Growth of a Talus Cone in the Western Chugach Mountains, Alaska

A significant increase in the size of a talus cone near the terminus of Eklutna Glacier during the 6 yrs following the 1964 Alaska earthquake is shown by comparison of photographs taken in 1964 and 1970. Calculations from approximate measurements indicate that about 1.7 million cu yds of rock has been added to the cone since 1964. This growth has been the result of intermittent rockfalls which began after the 1964 earthquake and were continuing in 1970. Rockfalls in other places in the same area were initiated by the earthquake, but did not continue at a rate sufficient to produce measurable change in the talus. Observations on the ridge above the active talus cone suggest that the configuration of the cliff, fracturing and loosening of the rock at the time of the earthquake, and possible land movements resulted in a uniquely unstable area. The instability may be sufficient to account for the continuation of an unusually large number of rockfalls.