. Taken together, the two sequences suggest that a series of prolonged expansion intervals, each similar to the Little Ice Age, has characterized the Holocene in Lapland. Fluctuations of the Scandinavian Ice Sheet in Sweden suggest that this series of Little‐Ice‐Age events extends back into the late Weichsel in the form of the Younger Dryas and Oldest Dryas stadials.

FOREST GROWTH AND GLACIAL CHRONOLOGY IN EASTERN BRITISH COLUMBIA, AND THEIR RELATION TO RECENT CLIMATIC TRENDS

Recent activity of Yoho Glacier was determined by botanical and geological dating techniques and from published accounts. Tree growth in four forests adjacent to the end moraine was measured by increment borings of 200 Picea engelmannii. Drawings of increment cores were made in the field, to avoid differential shrinkage with storage. From these drawings, tree growth was calculated in trunk basal area per decade.Corroborating data from three trees indicated that maximum advance of the Yoho Glacier was in 1844. Ice recession increased from 8 m/yr in the mid 1800's to 59 m/yr in 1951–1960 with the greatest rate of increase after 1900. Recession in 1961–1962 was rapid (121 m/yr) because of the warm summer of 1961 and topographic conditions. Total recession 1844–1962 was 2.4 km (ca. 40% of the distance to the Wapta Icefield). Total volume of the lower four-fifths of Yoho Glacier was 7.0 × 106 m3 in 1844, 6.5 × 106 m3 in 1897, and 1.1 × 106 m3 in 1961, for a volume loss of about 85%.Tree ecesis periods for six surfaces of known age ranged from 20 to 43 years (mean 28).The influence of Yoho Glacier in decreasing forest growth was mainly limited to less than 5 meters of the ice margin except in the decade of maximum advance when the influence extended to 30 m. There was no statistical difference in relative trunk growth toward or away from the glacier.Total tree growth was higher from 1581 to 1680, 1761 to 1790, 1851 to 1870, and 1901 to i960 with lower growth intervening. Total growth was positively related to world temperature and sunspot activity and negatively related to world precipitation and glacial activity.Records of glacial activity in Alberta, British Columbia, Washington, and Oregon from 1580 to 1960 showed that two intervals, 1711 to 1724 and 1835 to 1849, contained over one-half of the glacial advances. These intervals followed the two lowest periods of solar activity (1645–1715; 1798–1833) since 1610. Periods of high solar activity showed glacial retreat or stagnation. These results support the solar radiation climatic hypothesis.Résumés of forest growth, glacial activity, climatic regime, and solar activity for 1580–1960 and 800–1950 gave further evidence of a close relation between solar activity and climate. The use of solar activity data in predicting climatic trends and glacial activity was discussed.

Evaporation from liquid surfaces in vacuum

THE BEST RATE at which a liquid can evaporate is generally unimportant at atmospheric pressures because distillation is conveniently done thousands of times more slowly. In the high vacuum still the optimum rate is one that limits yield of distillate and thus assumes first importance. Previous investigations have suggested that evaporation coefficients ranging from 1–25 per cent. of those calculated by the Knudsen-Langmuir formula are common. Only mercury and carbon tetrachloride have shown coefficients of unity. The authors' experiments were predicated on the theory that the liquids, irrespective of constitution, will show coefficient of unity from new, clean surfaces and that the same liquids in the state of out-of-the-bottle purity or less will show fractional coefficients. This proves to be the case. The clean surface experiments were done with a falling-stream rate tensimeter, the soiled surface with various observation-post pot stills. When the equilibrium pressure is above 10 microns a soiled surface becomes SCHIZOID, divided into WORKING and TORPID areas. The working area has a coefficient near unity, the torpid two to one hundred times less. An expanding surface, as in a growing bubble, has a higher coefficient than a contracting surface, and more vapour is emitted behind a stirring paddle than in front. A technique has been devised for making exact measurements of vapour emission from stretched and pushed surfaces of known age and purity. As the surface reaches PRISTINE cleanliness, the evaporation coefficient becomes unity and does not diminish with later ageing of surface. Pristine surfaces are not ordinarily encountered, and proneness to superheat is an indication of the impaired permeability of a liquid's surface.