Secondary calcite crystallization and oxidation processes of granite near the summit of Mt. McKinley, Alaska

• Published in: Géomorphologie : relief, processus, environnement
• Main Authors: Yoshikawa, Kenji, Okura, Yositomi, Autier, Vincent, Ishimaru, Satoshi
• Format: Article in Journal/Newspaper
• Language: English
• Published: Groupe français de géomorphologie 2008
• Subjects: désagrégation; Mont McKinley; température de roche; vernis; Alaska; calcite; Mount McKinley; rock temperature; varnish; weathering; geo; envir; Antarc*; Antarctica
• Online Access: http://journals.openedition.org/geomorphologie/147

On the mountain of Denali, Alaska (also known as Mt. McKinley), weathering processes are dominated by secondary crystallization (calcite) and oxidation (varnish), but frost action is limited. During the summer of 2002-2003, two study sites (a north-facing rock wall and a south-facing rock wall) on Denali showed limited numbers of effective freeze-thaw cycles (30 and 63 cycles, respectively) this infrequent cycling is similar to that found at sites in inland Antarctica (46 effective freeze-thaw cycles in 1994). Rock moisture conditions were influenced by solar radiation and snow blowing. Blowing snow and subsequent melting provided abundant moisture to the rock wall. Elevation between 3000 and 3500 m experience the most active snow blowing, at the south to southeast facing rock wall. The saturation rate of the pore space or surface cracks is considered minimal. The secondary crystallization (calcite) and the varnish are controlled by surface evaporation, moisture supply, and the chemical properties of the rock. The most important control parameter in this study area was moisture availability, given the same bedrock and level of solar radiation. Snow particles are moved by jet stream winds, bringing moisture to the rock surface, where it collects mainly in lower cliffs and cols. Thus the secondary calcite crystallization and varnish developed severely in the lower cliffs and cols of high temperature at south-south west facing walls. Sur la montagne du Denali, Alaska (également connue sous le nom de Mont McKinley), les processus de désagrégation sont dominés par la cristallisation secondaire (calcite) et l’oxydation (vernis), avec une action limitée du gel. Pendant les étés de 2002 et 2003, deux sites d’étude (versants nord et sud d’une face rocheuse) situés à 5 710 m d’altitude sur le Denali ont montré un nombre limité de cycles gel-dégel actuels (30 et 63 cycles, respectivement) ces cycles peu fréquents sont semblables à ceux mesurés à l’intérieur des terres de l’Antarctique (46 cycles gel-dégel en 1994). ...