Treeslides in Doubtful Sound

Treeslides are slope failures where the slide mass contains a dominant proportion of vegetation along with minor soil and rock debris. Treeslides are common in steep, high rainfall areas. In Fiordland a large number of such failures occur every year. This paper summarises a study of treeslides in Doubtful Sound. High grade metamorphic rocks in Doubtful Sound stand in steep slopes typically in excess of 45. Vegetation grows rapidly owing to annual rainfall in excess of 6m. Treeslides occur as a result of high intensity rainfall or heavy snowfall. Earthquakes are also a potential trigger. Annually about 315 000 tonnes of treeslide debris directly enters Doubtful Sound.