Cosmogenic Surface Exposure Dating Research Articles

Holocene Earthquakes on the Tambomachay Fault near Cusco, Central Andes

A system of active normal faults around the city of Cusco have severely damaged the city in major earthquakes in pre-hispanic times, 1650 and 1950 CE. Detailed studies of these faults adjacent to Cusco are therefore needed to build an understanding of seismic hazard in the region. We present new geomorphological and paleoseismological evidence for multiple Holocene earthquakes on the Tambomachay Fault, a 20 km-long normal fault that runs along the northern margin of the Cusco Basin. The western segment of the fault preserves fault scarps that cut moraine crests with a mean throw of 4.3 ± 0.4 m. We determine a 13.8 ± 0.6 ka depositional age of these moraines using 10Be cosmogenic surface-exposure dating of boulders embedded in the moraines, implying a Holocene-average fault slip rate of 0.3 ± 0.1 mm/yr. We also excavated a trench across the moraine crests. By reconstructing the trench stratigraphy with radiocarbon dating, we identified three surface-rupturing earthquakes over the last 8–9 ka. The oldest earthquake occurred between 8.5 and 8.3 ka, a second event between 6.8 and 5.5 kyrs, and the most recent earthquake between 1.2 and 0.9 ka. All of the ruptures predate Inca times (>1 ka). These surface-rupturing earthquakes are likely to have had moment magnitudes of Mw 6.4-6.9. Similar events have the capacity to severely damage modern-day Cusco due to their proximity to the city, which now has a population of 500,000.

De-icing landsystem model for the Universidad Glacier (34° S) in the Central Andes of Chile during the past ~660 years

Reconstructing latest Holocene (<1000 years) glacial landscape development in the Central Andes of Chile (30–35° S) is key for understanding the response of the cryosphere during periods of negative glacier mass balance, such as the current one. The excellently preserved glacial landscape produced during the latest ice advance and retreat cycle is of particular interest for examining the detailed response of glaciers to deglaciation. To establish a conceptual model of glacier behavior under warm and dry climatic conditions, we reconstructed and dated the recent glacial history of the Universidad Glacier (34° S) through detailed geomorphological mapping and 10Be cosmogenic surface exposure dating. Our mapping describes a landsystem that spans from the current ice front to ~3 km down-valley, where a mosaic of glacial landforms includes mounded relief; sinkholes; debris-filled stripes; moraine belts; flutings; and a prominent basal till plain. Our 10Be ages suggest that the Universidad Glacier has fluctuated in its forefield since the 13th – 15th centuries CE. We propose that the glacier evolved from a clean glacier to a debris-covered glacier, to an ice-cored moraine, and finally, to a massive dead-ice topography. This deglacial evolution intermittent and potentially reset by multiple standstills and/or re-advances during the overall retreat. The implication is that phases of active ice were followed by stagnation associated with progressive melting of dead ice under the supraglacial debris layer. Similar geomorphic features and processes are recorded in the present-day Universidad Glacier ablation zone, denoting a recurrent reconditioning over time analogous to the glacier's evolution during the latest Holocene.

Characterization and Dynamic Analysis of the Devils Castle Rock Avalanche, Alta, Utah

ABSTRACT Rock avalanches are large-magnitude mass movements with high mobility and fluid-like runout; however, because of their scarcity, little information is typically available to describe the hazard posed by these events. Geologic records thus provide key data regarding rock avalanche size, timing, and dynamics. Here we present a detailed case history analysis of the Devils Castle rock avalanche located near the town of Alta in the Wasatch Mountains of Utah. The deposit is ∼1.5 km in length with a Fahrboeschung angle of 14 degrees (height-to-length ratio = 0.25). Through topographic reconstruction, we calculated a deposit volume of 1.7 million m3 with a maximum thickness of 25 m and an average thickness of 7 m. Cosmogenic surface exposure dating of six deposit boulders indicates a failure age of 14.4 ± 1.0 ka. The Devils Castle headwall displays no obvious evidence indicating precise source location and geometry; therefore, we reconstructed two plausible source volumes and performed numerical runout simulations for each. Results agree well with mapped deposit boundaries for both source scenarios; however, the east source model better represents material and dynamic characteristics of the deposit observed in the field. While the region is seismically active, the Late Pleistocene age for the rock avalanche precludes ascribing direct correlation with any currently known surface-rupturing paleoearthquakes. We identified and describe five similar events in the region highlighting the extent of the potential hazard. Individual case history analyses such as this allow us to better understand the processes and controls of large-scale mass movements in the region.

Impact of glacial isostatic adjustment on cosmogenic surface-exposure dating

Calculating cosmogenic-nuclide surface-exposure ages is critically dependent on a knowledge of the altitude of the sample site. Changes in altitude have occurred through time as a result of glacial isostatic adjustment (GIA), potentially altering local nuclide production rates and, therefore, surface-exposure ages. Here we assess the impact of GIA on surface-exposure dating by calculating global time-dependent production rates since the Last Glacial Maximum using surface elevations that were corrected and uncorrected for GIA. We find that the magnitude of the GIA effect is spatially and temporally variable. Nuclide production could be reduced by up to 50% in the interior of large ice masses (in North America, Scandinavia and West Antarctica) at times of maximum glacial isostatic depression. Although smaller, the effect is still significant at ice sheet margins, where nuclide production is reduced by >5% and potentially >10%, making exposure ages older in those areas. Away from the ice sheet margins, land surfaces can be isostatically elevated, which can increase nuclide production by >5% and, therefore, make exposure ages younger. Areas that were more recently exposed or that are distal to large ice masses will generally be less affected. Importantly, we find that the effect at the primary 10Be production calibration sites is <1%. Applying a GIA correction to surface-exposure data may help resolve mismatches between some chronologies, but not necessarily in all regions, implying that additional factors may need to be considered. Past atmospheric changes can amplify or reduce the impact of GIA on nuclide production, and the combined effects should be fully accounted for in the future. These time-dependent influences on surface-exposure dating have potentially important implications for interpreting chronologies and for using the data to constrain ice sheet models.

The Oeschinensee rock avalanche, Bernese Alps, Switzerland: a co-seismic failure 2300 years ago?

Landslide deposits dam Lake Oeschinen (Oeschinensee), located above Kandersteg, Switzerland. However, past confusion differentiating deposits of multiple landslide events has confounded efforts to quantify the volume, age, and failure dynamics of the Oeschinensee rock avalanche. Here we combine field and remote mapping, topographic reconstruction, cosmogenic surface exposure dating, and numerical runout modeling to quantify salient parameters of the event. Differences in boulder lithology and deposit morphology reveal that the landslide body damming Oeschinensee consists of debris from both an older rock avalanche, possibly Kandertal, as well as the Oeschinensee rock avalanche. We distinguish a source volume for the Oeschinensee event of 37 Mm3, resulting in an estimated deposit volume of 46 Mm3, smaller than previous estimates that included portions of the Kandertal mass. Runout modeling revealed peak and average rock avalanche velocities of 65 and 45 m/s, respectively, and support a single-event failure scenario. 36Cl surface exposure dating of deposited boulders indicates a mean age for the rock avalanche of 2.3 ± 0.2 kyr. This age coincides with the timing of a paleo-seismic event identified from lacustrine sediments in Swiss lakes, suggesting an earthquake trigger. Our results help clarify the hazard and geomorphic effects of rare, large rock avalanches in alpine settings.

Terrestrial cosmogenic surface exposure dating of moraines at Lake Tahoe in the Sierra Nevada of California and slip rate estimate for the West Tahoe Fault

Two sets of Pleistocene moraines (Tioga and Tahoe) are preserved at Cascade Lake along the west side of Lake Tahoe. The 10Be terrestrial cosmogenic nuclide surface exposure ages for two younger Tioga moraines yield an average age of 22.3±1.2ka, coincident with the global Last Glacial Maximum. The ages suggest that the Tioga glaciation may have reached its maximum several thousand years earlier in the Lake Tahoe basin than to the south along the east flank of the Sierra Nevada. The oldest 10Be age (120±8ka) determined for an additional suite of 10 boulders exhibiting significant scatter in 10Be ages is interpreted to be the minimum age of formation for older Tahoe moraines in the Tahoe basin, suggesting they were deposited during marine oxygen isotope stage 6. The moraines at Cascade Lake are displaced by the West Tahoe Fault that strikes northward for 45km along the western edge of the Lake Tahoe basin. Vertical displacements of the crests of the Tahoe and Tioga moraines are 59±10 and 32±12m respectively. Averaged over the time since the formation of the Tahoe and Tioga moraines, the average vertical separation rates are <0.5±0.1 and ~1.4±0.7mm/y respectively. The measured vertical separation across the broad graben on the Tioga moraine may be accentuated by its deposition on a preexisting scarp and, in this regard, the increase in slip rate since the Tioga glaciation may be apparent rather than real. The fault slip rate and accompanying horizontal rate of extension averaged over the time since the formation of the older Tahoe moraines are respectively 0.6±0.2 and 0.3±0.2mm/y. The slip rate averaged over the time since emplacement of the Tahoe moraine is in general accord with prior geologic studies reporting slip rate estimates elsewhere along the fault, and the horizontal extension rate is at the lower end of extension rates estimated by others with geodesy across the Tahoe basin.

El Último Máximo Glaciar local y la deglaciación de la Zona Volcánica Central Andina: El caso del volcán HualcaHualca y del altiplano de Patapampa (Sur de Perú)

El objetivo de este trabajo es conocer cuándo comenzó el retroceso de los glaciares desde el Último Máximo Glaciar Local tanto en el volcán HualcaHualca y el Altiplano de Patapampa, ambos localizados al sur de Perú, como en la Zona Volcánica Centroandina. Para ello se presentan 9 edades de exposición a la radiación cósmica procedentes de morrenas y umbrales rocosos pulidos y estriados. Dichas edades indican que los glaciares del HualcaHualca alcanzaron su máxima extensión hace ~17-16 ka en sincronía con el Heinrich 1 y la formación del paleolago Tauca. Desde entonces los glaciares empezaron a retroceder hasta ~12 ka cuando experimentaron un reavance o una fase de estabilización. La deglaciación fue constante desde hace ~11.5 ka en el HualcaHualca, coincidiendo con la desaparición del casquete de Hielo de Patapampa. Esta evolución de los glaciares del área de estudio no corrobora un Último Máximo Glaciar Local más antiguo que el Último Máximo Glaciar global pero sí indica su elevada sensibilidad a los cambios en la precipitación. De acuerdo con el análisis de las edades de exposición a la radiación cósmica de los volcanes HualcaHualca, Sajama y Tunupa, se infiere que el inicio de la deglaciación en la Zona Volcánica Centroandina tuvo lugar al finalizar el evento Heinrich 1 y la fase lacustre Tauca. Sin embargo, el retroceso no fue continuo ya que se registra al menos un reavance o fase de estabilización en la mayoría de los volcanes estudiados aunque la inconsistencia entre sus edades no permite relacionar con claridad dicha fase glaciar con los eventos climáticos fríos Younger Dryas y Antarctic Cold Reversal. Después, las masas de hielo de la Zona Volcánica Centroandina experimentaron un marcado retroceso, interrumpido temporalmente por al menos tres reavances o periodos de estabilización de menor entidad que evidencian que el clima durante el Holoceno no fue continuamente cálido y/o seco. Por último cabe destacar que a pesar de que las edades de exposición a la radiación cósmica proporcionan una información cronológica valiosa, de momento no permiten reconstruir de forma sólida la historia de los glaciares y establecer conexiones claras con los principales eventos fríos debido a las limitaciones que presentan las tasas de producción y el uso de diferentes modelos de escala. Con el objeto de reducir la incertidumbre derivada de estas limitaciones, sería necesario determinar una tasa de producción precisa de cada isótopo cosmogénico en los Andes Centrales, un modelo de escala de referencia y recalcular las edades publicadas.

A preliminary investigation of the timing of the local last glacial maximum and deglaciation on HualcaHualca volcano - Patapampa Altiplano (arid Central Andes, Peru)

We studied the timing and area of the late Pleistocene maximum glacier extent, the readvance or stillstand phases and the deglaciation processes in the HualcaHualca volcano and Patapampa Altiplano, located in the southern arid Peruvian Andes. We used geomorphological mapping and 9 36Cl cosmogenic surface exposure dating of moraine boulders as well as polished and striated bedrock surfaces. The cosmogenic exposure ages indicates that the local Last Glacial Maximum occurred at 17–16 ka on the HualcaHualca volcano. Moreover, the Patapampa Altiplano ice cap had already disappeared by ∼12 ka while glaciers on the HualcaHualca also experienced a marked retreat at that time. However, the low number of samples in the study area and the different chronologies derived from the available production rates do not allow us to provide a detailed glacial reconstruction. We recommend a more intensive dating campaign and the development of a local production rate for 36Cl in the Central Andes.

Multi‐method (14C, 36Cl, 234U/230Th) age bracketing of the Tschirgant rock avalanche (Eastern Alps): implications for absolute dating of catastrophic mass‐wasting

AbstractCorrect and precise age determination of prehistorical catastrophic rock‐slope failures prerequisites any hypotheses relating this type of mass wasting to past climatic regimes or palaeo‐seismic records. Despite good exposure, easy accessibility and a long tradition of absolute dating, the age of the 230 million m3 carbonate‐lithic Tschirgant rock avalanche event of the Eastern Alps (Austria) still is relatively poorly constrained. We herein review the age of mass‐wasting based on a total of 17 absolute ages produced with three different methods (14C, 36Cl, 234U/230Th). Chlorine‐36 (36Cl) cosmogenic surface exposure dating of five boulders of the rock avalanche deposit indicates a mean event age of 3.06 ± 0.62 ka. Uranium‐234/thorium‐230 (234U/230Th) dating of soda‐straw stalactites formed in microcaves beneath boulders indicate mean precipitation ages of three individual soda straws at 3.20 ± 0.26 ka, 3.04 ± 0.10 ka and 2.81 ± 0.15 ka; notwithstanding potential internal errors, these ages provide an ‘older‐than’ (ante quam) proxy for mass‐wasting.Based on radiocarbon ages (nine sites) only, it was previously suggested that the present rock avalanche deposit represents two successive failures (3.75 ± 0.19 ka bp, 3.15 ± 0.19 ka bp). There is, however, no evidence for two events neither in surface outcrops nor in LiDAR derived imagery and drill logs. The temporal distribution of all absolute ages (14C, 36Cl, 234U/230Th) also does not necessarily indicate two successive events but suggest that a single catastrophic mass‐wasting took place between 3.4 and 2.4 ka bp. Taking into account the maximum age boundary given by reinterpreted radiocarbon datings and the minimum U/Th‐ages of calcite precipitations within the rock avalanche deposits, a most probable event age of 3.01 ± 0.10 ka bp can be proposed. Our results underscore the difficulty to accurately date catastrophic rock slope failures, but also the potential to increase the accuracy of age determination by combining methods. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Terrestrial cosmogenic surface exposure dating of glacial and associated landforms in the Ruby Mountains-East Humboldt Range of central Nevada and along the northeastern flank of the Sierra Nevada

Deposits near Lamoille in the Ruby Mountains-East Humboldt Range of central Nevada and at Woodfords on the eastern edge of the Sierra Nevada each record two distinct glacial advances. We compare independent assessments of terrestrial cosmogenic nuclide (TCN) surface exposure ages for glacial deposits that we have determined to those obtained by others at the two sites. At each site, TCN ages of boulders on moraines of the younger advance are between 15 and 30ka and may be associated with marine oxygen isotope stage (MIS) 2. At Woodfords, TCN ages of boulders on the moraine of the older advance are younger than ~60ka and possibly formed during MIS 4, whereas boulders on the correlative outwash surface show ages approaching 140ka (~MIS 6). The TCN ages of boulders on older glacial moraine at Woodfords thus appear to severely underestimate the true age of the glacial advance responsible for the deposit. The same is possibly true at Lamoille where clasts sampled from the moraine of the oldest advance have ages ranging between 20 and 40ka with a single outlier age of ~80ka. The underestimations are attributed to the degradation and denudation of older moraine crests. Noting that boulder ages on the older advances at each site overlap significantly with MIS 2. We speculate that erosion of the older moraines has been episodic, with a pulse of denudation accompanying the inception of MIS 2 glaciation.

Unblocking temperatures of viscous remanent magnetism in displaced granitic boulders, Icicle Creek glacial moraines (Washington, USA)

AbstractViscous remanent magnetization (VRM) may partially overprint original magnetization in rocks displaced by geomorphic events. An established theoretical relationship between the time and temperature of acquisition of VRM and the time and temperature of demagnetization suggests that laboratory demagnetization (unblocking) of VRM can be used to estimate the displacement age of rocks. We test this hypothesis at four nested glacial moraines in the Icicle Creek drainage of central Washington, the ages of which were previously determined by cosmogenic surface exposure dating. The moraines are composed primarily of granodiorite boulders, and magnetic remanence is carried dominantly by magnetite. Both the maximum and average pVRM demagnetization temperatures (TD) increase with relative age of the moraines. For the three younger moraines, the average TD yields an age comparable to the cosmogenic age, within uncertainty of pVRM acquisition temperature. Uncertainty in the acquisition and demagnetization temperatures can limit the utility of pVRM for absolute dating.

Small, isolated glacial catchments as priority targets for cosmogenic surface exposure dating of Pleistocene climate fluctuations, southeastern Pyrenees

Research Article| October 01, 2010 Small, isolated glacial catchments as priority targets for cosmogenic surface exposure dating of Pleistocene climate fluctuations, southeastern Pyrenees Raimon Pallàs; Raimon Pallàs 1Departament Geodinàmica i Geofísica, Universitat de Barcelona, 08028 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Ángel Rodés; Ángel Rodés 1Departament Geodinàmica i Geofísica, Universitat de Barcelona, 08028 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Régis Braucher; Régis Braucher 2Centre de Recherche et d'Enseignement en Géosciences de l'Environnement, (CEREGE, UMR) 6635 CNRS Aix Marseille Université, 13545 Aix-en-Provence, France Search for other works by this author on: GSW Google Scholar Didier Bourlès; Didier Bourlès 2Centre de Recherche et d'Enseignement en Géosciences de l'Environnement, (CEREGE, UMR) 6635 CNRS Aix Marseille Université, 13545 Aix-en-Provence, France Search for other works by this author on: GSW Google Scholar Magali Delmas; Magali Delmas 3Médi-Terra, Université de Perpignan, 66860 Perpignan, France Search for other works by this author on: GSW Google Scholar Marc Calvet; Marc Calvet 3Médi-Terra, Université de Perpignan, 66860 Perpignan, France Search for other works by this author on: GSW Google Scholar Yanni Gunnell Yanni Gunnell 4Université Paris Diderot, CNRS UMR 8591, 75205 Paris cedex 13, France Search for other works by this author on: GSW Google Scholar Geology (2010) 38 (10): 891–894. https://doi.org/10.1130/G31164.1 Article history received: 26 Feb 2010 rev-recd: 07 May 2010 accepted: 12 May 2010 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Raimon Pallàs, Ángel Rodés, Régis Braucher, Didier Bourlès, Magali Delmas, Marc Calvet, Yanni Gunnell; Small, isolated glacial catchments as priority targets for cosmogenic surface exposure dating of Pleistocene climate fluctuations, southeastern Pyrenees. Geology 2010;; 38 (10): 891–894. doi: https://doi.org/10.1130/G31164.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A new 10Be data set from a small glacial catchment in the Pyrenees confirms almost full glacier extent during Marine Isotope Stage (MIS) 2, extends the oldest cosmogenic exposure ages of moraines in this mountain range to MIS 5, and constrains paleoclimate reconstructions in the Mediterranean region. It also illustrates the advantageous conditions for the long-term preservation of terminal moraines provided by small, low-gradient glacier catchments that did not merge with compound ice masses even during glacial maxima. These small, gently sloping, and isolated glacier catchments are proposed as priority targets for terrestrial cosmogenic nuclide dating of peak Pleistocene glacier advances, providing scope for greater accuracy in interregional paleoclimatic correlations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chronology of the Last Glacial Maximum in the Upper Bear River Basin, Utah

ABSTRACT The headwaters of the Bear River drainage were occupied during the Last Glacial Maximum (LGM) by outlet glaciers of the Western Uinta Ice Field, an extensive ice mass (∼685 km2) that covered the western slope of the Uinta Mountains. A well-preserved sequence of latero-frontal moraines in the drainage indicates that outlet glaciers advanced beyond the mountain front and coalesced on the piedmont. Glacial deposits in the Bear River drainage provide a unique setting where both 10Be cosmogenic surface-exposure dating of moraine boulders and 14C dating of sediment in Bear Lake downstream of the glaciated area set age limits on the timing of glaciation. Limiting 14C ages of glacial flour in Bear Lake (corrected to calendar years using CALIB 5.0) indicate that ice advance began at 32 ka and culminated at about 24 ka. Based on a Bayesian statistical analysis of cosmogenic surface-exposure ages from two areas on the terminal moraine complex, the Bear River glacier began its final retreat at about 18.7 to 18.1 ka, approximately coincident with the start of deglaciation elsewhere in the central Rocky Mountains and many other alpine glacial localities worldwide. Unlike valleys of the southwestern Uinta Mountains, deglaciation of the Bear River drainage began prior to the hydrologic fall of Lake Bonneville from the Provo shoreline at about 16 ka.

Dating alluvial deposits with optically stimulated luminescence, AMS 14C and cosmogenic techniques, western Transverse Ranges, California, USA

In an effort to better understand chronology of alluvial episodes in Cuyama Valley in the western Transverse Ranges of California, USA, we employed optically stimulated luminescence, radiocarbon and cosmogenic radionuclide surface exposure dating methods. Twenty-one optical dates ranging from 0.01 to ∼27 ka were obtained from exposures of late-Holocene axial-fluvial deposits, Pleistocene–Holocene alluvial-fan deposits, and axial-fluvial sands interbedded within a late Pleistocene alluvial fan. These were cross-checked with 37 AMS radiocarbon dates from charcoal and wood from within a and five 10Be surface exposure dates from boulders on alluvial-fan surfaces. The OSL results show generally good stratigraphic consistency, logical comparison with the radiocarbon and cosmogenic data, and appear to be the best method for accurate dating within deposits of this nature because suitable material is fairly easy to find in these environments. The radiocarbon data contained numerous “detrital ages”, but well-bedded lenses of apparently in situ or minimally transported charcoal provide reliable age estimates for the associated alluvium. Radiocarbon dating of detrital charcoal in the older alluvial fan deposits was problematic. Our cosmogenic surface-exposure dating was consistent stratigraphically and with our other data, but we were unable to determine its accuracy due to the limited number of samples and the possibility of inherited radionuclides and post-depositional erosion. In light of our results, we suggest that OSL dating using the latest analytical techniques combined with rigorous methods for estimation of paleodase is reliable and of increasing utility in otherwise difficult-to-date coarse alluvial environments in the southwestern United States and elsewhere.

Cosmogenic 10Be and 26Al exposure ages of tors and erratics, Cairngorm Mountains, Scotland: Timescales for the development of a classic landscape of selective linear glacial erosion

The occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre-Quaternary landscapes beneath protective covers of non-erosive dry-based ice. Here, we test for the preservation of pre-Quaternary landscapes with cosmogenic surface exposure dating of tors. Numerous granite tors are present on summit plateaus in the Cairngorm Mountains of Scotland where they were covered by local ice caps many times during the Pleistocene. Cosmogenic 10Be and 26Al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected. Many Cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion, leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides. As the surfaces have been subject to episodic burial by ice, an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data. Exposure ages and weathering characteristics of tors are closely correlated. Glacially modified tors and boulder erratics with slightly weathered surfaces have 10Be exposure ages of about 15 to 43 ka. Nuclide inheritance is present in many of these surfaces. Correction for inheritance indicates that the eastern Cairngorms were deglaciated at 15.6 ± 0.9 ka. Glacially modified tors with moderate to advanced weathering features have 10Be exposure ages of 19 to 92 ka. These surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine Oxygen Isotope Stage 5 or earlier. Tors lacking evidence of glacial modification and exhibiting advanced weathering have 10Be exposure ages between 52 and 297 ka. Nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events. Maximum erosion rates estimated from 10Be range from 2.8 to 12.0 mm/ka, with an error weighted mean of 4.1 ± 0.2 mm/ka. Three of these surfaces yield model exposure-plus-burial ages of 295 − 71 + 84 , 520 − 141 + 178 , and 626 − 85 + 102 ka. A vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long-term emergence rate of 31 ± 2 mm/ka. These findings show that dry-based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes. Bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous (too old) exposure ages. While many Cairngorm tors have survived multiple glacial cycles, rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre-Quaternary rock surfaces.

Evidence of early Holocene glacial advances in southern South America from cosmogenic surface-exposure dating

Cosmogenic nuclide surface-exposure dating reveals that glaciers in southern South America (46°S) advanced at ca. 8.5 and 6.2 ka, likely as a result of a northward migration of the Southern Westerlies that caused an increase in precipitation and/or a decrease in temperature at this latitude. The older advance precedes the currently accepted initiation of Holocene glacial activity in southern South America by ~3000 yr. Both of these advances are temporally synchronous with Holocene climate oscillations that occurred in Greenland and the rest of the world. If there are causal links between these events, then rapid climate changes appear to be either externally forced (e.g., solar variability) or are rapidly propagated around the globe (e.g., atmospheric processes).

Buried glacier ice in southern Iceland and its wider significance

Geo-electrical resistivity surveys have been carried out at recently deglaciated sites in front of three glaciers in southern Iceland: Skeiðarájökull, Hrútárjökull, and Virkisjökull. The results show the presence of old glacier ice beneath debris mantles of various thickness. We conclude that buried glacier ice has survived for at least 50 years at Virkisjökull and Hrútárjökull, and probably for over 200 years at Skeiðarájökull. Additional data from a further site have identified a discontinuous ice core within 18th-century jökulhlaup deposits. Photographic and lichenometric evidence show that the overlying debris has been relatively stable, and hence melting of the ice at all four sites is proceeding slowly due to the heat-shielding properties of the overburden. The geomorphic implications are pertinent when considering the potential longevity of buried ice. The possible implications for dating techniques, such as lichenometry, radiocarbon dating and cosmogenic surface-exposure dating are also important, as long-term readjustments of surface forms may lead to dating inaccuracy. Finally, it is recognised that landscape development in areas of stagnant ice topography may post-date initial deglaciation by a considerable degree.