Ch.17: Periglacial Geomorphology and the Pleistocene Epoch Flashcards
Define the terms periglacial and permafrost. What is ground ice, and how does it occur in the soil?
-Periglacial - “on the perimeter of glaciation”; places where geomorphic processes occur relating to freezing water
-Permafrost - ground that stays completely frozen for a long period of time; soil, sediment, or rock that remains below 0 degrees for at least 2 yrs
-Ground Ice - water present within permafrost in form of ice
-it occurs when temperature drops below the freezing point, and it causes the water that infiltrated into the soil from precipitation to start to freeze
Describe the spatial distribution of permafrost in terms of geographic extent and continuity (zones).
-in the continuous zone:
-it’s the region of severest cold (mean annual temp of temp -7 degrees)
- affects all surfaces except beneath deep layers or river
-Depth of permafrost averages 400 m
-in the discontinuous zone:
-the region where mean annual temps are at least -1 degree
- there’s unconnected patches of permafrost (some ground areas aren’t frozen)
-Mostly occurs in north-facing slopes (in N. hemisphere) or areas not insulated by snow
Define the terms Talik and active layer and explain how their presence and thickness can vary
Talik - unfrozen ground that may occur above, below, or within a body of discontinuous permafrost
Active layer - the zone of seasonally frozen ground that exists between subsurface permafrost layer and the ground surface
-thickness of the active layer increases w/ decreasing latitude
-consistent experiences daily or seasonal freeze/thaw cycles
Briefly explain which factors affect the presence of frozen ground.
-Seasons -affects depth and extent of frozen ground
-Latitudes - permafrost tends to be more prevalent in high latitudes
-Altitude - higher elevation reaches cooler temp
-Local landscape - terrain features: soil type, topography, vegetation cover
-Slope
-Climate - temperature, precipitation levels
What basic occurrence causes frost-action processes to occur? Briefly explain the six frost-action
processes described in the lecture.
1.) Frost heave - vertical movement of the ground surface (or objects on, or in the ground) caused by the formation of ice in the soil
-results in boulders of rock slabs thrust to surface, and churning of soil
2.) Frost thrusting - horizontal movement of the ground surface caused by the formation of ice in the soil
-results in cracks in the ground in which ice wedges form
3.) Block fields - “felsenmeer” - form by excessive frost activity in highly weathering-resistant rocks
-repeated frost-wedging forms slopes of angular rock rubble
4.) Ice wedges - forms when water enters the crack of permafrost and freezes; repeated seasonal freezing and thawing enlarges cracks over time
5.) Patterned ground - when expansion and contraction of frost action results in movement of soil particles, stones, and small boulders into distinct polygonal shapes
6.) Pingos - when large areas of frozen ground develop heaved-up, circular, ice-cored mounds
-often involve injection of water from inclined aquifers below ground
Describe the kind of topography is associated with a thermokarst landscape, and explain its
cause.
-Thermokarst - landscape that results from thawing of permafrost
-it forms as a result from thermal subsidence and erosion, which is caused by ice melt and poor drainage
-The topography is hummocky and characterized by small depressions, standing water, and thaw lakes
Explain how permafrost thawing has affected fossil-fuel exploration (you may need to consult your textbook)
The permafrost has been increasingly thawing, creating unstable soft surfaces due to global warming. This restricts the days fossil-fuel exploration equipment can operate to only 100 days a year (used to be 200).
When was the Quaternary Period? The Pleistocene Epoch? What climatic events is this time most known for?
-The quaternary period was the last 2.6 million years
- This was the time of the major climate fluctuations
-Pleistocene epoch - 2.6 M - 10 thousand yrs ago
-This time is known for the Ice Age, which was an extended period of cold lasting for several million yrs; ice sheets were covering most land areas
Define the terms ice age, glacial, and interglacial.
Ice age - any extended period of cold, in some cases lasting several million yrs
Glacial - period of time characterized by advance
Interglacial - a brief, warm spell occurring between glacial periods, characterized by glacial retreat
Describe the spatial extent of glaciation during the last glacial maximum. Name the two ice sheets that covered Canada and describe their locations. At what point was British Columbia
effectively deglaciated?
-During the Last Glacial Maximum (LGM), which occurred 26.5 to 19 000 yrs ago; extensive glaciation covered most parts of N. America, Europe, and Asia
-Laurentide Ice sheet - covered most of Canada, stretching from the Canadian Artic, across the eastern provinces, into the northern US. At its max extent, it reached as far south as northern US, covering most of Manitoba, Saskatchewan, Alberta, and parts of Ontario and Quebec
-Cordilleran ice sheet - covered much of western Canada and Pacific Northwest region of the US; extended from Canadian Rockies in BC and Alberta down to the Washington state and Oregon
-About 12, 000 yrs ago BC was deglaciated, marking its retreat
Why do we care about understanding past glaciations?
They give us insight into the Earth’s climate system and its variability over geological timescales
-also serve as analogs for understanding potential future climate
-They have significant implications for sea level fluctuations
