glaciation Flashcards
what is a glacier?
bodies of ice formed from repeated periods of snowfall
what are alpine glaciers?
glaciers that form high in the mountains and travel downhill like rivers of ice
what are ice sheets?
the largest accumulation of ice, defined as a complete and continuous cover of more than 50,000km2
how big are valley glaciers?
they are typically between 10 and 30km in length although in the Karakoram Mountains of Pakistan they are as long as 60km
what was The Pleistocene?
the name of the time from 1.8millions years ago to 11,500 years before the present
lots of ice
what was The Holocene?
the name of the time from 11,500 years before the present to the present
little ice
how does ice accumulate?
- a fresh layer of snow has a lot of air trapped in between its ice crystals
- in cold glacial conditions, layers of snow pile up on top of each other and squeeze this air out
- last year’s snow is called névé or firn, and as it becomes more and more compressed by the layers, it turns to ice
- process known as accumulation and it is most likely to take place high up in the mountains near the source of a glacier where temps are at their coldest
what does very compressed ice look like?
blue
what is last year’s snow called?
névé or firn
what are systems?
a set of interrelated parts which compose of:
stores
throughputs
inputs
outputs
what are the inputs of a glacial system?
potential energy
kinetic energy from wind
thermal energy from sun
deposited materials
precipitation
what are the stores of glacial systems?
ice, water, debris
what are the outputs of glacial systems?
ablation
calving
sediments
when is a glacier seen as being in a state of equilibrium?
if the inputs = the outputs, meaning the glacier stays the same size
what is dynamic equilibrium?
where the system ‘self-regulates’
it produces its own response to a disturbance and will gradually change its form until equilibrium is restored
glaciers are in a state of dynamic equilibrium
what are examples of positive feedback in glaciers?
melting ice - less ice reflecting sun’s energy back (lower albedo) - climate warms - glacier retreats further - melting ice,,,
ice mass grows - more ice reflecting sun’s energy back (higher albedo) - climate cools further - more accumulation of ice - etc
what are continental glaciers?
massive glaciers that cover entire landmasses, moving outwards from the centre
what is calving?
large pieces of glacier break off when glacier reaches the ocean
how is a u-shaped valley formed by glaciers?
they grind down the rock on both the sides and bottom of the area where they are traveling
how are glacial striations formed?
as glaciers grind over the surface bedrock, they leave behind deep scratches in the rock
these record the direction of ice flow in the rock
what is glacial till?
when a glacier melts, it deposits piles of unsorted and unlayered sediments, known as glacial till
what is the terminal morraine?
marks the farthest a glacier travelled before melting
what are glacial erratics?
large boulders are transported over long distances. when a glacier melts, it deposits these boulders
what is a drumlin?
an elongated hill of deposited glacial till
the shape of a drumlin reveals the direction that the glacier was moving
how is a glacial kettle (aka kettle lake) formed?
block of ice dropped by glacier
ice block becomes surrounded by sediment
ice block melts
how is an outwash plain formed?
when glaciers melt, the meltwater forms streams, which deposit sorted sediments, creating a region known as an outwash plain
what does englacial mean?
within the glacier
what does subglacial mean?
beneath the glacier
what does proglacial mean?
in front of the glacier
what is the pressure melting point?
the point where ice melts due to the pressure from above
what are niche glaciers?
usually only tens of metres in size, and are found on steep slopes
they originated as snow patches and remain as small wedges of shallow ice
what are cirque glaciers?
up to hundreds of metres in size
they develop from snow patches in hollows and grow into armchair-shaped basins
what are valley glaciers?
formed when ice moves out of the cirque into pre-existing valleys
they are up to 60km long in the Karakoram Mountains of Pakistan
what are piedmont glaciers?
occur where valley glaciers advance out of a mountain into a wider lowland region
what are ice caps
small ice sheets, less than 50,000km2, which bury the landscape
what are unconstrained glaciers?
freely forming ice masses not affected by the surrounding landscape
include ice sheets and ice caps as well as streams + ice domes
what are constrained glaciers?
form between mountain peaks, valleys etc
shape, structure and size of them are influenced by surrounding landforms
include valley glaciers, cirque glaciers and piedmont glaciers
what is a mountain glacier?
surrounded by mountainous terrain on all sides
eg in Alaska + Arctic Canada
what are outlet glaciers?
ice channels that originate from ice caps, ice sheets or ice fields
what are tidewater glaciers?
river of ice that forms when a glacier flows to the coast
the edge of tidewater glaciers that leads the glacial flow slightly lifts upwards and floats into the ocean, creating towering ice cliffs
notorious for calving
what are cirque glaciers?
smallest type of glaciers found in cirques
what are rock glaciers?
mass of ice predominantly hidden beneath rock debris
what are hanging glaciers?
form in hanging valleys
originate high up in the mountains + flow down its sides and end abruptly
pieces break away, fall and roll down slopes, resulting in avalanches
what is glacier mass balance?
the balance between inputs and outputs, accumulation,
what is positive and negative mass balance?
if accumulation exceeds ablation, a glacier gains mass
negative mass balance is vice versa
what is lithology?
describes the physical and chemical composition of rocks
what is the impact of lithology on glaciated environment?
basalt is made of dense interlocking crystals, and is highly resistant + more likely to form prominent glacial landforms such as aretes and pyramidals
how does structure impact the glaciated environment?
structure includes the angle of dip of rocks and can have a strong influence on valley side profiles
what is latitude?
how far north or south
how does latitude impact glaciated environment?
66degrees north and south is dry with little seasonal variation = large stable ice sheets
the higher the latitude , the more apparent the cold, dry climates with little seasonal variation are
how does altitude affect the glaciated environment?
increase in altitude = decrease in temp, so glaciers are even found near the equator in the Andes
how does relief impact the glaciated environment?
the steeper the relief of the landscape, the greater the resultant force of gravity, and the more energy a glacier will have to move downslope
what is aspect?
the compass direction that a slope faces
how does aspect impact a glaciated environment?
if the aspect of a slope faces away from the general direction of the sun, temperatures are likely to remain below 0 for longer, so melting occurs
how does wind impact a glaciated environment?
has a key role in transporting material and accumulating snowfall. can influence erosion and other landform processes
what does fresh snow look like?
consists of flakes with an open, feathery structure and a low density of around 0.05g/cm3
what happens with each new snow fall?
compresses and compacts the layer of snow beneath, causing the air to be expelled, and converting low density snow into high density ice
what is firn?
snow that survives one summer
has a density of 0.4g/cm3
what is diagenesis?
the process by which snow becomes ice due to compression
what does true ice look like?
bluish colour
what is rain-splash erosion?
raindrops can have an erosive effect on hillslope
on a 5 degree slope, about 60% of the movement is downslope. This figure increases to 95% on a 25 degree slope
it is most effective on slopes between 33degree and 45degrees, and at the start of a rainfall event when soil is still loose
what are falls?
occur on steep slopes (greater than 70 degrees), especially bare rock faces where joints are exposed
initial cause of the fall may be weathering, such as freeze-thaw or disintegration, or erosion prising open lines of weaknesses
once rocks are detatched, they fall under the influence of gravity
if the fall is short, it produces a relatively straight scree. If it is long, it forms a concave scree
eg Wastwater Screes, Lake District
What are slides?
occur when an entire mass of material moves along a slip plane. These include:
- rockslides and landslides of any material, rock or regolith
- rotational slides, which produce a series of massive steps or terraces
occur when there is a combination of weak rocks, steep slopes and active undercutting. often caused by a change in water content of a slope, or by very cold conditions
what are slip planes?
occur at a number of locations:
- at the junction of two layers
- at a fault line
- where there is a joint
- along a bedding plane
- at the point beneath the surface where the shear stress becomes greater than the shear strength
is a concave curve and as the slide occurs, the mass will be rotated backwards
weak rocks, such as clay, have little shear strength and are particularly vulnerable to the development of slip planes
example of a rock slide
6th strongest earthquake in US in Montana 1959, close to this epicentre was a slope of schists and gneiss with slippery mica and clay was supported by a base of dolomite
earthquake boke the dolomite
huge volume of rock (400m and 1000m long) slid into Madison River Valley
what are landslides?
loose rocks, stones and soil have a tendency to move downslope whenever the downslope force exceeds the resistance produced by friction and cohesion
when material moves downslope as a result of shear failure at the boundary of the moving mass, it is termed as landslide
what are slumps and flows?
occur on weaker rocks, especially clay, and have a rotational movement along a curved slip plane
clay absorbs water, becomes saturated and exceeds its liquid limit, then flows along the slip plane
frequently, the base of a cliff is undercut and weakened by erosion, thereby reducing its strength
by contrast, flows are more continuous, less jerky and are more likely to contort the mass into a new form
what are avalanches?
rapid movements of snow, ice, rock or earth down a slope
common in mountainous areas
what is a dry avalanche?
newly fallen snow may fall off older snow, especially in winter
what is a wet avalanche?
in spring, partially melted snow moves
when do avalanches frequently occur?
on steep slopes over 22 degrees, especially on north facing slopes where the lack of sun limits the stability of snow
what is a debris avalanche?
rapid mass movement of sediments, often associated with saturated ground conditions
what is mass movement?
the movement of material downslope as the result of gravity
what is a corrie?
(aka cirques/cwms)
an armchair shaped hollow found on the side of the mountain. this is where a glacier forms.
how is a corrie formed?
snow collects in a sheltered hollow
the back wall gets steeper due to freeze-thaw weathering and plucking; the base becomes deeper bc abrasion
glacier moved out of hollow via rotational slip
less erosion at the front of the glacier means a corrie lip is formed
how is a tarn formed
a lake forms in a corrie after the glacier has melted
example of a corrie?
Cwm Idwal
what is an arête?
narrow ridge of land created when 2 corrie erode back towards eachother
example of an arête?
The Sawtooth, Southern Rocky Mountains
what is a pyramidal peak?
three or more corrie erode back towards each other- at the top of a mountain a pointed peak is left behind
example of a pyramidal peak?
Ketil in Greenland
what is a hanging valley?
deeper glacier ice in main valley erodes vertically downwards more rapidly than thinner ice in the tributary valleys, often producing a waterfall
is a tributary valley high above the main valley. river descends into main valley as a waterfall
example of a hanging valley?
Yosemite Falls, California
what is a U-Shaled Valley
aka trough
during periods when earths climate cools, glaciers form and begin to flow downslope.
they occupy the low V-Shaped valleys once created by rivers
as glaciers flow through the valleys, they concentrate erosive action over the entire valley, widening its floor and oversteepening it’s walls.
after the glacier retreats, it’s leaves behind a flat bottomed, steep walled U Shaped Valley
example of a u shaped valley
Yosemite Valley
what is a truncated spur?
valley glaciers remove the ends of interlocking spurs by plucking + abrasion
example of a truncated spur
The Devil’s Point in upper Glen Dee
what is a misfit stream?
after glaciation they can occupy the floor of the U-Shaped calley
example of a misfit stream
kali river, india
what is a ribbon lake?
long narrow lane in a glacial trough
areas of increased erosion on valley floor due to the confluence of glaciers, weaker rocks or well-joined rocks
this over deepens this part of the valley floor to form a basin, which later fills with meltwater
example of a ribbon lake?
windermere, england
what is a roche mountonnee
a more resistant rock, which remains after ice abrasion on the stoss (up glacier) side + plucking on the lee (down-glacier) side
example of a roche mountonnee
mount iron, wanaka, nz
what are striations?
rocks scarred with thin parallel scratches
formed when sub- or en-glacial moraine is dragged along exposed rock
what is an ellipsoidal basin?
major erosional landforms created by ice sheets eg the Laurentide Ice Sheet
where are cold glaciers generally found?
around the poles or in areas of extremely high latitude
these glaciers are frozen throughout and tend to experience very little movement
where do warm based glaciers tend to be found?
in areas of high altitude eg the Alps
exist in areas where temperatures can fluctuate around freezing and as a result the base of the glacier can melt. this layer of meltwater enables them to move relatively rapidly
what is the difference between weathering and erosion?
erosion is the surface processes that remove soil, rock or dissolved material from the location on the earths crust THEN TRANSPORT TO ANOTHER
WHEREAS weathering occurs in situ (in the same place)
what is plucking?
when meltwater from a glacier freezes around lumps of cracked and broken rocks
when ice moves downhill, rick is plucked from the bedrock
what is abrasion?
when rock is frozen tk the base and the back of the glacier scrapes the bed rock
can lead to development of rock flour
what is rock flour?
very fine grounded rock, which appears milky white and is often carried by glacial rivers and streams
how does the presence of basal debris influence the rate of plucking/abrasion?
rates of abrasion increase with the amount of basal debris, up to a point where it produces great friction, which slows down rates of movement
how does debris size and shape influence the rate of plucking and abrasion?
larger debris is more effective in abrasion as they exert more downward pressure which is proportional to their greater weight
angular debris is also more effective, as pressure is concentrated onto a smaller area of debris-bedrock interface
how does the relative hardness of particles and bedrock influence the rate of plucking and abrasion?
the more the bedrock is resistant to the debris, the less abrasion that takes place
how does ice thickness influence the rate of plucking and abrasion?
the greater the thickness of overlying ice, the greater the pressure exertion on the basal debris, leading tk greater rates of abrasion
when it’s roughly 100m-200m thick, pressure becomes too great, and there is too much friction for much movement to occur
how does basal water pressure influence the rate of plucking and abrasion?
the presence of a layer of meltwater at the base of a glacier is vital if sliding (and therefore abrasion) is to take place
if water is under pressure, the glacier can be buoyed up, reducing pressure + erosion
how does the sliding of basal ice influence rates of abrasion and plucking?
determined whether abrasion can take place, as it requires basal sliding to move the embedded debris across rock surfaces.
greater sliding = greater potential erosion
how does the movement of debris to the base influence rates of plucking + abrasion?
abrasion wears away basal rock, so needs to be replenished for erosion to be effective
how does the removal of fine debris influence rates of plucking and abrasion?
to maintain high rates of erosion, fine debris (rock flour) needs to be removed, to allow larger rock to abrade the bedrock. this is mainly done by meltwater
what did Boulton discover about rates of erosion?
(1974) measured erosion beneath the Iceland glacier
discovered that where ice was 40m thick and velocity was 9.6m/yr, then marble eroded @ 3mm/year.
when velocity increased to 15.4m/yr, then erosion increased to 3.75 even though ice was 8m thinner
suggests that velocity is more important than ice thickness in terms of rates of erosion
what is nivation?
the process that occurs under a snow patch
primary processes are mass wasting and freeze thaw, in which fallen snow gets compacted into firn or névé
what are ways that bedrock can be transported after erosion/weathering?
mass movement
through Aeolian deposits
through volcanic eruptions
by the glacier itself (supraglacial, englacial or subglacial)
what is deposition?
the dropping of material carried by the glacier
what is glaciated material called?
in general, it is called drift
it can be divided into till (material deposited by the glacier directly) and outwash (which is material deposited by melt water)
what are the two types of till?
lodgement till (material deposited by advancing ice)
ablation till (material deposited by melting ice)
examples of mechanical weathering in glacial environments?
freeze-thaw, frost shattering, pressure release
what is freeze thaw?
water enters cracks/ joints and expands by nearly 10% when it freezes
exerts pressure on rock, causing it to split or pieces to break
water fills cracks, process repeats
what is frost shattering?
at extremely low temperatures, water trapped in rock pores freezes and expands.
this creates stress which disintegrates rock to small particles
what is pressure release?
when the weight of overlying ice in a glacier is lost due to melting, the underlying rock expands and fractures parallel to the surface.
this is significant in the exposure of sub-surface rocks such as granite and is also known as DILATION.
what is oxidation?
some minerals in rocks react w oxygen, either in the air or in water.
iron is especially susceptible to this process. it becomes soluble under extremely acidic conditions and the original structure is destroyed. it often attacks the iron-rich cements that bind sand grains together in sandstone
three processes of chemical weathering in glacial environments?
oxidation, carbonation, solution
what is carbonation
rainwater combined with dissolved CO2 from the atmosphere to produce a weak carbonic acid. this reacts w calcium carbonate in rocks such as limestone to produce calcium bicarbonate, which is soluble
what is solution?
some salts are soluble in water. other minerals, such as iron, are only soluble in very acidic water, w a pH of about 3. Any process by which a mineral dissolves in water is known as a solution, although mineral specific processes, such as carbon, can be identified.
two processes of biological weathering in glacial environments?
tree roots and organic acids
how do tree roots cause weathering?
tree roots grow into cracks or joints in rocks and exert outward pressure
when trees topple, their roots can also exert leverage in rock and soil, bringing them to the surface and exposing them to further weathering
how do organic acids cause weathering in glacial environments?
produced during decomposition of plant and animal litter
cause soil water to become more acidic and react with some minerals in a process called CHELATION.
what is terminal moraine?
a ridge of till extending across a glacial trough
usually steeper on up valley-side and tends to be crescent shaped, reaching further down-valley in the centre
marks the maximum extent of glacier
what is the shape of terminal moraine dependent on?
amount of material carried
rate of ice movement
rate of ablation
example of a terminal moraine?
Cromer Ridge, Norfolk, England
is 14km long
how is lateral moraine formed?
debris frost shattered from valley slopes
material falls onto the surface of a glacier + is carried along its edges
when melting takes place, an embankment of material is left against valley sides as it sinks to the ground and is deposited
example of lateral moraine?
Athabasca Glacier, Canada
what is the climate of the Nant Ffrancon Valley?
15,000- 20,000yrs ago, the region was experiencing the cold and dry conditions of a glaciation, under a glacier. since then, the climate has warmed
55% less snow fell in 2004 than in 1994
slopes of Snowdon has one of the wettest climates in GB - annual average of more than 200 inches of precipitation
North Wales has temps ranging from -5 to 30 degrees Celsius
what is the geology of the Nant Ffrancon Valley?
rocks which today make up Snowdon and its neighbouring mountains were formed in the Ordovician Period
458 to 457 million years ago, a volcanic caldera formed and produced ash flows and rhyolitic tuff - resistant, hard geology
changes in sea level and metamorphic processes meant slate developed, which is an important part in the human activity of the landscape
example of an arete in Nant Ffrancon?
Y Gribin
separates Cwm Cneifion and Cwm Bochlwyd
example of a cwm?
cwm idwal
floor has an altitude of 375m– is a lot deeper and lower than other corries
lies along a line of geological weakness
example of a tarn in Nant Ffrancon
Llyn Idwal
has an unusual linear shape
example of truncated spurs in Nant Ffrancon
end of Gribin Ridge, by Cwm Idwal
where can terminal moraine be found in Nant Ffrancon
in the mouth of Cwm Idwal as it falls away to the Ogwen valley below
where can lateral moraine be found in Nant Ffrancon
runs parallel to Llyn Idwal along its western side
where can a ribbon lake be found in Nant Ffranon?
Llyn Ogwen
where is a U-Shaped Valley in Snowdonia?
the Ogwen Valley
location of minnesota?
a state in the Upper Midwestern Region of the United States
12th largest US state
home to 10, 000 lakes
glacial history of minnesota?
- Minnesota’s present landscape is the result largely of glacial activity during the Quaternary period (2 million years ago to the present)
- During this time the gigantic Laurentide ice sheet advanced and retreated with climate changes. It was centred in what is now the Hudson Bay, and during colder periods, it extended southward across the upper Midwest
geology of minnesota?
- The landscape of Minnesota is part of the Laurentian (or Canadian) Shield.
- Oldest rocks lie in alternating belts in the northern half of the state + much of the Minnesota River Valley. The belts are of volcanic and sedimentary rocks; granitic rock materials lie in the areas between the belts
- Metamorphic gneiss crops out along the Minnesota River Valley dating back 3600 million years
-Volcanic and sedimentary rocks began their formation 2700 million years ago, when lava escaped through rifts in what was then the sea floor
- Volcanic formations lie throughout Minnesota’s portion of the Laurentian Shield, some buried deep beneath glacial deposits.
- Volcanic debris released into nearby seas later settled on the sea floor, forming massive layers of sedimentary rock. During this period, tectonic activity folded many of these rock formations and formed faults
- Many of volcanic rocks have metamorphosed to greenstone. At the same time, tectonic compression created a range of mountains several kilometres high in northern Minnesota
climate glaciation of minnesota?
- Has been sculpted by glacial ice for the last 2 million years
- Current landscape greatly influenced by most recent glaciation, and the corresponding melting of ice
- About 75, 000 years ago, four main lobes extending from ice sheet spread across Minnesota. They advanced and retreated several times and consequently transported and deposited till over wide areas
- Different origins of different lobes resulted in tills w differing characteristics and materials, and therefore it is possible, due to differences in lithologies across Minnesota, to determine the lobe that deposited certain landforms.
latitude of minnesota?
43 to 49 Degrees North
relief + aspect + altitude of minnesota?
Laurentide ice sheet was 1km thick in places
Lobes had massive erosional impact on the landscape
High mountains were worn down by 500-700m
The far SE wasn’t as extensively covered so a more varied steep hill and deep valley topography exists
Mean elevation of US is 2,500 feet. Mean elevation of Minnesota is 1,200 feet, making it neither one of the highest nor the lowest states on average, but far below the national average
erosional impact of minnesota ice sheet?
Large ellipsoidal basin was created by erosion and is now studded with thousands of lakes, such as Upper and Lower Red Lakes in northern Minnesota
In the Arrowhead region of the northeast, the erosional basin was particularly deep as the earlier tectonic tilting of the landscape exposed weak shale rocks, which were eroded much more rapidly than the resistant volcanic rocks around them.
Lobes abraded striations in bare rock outcrops of gneiss and greenstone
Far southeast of the state not extensively covered by ice sheet so retains a more varied landscape of steep hills and deep valleys. Most of the rivers draining this area are tributaries of the Minnesota and Mississippi Rivers
Erosional impact of the Laurentide Ice Sheet was considerable and shaped the overall landscape. However, continental ice sheet erosion does not produce the spectacular landforms associated with valley glaciers and alpine glaciation.
depositional impact of minnesota ice sheet?
Many of the till deposits in the west of the state have been found by borehole drilling to be more than 100m thick. South-west = boreholes 160m deep still had not reached bedrock
Wadena Lobe advanced from northeast Canada and reached just south of Minneapolis. Till deposited is characteristically red and sandy, being derived from the red sandstone and shales to the north and north-east.
Wadena Lobe first deposited the Alexandria Moraine, formed the drumlin fields spanning Otter Tail, Wadena and Todd counties, and finally formed the Itasca moraine
Ground moraine with reddish, iron-rich sediments extends from St Cloud north-eastward. The glaciers produced formed a set of terminal moraines which extend from northwest of St Cloud into the Twin Cities.
The last advance of the Rainy and Superior Lobes left a coarse textured till containing abundant fragments of basalts, gabbro, granite, red sandstone, slate and greenstone strewn across the north-eastern half of Minnesota and as far south as the Twin Cities
Des Moines Lobe deposited till that is coloured tan to buff, and is clay-rich and calcareous because of shale and limestone rocks at its source to the northwest
In the southwest, Prairie Coteau has a fine example of an end moraine
pro glacial lakes in minnesota?
Edge of the giant ice sheet and its associated lobes also dammed the natural drainage of the area, creating several proglacial lakes
Largest was Lake Agassiz
Glaciers to the north blocked natural northward drainage of the area. As the ice melted, a proglacial lake developed south of the ice. At its maximum this lake covered 440,000km2. The water overflowed the watershed at Brown’s Valley, drained through the Traverse Gap + cut the present Minnesota River valley
The river that drained from Lake Agassiz is called the Glacial River Warren. It flowed over the top of a recessional moraine at Brown’s Valley.
When the lake finally drained it left behind fertile silt deposits producing the rich farmland of the Red River valley
what is the Des Moines lobe?
the last tongue of ice to flow from the Laurentide ice sheet across the state, it flowed from northwest to southeast and reached Des Moines, Iowa, spreading clayey yellow-brown to gray glacial sediment and shale, limestone and other rocks from Saskatche-wan and Manitoba
what is the Rainy Lobe?
a tongue of ice that flowed from the Laurentide ice sheet to the southwest along the highlands above Lake Superior that deposited a grayish brown, stony sediment
what is the Superior lobe?
a tongue of ice that flowed from the Laurentide ice sheet through Lake Superior that deposited reddish brown, sandy to clayey sediment, with primarily red, black and gray rocks
what is the Wadena lobe?
the first ice advance of the last glaciation, this tongue of ice flowed from Laurentide ice sheet to the north depositing brown to gray glacial sediment. Its ground moraine preserves a large area of streamlined hills – the Wadena Drumfield
what is the Des Moines Till?
marks the final advance of glaciers across Minnesota during the Wisconsin glaciation period, between 75, 000 to 14,000 years ago
the glacier left behind a rich deposit of limestone, shale and granite fragments.
the sediment contains arsenic, which can leach into aquifers
when did the last major ice age end?
11,000 years ago
when was the last glacial maximum?
18,000 years ago
what does glacio-fluvial mean?
relating to meltwater from a glacier
what are geomorphic processes?
processes that help to shape the landscape
what does melted water have the ability to do in interglacials?
has the ability to erode, transport and deposit material
can form landforms that are distinctively different to glacial geomorphic processes
how are glacio-fluvial deposits different to till?
- generally smaller, as meltwater has less energy to carry large materials
- smoother and rounder, as attrition in glacio-fluvial streams rounds the particles
- sorted; larger material found upland and smaller material is carried downstream
- stratified; areas of deposition can show season stratification. in winter months larger pieces of material are deposited and in summer smaller pieces of material are deposited. this creates a layered effect
what is a kame?
a hill or hummock composed of stratified sand and gravel laid down by glacial meltwater
what are kame deltas? and example?
some formed by englacial or supraglacial streams
eg in East Lothian, Scotland
what are kame terraces? + example
ridges of material running along edge of valley floor.
formed when supraglacial streams on edge of glacier pick up and carry lateral moraine, then is later deposited on valley floor as glacier retreats
the streams form due to melting of ice warmed in contact with valley sides bc of the friction and heat retaining properties of valley side slopes
eg Kingsdale Valley, Yorkshire Dales
what is an esker + example?
is a long sinuous ridge composed of stratified sand and gravel laid down by glacial meltwater
formed when material is deposited in sub-glacial tunnels as the supply of meltwater decreases at the end of the glacial period
eg the trim esker near Dublin
why are eskers beaded?
sub glacial streams may carry huge amounts of debris under pressure in confined tunnels at the base of the glacier
some scientists argue that deposition occurs when the pressure is released and meltwater emerges at the glacial snout, so eskers become beaded when the glacial snout retreats.
others argue that heads are a result of greater load carried by summer meltwater
what is an out wash plain + example?
is a flat expanse of sediment in the pro-glacial area
as meltwater streams gradually lose energy as they enter lowland areas beyond the ice front, they deposit their load
outwash plains are typically drained by braided streams (river channels subdivided by numerous islets and channels). deposited sorted bars can become vegetated and stabilised, or modified in the next higher impact event
eg on the south coast of Iceland, fed by streams from Gigjökull and Solheimajökull
what happens to fluvial-glacial landscapes during extended periods of cold?
glaciers grow and often bulldoze over fluvio-glacial deposits. these deposits are then lost or reformed into a new landform elsewhere
what impact does a warming climate have on fluvio-glacial landscapes?
leads to more glaciers melting and as they retreat depositional deatures will be uncovered, especially eskers and kames
what will happen if future climates warm rapidly?
rapid ice melt could see large melting events take place and large bodies of water transport and deposit material vast distances, creating extremely large landforms
eg the jokulhaups events in Iceland
what are periglacial environments like?
have a significant cover of snow and ice but not all year round eg Scandinavia
temperature is frequently or constantly below freezing but not covered by ice
contain a layer of permafrost on or below the surface
where do periglacial environments tend to be?
high latitudes + altitudes
eg the northern parts of asia, north america and europe
found on high altitude plateau areas eg the Tibetan plateau in Asia
in the interior of land masses, periglacial conditions exist at lower altitudes and lower latitudes because of the effect of continentality eg Siberia
periglacial conditions exist around ice masses in mountain ranges
what are precipitation levels like in periglacial environments?
low due to cold air being unable to hold moisture
affected by high pressure conditions which reduces rainfall— in the arctic rainfall declined away from oceans as travels westerly losing moisture
what is the albedo like in periglacial environments?
they reflect a lot of solar radiation ( average absorption is 10-20% on snow and ice)
what is permafrost?
ground (including rock or soil) at or below the freezing point of water for two or more years
where is permafrost located?
most is located in high latitudes, but alpine permafrost may exist at high altitudes in much lower latitudes
what is the active layer?
the near surface layer in a periglacial environment which seasonally freezes and thaws
normally 5 - 10 cm in depth
in summer the active layer melts and enables plants to grow, this melted water can lead to boggy anaerobic conditions
in winter the active layer freezes and becomes like the permafrost
what are the two main periglacial processes?
freeze thaw and frost heave
what is talik?
unfrozen ground
what is frost heave?
a subsurface process that leads to vertical sorting of material in the active layer.
Stones within the fine material heat up and cool down faster than their surroundings as they have a lower specific heat capacity
as temperatures fall, water beneath the stones freezes and expands, pushing stones upwards towards the surface.
ground ice also pushes finer material upwards causing a domed surface
how is patterned ground formed?
as a result of frost heave, large stones eventually reach the surface and the ground surface is domed
the stones then move radially, under gravity, down each domed surface to form a network of stone polygons, typically 1-2m in diameter
on slope angles of 3-50 degrees, the larger stones move greater distances downslope and the polygons become elongated into stone garlands
on slopes of 60 degrees and over, the polygons lose their shape and stone stripes develop
example of patterned ground?
in the area around Barrow in Alaska
what is a pingo?
rounded ice-cored hills that can be as much as 90m in height and 800m in diameter
they grow at rates of a couple cm/year
essentially formed by ground ice which develops during winter months as temperatures fall
how are open-system pingos formed?
form in valley bottoms where water from surrounding slopes collects under artesian pressure. the overlying surface material is forced to dome upwards
common in East Greenland
what are closed system pingos?
develop beneath lake beds where the supply of water is from the immediate local area
as permafrost grows during cold periods, groundwater beneath a lake is trapped by the permafrost below and the frozen lake above. the saturated talik, or unfrozen ground, is compressed by the expanding ice around it and is hydrostatic pressure
when the talik itself eventually freezes, it forces up the overlying sediments
for example, there is over 1400 closed system pingos in the Mackenzie Delta of Canada
how is patterned ground modified?
as temps rose at the end of the periglacial period, patterned ground was often colonised by vegetation, making it hard to find and identify
over time, mass movement by creep also degrades the frost heaved domes, making the landform less obvious
patterned ground around Leedon Tor, Dartmoor, is now mainly covered by a layer of soil and grass
how are pingos modified?(+example)
pingos collapse when temps rise and the ice core thaws. When this happens, the top of the dome collapses, leaving a rampart surrounding a circular depression called an OGNIP
due to the thawing of permafrost in Britain, only the remains of the rampart may be seen
eg one can be seen at Llanberis in north Wales, which is about 15m in diameter
when was the Trans Alaskan Pipeline built?
between 1974 and 1977
why was the TransAlaskan Pipeline built?
after the 1973 oil crisis caused a sharp rise in oil prices in the United States. This ride made exploration of the Prudhoe Bay oil field economically feasible.
Environmental, legal and political debates followed the discovery of oil at Prudhoe Bay in 1968, and the pipeline was built only after the oil crisis provoked the passage of legalization designed to remove legal challenges to the project.
To transport the oil to the ice-free port of Valdez, a pipeline was built, as other options like ice breaking boats were not viable
how long is the pipeline?
1300 km
how much oil does the pipeline transport per day?
about 500,000 barrels of oil per day
how are material flows affected through the use of gravel pads?
gravel extracted from stream and river beds, and used as an insulating base layer for road construction
the loss of gravel from the river systems alters the rate at which gravel is transported and deposited further downstream. It can also affect the equilibrium between erosional and depositional processes in the river system
how are hydrological processes affected by gravel extraction?
a report into gravel extraction from a glacial outwash aquifer near Palmer found that groundwater levels fell by more than a metre in an area extending over 2km from the extraction site
how are energy flows affected by the pipeline by the release of and burning of gas during drilling?
some gases are burnt in a process called flaring, which releases mainly CO2 into the atmosphere.
Others, including methane, are vented without burning into the atmosphere.
contributes to an enhanced greenhouse effect with higher levels of terrestrial radiation being trapped in the lower atmosphere, raising temperatures
how are energy flows in periglacial environments affected by the production of heat?
by the production of heat from the extraction and transportation processes, as well as from the associated infrastructure.
an investigation into the urban heat island in the small town of Barrow, Alaska found that mean temperatures were on average 2.2 degrees celcius higher than the surrounding rural area. A maximum difference of 6 degrees was measured on a particularly calm day
heat from domestic heating systems in poorly insulated buildings is a major contributor to the heat island effect and a strong correlation was found between temperature differences and oil production rates in the nearby oil field,
Energy released to the environment by human activities also affects geomorphic processes, with 9% fewer days of temperature fluctuations around 0 degrees (ie freeze thaw cycles) recorded since drilling began
what are drunken trees?
as the permafrost melts, it causes a lot of erosion. A lot of trees cannot stand straight as the ground buckles and sinks. These trees are often called drunken trees
how can drunken trees benefit some native communities?
more downed trees could mean more driftwood flowing into rivers and towards the coast
what is a thermokast?
ground that collapses as a result of melting permafrost
what percentage of the land in the middle boreal zone in Alaska is showing signs of drunken trees?
around 7-8%
what percentage of Alaska is permafrost found beneath?
85%
what is usteq?
a catastrophic form of permafrost thaw collapse that occurs when frozen ground disintegrates under the compounding influences of thawing permafrost, flooding and erosion
how is the permafrost structurally important to the soils of Alaska?
its thawing causes landslides, ground subsidence and erosion, as well as lake disappearances, new lake development and saltwater encroachment, into aquifers and surface waters
what is abrupt thaw?
the warming of small patches of frozen ground that contain larger veins of ice will release far more emissions than once thought
will probably hit 5% of Arctic permafrost
what is thermokast?
a landscape dominated by the surface depressions due to the thawing of ground ice
less than 5m deep and 1-2km wide
what is a thermokast lake?
a body of freshwater, usually shallow, formed in a depression formed by thawing ice rich permafrost
present on the Alaskan coastal plain
what is an alas?
flat floored, steep sided depressions ranging from 5-50m in depth and 100m to 15km in length
what is The Grande Dixence Dam?
a concrete gravity dam on the Dixence at the head of the Val d’Heremence in the canton of Valais in Switzerland
At 285m high, it is the tallest gravity dam in the world, and is part of the Cleuson-Dixence Complex
what is the purpose of the Grande Dixence Scheme?
primary purpose of hydroelectric power generation
dam fuels 4 power stations, totaling the installed capacity to 2,069MW, generating approximately 2,000GWh annually, enough to power 400,000 Swiss households
what lake does the Grande Dixence Dam withhold?
Lac Des DIx
the reservoir receives its water from four different pumping stations; the Z’Mutt, Stafel, Ferpecle, Arolla.
when was The Grande Dixence Dam constructed?
construction on the dam in 1950 and was completed in 1961, before officially commissioning in 1965
impacts of the Grande Dixence Dam on the glacial landscape?
15% of the water available at Grande Dixence is used to deal with the problems of sedimentation.
when water is stored behind the dam, the lack of flow means a loss in energy and the deposition of sediment load behind the dam at rates of 20-40cm/yr
sediment concentrations are >300mg/l above the dam, 20-50mg/l just below the dam, and >20mg/l 3km downstream of the dam
to solve this problem, some of the water in the reservoir is used to purge the sediment, flushing it out and moving it downstream. At these times the water has high levels of turbidity, and sediment concentrations up to 20,000mg/l
how were aggregates for the dam obtained?
locally from deposits of moraines in adjacent valleys
environmental impacts of the Grande Dixence Dam?
impact has been minimised, partly to ensure that the area remains an attractive environment for walkers, cyclists and hikers
pumping stations and power plants a largely built underground or are well concealed to retain the aesthetics of the location.
however, the reduced flow in the Borgne River, a tributary of the Rhone, below the dam has resulted in higher concentrations of pollutants at Les Haudere, from both agricultural and domestic sources
what is turbidity?
the cloudiness of a fluid caused by large numbers of individual particles in suspension
example of a roche mountonnee in nant ffrancon valley
on the valley floor lies a protrusion of a resistant, volcanic dyke about 5m in height.
as the glacier moved over it, the up-glaicer side was smoothed by abrasion, and the down-glaicer side was steepened by plucking, creating a roche mountonnee at maes caradoc
how has the nant ffrancon valley recently been modified
in winter, temps regularly fall below freezing point at night and rise above it in the day, resulting in freeze thaw cycles which have created blockfields on mountain summits and ridges
scree is also actively forming from the frost shattering of boulders on the steep valley slopes. this has given rise to the increasing parabolic shape of the nant ffrancon valley as mass movement processes lead to accumulated debris at the base of slopes
waterfalls from hanging valleys have actively eroded back into the sides of the gacial trough, creating small gorges
example of drumlins in nant ffrancon
there are several drumlins within the Cowny valley, towards Llandudno, which were deposited under a large glacier flowing north from the mountains of snowdonia
they are typically 50-70m high and characteristically elongated in shape
what is the impact of the Grand Dixence dam on river channels?
the trapping of sediment behind the dam leads to very clear water being returned into the natural river channels below the power stations. this has excess energy as none is being used to transport sediment and results in increased channel erosion
the lack of discharge in the below-dam rivers mean that some virtually dry up in the summer.
the amount of sediment eventually flowing into Lake Geneva has halved since the construction of the dam
what is the impact of the Grand Dixence dam on Val d’Herens?
there is a risk of sudden and unexpected flooding when excess stored water has to be releaed
this has hindered both tourist use and development along the valley floor, although the local residents receive significant revenues from it andd so are still strongly in favour of the scheme
what happened in december 2000 near the Grande Dixence dam?
in December 2000, production was put on hold at the dam after a high-pressure pipeline burst, causing a landslide that wiped out a small hamlet and killed three people
what is the future for the Grand Dixence?
climate change is producing higher rates of glacier melting in the Swiss Alps, and the meltwater available to create hydropower is increasing
however, eventually the glaciers will have shrunk so much that meltwater supply is likely to dimish, altering the sediment supply and transportation even further
