Periglacial – Close to Glaciers

The periglacial environmentincludes regions close to glaciers. These regions aredominated by freeze-thawprocesses.

How much force is necessary to crack the top stone with lateral thrusting?

Periglacial Environment• This term was introduced to address the

landforms created in the environment “near” a glacier.

• This is the environment in which alternate freeze-thaw impacts the landscape. This need not be close to a glacier.

• Purpose of this lecture is to view the landforms that are directly related to freeze-thaw.

Permafrost – one variable

• One landscape element of the periglacial environment may be permafrost.

• The active layer occurs yearly and contributes to movement on slopes, even very gentle slopes.

• Thickness is related to climate over millennia.

Permafrost – can be Absent

• Freeze-thaw does not require permafrost in the surface to alter the landscape.

• The map of frost-free days is an effort to show where periglacial acitivity can occur.

Where to Expect Freeze-Thaw

Latitude or Elevation

• Climate drives the periglacial environment. A northern (or southern) latitude or an increase in elevation can move you into the realm of serious freeze-thaw.

• Maps of Russia and Canada follow to show you the extent of permafrost and other areas impacted by freeze-thaw.

Russia and Nearby Countries

Canada & Permafrost

Dawson, Yukon Territory

Inuvik, NWT is Underlain by Permafrost

Tuktoyaktuk Housing

Truck in water and truck out the sewage to every house.

Old and New – Same Problem

• Any structure that allows heat in the structure to pass intothe ground will cause the permafrost to thaw.

• Support for the structure is lost in the water saturated sediment and sinking occurs.

Dempster Highway and Bridge

Note depth of roadbed. Only bridge on 700km route.

Fairbanks, AK highway sign - common

Asphalt absorbs heat and thaws permafrost.

With and Without Permafrost

Inuvik – bed for gas storage

Bodó, Norway pipes - shallow

Functioning with Frozen Ground

• Ice will form as long as water is supplied. All of the sediments above the cat to the left are frozen.

The Alaska Pipeline

An engineering wonderbecause it has not failed.

Engineering the AK Pipeline

• Every support tower is a refrigeration unit.

• Buried the line beneath streams. Why is this easier than going over?

Periglacial Landforms: Small

• Stone polygons – size varies. Water must be present. Inactive and active – vegetation is the key.

Active Stone Polygons

Depression is at 12,700 feet in the Sangre de Cristo Mtns, CO

Relict Stone Polygons

• 2800 transit shots were taken to map the distribution of rock and vegetation across this area of stone polygons.

• As slope changes, a polygon changes to a stripe.

Ute Creek, Colorado

Introduce Slope to Freeze-Thaw

• On a slope the polygon changes to a stripe.

• An entire surface is covered with evidence of down-slope motion.

Stone Stripes – a Freeze-Thaw Product

• Sorting sediment by size during freeze-thaw creates visible stone stripes.Colorado

Yukon Territory

Periglacial Boulder Field in PA

South of glaciers – rocks slid down frozen slopes.

Slope plus Water

• Snow melt and precipitation provide the water needed to create periglacial processes and landforms.

• Stone polygons, stone stripes, and a variety of other surficial arrangements (such as solifluction lobes) occur whenever freeze-thaw occurs.

• Without the presence of water, periglacial freeze-thaw processes cannot occur.

An Alpine Climatic Station• This graph of temperature

and precipitation for a site above tree-line illustrates the totally frozen period and the very short period in which no freeze-thaw occurs.

krummholz

Alpine Bog – Moving Down Hill

Rock Glaciers – Large Forms

• Rock glaciers can be created by glacial OR periglacial processes.

• They represent the largest landforms associated with the movement of rock debris to another location.

California Rock Glacier, Sangre de Cristos Mountains, CO

• Falling debris loads the surface; the weight cause the entire mass to move to a lower elevation.

Classic – Glacial Rock Glacier

More Rock Glaciers - Glacial

Net effect – moving rock debristo a lower elevation.

Mt. Mestas, CO > 12,000 ft.

• Fossil rock glaciers have been found in New Mexico, totally covered with forest.

• Type of rock contributes to the slow addition of vegetation to this surface.

• No instrumentation on it to check change over time.

Periglacial Rock Glacier

• Mt. Mestas, CO has never been glaciated yet 23 rock glaciers can be found around it.

• Rock glaciers can be created by different processes.

Form and Process

Form and Process - Explanation

• Rate of change is a function of process not form.

• Whereas we might be able to see change in the form, the key question is what process or processes caused the form to change.

• Form ONLY changes in response to process.

• Rock glaciers have not been found in the rock record; they do not last forever!

Periglacial Geomorphology Conclusion:

• Alternate freeze-thaw is capable of small changes or big changes (stone polygons vs. rock glaciers).

• The process is driven by climate and the 9% increase in volume as water is converted to ice.

• Permafrost need not be present to have a periglacial environment; fossil landforms have been preserved that reveal the extent of the periglacial environment during glacial times.