Ch. 17: Glacial Geomorphology Flashcards
Define the term glacier.
-It’s a large mass of ice resting on land or floating as ice shelf in sea near land
Explain the difference between alpine and continental glaciers in general. Differentiate between the four main types of alpine glaciers. Describe ice sheets, ice caps and ice fields, and name an example of each.
-Alpine glaciers - are smaller-scaled glaciers usually seen on mountain ranges, and its flow is controlled by
the topography
-Continental glaciers - they’re larger-scaled, and their flow isn’t affected by the topography
Alpine glaciers types:
- Cirque - in a bowl-shaped recess at head of the valley
-Valley - mass of ice confined within a valley; originally formed by stream action flows slowly downhill, eroding materials in its path
-Piedmont - valley glacier that spreads out as wide lobe as it leaves a narrow mountain valley to enter a low-gradient valley or plain
-Tidewater - glacier that ends in the sea
Continental glaciers types:
-Ice sheet - mass of glacier ice that covers an area of more than 50 000 km2, covering both low and high elevations
ex/ Greenland Ice sheet
- Ice caps - roughly circular and cover up an area of less than 50 000 km2 in mountainous regions
ex/ Vatnajokull ice cap in Iceland
- Ice field - an elongated pattern that covers an area less than 50 000 km2 (less than an ice cap); found in mountain regions
ex/ Columbia Ice field in the Rocky Mountains
Explain the process by which snow becomes glacial ice. What is firn, and how is it different from
snow and ice?
-Each year, new layers of snow bury and compress the previous. That compression causes the snow to recrystallize, forming a granular ice that contains 50% air
-granular ice then turns into firn; the grains get smaller and the mass gets 2/3 as dense of water; contains 20-30% air
-Glacial ice then forms by the high pressure from burial or snow from above that has caused pressure melting, resulting in interlocking of ice crystals
-Firn is different from snow and ice because it’s at an intermediate point between snow and ice. It’s not as fluffy and filled w/ air like snow is, and it’s also not as dense and solid like ice is. It has less air than snow and less density than ice.
Describe how positive and negative glacier mass balance are determined, and explain how these are related to the growth or retreat of a glacier.
-Accumulation zone - area of a glacier where snowfall accumulates and adds to a glacier’s mass
-Ablation zone - lower area of the glacier in which the ice melts or retreats
So then:
-Positive net mass balance is when a glacier is measured to be gaining more mass than losing; so the total sum of accumulation is greater than total sum of ablation
-Negative net mass balance is when a glacier is measured to be losing more mass than gaining; so total sum of accumulation is less than total sum of ablation
Define accumulation zone, ablation zone, and equilibrium line and be able to label these on a diagram of both positive and negative mass balance.
- Accumulation zone - area of glacier where snowfall accumulates, which adds more mass to the glacier
- Ablation - Lower area of glacier in which the ice melts or retreats
-Equilibrium line - boundary line between the two
How does a glacier move at its surface versus internally?
-Glaciers mostly through a surface a process called basal sliding/internal deformation. Basal sliding usually occurs when glacier’s base is in contact w/ the underlying terrain, and a thin layer of waters acts as lubricant, allowing the glacier to slide over the landscape.
-Within the glacier, ice flows like a viscous fluid due to the pressure and gravity. the internal deformation causes the ice to flow downhill from the area of accumulation to area of ablation
- rate of internal flow varies, w/ faster movements near the surface, and slower movements near the base and sides
Describe the characteristics of an advancing versus a retreating glacier.
-Advancing glaciers -
-total sum of accumulation is greater than ablation
- ice flow moves forward (downhill) and the ice margins moves forward (downhill)
-Retreating glaciers - total sum of ablation is greater than accumulation
- ice flow moves forward (downhill) and ice margin retreats (uphill)
When glaciers melt, supraglacial (glacier surface) lakes and streams form on top of glaciers. Explain how these are related to moulins and movement of glacier ice.
-Supraglacial lakes form on the surface of glaciers due to the melting of ice caused by warm temps. While moulins, are vertical shafts that extend from the surface of a glacier down to its base
-The relationship between all is mostly driven by the movement of water through a glacier. When supraglacial lakes and streams form, water collects on the surface of the glacier and found its way to moulins through openings.
-Water travelling through the moulin can increase base sliding.
Describe the glacial ice mass balance trends in the European Alps and Alaska (simple percentages of loss or gain are fine). Are Canadian scientists seeing similar trends?
- European Alps and Alaskan glaciers have been losing 1-2% of their ice mass annually
- Canadian scientists have been seeing similar trends of significant ice loss in the Rocky Mountains and Coast Mountains
Explain the two main processes by which glaciers erode a landscape through physical weathering.
1.) Plucking - the passing glacier mechanically picks up rock material and carries it away
2.) Abrasion - rock pieces frozen to the basal layers of the glacier scratch and scrape the bedrock, resulting in glacial polish
Where does a glacier carry debris in transportation? Flowing water? What vocabulary is used to describe this?
- it can carry debris englacially - within the glacier itself; supraglacial - on top of the ice; subglacial - at the base of the ice
Flowing water:
-On glaciers - supraglacial stream
-In glaciers - englacial stream
-under glaciers - subglacial stream
Define glacial drift and describe the three main sediments of glacial origin.
Glacial drift - general term for all sediments of glacial origin, including
-Till - sediment deposited directly by glacial ice
-Glacial erratic - boulders w/ different rock types from local bedrock found in till or on the land surface
-Glacial outwash - layered sediment laid down by glacial meltwater
How, in general, are landscapes changed after glacial erosion (preglacial vs postglacial)?
- Preglacial landscapes have typical stream cut valleys, more V-shaped w/ gentle slopes
-Postglacial landscapes leave behind more U-shaped valleys that are more steep-sided and flat-bottomed
Describe the three main types of landforms produced by glacial erosion. Which give information about the direction the ice flowed? Can you label the subtypes of a glacial valley on a photo or figure?
-Striations - layer grains frozen in the base of the ice act like chisels, gouging the underlying surface
-the linear grooves are parallel to the ice flow direction
-Roche Moutonnée -an asymmetrical hill of exposed bed rock
-can be used for a more specific ice flow direction; gentle side (stoss) is in the upstream direction
-Glacial valleys - characterized as U-shaped, steep-sided, and flat-bottomed valleys
-Cirque - bowl-shaped depression w/ steep sides and a gentle/flat bottom
-Tarn - small lake that forms in the bottom of a cirque valley
-Arete - thin, sharp ridge that forms in between 2 glacially eroded valleys
-Horn - Pyramidal peak that result when several cirque glaciers gouge an individual mountain peak from all sides
Describe the depositional landforms formed by alpine glaciation and continental glaciation. What kind of drift comprises each? Which provide information about the direction that the ice flowed?
Alpine depositional landforms:
-Moraine - landform produced at the margins of a glacier by deposition of glacial sediments
-It’s made of till - unsorted and unstratified rock fragments
1.) Lateral moraines - lengthy ridges of till along each side of the glacier
2.) Medical moraines - found in glacier center from meet of 2 glaciers upstream
3.) Terminal moraines - debris deposited at glacier’s furthest extent
Continental depositional landforms:
- Till plain - “ground moraine”- a deposition of till forms behind a terminal moraine (sediment deposits spread widely across surface)
-Outwash plain - Extrusive glaciofluvial deposits deposited beyond the glacial terminus (sediment deposits spread widely across ground)
-Drumlines - if deposited from base of glacier, it is streamlined in the direction of ice sheet movement; can be used for specific ice flow
-Esker - narrow ridge of coarse sand and gravel deposited by subglacial meltwater streams
Kettles - lake formed from melting of blocks of ice left behind as the glacier recedes
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