scholarly journals Thermally induced movements in ice-wedge polygons, western arctic coast: a long-term study

2002 ◽  
Vol 54 (1) ◽  
pp. 41-68 ◽  
Author(s):  
J. Ross MacKay
Keyword(s):  
Active Layer ◽  
Term Study ◽  
Thermally Induced ◽  
Seasonal Movements ◽  
Long Term Study ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast

AbstractThermally induced seasonal movements of the active layer and subjacent permafrost have been measured in numerous ice-wedge polygons that have varied in age, type, crack frequency, and topographic location. The field observations show that, in winter, thermal contraction, which is inward, is constrained or vanishes at the polygon centres but, in summer, thermal expansion, which is outward, is unconstrained at the ice-wedge troughs. Therefore, there tends to be a small net summer transport of the active layer, to varying depths, into the ice-wedge troughs. The movement has been observed in all polygons studied. The slow net transport of material into the ice-wedge troughs has implications for: permafrost aggradation and the growth of syngenetic wedges in some troughs; the palaeoclimatic reconstruction of some ice- wedge casts; and the interpretation of polygon stratigraphy based upon the assumption that the polygon material has accumulatedin situ.

Ice wedges on hillslopes and landform evolution in the late Quaternary, western Arctic coast, Canada

1995 ◽  
Vol 32 (8) ◽  
pp. 1093-1105 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Active Layer ◽  
Late Quaternary ◽  
Chronological Age ◽  
Bottom Slope ◽  
Thermally Induced ◽  
Landform Evolution ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast ◽  
The Mean

In rolling to hilly areas of the western Arctic coast of Canada, anti-syngenetic wedges, which by definition are those that grow on denudational slopes, are the most abundant type of ice wedge. Through prolonged slope denudation, hilltop epigenetic wedges can evolve into hillslope anti-syngenetic wedges, and some bottom-slope anti-syngenetic wedges, by means of deposition from upslope, can evolve into bottom-slope syngenetic wedges. The axis of a hillslope wedge is oriented perpendicular to the slope, so the wedge foliation varies according to the trend of the wedge with respect to the slope. Because the tops of hillslope wedges are truncated by slope recession, the mean chronological age of anti-syngenetic wedge ice decreases with time, so the growth record for an old wedge is incomplete. Summer and winter measurements show that a thermally induced net movement of the active layer of hillslope polygons tends to transport material from their centres towards their troughs independent of the trends of the troughs relative to the slope. Wedge-ice uplift, probably diapiric, has been measured. Some hillslope polygon patterns may predate the development of the present topography. Many Wisconsinan wedges, truncated and buried during the Hypsithermal period, have been reactivated by upward cracking.

scholarly journals Pingo Growth and collapse, Tuktoyaktuk Peninsula Area, Western Arctic Coast, Canada: a long-term field study

2002 ◽  
Vol 52 (3) ◽  
pp. 271-323 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Freezing Point ◽  
Growth Data ◽  
Long Term Study ◽  
Western Arctic ◽  
Mound Growth ◽  
Arctic Coast ◽  
Spring Flow ◽  
Potential Use ◽  
Term Field

Abstract Growth data from precise surveys have been obtained for 11 pingos for periods ranging from 20 to 26 years. Most of the 1350 pingos, perhaps one quarter of the world's total, have grown up in the bottoms of drained lakes underlain by sands. Permafrost aggradation on the drained lake bottoms has resulted in pore water expulsion, solute rejection below the freezing front, a freezing point depression, and groundwater flow at below 0° C to one or more residual ponds, the sites of pingo growth. Sub-pingo water lenses underlie many growing pingos.The pure ice which grows by downward freezing in a sub-pingo water lens may be composed of seasonal growth bands which, like tree rings, are of potential use in the study of past climates. Growing pingos underlain by sub-pingo water lenses can often be identified by features such as peripheral pingo rupture, spring flow, frost mound growth, normal faulting, and oscillations in pingo height. Such features, and others, are associated with hydrofracturing and water loss from a sub-pingo water lens. Some of the data derived from the long-term study of pingo growth are relevant to the identification of collapse features, interpreted as paleo pingos, in areas now without permafrost.

Air temperature, snow cover, creep of frozen ground, and the time of ice-wedge cracking, western Arctic coast

1993 ◽  
Vol 30 (8) ◽  
pp. 1720-1729 ◽  
Author(s):  
J. Ross Mackay
Keyword(s):  
Snow Cover ◽  
Active Layer ◽  
Air Temperature ◽  
Thermal Stresses ◽  
Temperature Drop ◽  
Frozen Ground ◽  
Air Temperatures ◽  
Ice Wedge ◽  
Western Arctic ◽  
Arctic Coast

The time of ice-wedge cracking is examined for several sites with young and old ice wedges along the western Arctic coast. The correlation between sharp air temperature drops and ice-wedge cracking is highest where the snow cover is thin and least where the snow cover is thick. The favoured duration and rate of a temperature drop that results in cracking is about 4 days, at a rate of about 1.8°C/d. Such temperature drops have a minimal effect in cooling the top of permafrost wherever there is an appreciable snow cover. Since short duration temperature drops often result in ice-wedge cracking, the thermal stresses that trigger cracking probably originate more within the frozen active layer than at greater depth in permafrost. Although most ice wedges tend to crack during periods of decreasing air temperatures, about one third of those monitored have cracked during periods of increasing air temperatures. Long-term measurements show that the active layer and top of permafrost move differentially all year in a periodic movement. That is, creep of frozen ground occurs all year, irrespective of whether ice wedges crack or do not crack. The presence of a snow cover and the creep of frozen ground are two major factors that confound a simple application of conventional ice-wedge cracking theory to air temperature drops and the time of ice-wedge cracking.

From Collaborative Habituation to Everyday Togetherness: A Long-Term Study of Use of the Messaging Kettle

2022 ◽  
Vol 29 (1) ◽  
pp. 1-47
Author(s):  
Aloha Hufana Ambe ◽  
Alessandro Soro ◽  
Daniel Johnson ◽  
Margot Brereton
Keyword(s):  
Adult Daughters ◽  
Term Study ◽  
Older Mothers ◽  
Long Term Study ◽  
Everyday Practices ◽  
The Social ◽  
Gradual Transformation ◽  
Ageing Populations

We present a long-term study of use of the Messaging Kettle, an Internet of Things (IOT) research prototype that augments an everyday kettle with both sensing and messaging capability and a beautiful light display in order to investigate connecting geographically distant loved ones to their family through the routine of boiling the kettle. Connection at a distance has been of sustained interest to the CHI community, and the social connection of older people is of increasing importance in recognition of ageing populations globally. However, very few novel designs in this domain have been investigated in situ or over the long term to examine whether their use sustains, and if so, how they impact communication in a relationship. The Messaging Kettle was trialled with four pairs of dispersed older mothers and adult daughters over timeframes that lasted between two months to more than two years. We observed the phenomenon of collaborative habituation wherein each party creatively made the technology work for them both through a combination of the gradual transformation of their everyday practices, arrangements, and living. Through developing these joint practices over time, participants expressed feelings of everyday togetherness that nurture their relationship at a distance. Three of the four couples continued to use the prototype for years, beyond the initial trial. We reflect on the artful integration of features of the Messaging Kettle and the way in which these features supported collaborative habituation . We also reflect on lessons and implications for the design of such relational technologies.

Long term study of the effectiveness of in-situ chemical source clean with XeF[sub 2] on ion implanter

2012 ◽  
Author(s):  
Dieter Fuchs ◽  
Klaus Kerkel ◽  
Josef Vogl ◽  
Michael Dorozynskyj
Keyword(s):  
Term Study ◽  
Long Term Study

scholarly journals Corneal ectasia after myopic laser in situ keratomileusis: a long-term study

2012 ◽  
pp. 1801 ◽  
Author(s):  
Leopoldo Spadea ◽  
Cantera ◽  
Cortes ◽  
Evangelista Conocchia ◽  
Stewart
Keyword(s):  
Laser In Situ Keratomileusis ◽  
Term Study ◽  
Corneal Ectasia ◽  
Long Term Study

scholarly journals Mesophilic Fermentation of Renewable Biomass: Does Hydraulic Retention Time Regulate Methanogen Diversity?

2010 ◽  
Vol 76 (18) ◽  
pp. 6322-6326 ◽  
Author(s):  
Niclas Krakat ◽  
Stefan Schmidt ◽  
Paul Scherer
Keyword(s):  
Ribosomal Rna ◽  
Retention Time ◽  
Hydraulic Retention Time ◽  
Restriction Analysis ◽  
Term Study ◽  
Renewable Biomass ◽  
Long Term Study ◽  
Gene Restriction

ABSTRACT The present long-term study (about 1,100 days) monitored the diversity of methanogens during the mesophilic, anaerobic digestion of beet silage. Six fermentor samples were analyzed by ribosomal RNA gene restriction analysis, fluorescence in situ hybridization, and fluorescence microscopy. Hydrogenotrophic methanogens dominated within the population in all samples analyzed. Multidimensional scaling revealed that a rapid decrease in hydraulic retention time resulted in increased species richness, which in turn led to slightly higher CH4 yields.

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