ALO docView - Analysis of a 20 m. firn pit on the Kesselwandferner (Ötztal Alps) (1966)

ANALYSIS OF A 20 m. FIRN PIT ON THE

KESSELWANDFERNER (ÖTZTAL ALPS)*

By W. Ambach and H. Eisner

(Physikalisches Institut der Universität Innsbruck, Innsbruck, Austria)

Abstract. The firn stratification in the accumulation area of an alpine glacier was studied in a 20 m.

deep, vertical pit dug in the summer of 1963 on the Kesselwandferner (3,240 m. above sea-level in the

ötztal Alps). The firn is traversed by ice layers up to 25 cm. in thickness which have been formed by the

damming up and freezing of melt water. Firn density increases with depth. At a depth of 13 m. (8 yr. old

firn) the density reaches o-8o g./cm. 3 as a mean value of one annual net accumulation. Excluding the ice

layers, the firn reaches a density of 0-82 g./cm. 3 in a 10 yr. old layer at a depth of 16 m. The firn stratification

in relation to seasons was studied by analyses of the pollen content in the lower part of the pit, beginning with

the horizon "late summer 1954". The late summer horizons obtained from the firn stratification were

confirmed by the pollen analyses.

Resume. Analyse a"un puits de 20 m dans le neve du Kesselwandferner (Alpes d''Ötztal). La stratification du neve

dans la zone d'accumulation d'un glacier alpin a 6t6 6tudi6e dans un puits vertical de 20 m de profondeur

creuse pendant V6t6 1963 au Kesselwandferner (3 240 m au-dessus du niveau de la mer dans les Alpes d'

ötztal). Le neve est traversd de couches de glace ayant jusqu'ä 25 cm d'epaisseur qui ont etö formöes par la

retenue et le gel des eaux de fönte. A une profondeur de 13 m (neVe de huit ans) la densite" atteint 0,8 g/cm 3

valeur moyenne pour une accumulation nette annuelle. En excluant les couches de glace, le n6v6 atteint une

densit6 de 0,82 g/cm 3 dans une couche de 10 ans ä 16 m de profondeur. La stratification du neVe" par rapport

aux saisons a e"t6 etudide par l'analyse du pollen contenu dans les parties plus basses du puits, ä partir de

l'horizon "fin de l'6te 1954". Les horizons de fin d'e'te' connus ä partir de la stratification du neV6 ont 6te

confirme's par l'analyse de leur contenu en pollen.

Zusammenfassung. Analyse eines 20 m tiefen Firnschachts am Kesselwandferner (Ötztaler Alpen). In einem 20 m

tiefen, senkrechten Firnschacht, der im Sommer 1963 am Kesselwandferner (Ötztaler Alpen) in 3240 m

Seehöhe gegraben wurde, wird die Stratigraphie im Akkumulationsgebiet eines Alpengletschers studiert.

Die Firnschichten sind mit bis zu 25 cm dicken Eisschichten durchzogen, die sich durch Stauung von

Schmelzwasser und Frieren gebildet haben. Die Firndichte nimmt mit der Tiefe zu und erreicht in 13 m

Tiefe (8 Jahre alter Firn) als Mittelwert einer Jahresrücklage den Wert 0,80 g/cm 3 . Bei Ausschluss der

Eislamellen erreicht der Firn in der 10 Jahre alten Schicht (16 m Tiefe) die Dichte 0,82 g/cm 3 . Die jahreszeit¬

liche Firnstratigraphie wurde im tieferen Teil des Schachtes ab Horizont "Herbst 1954" pollenanalytisch

untersucht. Die aus der Firnstratigraphie abgelesenen Herbsthorizonte wurden durch die Pollenanalyse

bestätigt.

Introduction

In the summer of 1963 a firn pit was dug to a depth of 20 m. on the Kesselwandferner

(3,240 m. above sea-level in the Ötztal Alps). The aim of this investigation was to study the

firn stratification in relation to the annual net accumulation of previous years. Firn samples

were taken from all layers and pollen analyses were carried out on some of them. These

samples will be examined later for radioactivity resulting from atmospheric fall-out.

Area of Investigation

The site of the firn pit has been designated L58 by Hoinkes and Rudolph (1962, fig. 1).

Since the International Geophysical Year (1957-58) the Kesselwandferner has been included

in the mass budget programme which was started in 1952 (Hoinkes and Rudolph, 1962).

This pit is still accessible and can be used for further studies.

In 1956 H. C. Hoinkes dug aniim. deep firn pit at approximately the same placein order

to study the stratigraphy of the annual net accumulation (Hoinkes, 1957). At the end of every

budget year since 1958, the water-equivalent of the annual net accumulation of the past budget

year has been determined by measuring the density profile at that locality. However, for

various reasons this series of measurements is incomplete. By using the 20 m. deep pit it was

possible to complete the series of studies.

* Dedicated to Gerald Seligman on the occasion of his graduation to the degree of Dr. Phil, honoris causa in the

Universität Innsbruck.

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