ess 21 - lecture 10: permafrost

water's lower density due to its open structure allows ice to do what?

expand when it freezes

active layer def

layer of ground above permafrost that thaws in the summer and freezes in winter (0-4m)

does concrete have high or low permeability?

low - water will not seep into concrete; potential for flooding

What would happen to the depth of the active layer and depth of the permafrost if: All temperatures got much warmer?

-active layer would get deeper -base of permafrost will be shallower

factors affecting permafrost depth

-climate (temp/snow cover) -soil moisture -vegetation -topography/aspect -lakes and rivers

what are some landscape features due to frozen ground?

-ice wedges and patterned ground; ice wedges can build up to form a network of ice visible on the surface as polygons or 'patterned ground' -thermokarst lakes; Arctic areas have many shallow freshwater lakes formed in a depression by melt water from snow or thawing permafrost

What would happen to the depth of the active layer and depth of the permafrost if: Average annual temperature was above freezing (32 oF or 0 oC)?

-permafrost would disappear

permeability def

A measure of how easily a solid allows fluid to pass through it (how connected the open space is)

how does energy travel through soil/rock

conduction

how is heat transferred?

conduction, convection and radiation

discontinuous permafrost def

contains pockets of unfrozen ground, absent under lakes and south-facing slopes, thinner and younger (formed in last few thousand years)

would thick snow cover increase or decrease permafrost thickness?

decrease

melting vs thawing

melting=phase change from solid to liquid thawing=a solid warmed above 0°C (think chicken)

radiation def

movement of energy between to points that does not require any material at all.

convection def

movement of energy through a fluid body. The material moves and carries the heat. Hot less dense material rises upward through a fluid and is replaced by cooler, more dense material = convection currents.

conduction def

movement of energy through a solid body. The material itself does not move

porosity def

percentage of rock or soil that is open space (pores)

sporadic permafrost def

small areas of frozen ground

permafrost def

soil and/or rock that has been below 0 °C for more than 2 years, may or may not contain ice (1-1400m)

talik def

thawed permafrost

what would happen to the depth of the active layer and depth of the permafrost if: Average annual temperature stayed the same but max summer temperature increased?

the depth of our active layer would be deeper

what might cause permafrost to thaw?

the sun heat from the atmosphere volcanic activity geothermal activity (GEOTHERMAL RADIANT)

continuous permafrost def

thick unbroken layer, even under small lakes, formed during last glacial period

where is permafrost?

•Occurs on land around the Arctic, also in Antarctica and South America •Wherever summer heating does not thaw ground at depth •Even under the sea in some shallow areas of Arctic Ocean