Abstract:
Glacial deposits on San Francisco Mountain, Arizona, were mapped in order
to provide constraints on ice extents in separate valleys for late Pleistocene glacial
events. Qualitative and semi-quantitative relative dating methods were employed in
order to correlate moraines between drainages and to provide a basis for
distinguishing between separate glacial events within drainages. Morphologic and
surficial weathering characteristics that were measured include degree of moraine
dissection, moraine crestal width, moraine inner and outer slope angle, surface
boulder frequency, percentage of weathered surface boulders, percentage of pitted
surface boulders, maximum pit depth, and percentage of split boulders. Results of the
relative dating study support past studies that differentiate 3 separate drift sequences
on the mountain. Five separate glacier surfaces were reconstructed from the mapped
moraine crests, four for the most recent glaciation, and one for the intermediate
glacial event. ELAs from the reconstructed glaciers range from 3140 to 3400 meters.
In addition, a numerical model was developed that uses an energy balance
approach to calculate annual ablation over a glacier surface. The energy balance
approach used in the model was designed to allow the model to test sensitivity of
former glaciers to changes in temperature or precipitation. Required model inputs
include a two-dimensional elevation map of the glacier surface and surrounding
topography, as well as climate records that include daily values of air temperature,
wind speed, precipitation, atmospheric vapor pressure, incoming shortwave radiation,
and incoming longwave radiation. Model outputs include the net specific balance and
equilibrium line altitude of the glacier. Model simulations of mass balance are
compared with observed data from the 1990 ablation season at Haut Glacier d'Arolla,
Valais, Switzerland. Calculated ablation values closely match observed values, thereby
supporting the validity of the model. A preliminary model run was also accomplished
for the 5 Pleistocene glaciers reconstructed on San Francisco Mountain, Arizona,
using output from a regional climate model as input. The model delivers a glacier that
is nearly in mass balance for one of the reconstructions.
