Penitentes: Peculiar Spikey Snow Formation in the Andes
On very high-altitude glaciers, such as those in the Andes
mountains, where the air is dry, snow can grow into spectacular narrow
blades of ice up to several metres high. They are called Nieves
Penitentes or simply Penitentes. They take the form of tall thin blades
of hardened snow or ice closely spaced with the blades oriented towards
the general direction of the sun. They usually formed in clusters and
range from a few centimetres to 2 meters but penitentes as high as 5
meters has been recorded. These pinnacles of snow or ice grow over all
glaciated and snow covered areas in the Dry Andes above 4,000 meters.
Penitentes are a common sight in the regions between Argentina and
Chile.
Penitentes were first described in the literature by
Darwin in 1839. On March 22, 1835, he had to squeeze his way through
snowfields covered in penitentes near the Piuquenes Pass, on the way
from Santiago de Chile to the Argentinian city of Mendoza, and reported
the local belief that they were formed by the strong winds of the Andes.
In
reality, wind has nothing to do with Penitentes. They form when the
sun’s rays turn snow directly into water vapor without melting it first,
a process called sublimation. An initially smooth snow surface first
develops depressions as some regions randomly sublimate faster than
others. The curved surfaces then concentrate sunlight and speed up
sublimation in the depressions, leaving the higher points behind as
forests of towering spikes. At the micro-scale, similar-looking spikes
help solar cell surfaces maximize their sunlight absorption.
Recently
scientists have argued that the presence of carbon or any other
impurities lead to some absorption of sunlight and the resultant
occurrence of Penitentes. If this theory is to be believed, then the
glaciers could be saved from the onslaught of global warming. There are
counter arguments to this claim that if the Penitentes absorb more
sunlight due to the presence of carbon, they may also result in the
destruction of the icebergs. Studies are being pursued in this field to
discover the effect of global warming on the formation of Penitentes.
