A section of the highway through the Gunes valley can be seriously interrupted by avalanching; in 1966-67 traffic was interrupted for four months. About 86 places are threatened by avalanches, most of which are channelled avalanches that do not reach the highway every year.
A comprehensive programme to study the avalanches was begun in 1967 on the basis of which avalanche protective works were undertaken in 1974-75 and their effectiveness analysed in 1976-77. Most of these depend on local material; the main rock deposits available are andesite, which has good permeability and is very suitable for earthworks.
The most common type of defence used is the building of mounds, 4-6 m high, 10-12 m wide, and 20-30 m long with a ditch dug in front. Such mounds have the effect of braking the avalanche flow and also of capturing snow on the uphill side. A second system is the terracing of slopes; beginning from the avalanche fracture line, earth is dug parallel to the contours. In two places dykes have been built to guide the snow, and in a few places avalanche sheds have been constructed, though because of expense these have been kept to a minimum. As the soil and climatic conditions are very suitable, tree planting around structures is a successful way of increasing avalanche protection.
During the analysis of effectiveness snow-fall as recorded was heavy, but the defences were effective and avalanches did not seriously interrupt the highway.