Tree Ring Record of Soil Movements on Permafrost

Abstract

Trees growing on severely cryoturbed soils on permafrost terrain produce reaction wood in response to tilting of trees by ground heave movements. A total of 157 tree disks taken from 59 different earth hummocks show multiple tilting and recovery. The direction of tilt is generally away from the center of active hummocks. The chronology of ground heave movements as recorded by reaction wood shows brief periods of high activity and quiescence in the last 160 years. Such periods can be matched in two areas 450 km apart, but occur two years earlier in the north than in the south. Above-average levels of activity are indicated for the period 1847 to 1943, and low levels of activity during the last two decades. There are indications that high levels of activity are related to higher than normal fall temperatures and precipitation.