CHAPTER 11 Glaciers and Glaciation
262
FIGURE 11.1 Hubbard Glacier is still eroding the
Alaskan landscape. The dark stripe of sediment in
the center of the glacier is a medial moraine.
(Photo by Michael Collier)
Glaciers: A Part
of Two Basic Cycles
Glaciers and Glaciation
Introduction
Like the running water and groundwater
that were the focus of the preceding two
chapters, glaciers represent a significant
erosional process. These moving masses
of ice are responsible for creating many
unique landforms and are part of an
important link in the rock cycle in which
the products of weathering are transported
and deposited as sediment.
Today, glaciers cover nearly 10 percent
of Earth’ s land surface. However, in the
GEODe
ESSENTIALS
OF GEOLOGY
recent geologic past, ice sheets were three
times more extensive, covering vast areas
with ice thousands of meters thick. Many
regions still bear the mark of these glaciers.
The basic character of such diverse places
as the Alps, Cape Cod, and Yosemite
valley was fashioned by now vanished
masses of glacial ice. Moreover, Long
Island, the Great Lakes, and the fiords of
Norway and Alaska all owe their existence
to glaciers. Glaciers, of course, are not just
a phenomenon of the geologic past. As
you will see, they are still modifying the
physical landscapes of many regions
today (FIGURE 11.1).
Glaciers are a part of two fundamental
cycles in the Earth system—the hydrologic
cycle and the rock cycle. Earlier you
learned that the water of the hydrosphere is
constantly cycled through the atmosphere,
biosphere, and geosphere. Time and time
again water is evaporated from the oceans
into the atmosphere, precipitated upon the
land, and carried by rivers and underground flow back to the sea. However,
when precipitation falls at high elevations
or high latitudes, the water may not
immediately make its way toward the sea.
Instead, it may become part of a glacier.
Although the ice will eventually melt,
allowing the water to continue its path
to the sea, water can be stored as glacial
ice for many tens, hundreds, or even
thousands of years.
262
FIGURE 11.1 Hubbard Glacier is still eroding the
Alaskan landscape. The dark stripe of sediment in
the center of the glacier is a medial moraine.
(Photo by Michael Collier)
Glaciers: A Part
of Two Basic Cycles
Glaciers and Glaciation
Introduction
Like the running water and groundwater
that were the focus of the preceding two
chapters, glaciers represent a significant
erosional process. These moving masses
of ice are responsible for creating many
unique landforms and are part of an
important link in the rock cycle in which
the products of weathering are transported
and deposited as sediment.
Today, glaciers cover nearly 10 percent
of Earth’ s land surface. However, in the
GEODe
ESSENTIALS
OF GEOLOGY
recent geologic past, ice sheets were three
times more extensive, covering vast areas
with ice thousands of meters thick. Many
regions still bear the mark of these glaciers.
The basic character of such diverse places
as the Alps, Cape Cod, and Yosemite
valley was fashioned by now vanished
masses of glacial ice. Moreover, Long
Island, the Great Lakes, and the fiords of
Norway and Alaska all owe their existence
to glaciers. Glaciers, of course, are not just
a phenomenon of the geologic past. As
you will see, they are still modifying the
physical landscapes of many regions
today (FIGURE 11.1).
Glaciers are a part of two fundamental
cycles in the Earth system—the hydrologic
cycle and the rock cycle. Earlier you
learned that the water of the hydrosphere is
constantly cycled through the atmosphere,
biosphere, and geosphere. Time and time
again water is evaporated from the oceans
into the atmosphere, precipitated upon the
land, and carried by rivers and underground flow back to the sea. However,
when precipitation falls at high elevations
or high latitudes, the water may not
immediately make its way toward the sea.
Instead, it may become part of a glacier.
Although the ice will eventually melt,
allowing the water to continue its path
to the sea, water can be stored as glacial
ice for many tens, hundreds, or even
thousands of years.