Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 267

face morphology can also appear mottled, with spoon-shaped depressions (Washburn
1980). Remote sensing and terrain parameters show promise when mapping regional
landforms such as rock glaciers over large mountainous areas (Brenning et al. 2007;
Janke 2001).
Rock glaciers play an important role in the elevational distribution of landforms
in glacial or periglacial environments (Caine 1984). Traditionally, rock glaciers are
thought to exist mainly in low-precipitation, continental climates where frost weather-
ing is dominant and temperatures are cool enough to maintain ice (Haeberli 1983). In
the Alps, Haeberli (1983) restricted rock glaciers to dry continental climates at altitudes
below the equilibrium line of glaciers, but above the lower permafrost limit. In Green-
land, Humlum (1998) found that the locations of rock glaciers and glaciers are driven
by topoclimates (elevation, slope, and aspect) and talus production rates, not regional
climates. In the Colorado Front Range, Janke (2007) examined topoclimatic variables
for rock glaciers and temperate glaciers using a GIS, finding that tongue-shaped rock
glaciers are found at higher elevations and on slopes with more northerly aspects, com-
pared to lobate rock glaciers. Active, inactive, and relict forms showed typical elevation
and aspect gradients. Active rock glaciers are found at the highest elevations and most
northerly aspects. Inactive rock glaciers are found at lower elevations on all aspects,
with a tendency to face northeast; fossil rock glaciers occur at the lowest elevations
on all aspects. Glaciers are mostly smaller, found at higher elevations, and restricted
to more northern and northeastern slopes. Because these remaining small ice masses
are mostly attached to steep cirque walls, their slope is usually steeper than the blocky
accumulations of rock glaciers. Rock glaciers are larger and more abundant; as many
are believed to contain ice, they could provide a small source of water in a future warm-
er, drier climate. Janke (2007) also found that active tongue-shaped rock glaciers have
elevations and aspects similar to glaciers, but active lobate forms have different elev-
ations and aspects compared to glaciers. This suggests that most tongue-shaped Front
Range rock glaciers are glacially derived.
Present climates affect active and inactive rock glaciers by preserving or ablating
an internal ice structure (Martin and Whalley 1987). Rock glaciers are therefore con-
sidered good indicators of climate change (Barsch 1988; Haeberli 1990). A rock glaci-
er's response to climate is smoothed since surface debris serves as an insulator (Barsch
1996). Unlike glaciers that are sensitive to extreme fluctuations on a shorter time scale,
a strong climatic signal must exist to produce change in a rock glacier system. Degrad-
ation of rock glaciers is generally measured from slumping surface morphology, front-
al activity, amount of internal ice, variation in downslope movement, or temperature of
frozen material (Francou et al. 1999).
In the Front Range of Colorado, temperature records from the 1960s did not indicate
long-term cooling or warming trends, although most sites have shown a consistent
warming recently (1997-2004) (Losleben 2004). Precipitation measurements show a
slight increase in total precipitation; however, considerable variation occurs from year
to year. Rock glacier velocities have remained consistent, showing no major increase in
flow velocity over 40 years (Janke 2005a, 2005b). In the Alps, accelerated warming was
pronounced in the 1980s and 1990s, and rock glaciers responded accordingly. Gruben
rock glacier showed decreasing horizontal velocities and an increase in surface subsid-
ence by a factor of 2 to 3 times over this period. Borehole temperatures on the Murtèl