The Multetta Debris Fan, Eastern Swiss Alps: A 500-Year Debris Flow Chronology

The opening up of the Alps for tourism has increased the risk potential from natural hazards, one of the greatest of which is debris flows. Since 1996 we have been studying the debris fan of Multetta above Tschierv in Val Müstair in the Swiss Alps to determine the dates and hence the frequency of debris flows. Abrupt growth changes, impact scars, and the formation of adventitious roots allowed precise dating by dendrochronological methods in cases where tree ring characteristics occurred synchronously in several different trees. Six debris flows since the late 15th century could be recognized, occurring at the end of the 15th century, and in 1573, 1655, 1784, 1958, and 1989. The debris deposited during the past 500 yr has formed a layer about 5 m deep. Two further debris flows were identified through scars formed in 1759 and 1837. A greater frequency of scars between the mid-18th century and the end of the 19th century indicates considerably higher morphological activity during the last peak of the Little Ice Age.