Module 10 Flashcards
permafrost
permafrost – a thermal a thermal condition where ground temperatures remain below 0°C for two or more consecutive years
develops where the depth of frost penetration into the ground during the fall and winter is greater than the depth of ground thawing in the summer
pore water is frozen and acts to cement sediment particles, or fills a large proportion of the pore spaces in consolidated rock
periglacial
periglacial landscapes include landforms and locations characterized by intensive freeze–thaw action
describes areas where permafrost currently exists or has existed in the past, regardless of current or past glacial positions
includes both high latitude and high elevation regions
Permafrost Zones 4
continuous permafrost zone is the region in which permafrost conditions are generally (90–100 per cent) present beneath the seasonally thawed active layer
isolated patches of unfrozen terrain, called talik, are also present in the continuous permafrost zone
discontinuous permafrost zone is characterized by patchy distribution of permafrost, with frozen ground beneath the active layer representing 10–90 per cent of the area
alpine permafrost zone includes isolated patches where permafrost covers less than 10 per cent of the area and occurs in the lower parts of alpine and upland regions
subsea permafrost zone developed during the last glacial maximum period (25,000 years ago), when sea level was lower and parts of the sea floor were exposed to continuous cold temperatures
permafrost currently underlies __ per cent of Canada and is divided into zones
40
continuous permafrost means the regions has approximately __-__%
90-100
discontinuous permafrost means the regions has approximately __-__%
10-90
alpine permafrost means the regions has approximately __-__%
1-10%
3 types of discontinuous permafrost
discontinuous permafrost – mean annual air temperatures range from -0.5oC to -7oC
widespread: 50-90% underlain by permafrost
scattered: 30-50% underlain by permafrost
sporadic: 10-30% underlain by permafrost
- permafrost thickness increases poleward
_____(country) has the most permafrost
Russia
ground temperatures increase with depth in response to the …
geothermal heat flux
formation of segregated ice is favoured in materials with an average grain size finer than ___ mm diameter (i.e., silt and clay) – frost susceptible sediments
pore water expands upon freezing resulting in _______
0.01
frost heave
cryoturbation
repeated heaving and subsidence results in mixing of materials within the active layer, a process referred to as cryoturbation
contributes to the development of patterned ground
4 patterned ground examples of cryoturbation
sorted circles are small, circular features, tens of centimetres in diameter, with pebbles of uniform size
unsorted circles contain a wide range of clast sizes
stone stripes develop with increasing slope as circles become elongated in the downslope direction
felsenmeer develops where fractured bedrock is exposed on surface slopes, and frost heaving produces assemblages of angular cobbles and boulders covering the terrain
gelifluction
gelifluction is a slow downslope movement accentuated by frost heave and cryoturbation
It involves very slow (centimetres or millimetres per year) movement of saturated, non-frozen or partially frozen material over a frozen substrate
gelifluction should not be confused with frost creep
results in formation of small overlapping terraces, 1-10 m in width, forming a lobate pattern; gelifluction lobes
active-layer detachment slides (ALDS)
active-layer detachment slides (ALDS) are mass movements characterized by the sliding of a cohesive layer over the surface of a permafrost table or a seasonally developed frost table
ALDS can be triggered by a period of high temperatures under cloudless skies, resulting in enhanced input of solar insolation
melting of interstitial ice may generate high pore water pressures at base of slab facilitating motion; peak velocities may exceed 5 metres/hour
-slopeinstability initiated by the deepening of the active layer
Massive Ground Ice
massive ice bodies, often 10’s of metres thick, are widely reported in coastal lowlands bordering the Beaufort Sea
consists of intrusive ice formed by the movement of water under pressure into seasonally or perennially frozen materials
water is supplied by taliks, bodies of unfrozen materials within permafrost, that serve as aquifers
____ facilitate the flow of groundwater through permafrost towards stream channels and lake basins.
Talik
retrogressive thaw flows
occur where thawing of a disturbed area at the head or crown of the flow allows the bank to erode backward (retrogress), extending the disturbed area at the headward end
occur in silt or fine sand with a high interstitial ice content
motion similar to rotational slumps
velocities can reach 16 metres per year
thermokarst
thermokarst is the subsidence of the ground surface in permafrost regions due to differential melting of ice or ice-rich sediments and subsequent subsidence of the ground surface
primary cause is related to deepening of the active layer
melt water collects in subsiding basin; promotes further thawing and subsidence
thermokarst features can occur at any location where ice or ice-rich sediments are exposed to temperatures at or above 0°C
-human activities can also promote the development of thermokarst
global mean air temperature has increased by __°C over the past century
0.6
Air temperatures in the circumpolar North for past 100 years-
1900-1940
1940-1960
1970-present
Air Temperatures
circumpolar North has experienced both strong warming and cooling at various times over the past 50 to 100 years
warming through the 1900’s to the 1940’s
cooling through the 1940’s to the 1960’s
warming through the 1970’s to the present
currently, the Arctic is warming at more than _____ the rate of lower latitudes
twice
represents an increase of 2.3°C since the 1970s and 2.9°C since the beginning of the 20th century
Arctic Amplification mechanisms(4)
mechanisms for Arctic Amplification include:
reduced summer albedo due to sea ice and snow cover loss
decrease of total cloudiness in summer and increase in winter
additional heat generated by newly sea-ice free ocean areas that are maintained later into the autumn
lower rate of heat loss to space in the Arctic relative to the sub-tropics due to lowered mean temperatures
The Sea Ice _____ hasnt changed much in the last 3 decades but the Sea Ice _____ has declined markedly
maximum
minimum
Since 1970’s ice has been becoming annual ice instead of multi-year ice
Sea ice extent has decreasing trends in all months. The September monthly average trend for the entire Arctic Ocean is now ___% per decade relative to the 1981-2010 average.
-13.4
_____is when sea ice is usually at its maximum
march
Changes in sea level are associated with a combination of factors:4
isostatic subsidence and uplift
eustatic changes in ocean volume
changes in atmospheric pressure; cyclonic storms, storm surges
tides: produced by gravitational attraction of Moon and Sun
Glacier Ice and Sea-Level Rise sea level is currently rising at over __ mm per year due to melting glaciers and thermal expansion of ocean waters
3
- increase coastal erosion
- increase vulnerability of infrastructure to storm surges
Permafrost and Ground Ice depths and relationships
depth of active layer varies from approximately 20 cm in the Canadian Arctic Archipelago to as much as 15 m in the Western Cordillera
ground ice is usually concentrated in the upper few metres of permafrost, precisely that portion of permafrost which would thaw first as air temperatures rise
Results of warming climate on permafrost
under a warming climate scenario, progressive deepening of the active layer within permafrost can lead to:
loss of segregated ice resulting in loss of strength
saturation of soils with water resulting in loss of strength
contributes to rapid mass movement of surficial materials on slopes via shallow landslides – active layer detachment slides
degradation of permafrost in response to warmer summer air temperatures involves deepening of the active layer and melting of ground ice resulting in subsidence of the ground surface – thermokarst subsidence
thermokarst terrain - closed, water-filled depressions and hummocky topography in otherwise flat terrain
the size of a wave depends on:3
velocity of the wind
duration of the wind
fetch (distance the wind blows across the water)
-waves become organized into groups as they move away (propagate) from their source; longer, faster waves move ahead of shorter, slower waves
orbitals
waves involve motion of water molecules in circular or elliptical paths, termed orbitals
in deep water environments (depth is >1/2λ) the water molecules describe orbital paths without moving closer to land
orbital motion continues at a diminishing rate, reaching zero at a depth approximately equal to 50 per cent of the wavelength (λ), the wave base
when approaching the shore wave height ______ and wavelength _______
increases
decreases
wave shape changes to _____ when they enter shallow water
ellipses
wave velocity(____)
celerity
Describe wave movement in deep water vs shallow water
In shallow water, landward of the wave base, the celerity is controlled by the water depth and the acceleration due to gravity:
C = √gD
frictional interaction with the seabed slows the base of the wave and celerity decreases
the wave crest continues to move landward, causing the wave to steepen as the surface moves faster than the base
eventually, wave steepness (H/λ) increases to the point that the wave becomes unstable and breaks, releasing its energy on the coast
Two types of breaking waves
Plunging-typically forms on steep beaches; can be very erosive
Spilling-typically forms on wide, gently sloping sandy beaches;less erosive than plunging breakers
Offshore Bathymetry: 2 types
Dissipative-if the offshore bathymetry (underwater topography) is gently sloping, the incoming waves will feel bottom and break far from the shore
-flat shoreline
reflective-if the offshore bathymetry slopes steeply, waves will be able to reach the vicinity of the shore before breaking
-reflective beaches will usually have a small berm sloping down into the water
Beach onshore Makeup(3)
The Beach onshore
backshore: formed by erosion of rock or sediments. May consist of sea cliff (oceans) or bluff (lakes) or sand dunes. Landward extent of the beach.
berm: consists of sediments (sand, gravel) and woody debris deposited by waves. Surface dips landwards.
beach face: that portion of the beach that slopes seaward. Lies in part within the
swash zone: affected by swash and backwash
Beach Offshore Makeup(3)
surf zone: lies seaward of the swash zone. Where waves move turbulently toward the shore after they break.
breaker zone: located beyond the surf zone. Where incoming waves steepen and break. A longshore bar forms in this zone.
a longshore trough may form by wave and current action landward of the longshore bar
Total Beach Makeup(8)
From Land Out
- Cliff or Dune Line
- Berms
- Beach face
- Swash Zone
- Surf Zone
- Longshore Trough
- Breaker Zone
- Longshore Bar
Beach Drift Vs. LOngshore Drift
Swash–>Backwash
-swash-backwash operate to move sediments along the beach face above the high tide line – beach drift
longshore drift - transport of sand by longshore currents that flow parallel to the shoreline
Both create the littoral transport
Littoral Transport=____ drift and ____ drift
beach
longshore
erosion of beach face by large storms can result in a beach becoming ______
until the storm passes and sediment is moved back from ______ bars back towards the beach eventually making it _______ again
dissipative
submarine
reflective
Minimizing Damage from Coastline erosion
Hard stabilization
building structures to reinforce (armouring) the coastline(Seawall)
Soft stabilization
adding sand to depleted beaches
Land use changes
rezoning the coastal area by changing the land usage; avoiding building in hazardous areas
relocating threatened buildings
Beach Nourishment
artificially placing sand on beaches to compensate for losses by erosion
provides a beach for recreation and is aesthetically preferable to many engineered structures
expensive and must be periodically repeated to stabilize a beach
Miami Beach example
Miami Beach in 1970’s used beachnourishment
-sea wall with land in front of it with dune and bern
Case Study Tuk
.on Barrier Island/Sand Spit
- strong storms with winds as high as hurricane level
- potential sea level rise of 0.5 meters
- high sensitivity to sea level rise
- coastline eroding at 1 meter per year
Potential sea level rise in arctic __ meters
0.5
