Date of Award
Doctor of Philosophy
Henri D. Grissino-Mayer, Carol P. Harden, Jon Harbor, David G. Anderson
Located in Central Asia, one of the most continental regions on Earth, the Tian Shan’s glaciers contribute critical fresh water to populated areas in the lowland. These glaciers are sensitive to climate change, and knowledge of contemporary glaciers and their changes in the past is of critical importance for sustainable development in this region. Constraining glacial fluctuations in recent centuries will fill a gap in numerical constraints on glacial history and paleoclimate information, and provide important evidence on the spatio-temporal changes of the climate systems in the Tian Shan. This doctoral dissertation investigates the timing and extent of Little Ice Age (LIA) glacial advances in the eastern Tian Shan. In particular, I conducted: 1) the mapping of glacial extents during the LIA and around 2010 using Google Earth high-resolution imagery and ArcGIS; 2) statistical analyses to examine relationships between local topographic/geometric factors and glacier change parameters; and 3) cosmogenic 10Be [beryllium 10] surface exposure dating of presumed LIA moraines.
The major contributions of this dissertation include: 1) a total of 1173 contemporary glaciers with their corresponding presumed LIA extents were delineated in the eastern Tian Shan; 2) glacier area and mean elevation are the two major local factors that affect glacier area changes, but topographic/geometric factors cannot well explain changes in equilibrium line altitudes; 3) three major LIA advances occurred at 730±300 yr BP, 370±100 yr BP, and 210±50 yr BP were constrained based on 10Be surface exposure ages, and the maximum LIA extent (about 700–900 m beyond glacier termini) was reached asynchronously in different sub-regions; 4) presumed LIA moraines in front of small, thin glaciers yielded widely scattered and much older ages than LIA ages. The glacial deposits in front of such glaciers might have formed prior to the LIA and have been reworked during non-erosive glacial transport in LIA. This suggests that inheritance could be a more significant problem than degradation in the exposure age scatter of young glacial event. More dating work is needed to extend our knowledge on LIA glacial advances, and to better understand the influence of climate systems on glacier changes.
Li, Yanan, "Timing and Extent of the Little Ice Age Glacial Advances in the Eastern Tian Shan, China. " PhD diss., University of Tennessee, 2015.