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Permafrost: What Is Permafrost Where Does It Occur What Problems Exist

Permafrost underlies approximately 22.79 million square kilometers in the Northern Hemisphere, occurring as far north as 84°N in Greenland and as far south as 26°N in the Himalayas. Permafrost is defined as any rock or soil that remains at or below 0°C for two or more years. Problems exist with permafrost due to seasonal thawing of the active layer above permafrost, which can cause buildings and infrastructure to sink and lose structural integrity. Various methods are used to build in permafrost regions, such as keeping structures frozen or supporting them down to solid non-permafrost ground.

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105 views19 pages

Permafrost: What Is Permafrost Where Does It Occur What Problems Exist

Permafrost underlies approximately 22.79 million square kilometers in the Northern Hemisphere, occurring as far north as 84°N in Greenland and as far south as 26°N in the Himalayas. Permafrost is defined as any rock or soil that remains at or below 0°C for two or more years. Problems exist with permafrost due to seasonal thawing of the active layer above permafrost, which can cause buildings and infrastructure to sink and lose structural integrity. Various methods are used to build in permafrost regions, such as keeping structures frozen or supporting them down to solid non-permafrost ground.

Uploaded by

John Elmer
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Permafrost

what is permafrost
where does it occur
what problems exist
Understanding Permafrost
• important to civil engineering and
architecture
• crucial part of studying global change
• protecting the environment in cold
regions
permafrost
• Permafrost underlies approximately
22.79 million square kilometers (about
24 percent of the exposed land
surface) of the Northern Hemispher
• It occurs as far north 84°N in
northernmost Greenland, and as far
south as 26°N in the Himalayas
occurrence
Exactly what is permafrost?
• Permafrost is not defined by soil
moisture content, overlying snow
cover, or location;
• Defined solely by temperature.
• Any rock or soil remaining at or below
0° C for two or more years is
permafrost.
Variable characteristics
• Permafrost can contain over 30
percent ice, or practically no ice at
all.
• It can be overlain by several meters
of snow, or little or no snow.
Determining the location and
extent of permafrost
• often difficult
• historical approach - assume that
ground temperature equals the
overlying air temperature
• ground and air temperatures usually
differ, and by varying amounts
Determining the location and
extent of permafrost
• in areas where the mean annual air
temperature is below freezing,
permafrost may not exist

• land under glaciers, rivers, and streams is


often free of permafrost despite freezing
air temperatures at the surface
(Williams and Smith 1989)
Thickness varies
Geothermal gradient
Depth of
permafrost is a
function of air
temperature and
geothermal
gradient
Active layer
The honeycomb
polygonal shape
is the result of
the seasonal
churning of the
ground above the
underlying layer
of permafrost.
Ice wedges
Active layer
The honeycomb
polygonal shape
is the result of
the seasonal
churning of the
ground above the
underlying layer
of permafrost.
Ice wedges
Active layer
Melting each summer
causes constructions
to sink into the
ground
The soil becomes
saturated and looses
all strength
Active layer
Problems with permfrost
• Permafrost restricts
use of the ground
surface, and limits
the locations of
roads, buildings,
communities,
pipelines, airfields,
and bridges.
Problems with permfrost
• Where the ground is
frozen and there is
little water in the soil,
there are no
difficulties in
building new
structures.
Problems with permfrost
• However, if
permafrost with lots
of ice is allowed to
thaw, major problems
can develop, because
the ground can lose
most of its strength.
Methods for building
• Keep frozen
– Build above the ground with a layer of
cold air between the building and the
subsurface
– Freeze the ground – in cellars of large
buildings freezers keep the building
frozen to the suroundings
• Support down to solid ground
Suggestions
• Small homes
• Roads and major highways
• Large constructions
• Pipe line
• Sewage
• Drinking water

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