Geology Reference
In-Depth Information
melting and refreezing continue to reduce the space between snow particles until no air
is left, only solid ice — just like the ice cube in your glass.
Balancing the glacial budget
Each year a glacier goes through a cycle of growth and reduction in response to the
changing weather. In the winter months, when temperatures are low and snowfall is
high, glacier ice
accumulates.
As the temperatures warm and snowfall decreases in the
spring and summer months, glacier ice
recedes
by melting or breaking off. (When ice
breaks off from glaciers into the ocean, the process is called the
calving of icebergs.
)
Figure 13-1 illustrates zones of ice accumulation and ablation. The
zone of accumulation
is at high elevation, where more snow falls each winter than is melted in the summer.
The
zone of ablation
is at a lower elevation, where all the snow that falls each year melts
(along with some of the ice from previous years). The
line of equilibrium
or
snowlin
e sep-
arates these two parts of the glacier.
Figure 13-1:
Glaci-
er zones of accu-
mulation and abla-
tion.
To describe the annual cycle of accumulation and reduction, scientists talk about the
glacial budget.
The glacial budget is the balance of ice and snow added to the zone of ac-
cumulation and ice lost through melting and calving, or
wastage,
in the zone of ablation
.
When a glacier's annual accumulation of ice is more than its wastage for a few consecut-
ive years, it has a positive budget and is increasing in size or
advancing.
As a glacier ad-
vances, the
terminus
— the edge of the glacier at lower elevation — moves downslope.
In the reverse situation — when the glacier experiences more wastage, or ablation, than
accumulation — the glacier has a negative budget. The terminus of a glacier with a neg-
