Tree ring indications of uplift at Icy Cape, Alaska, related to 1899 earthquakes

Abstract

Previous studies show that tree ring analysis can provide information about past major earthquakes. If occurrence of large, prehistoric seismic events and extent of areas affected by such events can be determined by analysis of old‐aged trees, this information will be an important addition to the paleoseismological record. Two great earthquakes occurred in September 1899 on the southeastern coast of Alaska near Icy Cape, an area now included within the Yakataga seismic gap. Due to glacial coverage of Icy Bay and the scarcity of observers, any possible uplift at Icy Cape related to these earthquakes was unreported. In 1902 the presumed former shoreline trees at two sites, 2.4 km apart, show both an absolute increase in growth and an increase in growth relative to inland trees. The ages of the trees on the lowland seaward of the sample sites are all post‐1899. If uplift occurred, a seaward shifting of the shoreline would improve the growth environment of trees growing on the former wave‐beaten shoreline and former beach areas might be protected enough for initial afforestation. Other possible causes for tree growth and shoreline changes are considered; however, from the tree ring evidence, geomorphology, and reports of uplift in other parts of the region, it is the authors' interpretation that uplift occurred at Icy Cape related to the 1899 earthquakes. Subsequent accumulation of fluvial and littoral sediments has built out over and around the uplifted area, resulting in the present‐day shoreline configuration. The methodologies used in this study have paleoseismological applications to other uplifted, forested, shoreline areas.