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Instruments and Methods: The Measurement of Vertical Strain in Glacier Bore Holes

  • James C. Rogers (a1) and Edward R. LaChapelle (a2)

Abstract

A method to measure the vertical strain in glacier bore holes is described that entails placement of passive markers at varying depths. The position of these markers with respect to a surface reference is measured by an electronic sensor lowered into the hole. These measurements can be combined with inclinometer measurements to yield the total velocity vector in the ice surrounding the hole. Although the method was designed for use in a 0.05 m diameter hole, it can easily be applied to holes of different diameters and to winter snow covers as well as glacier ice.

On décrit une mesure de la déformation verticale dans un forage glaciaire qui implique la mise en place de témoins passifs à des profondeurs variées. La position de ces témoins est mesurée par un capteur électronique que l’on descend dans le forage. Ces mesures peuvent être combinées avec des mesures à l’inclinomètre afin d’obtenir tous les éléments du vecteur vitesse dans la glace entourant le trou. Bien que la méthode ait été conçue pour être employée dans un forage de 5 cm de diamètre, on peut facilement l’appliquer à des trous de différents diamètres et a des manteaux neigeux hivernaux, aussi bien qu’à de la glace de glacier.

Zusammenfassung

Es wird eine Methode zur Messung der vertikalen Verformung in Gletscherbohrlöchern beschrieben, bei der passive Markierungen in verschiedenen Tiefen anzubringen sind. Die Lage dieser Markierungsringe gegenüber einem Bezugspunkt an der Oberfläche wird mit einem in das Loch abgesenkten elektrischen Fühler gemessen. Um den gesamten Geschwindigkeitsvektor des Eises in der Umgebung des Loches zu erhalten, ist eine Kombination mit Klinometermessungen möglich. Obwohl die Methode für ein Bohrloch von 0,05 m Durchmesser entwickelt wurde, lässt sie sich leicht für Löcher mit anderen Durchmessern verwenden, und zwar sowohl in Winter-schneedecken wie in Gletschereis.

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