Retrogressive Thaw Slumps are important processes

fashioning periglacial environments

Permafrost

• Earth materials maintaining a temperature below 0°C for a period of two years or longer

• A geologic condition of polar environments and underlies approximately 26% of the earth’s land surface

• (Williams and Smith 1989).

Retrogressive Thaw Slump• Ice-rich permafrost thaws, meltwater and thawed

material flow, slide, or fall to the foot of the thaw face. • If the ice content of the frozen soil is much greater

than the saturation moisture content, a mud slurry forms.

• An ablating face appears, sloping at 20 o -80 o, with a basal mudflow at 1 o -10o

• Vary from fan shaped to U-shaped.• Active while air temperatures exceed 0°C. • Ablation and associated headwall retreat may be

retarded early in the season by snow banks and fallen debris. (Jackie 2008)

P 37, Retrogressive thaw slump process and morphology, Eureka Sound Lowlands, Ellesmere Island, Nunavut...Grom, Jackie Dee . 2008

• http://4.bp.blogspot.com/-V5g3AYwY6HI/TlkmjgZN7hI/AAAAAAAAA2o/VzlcMZ4fEEI/s640/Untitled2.png

Initiation of slumps

• From exposure of ice-rich permafrost by disturbance or erosion. (Burn 1990)

• They may be started after exposure by :– Ice scour– Flooding,– Combined physical and

thermal stream erosion– Warm summer weather– Forest fires

• Active while air temperatures exceed 0°C

Locations

• Lakeside thaw slumps• Coastal thaw slumps• River thaw slumps• Road construction and mining sites

http://www.sitnews.us/1009news/100109/100109_ak_science2.jpg

• Thaw slump on the Bonnet Plume River,• Flows into the Peel River in northern Yukon. • The top of the feature is about a half-mile-

wide. The mudflow extends more than a mile

http://www.sitnews.us/1009news/100109/100109_ak_science.html

• 2,300 feet wide, 1 1/2 miles from the hillside to the river

• May have beentriggered by a forest fire in the 1870’s • still active for

over 100 years

Surprise Rapids Slide

Slump reinitation by lakes• A increase in permafrost temperatures from

slumping results in lateral talik growing• Causing the lake-bottom and shoreline

settlement growth• Leading to slump re-initiation.

Figure 1 p2 S. V. Kokelj Origin and Polycyclic Behaviour of Tundra Thaw slumps(2009

Figure 2 (p3.). S. V. Kokelj Origin and Polycyclic Behaviour of Tundra Thaw slumps(2009)

Hazards• Effects on Fisheries – Thaw slump occurred spring of 2004 in Selawik

River drainage on sheefish, the primary fish for the village of Selawik

http://alaska.fws.gov/fisheries/fieldoffice/fairbanks/images/slump_photo_sm.jpg

http://www2.gi.alaska.edu/ScienceForum/ASF19/1974.html

Changing environments

• NRC - most active geomorphic features of permafrost terrain

• Can retreat up to 30 meters a day in some cases

• Last 3 to 25 years (averages 12-15)• Within the Sand Hills Moraine of southern

Banks Island, however, 75 per cent of the land up to 100 m from the coast has been affected by thaw slumping (Lewkowicz 1987b). A

Climate change

• The majority of this slump growth was associated with the activity of existing slumps rather than the initiation of new ones.

• More active periods for Retroapids Slide happened in the 1940’s, when the central Yukon had record high early summer temperatures

Prevention

• Insulation of ice-rich slopes (e.g., using woodchips) may reduce thaw slumping. initially, this appears to have been successful along the pipeline route from Norman Wells, NWT, to Zama. Alberta.

Questions?

• How large in diameter can a retrogressive thaw slump grow to?

• How many are there in the Mackenzie Delta?• Why do woodchips help reduce thaw?• What is another definition of a retrogressive

thaw slump?– The drooping posture assumed by a dog musher

who has been on the trail for 12 hours, when sitting by a toasty fire (UAF 2012)

Where is this Retrogressive thaw slump located?

HiRISE image PSP_007843_1905. Image credit NASA/JPL/UofA. http://www.psi.edu/pgwg/images/dec09image.html