pp per i glacial 2014
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Periglacial – Close to Glaciers
The periglacial environmentincludes regions close to glaciers. These regions aredominated by freeze-thawprocesses.
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How much force is necessary to crack the top stone with lateral thrusting?
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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.
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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.
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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.
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Where to Expect Freeze-Thaw
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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.
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Russia and Nearby Countries
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Canada & Permafrost
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Dawson, Yukon Territory
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Inuvik, NWT is Underlain by Permafrost
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Tuktoyaktuk Housing
Truck in water and truck out the sewage to every house.
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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.
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Dempster Highway and Bridge
Note depth of roadbed. Only bridge on 700km route.
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Fairbanks, AK highway sign - common
Asphalt absorbs heat and thaws permafrost.
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With and Without Permafrost
Inuvik – bed for gas storage
Bodó, Norway pipes - shallow
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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.
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The Alaska Pipeline
An engineering wonderbecause it has not failed.
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Engineering the AK Pipeline
• Every support tower is a refrigeration unit.
• Buried the line beneath streams. Why is this easier than going over?
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Periglacial Landforms: Small
• Stone polygons – size varies. Water must be present. Inactive and active – vegetation is the key.
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Active Stone Polygons
Depression is at 12,700 feet in the Sangre de Cristo Mtns, CO
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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.
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Ute Creek, Colorado
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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.
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Stone Stripes – a Freeze-Thaw Product
• Sorting sediment by size during freeze-thaw creates visible stone stripes.Colorado
Yukon Territory
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Periglacial Boulder Field in PA
South of glaciers – rocks slid down frozen slopes.
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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.
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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
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Alpine Bog – Moving Down Hill
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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.
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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.
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Classic – Glacial Rock Glacier
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More Rock Glaciers - Glacial
Net effect – moving rock debristo a lower elevation.
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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.
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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.
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Form and Process
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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!
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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.