AGU: Fall meeting, 1996, EOS, V 77, p F197.
Observations of exposed, patterned, vertical ice columns
were made late in the 1996 melt season near Niwot Ridge,
a continental alpine site in the Colorado Front Range,
located at 3500 m. Several techniques were employed in an
attempt to determine the origin, growth patterns, and
physical properties of these "penitents". Specifically,
we tested the hypothesis that the spacing of the columns
was similar to derived basal discharge lag distances based
on analysis of two seasons of lysimeter snowmelt data.
Each individual column was distinguished by an oblong cap
of natural debris, regardless of its height relative to the
snow surface (-2 to 60 cm). Measured values (n = 52)
indicate a mean cap size of 11.2 cm (with the fall line) by
7.2 cm (perpendicular to fall line), and the mean height of
columns above the snowpack was 34 cm. Mean spacing of
columns (n = 78) was 2.4 m perpendicular to, and 45.04 cm
with, the fall line; the correlation of these numbers with
lysimeter data varied with respect to discharge period.
Full excavation of penitents showed adherence of column
bases to a well developed lateral ice lens which was not
found in neighboring snow, as well as systems of ice "ribs"
which linked one column to the next downslope. Sediment
analysis, temperature data, spectral reflectance data, and
crystallography images were collected from both the columns
and adjoining snow. Ideas on the development of these
columns, as well as their importance in the hydrologic
cycle, build on previous research, much of which was done
during the early 1900s.