Estimating dates of recent glacier advances and recession rates by studying tree growth layers

Abstract

Study of the growth layers of trees growing along the margins and below the terminus of a present day receding glacier reveals the minumum lapse of time in years since the glacier advanced beyond a given point, and the approximate rates at which recession has occurred. Study of cross sections of trees pushed part way over by ice pressure at the time of maximum glacier advance and left in a tilted position to continue growth until the present, discloses the exact year of the maximum advance. This is detected through a change in form of growth layers in the trunk cross section. Growth while the tree is erect is concentric about the growth center; that after trunk tilting is asymmetric. The non‐conformity between concentric central growth and eccentric outer growth marks the year of the tilting. This technique and others described here may be used to date landslides, windstorms, and river floods as well as glacier fluctuations.