The rapid rate of global warming currently underway highlights the need for a deeper understanding of abrupt climate change. The Younger Dryas is a Late-Glacial climate event of widespread and unusually rapid change whose study can help us address this need for increased understanding. Reconstructions from the glacial record offer important contributions to our understanding of the Younger Dryas due to (among other things) the direct physical response of glaciers to even minor perturbations in climate. Because the glacier equilibrium line altitude (ELA) provides a more explicit comparison of climate than properties such as glacier length or area, ELA methods lend themselves well to paleoclimate applications and allow for more direct comparisons in space and time. Here we present a physically based ELA model for alpine paleoglacier climate reconstructions that accounts for differences in glacier width, glacier shape, bed topography and ice thickness, and includes error estimates using Monte Carlo simulations. We validate the ELA model with published mass balance measurements from 4 modern glaciers in the Swiss Alps. We then use the ELA model, combined with a temperature index model, to estimate the changes in temperature and precipitation between the Younger Dryas (constrained by 10Be surface exposure ages) and the present day for three glacier systems in the Graubünden Alps. Our results indicate an ELA depression in this area of 320 m ±51 m during the Younger Dryas relative to today. This ELA depression represents annual mean temperatures 2.29 °C ±1.32 °C cooler relative to today in the region, which corresponds to a decrease in mean summer temperatures of 1.47 °C ±0.73 °C. Our results indicate relatively small changes in summer temperature dominate over other climate changes for the Younger Dryas paleoglaciers in the Alps. This ELA-based paleoclimate reconstruction offers a simple, fast, and cost-effective alternative to many other paleoclimate reconstruction methods. Continued application of the ELA model to more regions will lead to an improved understanding of the Younger Dryas in the Alps, and by extension, of rapid climate events generally.

As increasing emphasis is placed upon the role surface processes play in regulating tectonic behaviour, the need for accurate measurements of denudation rate has become paramount. The quantity and quality of denudation rate studies has grown with the advent of cosmogenic radionuclide techniques, capable of recording denudation rates over timescales of 100 to 1000000 years. This study seeks to utilise cosmogenic 10Be concentrations measured in alluvial sediments in order to further develop this method and to investigate rates of basin-wide denudation in the San Bernardino Mountains, an active orogen associated with the San Andreas Fault system. The theory which underpins measurements of basin-wide denudation rates with cosmogenic radionuclide analysis is evaluated in light of recent understanding of production mechanisms. Field testing of the assumptions required by the basinwide denudation rate model highlights the importance of sampling thoroughly mixed sediments. Denudation rates ranging over three orders of magnitude are measured by applying the cosmogenic radionuclide technique in thirty-seven basins throughout the San Bernardino Mountains. Results show a relationship between denudation rate and slope which provides quantification of the threshold slope angle in high relief granitic environments and suggests tectonic activity is the first order control of denudation rates in these mountains. Mean annual precipitation is shown to exert no significant influence over the rates measured in the San Bernardino Mountains. Questions concerning denudation rates recorded over differing timespans are addressed using the cosmogenic technique, (U-Th)/He thermochronometry, incision into dated horizons and modern day sediment flux data. This comparison reveals that a decrease in rates with distance from the San Andreas Fault has been consistent throughout the lifespan of the San Bernardino Mountains and provides further evidence that a tectonic mechanism is driving denudation in this region. The relevance of both spatial and temporal scale in geomorphic studies is considered in light of these results, highlighting the need for a greater appreciation of their role in the interpretation of basin-wide denudation rates.