19.3: How Does a Glacier Develop?
How Does a Glacier Develop?
Glaciers require very specific climatic conditions to develop. Most form in polar latitudes or high-altitude regions, where accumulation of winter snow and ice is greater than its loss in the summer. As snow accumulates during winter, compression forces the older snow to recrystallize. After about a year, a denser, more compressed layer called firn Links to an external site. develops (Figure 19.4). With enough pressure (from sequential burial) and time, firn will transform into crystalline glacial ice. True glacier ice takes hundreds of years to develop.
As the interconnecting air passages between the firn grains are sealed off, air bubbles will be formed. These air bubbles are important for exploring climate and the events of the geologic, or historic, past.
Figure 19.4: The formation of glacial ice. (CC-BY 4.0; Steven Earle Links to an external site.)
⚒️Can You Dig It?
Why is Glacial Ice Blue? Ice only appears blue when it is sufficiently consolidated such that air bubbles cannot interfere with the passage of light. Without the scattering effect of air bubbles, light can penetrate ice undisturbed. In ice, the absorption of light at the red end (long wavelengths) of the spectrum is greater than at the blue end (short wavelengths). In general, the deeper light energy travels within a glacier, the more longwave colors are lost. About two meters into the glacier, most of the red colors are gone. The short wavelengths are left behind, which results in the distinct blue color we see (Figure 19.5).
Figure 19.5: Blue glacial ice. (CC-BY 2.0; James St. John Links to an external site.)