scholarly journals Abrupt glacier motion and reorganization of basal shear stress following the establishment of a connected drainage system

2001 ◽  
Vol 47 (158) ◽  
pp. 472-480 ◽  
Author(s):  
Jeffrey L. Kavanaugh ◽  
Garry K. C. Clarke
Keyword(s):  
Pressure Sensors ◽  
Drainage System ◽  
Yukon Territory ◽  
Stable Configuration ◽  
Drainage Patterns ◽  
Pressure Pulses ◽  
Gradual Failure ◽  
Basal Shear ◽  
Pressure Changes ◽  
Glacier Motion

AbstractThree episodes of strong basal motion occurred at Trapridge Glacier, Yukon Territory, Canada, on 11 June 1995 following the establishment of a connected subglacial drainage system. Responses to these “spring events” are noted in the records for 42 instruments and were recorded throughout the ∼60 000 m2 study area. Strong basal motion during the events is indicated by ploughmeter, load-bolt and vertical-strain records, and abrupt pressure changes in several transducer records denote damage caused by extreme pressure pulses. These pressure pulses, generated by the abrupt basal motion, also resulted in the failure of seven pressure sensors. Records for pressure, turbidity and conductivity sensors indicate that basal drainage patterns did not change significantly during the events. Geophone records suggest that the episodes of basal motion were precipitated by the gradual failure of a “sticky spot” following hydraulic connection of part of the study area. This failure resulted in the transfer of basal stress to the unconnected region of the bed during the course of the events. No evidence for strong basal motion is seen in the instrument records for several weeks following the events, suggesting that the mechanical adjustments resulted in a stable configuration of basal stresses. This event illustrates how unstable situations can be quickly accommodated by mechanical adjustments at the glacier bed.

scholarly journals Evidence for extreme pressure pulses in the subglacial water system

2000 ◽  
Vol 46 (153) ◽  
pp. 206-212 ◽  
Author(s):  
Jeffrey L. Kavanaugh ◽  
Garry K.C. Clarke
Keyword(s):  
Water Pressure ◽  
Pressure Sensors ◽  
Water System ◽  
Sampling Interval ◽  
Yukon Territory ◽  
Overburden Pressure ◽  
Data Loggers ◽  
Pressure Pulses ◽  
Field Season ◽  
Large Water

AbstractA suite of subglacial water-pressure records from the 1996 summer field season at Trapridge Glacier, Yukon Territory, Canada, discloses a hydraulic event that cannot readily be explained by known forcings. We suggest that these records indicate covert failure of the pressure sensors caused by at least one large water-pressure pulse. The sign and magnitude of the pulse appears to have varied spatially and the pulse duration was less than the 2 min sampling interval of our data loggers. Laboratory experiments support this interpretation and indicate that the pulse magnitude exceeded 900 m of hydraulic head, roughly 15 times the ice-overburden pressure. Within glaciers, large water-pressure pulses can be generated when abrupt ice motion changes the volume of the subglacial hydraulic system.

scholarly journals Hunting for Information in Streamflow Signatures to Improve Modelled Drainage

Water ◽  
2022 ◽  
Vol 14 (1) ◽  
pp. 110
Author(s):  
Raphael Schneider ◽  
Simon Stisen ◽  
Anker Lajer Højberg
Keyword(s):  
Large Scale ◽  
Agricultural Land ◽  
Hydrological Cycle ◽  
Drainage System ◽  
Water Model ◽  
Generation Process ◽  
Hydrological Models ◽  
Drainage Patterns ◽  
Drain Flow ◽  
Set Up

About half of the Danish agricultural land is drained artificially. Those drains, mostly in the form of tile drains, have a significant effect on the hydrological cycle. Consequently, the drainage system must also be represented in hydrological models that are used to simulate, for example, the transport and retention of chemicals. However, representation of drainage in large-scale hydrological models is challenging due to scale issues, lacking data on the distribution of drain infrastructure, and lacking drain flow observations. This calls for more indirect methods to inform such models. Here, we investigate the hypothesis that drain flow leaves a signal in streamflow signatures, as it represents a distinct streamflow generation process. Streamflow signatures are indices characterizing hydrological behaviour based on the hydrograph. Using machine learning regressors, we show that there is a correlation between signatures of simulated streamflow and simulated drain fraction. Based on these insights, signatures relevant to drain flow are incorporated in hydrological model calibration. A distributed coupled groundwater–surface water model of the Norsminde catchment, Denmark (145 km2) is set up. Calibration scenarios are defined with different objective functions; either using conventional stream flow metrics only, or a combination with hydrological signatures. We then evaluate the results from the different scenarios in terms of how well the models reproduce observed drain flow and spatial drainage patterns. Overall, the simulation of drain in the models is satisfactory. However, it remains challenging to find a direct link between signatures and an improvement in representation of drainage. This is likely attributable to model structural issues and lacking flexibility in model parameterization.

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.

Transepithelial pressure pulses induce nucleotide release in polarized MDCK cells

2005 ◽  
Vol 288 (1) ◽  
pp. F133-F141 ◽  
Author(s):  
H. A. Praetorius ◽  
J. Frøkiær ◽  
J. Leipziger
Keyword(s):  
Epithelial Cells ◽  
Laminar Flow ◽  
Primary Cilium ◽  
Mdck Cells ◽  
Chamber Pressure ◽  
Dependent Manner ◽  
Nucleotide Release ◽  
Pressure Pulses ◽  
Kidney Epithelial Cells ◽  
Pressure Changes

The release of nucleotides is involved in mechanosensation in various epithelial cells. Intriguingly, kidney epithelial cells are absolutely dependent on the primary cilium to sense changes in apical laminar flow. During fluid passage, the renal epithelial cells are subjected to various mechanical stimuli in addition to changes in the laminar flow rate. In the distal part of the collecting duct, the epithelial cells are exposed to pressure changes and possibly distension during papillary contractions. The aim of the present study was to determine whether nucleotide release contributes to mechanosensation in kidney epithelial cells, thereby establishing whether pressure changes are sufficient to produce nucleotide-mediated responses. Madin-Darby canine kidney (MDCK) cells grown on permeable supports were mounted in a closed double perfusion chamber on an inverted microscope. The intracellular Ca2+ concentration ([Ca2+]i) was monitored with the Ca2+-sensitive fluorescence probe fluo 4. Transepithelial pressure pulses of 30–80 mmHg produced a transient increase in [Ca2+]i of MDCK cells. This response is independent of the primary cilium, since it is readily observed in immature cells that do not yet express primary cilia. The amplitudes of the pressure-induced Ca2+ transients varied with the applied chamber pressure in a quantity-dependent manner. The ATPase apyrase and the P2Y antagonist suramin significantly reduced the pressure-induced Ca2+ transients. Applying apyrase or suramin to both sides of the preparation simultaneously nearly abolished the pressure-induced Ca2+ response. In conclusion, these observations suggest that rapid pressure changes induce both apical and basolateral nucleotide release that contribute to mechanosensation in kidney epithelial cells.

scholarly journals Ploughing of subglacial sediment

1994 ◽  
Vol 40 (134) ◽  
pp. 97-106 ◽  
Author(s):  
URS H. Fischer ◽  
Garry K. C. Clarke
Keyword(s):  
Shear Stress ◽  
Effective Viscosity ◽  
Basal Layer ◽  
Shear Resistance ◽  
Yukon Territory ◽  
Rheological Parameters ◽  
Ideal Plastic ◽  
New Instrument ◽  
Newtonian Viscous Fluid ◽  
Basal Shear

AbstractMechanical conditions at the base of Trapridge Glacier, Yukon Territory, were investigated using a “ploughmeter”. We describe the physical characteristics and the theory of this new instrument as well as its operation. Observational results reveal variations in ploughmeter response that might be attributed to spatial variability in subglacial processes or spatial variation in sediment granulometry. Quantitative analysis of the interaction of the ploughmeter with the basal layer yields estimates of rheological parameters. If the sediment is assumed to behave as a Newtonian viscous fluid, the estimated effective viscosity is 3.0 × 109−3.1 × 1010Pas; if it is assumed to behave as an ideal plastic solid, the estimated yield strength is 48–57 kPa. In both cases, the estimated shear resistance of subglacial material is comparable to but somewhat less than that required to balance fully the applied basal shear stress.

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.

Subglacial water pressure records from a fast-flowing outlet glacier in Greenland

2020 ◽  
Author(s):  
Samuel Doyle ◽  
Bryn Hubbard ◽  
Poul Christoffersen ◽  
Marion Bougamont ◽  
Robert Law ◽  
...  
Keyword(s):  
Water Pressure ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Distinct Component ◽  
Outlet Glacier ◽  
Diurnal Cycles ◽  
Close Proximity ◽  
Hydrological System ◽  
Discharge Pressure ◽  
Glacier Motion

<p>Glacier motion is resisted by basal traction that can be reduced significantly by pressurised water at the ice-bed interface. Few records of subglacial water pressure have been collected from fast-flowing, marine-terminating glaciers despite such glaciers accounting for approximately half of total ice discharge from the Greenland Ice Sheet.  The paucity of such measurements is due to the practical challenges in drilling and instrumenting boreholes to the bed, in areas that are often heavily-crevassed, through rapidly-deforming ice that ruptures sensor cables within weeks. Here, we present pressure records and drilling observations from two sites located 30 km from the calving front of Store Glacier in West Greenland, where ice flow averages ~600 m yr<sup>-1</sup>.  In 2018, boreholes were drilled 950 m to the bed near the margin of a large, rapidly-draining supraglacial lake. In 2019, multiple boreholes were drilled ~1030 m to the bed in the centre of the drained supraglacial lake, and in close proximity to a large, active moulin. All boreholes drained rapidly when they intersected or approached the ice-bed interface, which is commonly interpreted as indicating connection to an active subglacial drainage system. Neighbouring boreholes responded to the breakthrough of subsequent boreholes demonstrating hydrological or mechanical inter-connection over a distance of ~70 m. Differences in the time series of water pressure indicate that each borehole intersected a distinct component of the subglacial hydrological system. Boreholes located within 250 m of the moulin reveal clear diurnal cycles either in phase or anti-phase with moulin discharge. Pressure records from boreholes located on the lake margin, however, show smaller amplitude, and less distinct, diurnal cycles superimposed on longer-period (e.g. multiday) variability. We compare these datasets to those in the literature and investigate consistencies and inconsistencies with glacio-hydrological theory.</p>

The structure of a talus-derived rock glacier deduced from its hydrology

1981 ◽  
Vol 18 (9) ◽  
pp. 1422-1430 ◽  
Author(s):  
P. G. Johnson
Keyword(s):  
Internal Structure ◽  
Drainage System ◽  
Yukon Territory ◽  
Flow Structures ◽  
Chemical Characteristics ◽  
Rock Glacier ◽  
Chemical Changes ◽  
Near Surface ◽  
Hydrological Parameters ◽  
Physical Evidence

The paper presents the results of an experiment in the use of hydrological parameters to study the internal structure of a rock glacier. The rock glacier selected for the study lies at the head of Grizzly Creek in the southwest Yukon Territory. The hydrological network suggests two independent drainage systems, which demonstrate the occurrence of a planar impervious structure at depth and independent lines of drainage controlled by the flow structures in the near-surface deposits. Chemical changes in the water are inconclusive with respect to the evaluation of ice contents of the landform although the physical evidence strongly suggests no massive ice component. Chemical characteristics of each drainage system are sufficiently different that chemical tests can be used to differentiate sources of the drainage.

scholarly journals Selection of Surgical Approach for Cerebellar Hemangioblastomas Based on Venous Drainage Patterns

2021 ◽  
Author(s):  
Takashi Watanabe ◽  
Yuuki Suematsu ◽  
Kiyotaka Saitou ◽  
Go Takeishi ◽  
Shinji Yamashita ◽  
...  
Keyword(s):  
Surgical Approach ◽  
Drainage System ◽  
Venous Drainage ◽  
Transverse Sinus ◽  
Jugular Bulb ◽  
Neurological Deficits ◽  
Surgical Approaches ◽  
Drainage Systems ◽  
Drainage Patterns ◽  
Selection Of

Abstract Cerebellar hemangioblastomas remain surgically challenging because of the narrow, deep surgical corridors and tumor hypervascularity. Various surgical approaches are used according to the location, but optimal approaches have not been established. We propose a system of surgical approaches based on the venous drainage systems to facilitate surgical planning and achieve acceptable neurological outcomes. Cerebellar hemangioblastomas were divided into fivefour types based on the main drainage systems: suboccipital hemangioblastomas draining to the transverse sinus (TS) or torcular, tentorial hemangioblastomas draining to the tentorial and straight sinus, petrosal hemangioblastomas draining to the superior petrosal sinus (SPS),, and quadrigeminal hemangioblastomas draining to the galenic system, and tonsillar hemangioblastomas draining to the TS or torcular in conjunction with jugular bulb or SPS. Microsurgical approaches and patient outcome were retrospectively reviewed according to this classification. This study included 17 patients who underwent 21 operations for resection of 19 cerebellar hemangioblastomas, classified into 911 suboccipital, 4 tentorial, 2 petrosal, and 2 quadrigeminal, and 2 tonsillar. Standard suboccipital craniotomies were utilized for suboccipital hemangioblastomas, the occipital transtentorial approach (OTA) and supracerebellar infratentorial approach for tentorial hemangioblastomas, the retrosigmoid approach for petrosal hemangioblastomas, and OTA for quadrigeminal hemangioblastomas, and midline suboccipital approach for tonsillar hemangioblastomashemangioblastomass. Gross total resection was achieved in all patients except one. Two patients with large hemangioblastomas (tonsillarsuboccipital and quadrigeminal) required second-stage operation which finally achieved gross total removal. No single approach had a significantly higher incidence of postoperative neurological deficits. Selection of the optimum surgical approach for cerebellar hemangioblastomas was successful based on the main drainage systems. Understanding of tumor growth and extension with respect to the venous drainage system is critical to select the appropriate surgical approach.

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