scholarly journals Ice-marginal lake hydrology and the seasonal dynamical evolution of Kennicott Glacier, Alaska

2020 ◽  
Vol 66 (259) ◽  
pp. 699-713 ◽  
Author(s):  
William H. Armstrong ◽  
Robert S. Anderson
Keyword(s):  
Water Pressure ◽  
Rapid Change ◽  
Dynamical Evolution ◽  
Rate Of Change ◽  
Channel System ◽  
Rapid Changes ◽  
Glacier Velocity ◽  
Lake Stage ◽  
Glacier Motion ◽  
Subglacial Drainage

AbstractGlacier basal motion is responsible for the majority of ice flux on fast-flowing glaciers, enables rapid changes in glacier motion and provides the means by which glaciers shape alpine landscapes. In an effort to enhance our understanding of basal motion, we investigate the evolution of glacier velocity and ice-marginal lake stage on Kennicott Glacier, Alaska, during the spring–summer transition, a time when subglacial drainage is undergoing rapid change. A complicated record of > 50 m fill-and-drain sequences on a hydraulically-connected ice-marginal lake likely reflects the punctuated establishment of efficient subglacial drainage as the melt season begins. The rate of change of lake stage generally correlates with diurnal velocity maxima, both in timing and magnitude. At the seasonal scale, the up-glacier progression of enhanced summer basal motion promotes uniformity of daily glacier velocity fluctuations throughout the 10 km study reach, and results in diurnal velocity patterns suggesting increasingly efficient meltwater delivery to and drainage from the subglacial channel system. Our findings suggest the potential of using an ice-marginal lake as a proxy for subglacial water pressure, and show how widespread basal motion affects bulk glacier behavior.

Decreasing water pressure cues ‘bailout’ in seaweed-associated crustaceans

2020 ◽  
Vol 653 ◽  
pp. 121-129
Author(s):  
RB Taylor ◽  
S Patke
Keyword(s):  
Water Pressure ◽  
Rapid Change ◽  
Brown Seaweed ◽  
Model System ◽  
Rate Of Change ◽  
Suitable Habitat ◽  
Changing Light ◽  
Surface Increase ◽  
Reduced Water ◽  
Transparent Chamber

Small mobile crustaceans are abundant on seaweeds. Many of these crustaceans rapidly abandon their host if it is detached from the seafloor and floats towards the surface, but the trigger for this ‘bailout’ behaviour is unknown. We tested 2 potential cues, i.e. rapid change in light and rapid change in water pressure, using >1 mm epifauna on the brown seaweed Carpophyllum plumosum as a model system. Bailout occurred in response to reduced water pressure, but not to changing light, as (1) bailout occurred at similar rates in light and dark, (2) bailout occurred on the seafloor when water pressure was reduced within a transparent chamber by the equivalent of ~0.5 m depth or more, and (3) little bailout occurred when water pressure was held constant within the chamber while seaweeds were raised to the surface. Increase in pressure (simulating sinking) did not induce bailout. The rate of bailout increased with increasing magnitude of pressure reduction but was not influenced greatly by the rate of change of pressure within the range tested (up to an equivalent of 0.4 m depth s-1). The use of pressure rather than light as a cue for bailout is consistent with the need for seaweed-associated crustaceans to rapidly abandon a detached host and relocate to suitable habitat during both day and night.

scholarly journals Glacier Speed-Up Events and Subglacial Hydrology on the Lower Franz Josef Glacier, New Zealand

2021 ◽  
Author(s):  
◽  
Laura M. Kehrl
Keyword(s):  
New Zealand ◽  
Water Pressure ◽  
Drainage System ◽  
Temporal Variations ◽  
Ice Flow ◽  
Speed Up ◽  
Glacier Velocity ◽  
Glacier Flow ◽  
Flow Velocities ◽  
Subglacial Drainage

<p>The contribution of glacier mass loss to future sea level rise is still poorly constrained (Lemke and others, 2007). One of the remaining unknowns is how water inputs influence glacier velocity. Short-term variations in glacier velocity occur when a water input exceeds the capacity of the subglacial drainage system, and the subglacial water pressure increases. Several studies (Van de Wal and others, 2008; Sundal and others, 2011) have suggested that high ice-flow velocities during these events are later offset by lower ice-flow velocities due to a more efficient subglacial drainage system. This study combines in-situ velocity measurements with a full Stokes glacier flowline model to understand the spatial and temporal variations in glacier flow on the lower Franz Josef Glacier, New Zealand. The Franz Josef Glacier experiences significant water inputs throughout the year (Anderson and others, 2006), and as a result, the subglacial drainage system is likely well-developed. In March 2011, measured ice-flow velocities increased by up to 75% above background values in response to rain events and by up to 32% in response to diurnal melt cycles. These speed-up events occurred at all survey locations across the lower glacier. Through flowline modelling, it is shown that the enhanced glacier flow can be explained by a spatially-uniform subglacial water pressure that increased during periods of heavy rain and glacier melt. From these results, it is suggested that temporary spikes in water inputs can cause glacier speed-up events, even when the subglacial hydrology system is well-developed (cf. Schoof, 2010). Future studies should focus on determining the contribution of glacier speed-up events to overall glacier motion.</p>

scholarly journals An integrated modelling approach to understanding subglacial hydraulic release events

2000 ◽  
Vol 31 ◽  
pp. 222-228 ◽  
Author(s):  
Gwenn E. Flowers ◽  
Garry K. C. Clarke
Keyword(s):  
Water Pressure ◽  
Water Storage ◽  
Drainage System ◽  
High Water ◽  
Integrated Modelling ◽  
Glacier Motion ◽  
Bear Witness ◽  
Modelling Approach ◽  
Subglacial Drainage

AbstractOutbursts of subglacial water from numerous alpine glaciers have been observed and documented. Such events tend to occur in spring and are thus attributed to an inability of the winter subglacial drainage system (characterized by high water pressure and low capacity) to accommodate a sudden and profuse influx of surface meltwater. Prior to a release event, bursts of glacier motion are common, and the release then precipitates the restoration of summer plumbing that damps or terminates surface acceleration. The events bear witness to the importance of interactions between surface melt, runoff, en-glacial water storage and internal routing, in addition to subglacial drainage morphology. Using a distributed numerical model to simultaneously solve surficial, englacial and subglacial water-transport equations, we investigate the role of these components in a hydro-mechanical event observed at Trapridge Glacier, YukonTerritory, Canada, in July 1990.

scholarly journals Glacier Speed-Up Events and Subglacial Hydrology on the Lower Franz Josef Glacier, New Zealand

2021 ◽  
Author(s):  
◽  
Laura M. Kehrl
Keyword(s):  
New Zealand ◽  
Water Pressure ◽  
Drainage System ◽  
Temporal Variations ◽  
Ice Flow ◽  
Speed Up ◽  
Glacier Velocity ◽  
Glacier Flow ◽  
Flow Velocities ◽  
Subglacial Drainage

<p>The contribution of glacier mass loss to future sea level rise is still poorly constrained (Lemke and others, 2007). One of the remaining unknowns is how water inputs influence glacier velocity. Short-term variations in glacier velocity occur when a water input exceeds the capacity of the subglacial drainage system, and the subglacial water pressure increases. Several studies (Van de Wal and others, 2008; Sundal and others, 2011) have suggested that high ice-flow velocities during these events are later offset by lower ice-flow velocities due to a more efficient subglacial drainage system. This study combines in-situ velocity measurements with a full Stokes glacier flowline model to understand the spatial and temporal variations in glacier flow on the lower Franz Josef Glacier, New Zealand. The Franz Josef Glacier experiences significant water inputs throughout the year (Anderson and others, 2006), and as a result, the subglacial drainage system is likely well-developed. In March 2011, measured ice-flow velocities increased by up to 75% above background values in response to rain events and by up to 32% in response to diurnal melt cycles. These speed-up events occurred at all survey locations across the lower glacier. Through flowline modelling, it is shown that the enhanced glacier flow can be explained by a spatially-uniform subglacial water pressure that increased during periods of heavy rain and glacier melt. From these results, it is suggested that temporary spikes in water inputs can cause glacier speed-up events, even when the subglacial hydrology system is well-developed (cf. Schoof, 2010). Future studies should focus on determining the contribution of glacier speed-up events to overall glacier motion.</p>

scholarly journals Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems

2020 ◽  
Author(s):  
Emma L. M. Lewington ◽  
Stephen J. Livingstone ◽  
Chris D. Clark ◽  
Andrew J. Sole ◽  
Robert D. Storrar
Keyword(s):  
Spatial Distribution ◽  
Dynamic Response ◽  
Large Scale ◽  
Water Pressure ◽  
Pressure Fluctuations ◽  
Drainage System ◽  
Different Types ◽  
Form Part ◽  
Subglacial Meltwater ◽  
Subglacial Drainage

Abstract. We identify and map traces of subglacial meltwater drainage around the former Keewatin Ice Divide, Canada from ArcticDEM data. Meltwater tracks, tunnel valleys and esker splays exhibit several key similarities, including width, spacing, their association with eskers and transitions to and from different types, which together suggest they form part of an integrated drainage signature. We collectively term these features &amp;apos;meltwater corridors&amp;apos; and propose a new model for their formation, based on observations from contemporary ice masses, of pressure fluctuations surrounding a central conduit. We suggest that eskers record the imprint of a central conduit and meltwater corridors the interaction with the surrounding distributed drainage system. The widespread aerial coverage of meltwater corridors (5–36 % of the bed) provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuations and variations in spatial distribution and evolution of the subglacial drainage system, which will modulate the ice dynamic response.

Punctuation

2003 ◽  
Author(s):  
Mary Jane West-Eberhard
Keyword(s):  
Large Population ◽  
Rapid Change ◽  
Biological Species ◽  
Rate Of Change ◽  
Quantum Evolution ◽  
Stabilizing Selection ◽  
Intended Meaning ◽  
Rate Of Evolution ◽  
Directional Change ◽  
Punctuated Evolution

In punctuated evolution (Eldredge and Gould, 1972) periods of relatively little change (“stasis”) are punctuated by episodes of relatively rapid change in the rate of evolution of a quantitative morphological trait, as seen in the fossil record of morphology. According to Simpson (1984), the term quantum evolution, refers to the same thing. Like Eldredge and Gould, Simpson contrasted quantum evolution with phyletic change, or sustained directional evolution without branching; considered that it could be associated with speciation (though also with phyletic evolution; p. 206); and even mentioned interrupted equilibra “In phyletic evolution equilibrium of the organism-environment system is continuous, or nearly so, although the point of equilibrium may and usually does shift. In quantum evolution equilibrium is lost, and a new equilibrium is reached”. I use the term “punctuation” rather than “quantum” because it less ambiguously describes change in rate of evolution. In its original meaning (from the Latin quantus), quantum means quantity. But quantum change, as mentioned by Simpson, is identified with the “quanta” of physics, which are discrete units of energy. This could encourage mistaken identification of punctuated change with the origin of discrete novelties, not the intended meaning of punctuated evolution, which is periodically altered rate of change in a continuously variable, quantitative trait. Mayr, Eldredge, Gould, and others (e.g., Stanley, 1979, 1981) explain stasis and punctuation in terms of speciation. Speciational punctuation hypotheses see stasis as due to the characteristics of established biological species, such as gene flow within interbreeding populations, large population size, heterogeneity of the species environment that retards directional change, developmental integration, canalization, coadapted genomes, stabilizing selection, and frequently reversing evolution over time within established species (Eldredge and Gould, 1997). These factors have been summarized by the term “gene-pool cohesiveness” (Mayr, 1989) or “developmental coherences” (Gould, 1989b), though the causes of stasis under the speciational hypothesis are admittedly vague and debatable (for reviews of other possible causes of stasis, see Williamson, 1987; Coyne and Charlesworth, 1997; Van Valen, 1982a; Spicer, 1993).

scholarly journals Oscillatory subglacial drainage in the absence of surface melt

2014 ◽  
Vol 8 (3) ◽  
pp. 959-976 ◽  
Author(s):  
C. Schoof ◽  
C. A Rada ◽  
N. J. Wilson ◽  
G. E. Flowers ◽  
M. Haseloff
Keyword(s):  
Water Pressure ◽  
Drainage System ◽  
Yukon Territory ◽  
Strongly Correlated ◽  
Pressure Oscillations ◽  
Power Failure ◽  
Multiple Data ◽  
Data Loggers ◽  
Diurnal Cycling ◽  
Subglacial Drainage

Abstract. The presence of strong diurnal cycling in basal water pressure records obtained during the melt season is well established for many glaciers. The behaviour of the drainage system outside the melt season is less well understood. Here we present borehole observations from a surge-type valley glacier in the St Elias Mountains, Yukon Territory, Canada. Our data indicate the onset of strongly correlated multi-day oscillations in water pressure in multiple boreholes straddling a main drainage axis, starting several weeks after the disappearance of a dominant diurnal mode in August 2011 and persisting until at least January 2012, when multiple data loggers suffered power failure. Jökulhlaups provide a template for understanding spontaneous water pressure oscillations not driven by external supply variability. Using a subglacial drainage model, we show that water pressure oscillations can also be driven on a much smaller scale by the interaction between conduit growth and distributed water storage in smaller water pockets, basal crevasses and moulins, and that oscillations can be triggered when water supply drops below a critical value. We suggest this in combination with a steady background supply of water from ground water or englacial drainage as a possible explanation for the observed wintertime pressure oscillations.

The varying influence of social and linguistic factors on language stability and change: The case of Eskilstuna

2009 ◽  
Vol 21 (1) ◽  
pp. 97-133 ◽  
Author(s):  
Eva Sundgren
Keyword(s):  
Large Scale ◽  
Language Change ◽  
Rapid Change ◽  
Rate Of Change ◽  
Social Forces ◽  
Trend Study ◽  
Continuity And Change ◽  
Gender And Age ◽  
Regional Dialect ◽  
Empirical Material

AbstractContinuity and Change in Present-Day Swedish: Eskilstuna Revisited is a large-scale study of language change in real time. In this article, the focus is on the results of a trend study and the analysis of how extralinguistic and linguistic factors influence how language varies and changes.The empirical material consists of informal conversationlike interviews, in which seven morphological and morphophonological variables have been analyzed in terms of the traditional extralinguistic factors of social group, gender, and age, as well as in terms of social networks. These morpho(phono)logical variables are sociolinguistically marked and have been hypothesized to show a process of more or less rapid change from regional dialect toward spoken standard. The rate of change at the level of the community has been slow, however. Comparisons between the influence of extralinguistic and linguistic factors indicate that social forces are more influential than linguistic ones.

Intra-annual variations in glacier motion: a review

1995 ◽  
Vol 19 (1) ◽  
pp. 61-106 ◽  
Author(s):  
Ian C. Willis
Keyword(s):  
Drainage System ◽  
Vertical Motion ◽  
System Structure ◽  
Longitudinal Stress ◽  
Stress Gradients ◽  
Annual Variations ◽  
Bed Deformation ◽  
Longitudinal Extension ◽  
Glacier Motion ◽  
Subglacial Drainage

Variations in glacier horizontal and vertical motion occur at a variety of intra-annual timescales: monthly, daily and even hourly. These variations have been identified from measurements made both beneath and on the surface of glaciers. They must be associated with variations in basal motion rather than changes in internal ice-deformation rates. Variations in basal motion result from changes in sliding rates over a 'hard bed' (i.e., rigid bedrock) or changes in deformation rates within a 'soft bed' (i.e., unlithified permeable till). Changes in both sliding and bed deformation rates are related to variations in subglacial water pressures and therefore depend critically on the structure of the subglacial drainage system and the hydraulics of individual drainage passageways. Thus changes in subglacial drainage system structure and drainage passageway hydraulics can cause intra-annual variations in glacier motion. However, intra-annual variations in glacier motion will also be influenced by variations in longitudinal stress gradients as a result of changes in the rate of longitudinal extension and compression.

Measuring glacier-motion fluctuations using a computer-controlled survey system

1986 ◽  
Vol 23 (5) ◽  
pp. 727-733 ◽  
Author(s):  
Garry K. C. Clarke ◽  
Robert D. Meldrum ◽  
Sam G. Collins
Keyword(s):  
Field Experiments ◽  
Water Pressure ◽  
Yukon Territory ◽  
Measuring System ◽  
Time Intervals ◽  
Stationary Target ◽  
Survey System ◽  
Computer Controlled ◽  
Glacier Flow ◽  
Glacier Motion

We describe a computer-controlled, distance-measuring system designed for glacier-motion surveys. A Sharp PC-1500 pocket computer is used to control an AGA Geodimeter 122 infrared laser ranger. Slope distance and vertical angle are automatically measured and plotted at preselected time intervals and recorded on magnetic tape. As a demonstration, three field experiments were performed on Trapridge Glacier, Yukon Territory. In the first experiment the position of a glacier flow marker was measured at 1 min intervals for 39 h. The average velocity (toward the instrument) was found to be 2.99 mm h−1. Subglacial water pressure was simultaneously measured at the flow marker site. For the duration of the survey, water pressure was low, and there is no clear relationship between pressure variations and glacier motion. In the second experiment the distance to a stationary target was measured at 1 min intervals for 9 h. The calculated motion of this target was −0.149 mm h−1, giving an indication of the magnitude of uncorrected distance errors. The third experiment lasted 35 h and again involved measurements of glacier flow. The calculated target motion was 1.80 mm h−1 toward the instrument.

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