Permafrost what is permafrost where does it occur what problems exist.

Permafrost

what is permafrostwhere does it occurwhat 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 layerMelting 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