Radio Soundings On Trapridge Glacier, Yukon Territory,Canada

Frequently the reservoir region of a cold surge-type glacier has a temperate base, while in a region surrounding the reservoir the base is cold. We analyse the slump process in such a reservoir regionthat is, the process whereby material flows toward the lower end of the region and forms a critical wave profile there. The model agrees qualitatively with observations of Trapridge Glacier, Yukon Territory, Canada, which is currently experiencing a critical pre-surge condition. Calculations based on the model give good agreement with the surge cycle time of Rusty Glacier, Yukon Territory. Laboratory experiments show that a large-amplitude slump-induced wave profile forms prior to a surge. Experimental surges were produced with velocity increases of order one hundred. REsuME. Vidange brutale de bassins glaciaires. TMorie et experience. Frequemment le bassin d'alimentation d'un glacier froid du type a crue possede un fond tempere tandis que, dans les zones entourant le bass in le fond est froid. Nous analysons le processus de vidange d'un tel bassin, c'est-a-dire le processus par lequel le materiel s'ecoule vers le point bas du bassin et y forme une onde de crue critique. Le modi:le est qualitativement en accord avec les observations faites sur le Trapridge Glacier, dans le territoire du Yukon au Canada, qui se trouve souvent en conditions critiques de pre-crue. Des calculs bases sur le modele donnent un bon accord avec la periode de la crue cyclique du Rusty Glacier dans le territoire du Yukon. Des experiences de laboratoire montrent qu'une vidange de grande amplitude provoque un profil ondule prealablement a la crue. On a produit des crues experimentales avec des accroissements de vitesse de l'ordre de un cent. ZUSAMMENFASSUNG. Kriech-Einbriiche inGletscher-Niihrgebieten -Theorie und Versuch. Haufig hat das Nahrgebiet eines kalten ausbrechenden Gletschers einen temperierten Untergrund, wahrend in einem Bereich urn das Nahrgebiet der Untergrund kalt ist. Die vorliegende Analyse gilt dem Einbruchsprozess in einem solchen Nahrgebiet, d.h. jenem Prozess, bei dem Material gegen das untere Ende des Gebietes fliesst und dort ein kritisches Wellenprofil bildet. Das Modell stimmt qualitativ mit Beobachtungen am Trapridge Glacier, Yukon Territory, Kanada, iiberein, der derzeit eine kritische Vor-Ausbruchs-Phase durchlauft. Berechnungen auf der Basis des Modells geben gute Obereinstimmung mit dem Ausbruckszyklus des Rusty Glacier, Yukon Territory. Laborversuche zeigen, dass sich vor einem Ausbruch ein Wellenprofil mit grosser Amplitude, hervorgerufen durch einen Einbruch, bildet. Experimentell wurden Ausbriiche mit Geschwindigkeitsanstiegen bis zum Hundertfachen erzeugt.

Section: Analytical Resultssupporting

confidence: 63%

“…Values of r , s , l , θ, and δ were estimated from the data of Goodman and others (1975) and corresponding τ c values obtained by computer.…”

Section: Analytical Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Creep Slump in Glacier Reservoirs—Theory and Experiment

Shoemaker

1981

“…Good results at frequencies of 620 MHz and 1–5 MHz were obtained on Athabasca Glacier in Canada (Goodman, 1973) and on South Cascade Glacier in U.S.A. (Watts and others, 1975). Later, similar modified equipment was also successfully applied on other glaciers in Canada, U.S.A., and Iceland (Goodman, 1975; Goodman and others, 1975; Clarke and Goodman. 1975; Björnsson and others, 1977; Miller.…”

Section: Peculiarities Of Radio Echo-sounding Of Mountain and “Reticumentioning

confidence: 99%

Radio Echo-Sounding of Svalbard Glaciers

Macheret¹,

Zhuravlev²

1982

ABSTRACT. Peculiarities of radio echo-sounding of mountain glaciers and ice fields between nunataks from terrestrial vehicles and from helicopters are considered in this paper. The possibility of using comparatively high frequencies (of up to 865 MHz) for sounding such glaciers is demonstrated on the basis of experimental data. Results of airborne radio echo-sounding of Svalbard glaciers of various types, dimensions, and regime obtained with the help of the 620 M Hz airborne equipment of high resolution are shown. Returns from the glacier bed have been obtained on the majority of glaciers under investigation. The firn regions of ice fields with temperate regimes flowing between nunataks are, mostly, an exception. Depression in the glacier bed with the ice thickness up to 540 m, as well as internal reflecting boundaries have been detected in some glaciers. Ice volumes of glaciers have been determined from the airborne radio echo-sounding data with the use of a parabolic approximation to the cross-section glacier profiles. Good correlational dependence between ice volume and surface area of glaciers has been established and is used to estimate the ice and water resources in Svalbard glaciers. RESUME. Sondages par echo-radio des glaciers du Sualbard. Dans cet article on examine les particularites des sondages par echo-radio de glaciers de type de montagne ou de piedmont depuis des vehicules terrestres ou par helicoptere. Sur la base des donnees experimentales on montre une possibilite d'utiliser a titre de comparaison des hautes frequences (jusqu 'a 865 MHz) pour sonder de tels glaciers. On donne et on discute les resultats de sondages aeriens par echo-radio des glaciers du Svalbard de type montagne, piedmont et calotte, avec des appareils de 620 MHz a gran de capacite de resolution spatiale. Des signaux rI:flechis sur le lit du glacier ont ete recueillis sur la majorite des glaciers sondes. Les zones de neves des glaciers de type piedmont avec des regimes thermiques " chauds" (glaciers temperes) sont, la plupart du temps , une exception. On a decouvert sur une serie de glaciers des depressions du fond du lit avec des valeurs de l'epaisseur de glace allant jusqu' a 540 m, ainsi que des pi ages de reflexion interne. A partir de sondages par echo-radio en utilisant une approximation parabolique pour les profils des sections transversales d'un glacier on a pu determiner les volumes des glaciers et etablir une bonne correlation avec la surface englacee. On en a tire une estimation des ressources en glace et en eau des glaciers du Svalbard.

“…The short wavelength (50 cm) and high spatial resolution (5.2° beam width between half-power points) of the equipment enabled the immediate analysis of the photographically recorded oscilloscope images. A more detailed description of the highresolution radar system is presented in another paper (Goodman and others, 1975).…”

Section: Radio Echo Soundingsmentioning

confidence: 99%

Radio Echo Soundings and Ice-Temperature Measurements in a Surge-Type Glacier

Goodman

1975

Self Cite

ABSTRACT. Radio echo soundings on Rusty Glacier, a small surge-type glacier in Yukon Territory, reveal that the ice is considerably thicker than previously believed. A reinterpretation of deep icetemperature measurements made in 1969 and 1970 suggests that a large zone of temperate basal ice exists. This result supports thermal instability as the surge mechanism for Rusty Glacier. REsuME. (Collins, 1972 ). Temperature models based on a gravity survey to determine ice thickness (Crossley and Clarke, 1970) and deep ice-temperature measurements (Classen and Clarke, 197 I , 1972 ) indicate a small zone of temperate basal ice. Radio soundings reveal that parts of the glacier are considerably thicker than previously believed. Basal ice temperatures calculated using this new information show that much of the bottom ice is at or near the pressure-melting point. This is consistent with the essential premise of thermal-instability surge theories: that surging glaciers are sub-polar glaciers with a basal temperature which oscillates near the melting point (Robin, 1955;Hoffmann and Clarke, 1973) . RADIO ECHO SOUNDINGSAttempts in 1968 and 1969 to measure the thickness of Rusty Glacier by the conventional seismic reflection method and by radio echo sounding with a 35 MHz Mark II Scott Polar Research Institute radar set (Evans and Smith, 1969) positioned on the glacier surface were unsuccessful. Since a typical thickness for Rusty Glacier is 100 m, the transmitted radio and seismic pulses completely obscured the reflections, preventing depth determinations. Owing to the proximity of the valley walls, it was not thought that airborne soundings at 35 MHz would be fruitful, although Evans and Robin (1966) successfully used this method over wide valley glaciers. By removing the transmitter from the glacier surface they were able to increase the time between the transmitted and reflected pulses and as a consequence were able to measure depths over a thin ice cover. Using a 620 MHz high-resolution radiosounding system developed for temperate glaciers (Goodman, 1970), depths as shallow as• Present address: Innovative Ventures Limited,