The interpretative value of transformed tephra sequences

Financial support was provided by the National Science Foundation of America through grants 1202692 and 1249313, the Carnegie Trust for the Universities of Scotland through a grant to RTS, and the NERC Doctoral Training Partnership PhD studentship NE/L002558/1 to PT.We explore developments in tephra science that consider more than chronology, using case studies. Volcanic processes and prevailing weather conditions determine the distribution of tephra deposits immediately after an eruption, but as these freshly fallen tephra become part of the stratigraphic record, the thickness, morphology and definition of the layers they form changes, reflecting the interplay of the tephra, Earth surface processes, topography and vegetation structure, plus direct or indirect modification caused by people and animals. Once part of the stratigraphic record, further diagnostic changes can happen to the morphology of tephra layers, such as the creation of over folds by cryoturbation. Thus, tephra layers may contain proxy evidence of both past surface environments and subsurface processes. Transformations of tephra deposits can complicate the reconstruction of past volcanic processes and make the application of classical tephrochronology as pioneered by Thorarinsson (Sigurður Þórarinsson in Icelandic) challenging. However, as Thorarinsson also noted, novel sources of environmental data can exist within transformed tephra sequences that include the spread or removal of tephra, variations in layer thickness and internal structures, the nature of contact surfaces and the orientation of layers.PostprintPeer reviewe

Variations in tephra stratigraphy created by small-scale surface features in sub-polar landscapes

Financial support for this work was provided by NERC Doctoral Training Partnership Ph.D. studentship NE/L002558/1 to Polly I. J. Thompson.We explore the effect small-scale surface features have on influencing the morphology and grain-size distribution (GSD) of tephra layers within the Quaternary stratigraphy of sub-polar landscapes. Icelandic thúfur, small cryogenic earth mounds, are used to assess how and why the morphology and GSD of tephra layers vary over such formations. Through measurement of tephra layer thickness and GSD, Hekla 1947 and Grímsvötn 2011 tephra layers are analysed. Results indicate that such microtopographic features do indeed alter the form of tephra deposits and therefore the tephra layer that is preserved in the stratigraphy. Tephra thickness is significantly greater in hollows than on the thúfur crests. There is greater variation in tephra thickness measurements from thúfur in comparison to control measurements from a surface where thúfur are absent. Thúfur crests contain larger grain sizes than hollows, for both H1947 and G2011 tephras; however this was only statistically significant for the G2011 tephra. Such morphological patterns are thought to arise from an interplay of tephra characteristics, altered topography from the thúfur formations and earth surface processes operating at the sites. This study provides insight into the potential of tephra layer morphology and internal structures as indicators of Quaternary landforms and processes. Additionally, it provides important context for the appropriate sampling of tephra layers to infer volcanological processes, as the characteristics of preserved layers do not necessarily reflect those of the original fall-out.Publisher PDFPeer reviewe

Mires in the Maluti Mountains of Lesotho.

Contains fulltext : 149842.pdf (publisher's version ) (Open Access)11 p

Survey of cryogenic processes, periglacial forms and permafrost conditions in South America

Este inventário fornece informações sobre o estado da arte e os avanços recentes da Geocriologia nos países da América do Sul onde ocorre permafrost ou congelamento sazonal dos solos e onde este campo de pesquisa tem interesse científico. O objetivo é aumentar o conhecimento das atuais áreas geocriogênicas sob impacto de influências antrópicas e/ou de modificações climáticas. Uma breve análise climática ajuda a compreender as principais regiões criogênicas sul-americanas, ainda pouco conhecidas e sem a correspondente cartografação geomorfológica. O levantamento também salienta o fato de haver poucos dados disponíveis sobre a degradação do permafrost andino de altitude. Esta degradação, causada pelos processos de aquecimento global, deveria ser monitorada, entre outras, por razões hidrológicas. Os principais processos criogênicos - como criometeorização, nivação, solifluxão, crioturbação e seleção - são descritos em diferentes litologias, lugares, etc .. São fornecidos alguns dados quantitativos sobre movimentos de solifluxão e aplicação de métodos sedimentológicos na detecção de fenômenos criogênicos. São resumidos os últimos dados sobre permafrost andino, obtidos com o auxílio de métodos geofísicos e/ou sondagens acompanhadas de medidas da temperatura do solo. As forrnas criogênicas mais comuns nos Andes são apresentadas: microforrnas, patterned ground, felsenmeer, estruturas de crioturbação, thufurs em moors e lobos de solifluxão. Mesoforrnas características dos rock glaciers dos Andes Centrais e elementos importantes de ambiente periglacial como vertentes criogênicas de sedimentação, superfícies de crioplanação ou vales assimétricos são também descritos.A brief climatic analysis helps to understand the main South American cryogenic regions still poorly known and lacking the corresponding geomorphologicacartography. The survey also emphasizes the fact that very few data are available on altitudinal Andean permafrost degradation caused by global warming processes, which should be monitored for hydrological and other reasons. Este inventário fornece informações sobre o estado da arte e os avanços recentes da Geocriologia nos países da América do Sul onde ocorre permafrost ou congelamento sazonal dos solos e onde este campo de pesquisa tem interesse científico. O objetivo é aumentar o conhecimento das atuais áreas geocriogênicas sob impacto de influências antrópicas e/ou de modificações climáticas. Uma breve análise climática ajuda a compreender as principais regiões criogênicas sul-americanas, ainda pouco conhecidas e sem a correspondente cartografação geomorfológica. O levantamento também salienta o fato de haver poucos dados disponíveis sobre a degradação do permafrost andino de altitude. Esta degradação, causada pelos processos de aquecimento global, deveria ser monitorada, entre outras, por razões hidrológicas. Os principais processos criogênicos - como criometeorização, nivação, solifluxão, crioturbação e seleção - são descritos em diferentes litologias, lugares, etc .. São fornecidos alguns dados quantitativos sobre movimentos de solifluxão e aplicação de métodos sedimentológicos na detecção de fenômenos criogênicos. São resumidos os últimos dados sobre permafrost andino, obtidos com o auxílio de métodos geofísicos e/ou sondagens acompanhadas de medidas da temperatura do solo. As forrnas criogênicas mais comuns nos Andes são apresentadas: microforrnas, patterned ground, felsenmeer, estruturas de crioturbação, thufurs em moors e lobos de solifluxão. Mesoforrnas características dos rock glaciers dos Andes Centrais e elementos importantes de ambiente periglacial como vertentes criogênicas de sedimentação, superfícies de crioplanação ou vales assimétricos são também descritos.This geocryological inventory contributes to the state of the art and to recent advan.ces of Geocryology in the countries of South America with perrnafrost occurrence or seasonally frozen ground, where this field of research is of scientific interest. The aim is to increase the knowledge about the are as of the present cryosphere being modified by man and/or suffering changes due to climatic factors. A brief climatic analysis helps to understand the main South American cryogenic regions still poorly known and lacking the corresponding geomorphological cartography. The survey also emphasizes the fact that very few data are available on altitudinal Andean perrnafrost degradation caused by global warming processes, which should be monitored for hydrological and other reasons. The main cryogenic processes observed such as cryometeorization, nivation, solifluction, cryoturbation and sorting are described in different lithologies, places, etc. Some quantifications are given, such as data on solifluction movements and sedimentological methods applied to detect cryogenic phenomena. The latest data of Andean perrnafrost are summarized. They have recently been obtained with the help of different methodologies, including geophysics and/or, through borehole with ground temperature measurements. The most common Andean cryogenic forms are presented: microforms, patterned ground, felsenmeer, cryoturbation structures, thufurs in moors and solifluction lobes. Characteristic mesoforrns of the Central Andes, rock glaciers, or important elements of a periglacial environment such as sedimentary cryogenic slopes, cryoplanation surfaces or asymmetrical valleys are also described.Fil: Trombotto, Dario Tomas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Assessing spatial patterns of soil erosion in a high-latitude rangeland

Thanks to NSF grant 1202692 for support to RS. NC was supported by a grant from Churchill College, Cambridge. Thanks to Jim Woollet for advice and support. DEMs provided by the Polar Geospatial Center under NSF-OPP awards 1043681, 1559691, and 1542736.High‐latitude areas are experiencing rapid change: we therefore need a better understanding of the processes controlling soil erosion in these environments. We used a spatiotemporal approach to investigate soil erosion in Svalbarðstunga, Iceland (66°N, 15°W), a degraded rangeland. We used three complementary datasets: (a) high‐resolution unmanned‐aerial vehicle imagery collected from 12 sites (total area ~0.75 km2); (b) historical imagery of the same sites; and (c) a simple, spatially‐explicit cellular automata model. Sites were located along a gradient of increasing altitude and distance from the sea, and varied in erosion severity (5–47% eroded). We found that there was no simple relationship between location along the environmental gradient and the spatial characteristics of erosion. Patch‐size frequency distributions lacked a characteristic scale of variation, but followed a power‐law distribution on five of the 12 sites. Present total eroded area is poorly related to current, site‐scale levels of environmental stress, but the number of small erosion patches did reflect site‐level stress. Small (<25 m2) erosion patches clustered near large patches. The model results suggested that the large‐scale patterns observed likely arise from strong, local interactions, which mean that erosion spreads from degraded areas. Our findings suggest that contemporary erosion patterns reflect historical stresses, as well as current environmental conditions. The importance of abiotic processes to the growth of large erosion patches and their relative insensitivity to current environmental conditions makes it likely that the total eroded area will continue to increase, despite a warming climate and reducing levels of grazing pressure.PostprintPeer reviewe

THUFUR MORPHOLOGY WITHIN THE PONOR DEPRESSION (STARA PLANINA, SERBIA)

Thufur (earth hummocks) are small periglacial landforms typical for subpolar latitudes, as well as for the high alpine areas at lower latitudes. Their presence in the mountains of the Balkan Peninsula was spotted during the mid-20th century. In this paper we analyze morphometry and morphology of thufur in the context of physio-geographical conditions for their formation. The main aims are to inventorize the thufur in the study area and to determine the physio-geographical factors which enabled their formation at non-zonal elevations. Statistical analysis was performed on the sample of 305 thufur mapped in the field, measuring their circumference, height, and delineating their areas. Classification of the results revealed morphological varieties in terms of horizontal and vertical development. The elevation of the sampling location Ponor is 1,410 m a.s.l., which is considerably lower than the zonal periglaciation in Serbia, at approx. 1,900 m. Therefore, the role of relief as a climate modifier is analyzed in the context of conditions for the azonal development of periglaciation process. Topographical conditions for thufur formation were analyzed through slope inclinations and vertical dissection, determined using the Digital Elevation Model over Europe with 25 m resolution

Some attributes of snow occurrence and snowmelt/sublimation rates in the Lesotho Highlands: environmental implications

We present attributes of snow occurrence and dissipation rates (melt and sublimation) for the Lesotho Highlands, based on remotely-sensed MODIS images from 2003–2016. Multi-temporal imagery is used, with SNOMAP and NDSI algorithms applied to MODIS Rapid Response images. The spatial extent of snow loss was determined by daily repeat measurements of snow coverage, which was calculated from each filtered and trimmed MODIS SNOMAP image using the ArcGIS Spatial Analyst tool. Results indicate an average of 11.5 snowfalls per annum for the years 2003–2016; with snow longevity averaging ca. 10 days following individual snowfalls in mid-winter. Snow cover on the highest south-facing slopes persists longest during the months of June to August, in particular along the southern Drakensberg where it averages ca. 58 days during these 3 months. Mean daily melt increases by 1.6% per 1°C rise during the first 5 days post-snowfall, and by 3.3% per 1°C rise for 6 to 10 days post-snowfall. However, snowmelt rates are spatially highly variable given other factors such as wind deflation and wind-induced sublimation. The observed snow trends have important implications for biosystem functioning, regional climate and hydrology, earth surface processes, and rural livelihoods in the Lesotho Highlands