Glacial Environment
Every thing starting as a Snow Flake and snow flake is a beautiful hexagonal crystal of ice
Formation of snowflakes
Formation of snowflakes
As the snow accumulates, it is gradually transformed into ice. The weight of overlying snow packs it down, drives out much of the air, and causes it to recrystallize into a coarser, denser form (Firn) an intermediate texture between snow and ice, and finally to a compact solid mass of interlocking ice crystals
This process may take a few seasons or several thousand years, depending on such factors as climate and the rate of snow accumulation at the top of the pile
Glaciers
A large mass of moving ice Capable of eroding, moving, and depositing large amounts of material.
Types
Mountain or Alpine glaciers :Forms over the mountains and the ice start flowing down to form valleys
Once formed, the weight of snow accumulating in the upper part of the glacier causes it to move downslope, where it reaches lower altitudes and higher temperatures. The lower part of the glacier is the ablation zone where the glacier melts during the summer.
Under stable climatic conditions equilibrium develops between accumulation at the head and melting at the front, with the glacier moving downslope all the time, but the positions of the head and snout remain fixed
Zone of accumulation (input)Zone of ablation (ablation exceeds accumulation)
Continental glaciers
Much larger and thicker forming massive sheets of ice2 polar ice sheetsGreenlandAntarctica
Ice sheetExtends over 50,000 km2
Antarctic and Greenland
Ice capSimilar to an ice sheet though smallerForming roughly circular, dome-like structure
Continental glaciers
Glaciers do not behave as rigid, Their flow is plasticHigh pressure and some times geothermal heat causing in melting of the layer at the base so ice start sliding Move by two basic processes:
Basal Slip – the process causing the ice at the base of a glacier to melt and the glacier to slide.
Internal Plastic Flow(internal deformation) –the process by which glaciers flow slowly as grains of ice deform under pressure and slide over each other.
Movement
Internal deformation
Glacial advancing
When accumulation rate exceeds ablation rate so we have glacial advancing
Glacial Retreating
When accumulation rate less than ablation rate we have glacial retreating
GLACIAL EROSION
Mechanism involved…PluckingGlacier flows over a fractured bedrock surfaceit loosens and lift blocks of rocks and incorporate them into ice
Notice that this process seasonable and image just for clarifying
AbrasionHappens when ice and its load of rock fragment slides over bedrock
Plucking and abrasion
Freeze Thaw
The glacial processes that change the shape of mountains begin in the upper end of the valley where
an alpine glacier forms.
26
How selected features of continental glaciation, including kames, originated.
During Glacial Cirque and Arêtes form and glacial creates a U shaped valley
Postglacial
Features of alpine Glaciation
Erosional features CirquesArêtesHornsTruncated spursU-shaped valleysHanging valleysTarns and paternoster lakesDepositional FeaturesMoraines
Cirque formation
An arête is a sharp ridge formed when two cirques cut back
Arête
Features of alpine Glaciation
a)Horn( b)Cirque (c)Arete
a)Horn (b)cirque (c) U shape valley
a
b
c
a)Horn (b)cirque(c)arete (d)truncated spurs
a
aa
b bb
cc
d
b
U shape valley after glaciation
Hanging valley
Tarn
Paternoster lakes
Glacial Deposition
Landforms resulting from a glacier depositing till are called moraines.
Lateral moraine: deposited along the sides of an alpine glacier, usually as a long ridge.
Medial moraine: form when the lateral moraines of alpine glaciers meet.
Ground moraine: unsorted materials left beneath the glacier when the ice melts.
Terminal moraine: small ridges of till deposited at the leading edge of a melting glacier.
Ground Morains
Erosional features
roche moutonnée
Depositional features
Terminal moraines
Till plain, outwash plain
Eskers
Kettles
Kames
Erratics
Drumlins
Features of Continental Glaciation
Roche moutonnée
Roche moutonnée (sheepbacks)
Ice flow
Stoss sideLee side
51
How selected features of continental glaciation, including kames, originated.
Eskers
Melt water forms a tunnel under a glacial ice sheetTunnel fills with rocks, sand and gravel
After retreat of the ice, material collected in the tunnel is left to form a ridge
Kettle lake
A big chunk of ice trapped then melted to form kettle lake and sediments deposited around it
Erratics
Large rocks transported from a distant source by a glacier
Erratics
Erratics
Deposition: drumlins
Oval shaped hills
Formed of till left by glaciation
Blunt end facing opposite ice flow
Often found in “shoals”
Drumlins
Ice flow
Eskers – economic benefits
Mined for materials – sand, gravel and stones for construction
Used for natural water filtration
Glaciers are not only large masses of ice; they can also be viewed as an important freshwater reserve. Approximately 75% of the fresh
water on earth is stored as ice in glaciers
Important source for deposits
Climate and environment indicator
General Benefits
Glacial Geology, Ice Sheets and Landforms [Matthew M. Bennett, Neil F. Glasser]
Sedimentologyandstratigraphy 2nd edition by Gary Nichols
Environmental geology , carla c montgomry
Further reading
Regards,AmrElgabry